the giant grenadier in alaska · the giant grenadier in alaska 415 japan (mecklenburg et al. 2002)....

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†Corresponding author: [email protected].

The Giant Grenadier in Alaska

DaviD M. Clausen†

U.S. National Marine Fisheries Service, Alaska Fisheries Science Center Auke Bay Laboratories

17109 Point Lena Loop Road, Juneau, Alaska 99801, USA

American Fisheries Society Symposium 63:413–450, 2008

Introduction

At least seven species of grenadier are known to occur in Alaskan waters (Meck-lenburg et al. 2002), but only three are com-monly found at depths shallow enough on the continental slope to be encountered in commercial fishing operations or in fishery-

independent surveys: giant grenadier Alba-trossia pectoralis, Pacific grenadier Cory-phaenoides acrolepis, and popeye grenadier Coryphaenoides cinereus. Of these, giant grenadier has the shallowest depth distribu-tion and the largest apparent biomass, and hence is by far the most frequently caught grenadier in Alaska.

Despite this importance, there is little

Abstract.—This report summarizes biological, fishery, and survey information on giant grenadier, Albatrossia pectoralis, in Alaskan waters. Catch estimates of giant grenadier in Alaska for the years 1997–2005 have averaged over 16,000 metric tons (mt), and most of this catch has been taken as bycatch in longline fisheries for sable-fish, Anoplopoma fimbria, and Greenland halibut, Reinhardtius hippoglossoides. The giant grenadier catch is all discarded, and none of the fish survive due to the pressure change when they are brought to the surface. Most of the catch is from the Gulf of Alaska. Data from bottom trawl and longline surveys in Alaska indicate that giant grenadier are extremely abundant in depths 300–1,000 m, and it appears this species is very important ecologically in this environment. Greatest abundance is in the west-ern Gulf of Alaska, eastern Aleutian Islands, and in some areas of the eastern Bering Sea; abundance declines in the eastern Gulf of Alaska. Relative abundance of giant grenadier is much higher off Alaska than off the U.S. West Coast. Fish in the eastern Bering Sea and Aleutian Islands were consistently larger than those in the Gulf of Alaska. Mean size of females was larger in shallower water, and decreased with depth. Females and males appear to have different depth distributions, with females greatly predominating in depths less than 800 m. Although sex composition of giant grenadier caught in the fishery is unknown, nearly all the fishing effort is believed to be in waters less than 800 m, which indicates females are disproportionately har-vested. Because of the great abundance of giant grenadier in Alaska and the relatively modest catch, overfishing of giant grenadier does not appear to be a problem at pres-ent. However, because information on the population dynamics of giant grenadier is very sparse, and because of the 100% discard mortality, the disproportionate harvest of females, and the general susceptibility of deep-sea fish to overharvest, fishery managers should monitor this species closely if catches increase in the future.

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information on the biology, distribution and abundance, and commercial catch of giant grenadier in this area. The only research to focus exclusively on giant grenadier in Alas-ka consists of two food technology studies that investigated ways to improve the palat-ability of these fish for human consumption (Crapo et al. 1999a, 1999b), but these do not provide any biological information. Two studies have included data on the biology of Alaskan giant grenadier as part of larger studies on this species in the North Pacific Ocean (Novikov 1970; Burton 1999). The Novikov study was based on information from the Bering Sea and Aleutian Islands in what are now U.S. territorial waters, as well as on data from Russian waters in the north-west Pacific Ocean and Sea of Okhotsk. Although this study was extensive and in-cluded information on many aspects of giant grenadier biology, it is now somewhat out-dated, as all the data were collected nearly 40 years ago. Burton’s (1999) study was an investigation of the age and growth of gi-ant grenadier in the northeast Pacific Ocean based on fish from the U.S. West Coast, the Gulf of Alaska, and the Aleutian Islands. Except for the Novikov and Burton papers, additional information on giant grenadier in Alaska is scattered in various survey reports and in survey and fishery databases.

The purpose of this report is to provide a summary of information currently available on giant grenadier, with a particular empha-sis on Alaskan waters. This information is especially needed at this time because of the possibility that giant grenadier in Alaska may be assigned catch quotas in the future. The information is also timely due to the recent emphasis in fishery science on the ecosystem approach to management, and the fact that gi-ant grenadier are so abundant on the slope that they are an extremely important component of the ecosystem. This paper will examine literature available on giant grenadier from other areas besides Alaska and also present

information on giant grenadier in Alaska from commercial fishery data and from fish surveys. In addition, the paper will address overfishing as it relates to present and future catches of giant grenadier in Alaska.

Biological Information

Taxonomy

The taxonomy of giant grenadier has long been controversial, although its species name has always been pectoralis. Since it was first described in 1892, taxonomists have assigned giant grenadier to various genera, including Macrurus, Albatrossia, Coryphaenoides, Nematonurus, and Chalinura (Iwamoto and Stein 1974). The most recent detailed mor-phological description of the giant grena-dier (Iwamoto and Stein 1974) placed it in Coryphaenoides, but Iwamoto and Sazonov (1988) suggested it was more appropriately in its own monotypic genus because of some unique morphological characteristics. Hence, they resurrected the genus name Albatrossia for this fish, and this name was adopted by the American Fisheries Society as official. However, subsequent biochemical and DNA phylogenetic studies have concluded that gi-ant grenadier do indeed bear such close affin-ity to Coryphaenoides that the species should be returned to this genus (Wilson 1994; Morita 1999; and Wilson and Attia 2003). The molecular genetics evidence for placing giant grenadier in Coryphaenoides is com-pelling, and it appears likely that sometime in the future the American Fisheries Society will again adopt Coryphaenoides as its offi-cial name.

Geographic and depth range

Giant grenadier is a continental slope species that ranges from northern Baja Cali-fornia, Mexico, around the arc of the North Pacific Ocean to northern Honshu Island,

415The Giant Grenadier in Alaska

Japan (Mecklenburg et al. 2002). The fish also extends north in the Bering Sea to ap-proximately 62°N latitude and is found in the Sea of Okhotsk (Novikov 1970). In addition, giant grenadier have been caught on at least nine seamounts in the Gulf of Alaska (Ma-loney 2004) and on at least five seamounts in the Emperor Seamount chain of the North Pacific (Pakhorukov 2005). Giant grenadier are reported to have a depth range of 140–2,189 m (Mecklenburg et al. 2002), although the fish are usually found in depths greater than 300 m (Allen and Smith 1988).

Size

A unique characteristic of giant grenadier is its large size. The grenadier family (Mac-rouridae) is quite speciose with well over 300 species worldwide, and giant grenadier is the largest in size of all these species (Iwamoto and Stein 1974). Total length (TL) is reported to exceed 150 cm. Largest known weight of an individual is 41.8 kg, based on a specimen sampled in a trawl survey of the eastern Ber-ing Sea.1

One problem with length measurements for all grenadiers is that their long, whip-like tails are frequently broken off when brought to the surface by fishing gear. This renders measurement of TL impossible. To remedy this situation, an alternative length measure-ment, called “pre-anal fin length” (PAFL), has now been adopted by most scientists when measuring grenadiers (Andrews et al. 1999). PAFL is defined as the length be-tween the tip of the snout and the insertion of the first anal fin ray. Because many of the older length measurements have been in TL, Burton (1999) computed a linear regression to describe the relationship between TL and PAFL for a sample of giant grenadier (males

and females combined) collected off Kodiak Island, Alaska:

TL = 2.15(PAFL) + 25.9, r2 = 0.93, n = 136,

where TL and PAFL are in cm.

The following length-weight relation-ships were computed for giant grenadier in the Gulf of Alaska based on data collected in a trawl survey in 1999:2

W is weight in grams and PAFL is in mm:

males, W = 1.054 × 10−3(PAFL2.622), n = 22

female W = 1.333 × 10−3(PAFL2.597), n = 45

combined sexes, W = 4.487 × 10−4 (PAFL2.785), n = 67

Morphs of giant grenadier

Recently, scientists on trawl surveys in Alaska have noted that two distinct morphs of giant grenadier occur in Alaska: one has a much larger eye than the other.3 These two morphs have been found in all the major ar-eas surveyed in Alaska (the Gulf of Alaska, the Aleutian Islands, and the eastern Ber-ing Sea), and both morphs have commonly co-occurred in individual hauls. However, no taxonomic or genetic work has yet been done to investigate the possibility that these morphs are different species or subspecies.

1 G. Hoff, U.S. National Marine Fisheries Service, Alaska Fisheries Science Center, RACE Division, 7600 Sand Point Way NE, Seattle, WA 98115. Personal communication. March 2005.

2 Values for the length-weight relationships of giant grenadier were reported for this survey by Britt and Martin (2001), but their listed values are incorrect. I recalculated these values based on the original data listed in the U.S. National Marine Fisheries Service, Alaska Fisheries Science Center’s “Racebase” trawl survey database, and the recalculated values are listed here.3 J. Orr, U.S. National Marine Fisheries Service, Alaska Fisheries Science Center, RACE Division, 7600 Sand Point Way NE, Seattle, WA 98115. Personal communication. March 2006.

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Age and growth

Only one study of giant grenadier age and growth has been conducted that used modern techniques of otolith age determi-nation to estimate age of the fish (Burton 1999). Older studies (e.g., Novikov 1970) all relied on age determinations from scales, which is a method now thought to signifi-cantly underage many marine fish, espe-cially those that are relatively long-lived. Burton’s study used otoliths collected from 357 adult fish in the Aleutian Islands, Gulf of Alaska, and off Oregon and California to determine age. Results indicated ages ranged between 13 and 56 years, and the 56 year-old came from the Gulf of Alaska. However, the otoliths were reported to be very difficult to age, and von Bertalanffy growth curves yielded an unreasonable fit to the size and age data. No analysis was done to determine if ages differed by geo-graphic area. Radiometric aging methods were also applied to the otoliths, and con-firmed that giant grenadier live to at least 32 years.

Recent age information for other mac-rourid species suggests that many are very long-lived. For example, the roundnose grenadier, Coryphaenoides rupestris, an important commercial species in the Atlan-tic, is thought to live up to 70 years (Mer-rett and Haedrich 1997). Two age determi-nation studies of Pacific grenadier off the U.S. West Coast found maximum ages of 73 (Andrews et al. 1999) and 62 (Matsui et al. 1990), and radiometric aging in the former study verified the species lives to at least 56 years. Based on these other grena-dier age determination studies, it is not un-reasonable to expect a large-sized macrou-rid such as giant grenadier to have a similar old maximum age. Therefore, the other studies suggest that Burton’s unconfirmed maximum age of 56 years is certainly plau-sible.

Natural mortality

Clausen and Gaichas (2004) used the method of Hoenig (1983) to estimate natu-ral mortality for giant grenadier. This meth-od uses the maximum age of a species in a regression equation to yield an estimate of total mortality. Clausen and Gaichas (2004) assumed that if stocks of giant grenadier in Alaska are lightly fished, i.e., catch remov-als are only a very small portion of the popu-lation, total mortality should approximately equal natural mortality. Based on a maximum age of 56 years from Burton’s (1999) study, Hoenig’s method estimates a natural mortal-ity rate for giant grenadier of 0.074.

Life history, habitat, and ecological relationships

Very little is known about the life his-tory of giant grenadier. The spawning period is thought to be protracted and may even ex-tend throughout the year (Novikov 1970). Recent (2004–2006) macroscopic observa-tions of giant grenadier ovaries in the Gulf of Alaska by the present author also suggest that the spawning period is prolonged.4 No fecundity studies have been done. Two pa-pers provide purported descriptions of larvae of giant grenadier in the North Pacific (Endo et al. 1993 and Ambrose 1996), but Busby (2005) points out that these descriptions ap-pear so different that they probably repre-sent separate species. At any rate, no larvae have ever been collected in Alaska that cor-respond to either of these descriptions or to the description of a third form (Busby 2005) that is also giant grenadier-like.5 Small, ju-4 D. Clausen, U.S. National Marine Fisheries Service, Alaska Fisheries Science Center, Auke Bay Laboratories, 17109 Pt. Lena Loop Rd., Juneau, AK 99801. Unpublished data, August 2006.5 M. Busby, U.S. National Marine Fisheries Service, Alaska Fisheries Science Center, RACE Division, 7600 Sand Point Way NE, Seattle, WA 98115. Personal communication. October 2006.


venile giant grenadier less than ∼15–20 cm PAFL are very uncommon in bottom trawl catches (Novikov 1970; Ronholt et al. 1994; Hoff and Britt 2003, 2005), and juveniles may be pelagic in their distribution. The only published information on sexual matu-rity of giant grenadier comes from Novikov (1970) who stated that sexual maturity is reached at about 56 cm total length (=14 cm PAFL based on Burton’s (1999) conversion factor), when the fish presumably assume a more benthic existence. However, he gives no data as to how this value was determined or to which sex it applies, and the size seems unreasonably small. Bottom trawl studies indicate that females and males have dif-ferent depth distributions, with females in-habiting shallower depths than males. For example, both Novikov (1970) and Britt and Martin (2001) found that nearly all fish at depths <700 m depth were female, and the Novikov study was based on trawl sampling throughout the year. Presumably, some ver-tical migration of one or both sexes must oc-cur for spawning purposes; Novikov (1970) speculates that females move to deeper wa-ter inhabited by males for spawning. Stock structure and migrational patterns of giant grenadier in Alaska are unknown, as no ge-netic studies have been done, and the fish cannot be tagged because all individuals die due to barotrauma when brought to the surface. One study in Russian waters, how-ever, used indirect evidence to conclude that seasonal feeding and spawning migrations occur of up “to several hundred miles” (Tu-ponogov 1997).

The habitat and ecological relationships of giant grenadier are likewise little known and uncertain. Clearly, adults are often found in close association with the bottom, as evidenced by their large catches in bottom trawls and on longlines set on the bottom. However, based on a study of the food habits of giant grenadier off the U.S. West Coast, Drazen et al. (2001) concluded that the fish

feeds primarily in the water column. Most of the prey items found in the stomachs were meso- or bathypelagic squids and fish, and there was little evidence of benthic feeding. Smaller studies of giant grenadier food hab-its in the Aleutian Islands (Yang 2003) and Gulf of Alaska (Yang et al. 2006) showed generally similar results. In the Aleutian Is-lands, the diet comprised mostly squid and bathypelagic fish (myctophids), whereas in the Gulf of Alaska, squid and pasiphaeid shrimp predominated as prey. The hypoth-esis about the tendency of the fish to feed off bottom is supported by observations of sablefish longline fishermen, who report that their highest catches of giant grenadier often occur when the line has been inadvertently “clothes-lined” between two pinnacles, rath-er than set directly on the bottom.6 The only documented predators of giant grenadier are Pacific sleeper sharks Somniosus pacificus and Baird’s beaked whales Beradius bair-dii. In a study of the diet of Pacific sleeper sharks in Russian waters of the northwest-ern Pacific, giant grenadier was ranked third in relative importance as a food item (Orlov and Moiseev 1999). A study of the stom-ach contents of Baird’s beaked whales off Japan in the western North Pacific and Sea of Okhotsk indicated their diet included six species of grenadier, one of which was gi-ant grenadier (Walker et al. 2002). Sperm whales Physeter macrocephalus are another likely predator, as they are known to dive to depths inhabited by giant grenadier on the continental slope and have been observed in Alaska depredating on longline catches of giant grenadier.7

6 D. Clausen, U.S. National Marine Fisheries Service, Alaska Fisheries Science, Auke Bay Laboratories, 17109 Pt. Lena Loop Rd., Juneau, AK 99801. Personal observation. October 2004.7 C. Lunsford, U.S. National Marine Fisheries Service, Alaska Fisheries Science Center, Auke Bay Laboratories, 17109 Pt. Lena Loop Rd., Juneau, AK 99801. Personal communication. October 2006.

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Fishery Information

Background information

All species of grenadier in Alaska are presently considered “nonspecified species” by the U.S. North Pacific Fishery Manage-ment Council (NPFMC), which is respon-sible for setting groundfish quotas in Federal waters in Alaska. This means that grenadiers have not been included in any of the NPFMC fishery management plans and that there have been no limitations on catch or retention, no reporting requirements, and no official track-ing of grenadier catch by management. How-ever, in 2005 the NPFMC began examining a proposal that would modify the existing management structure to include grenadiers in the management plans. If this proposal is adopted, the NPFMC would then need to es-tablish levels of overfishing (OFL), accept-able biological catch (ABC), and total allow-able catch (TAC) for grenadiers in Federal waters of Alaska. The possibility that giant grenadiers may soon be part of the ground-fish management structure in Alaska was a major impetus for writing this report.

Catch history

Although no official catch statistics ex-ist for giant grenadier in Alaska, catches for all species of grenadiers combined have been estimated for the years 1997–2005 (Ta-ble 1). These estimates are based largely on data collected by the U.S. National Marine Fisheries Service Alaska Fisheries Science Center’s Groundfish Observer Program, which places observers aboard commer-cial fishing vessels. The estimates are pre-sented for three major management regions in Alaska, the eastern Bering Sea (EBS), Aleutian Islands (AI), and the Gulf of Alas-ka (GOA), whose geographic locations are shown in Figure 1. The details of the meth-odology used to estimate the catches for

1997–2002 are described in Gaichas (2002). Essentially, the method attempted to simu-late as much as possible the method used by the U.S. National Marine Fisheries Service to officially determine catches of managed groundfish species in Alaska. For the years 2003–2005, grenadier catches were esti-mated by the U.S. National Marine Fisher-ies Service Alaska Regional Office using a slightly different methodology that again tried to emulate the official catch determina-tion methods. Although these estimates may not be as accurate as the official catch es-timates determined for managed groundfish species, they are believed to be the best pos-sible based on the data available. They do not appear unreasonable compared to the of-ficial catches of other species caught along with giant grenadier on the continental slope in Alaska, such as sablefish Anoplopoma fimbria and Greenland halibut Reinhardtius hippoglossoides.

One important caveat is that the catch estimates for the EBS and AI may be more accurate than those for the GOA. In the catch-estimation process, it is assumed that grenadier catch aboard observed vessels is representative of grenadier catch aboard un-observed vessels. This is a possible problem because observer coverage in the EBS and AI fisheries is considerably higher than those in the GOA. In general, smaller vessels fish in the GOA, especially in longline fisheries, and many of these vessels are not required to have observers, which could introduce a bias into the GOA estimates.

Unfortunately, the data have to be pre-sented as “grenadiers, all species combined,” because observers were not instructed to specifically identify giant grenadiers until 2005. Even in 2005, the catch data suggest that many observers did not properly iden-tify giant grenadier to species. Although the species breakdown of the grenadier catch is unknown, it can be surmised that giant grena-dier comprise by far the majority of the fish


Eastern Aleutian Gulf ofYear Bering Sea Islands Alaska

Total

1997 2,964 2,887 12,029 17,881

1998 5,011 1,578 14,683 21,272

1999 4,505 2,883 11,388 18,776

2000 4,067 3,254 11,610 18,931

2001 2,294 1,460 9,685 13,439

2002 1,891 2,807 10,479 15,177

2003 2,853 3,556 11,165 17,573

2004 2,225 1,123 10,511 13,858

2005 2,581 1,676 6,581 10,838

Mean 3,154 2,358 10,903 16,416

Table 1. Estimated catch (mt) of grenadiers in the eastern Bering Sea, Aleutian Islands, and Gulf of Alaska, 1997–2005. (Catch is for all species of grenadiers combined, but almost all of the catch is believed to be giant grenadier Albatrossia pectoralis).

Russia

AlaskaU.S.

Canada

EasternBering Sea

Aleutian IslandsShumagin

Gulf of Alaska

Chirikof

Kodiak

WestYak

NE Aleutians

SE Aleutians

EastYak

SoutheasternBering 1

Bering 2Bering 3

Bering 4

SW Aleutians

NW Aleutians

Figure 1. Map of Alaska showing the three major management regions for groundfish: eastern Bering Sea, Aleutian Islands, and Gulf of Alaska. Also shown are sampling areas in longline sur-veys of the continental slope in Alaska, and the 200 m and 1,000 m bathymetric contour lines. (West Yak = West Yakutat area; East Yak = East Yakutat area).

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caught. The only other grenadier species en-countered on the continental slope in Alaska are Pacific and popeye grenadiers. Bottom trawl and longline surveys all show that very few Pacific and popeye grenadiers are found shallower than 800 m deep, whereas giant grenadier are abundant in these depths (see Survey Information section in this report). Although there are no analyses of the depth distribution of commercial fishing effort in Alaska, it is likely that very little effort oc-curs in depths deeper than 800 m. In the par-ticular case of the sablefish longline fishery (the source of most of the grenadier catch in Alaska), the fishery is probably focused at depths of 400–800 m, where longline surveys have generally found the highest catch rates of sablefish (Zenger and Sigler 1992). Hence, this indirect evidence can be used to conclude that giant grenadier are the overwhelmingly predominant species in the grenadier catch.

The estimated annual catches of grena-diers in Alaska for the years 1997–2005 have ranged between ∼11,000–21,000 metric tons (mt), with an average for this period of over 16,000 mt (Table 1). Highest catches have consistently been in the GOA, followed generally by the EBS and then the AI. An-nual catches by region have ranged between ∼7,000–15,000 mt in the GOA, ∼2,000–5,000 mt in the EBS, and ∼1,000–4,000 mt in the AI.

Description of the fishery

Virtually all the catch of giant grenadier in Alaska has been taken as bycatch in fish-eries directed at other species, particularly sablefish and Greenland halibut. All the giant grenadier catch is discarded, and the discard mortality rate is 100% because the pressure difference experienced by the fish when they are brought to the surface invariably causes death. A breakdown of the catch estimates for 1997–1999 indicated that in the GOA most of the grenadier catch was taken in the sablefish

fishery, whereas in the EBS and AI combined it predominantly came from the Greenland halibut fishery and secondarily from the sa-blefish fishery (Table 2). Similarly, in 2003–2005 the grenadier catch in the GOA and AI came mostly from the sablefish fishery, and in the EBS from the flatfish fishery. A species breakdown for flatfish targeted fishing was not available for 2003–2005, but based on the 1997–1999 data, it can be presumed that most of the grenadier catch in flatfish hauls in the EBS and AI was taken in the Greenland halibut fishery. (Grenadier catch data by tar-get fishery are not available for 2000–2002.) The high bycatch of grenadiers in fisheries for sablefish and Greenland halibut is not surprising, as the latter two species inhabit waters of the continental slope where giant grenadier are abundant. Both the sablefish and Greenland halibut fisheries are predomi-nantly longline, and an analysis of grenadier catches by gear type for 1997–2002 showed that over 90% of the grenadier catch in Alas-ka was taken on longlines (Clausen and Gai-chas 2005). Recently, some longline fisher-men in the EBS have switched to using pots to protect their catches from whale depreda-tion, and it is uncertain what effect, if any, this change may have on grenadier catches.

There have been only two known attempts to develop a directed fishery for grenadiers in Alaska. The first was an endeavor to process longline-caught giant grenadier for surimi at the port of Kodiak in 1998.8 This small effort was apparently unsuccessful, as it ended in 1999. The second, also from the port of Ko-diak, was an exploratory effort in 2005 using trawls to target giant grenadier and develop a fillet and roe market.9 This second venture 8 J. Ferdinand, National Marine Fisheries Service, Alaska Fisheries Science Center, REFM Division, 7600 Sand Point Way NE, Seattle WA 98115. Personal communication. September 2004.9 T. Pearson, Kodiak Fisheries Research Center, National Marine Fisheries Service, Sustainable Fisheries, 302 Trident Way, Room 212, Kodiak AK 99615. Personal communication. October 2005.


Table 2. Estimated breakdown (%) of the grenadier catch in the eastern Bering Sea, Aleutian Islands, and Gulf of Alaska, by target species/species group, 1997–1999 and 2003–2005. (Catch is for all species of grenadiers combined, but almost all of the catch is believed to be giant grenadier Alba-trossia pectoralis; methodology for estimating catches is described in Gaichas (2002)). Gr. halibut = Greenland halibut Reinhardtius hippoglossoides; P. cod = Pacific cod Gadus macrocephalus.

1997–1999:

Target species/species groupYear Sablefish Gr. halibut P. cod Rockfish Flatfisha Other Total

Eastern Bering Sea and Aleutian Islandsb

1997 39.5 38.9 14.3 6.5 0.1 0.8 100.01998 13.4 71.5 10.5 2.3 0.2 2.0 100.01999 27.2 60.9 7.7 1.6 0.7 1.9 100.0

Gulf of Alaska1997 89.8 0.0 1.6 2.9 5.4 0.2 100.01998 95.5 0.0 trace 2.0 2.5 trace 100.01999 90.9 0.0 3.9 0.6 4.0 0.7 100.0

aFlatfish species other than Greenland halibut. bThe only data available are for the eastern Bering Sea and Aleutian Islands combined. 2003–2005:

Target species/species group

Year SablefishGreenland halibuta P. cod Rockfish Flatfisha Other Total

Eastern Bering Sea2003 21.0 - 8.3 0.3 68.7 1.8 100.02004 12.8 - 10.8 0.9 74.0 1.5 100.02005 4.3 - 13.1 0.3 81.5 0.7 100.0

Aleutian Islands2003 56.6 - 1.3 0.2 41.9 trace 100.02004 66.7 - 1.2 3.4 26.6 2.1 100.02005 60.2 - trace 1.2 37.6 1.0 100.0

Gulf of Alaska2003 76.1 - trace 5.6 17.8 0.5 100.02004 73.1 - trace 21.4 5.5 0.1 100.02005 87.6 - trace 3.5 8.1 0.8 100.0

aData not available to separate catches of grenadiers in the Greenland halibut target fishery from those in target fisheries for other flatfish species. Therefore, grenadier catches in flatfish fisheries for 2003–2005 include those caught in the Greenland halibut fishery.

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was not continued in 2006. Because of the large biomass of giant grenadier on the con-tinental slope, however, research to develop marketable products from this species is on-going (Crapo et al. 1999a and 1999b), and it is likely that Alaskan fishermen will continue their efforts at utilizing this species.

Survey Information

Fishery-independent surveys of the con-tinental slope off Alaska have been conducted since the late 1970s using both bottom trawls and longlines, and these surveys provide much information on distribution and abun-dance of giant grenadier. Area-wide biomass estimates are computed from the trawl sur-veys, whereas indices of abundance are com-puted from the longline surveys.

Trawl Surveys

Trawl survey methods

Since 1979, the U.S. National Marine Fisheries Service has conducted a series of standardized bottom trawl surveys in the EBS, AI, and GOA that have attempted to sample the entire continental shelf and upper slope of each area during summer months. However, relatively few of the surveys have extended deep enough on the continental slope to yield comprehensive abundance estimates for gi-ant grenadier. For example, many surveys of the AI and GOA have sampled only to 500 m; thus, they barely entered the main depth range of giant grenadier and are only useful for information on the shallowest portion of the population. Giant grenadier biomass es-timates for those surveys that have extended to 800 m or deeper are listed in Table 3. It should be noted that the estimates for the ear-lier EBS surveys (1979–1991) likely include some popeye and Pacific grenadier in addi-tion to giant grenadier because grenadiers in these surveys were usually identified only to

the level of family. However, based on the fact that these surveys did not extend deeper than 800–1,000 m on the slope, giant grena-dier is believed to comprise by far the major-ity of the biomass.

The surveys have been based on a strati-fied random design, in which the survey areas are divided into a number of strata based on depth and sometimes habitat features such as gullies. Haul locations are randomly selected within these strata, and haul duration (time the net is towing on-bottom) is usually 15 or 30 min. Survey gear and procedures are stan-dardized to allow comparisons between years. For the surveys in Table 3, the number of suc-cessful hauls on the slope at depths deeper than 200 m that could potentially catch giant grenadier have ranged between 133 and 311, depending on the particular survey. All the surveys provide abundance data in terms of catch-per-unit-effort (CPUE) and estimates of biomass. The biomass estimates are based on the area-swept method, which assumes all the fish in the path of the net are caught and which extrapolates these catches over the entire survey area to yield estimates of total biomass. The biomass estimates also assume a catchability value of 1.0 for giant grenadier, i.e., that no herding of the fish occurs due to the trawl’s doors and bridles, and that no fish escape under or over the net. For more information on the methods of these surveys and the gear used, the reader is referred to the following reports: Wakabayashi et al. (1985); Britt and Martin (2001); and Hoff and Britt (2005).

Biomass estimates

The biomass estimates indicate that sizeable populations of giant grenadier are found in each of the three regions surveyed, but the survey time series are too intermit-tent to show any trends in abundance. High-est estimates of giant grenadier biomass in each region were 667,000 mt in the EBS


Table 3. Estimated biomass (mt) of giant grenadier Albatrossia pectoralis in U.S. National Marine Fisheries Service trawl surveys in Alaska that sampled the upper continental slope to depths of ≥800 m.

Year Eastern Bering Sea Aleutian Islands Gulf of Alaska1979 91,500a - -1980 - 313,480 -1981 90,500a - -1982 104,700a - -1983 - 349,538 -1984 - - 169,7081985 107,600a - -1986 - 600,656 -1987 - - 135,9711988 61,400a - -1989 - - -1990 - - -1991 73,520a - -1992 - - -1993 - - -1994 - - -1995 - - -1996 - - -1997 - - -1998 - - -1999 - - 389,9082000 - - -2001 - - -2002 426,397 - -2003 - - -2004 666,508 - -2005 - - 587,346

aEstimates are for all species of grenadiers combined

Notes and data sources:a) Eastern Bering Sea: Depths sampled were to 1,000 m in 1979, 1981, 1982, and 1985; to 800 m in 1988 and 1991; and to 1,200 m in 2002 and 2004. Data sources: 1979 to 1988, Bakkala et al. (1992); 1991, Goddard and Zimmermann (1993); 2002, Hoff and Britt (2003); 2004, Hoff and Britt (2005). b) Aleutian Islands: Depths sampled were to 900 m in each survey. Data source: Ronholt et al. (1994).c) Gulf of Alaska: Depths sampled were to 1,000 m in each survey. Data sources: 1984, 1987, 1999, and 2005, data on the Alaska Fisheries Science Center’s “Racebase” trawl survey database, Oct. 2006, available from the U.S. National Marine Fisheries Service, Alaska Fisheries Science Center, RACE Division, 7600 Sand Point Way NE, Seattle WA 98115.

424 Clausen

(2004), 601,000 mt in the AI (1986), and 587,000 mt in the GOA (2005). In the EBS, the biomass estimates for 1979–1991 appear to be unreasonably low compared to the bio-mass estimates in 2002 and 2004. Given the apparent longevity and slow growth of gi-ant grenadier, it is unlikely that its biomass could have increased nearly six-fold from 74,000 mt in 1991 to 426,000 mt in 2002. The EBS slope surveys in 2002 and 2004 are considered to be better than their predeces-sors because they were the only ones spe-cifically designed to sample the continental slope, they trawled deeper water (to 1,200 m) that encompassed more of the depth range of giant grenadier, and they had good geographical coverage in all areas.10 Also, in comparison to the steep and rocky slopes of the AI and GOA, the EBS slope is much easier to sample with a bottom trawl, which means a trawl survey in the latter region may yield more reliable results. Therefore, the biomass estimates for the EBS in 2002 and 2004 may be the most valid of any of the surveys in Table 3.

Data from recent EBS and GOA trawl surveys can be used to examine the variability of the biomass estimates for giant grenadier (Table 4). The low values for the coefficients of variation for each biomass estimate indi-cate that the estimates are relatively precise for giant grenadier compared with those of many other groundfish species.

One factor that could have a significant effect on the biomass estimates is the extent that giant grenadier move off bottom. As discussed, there is indirect evidence from feeding studies that giant grenadier may be somewhat pelagic in their search for prey. If so, some of the population may be unavail-able to the bottom trawl, which would mean that true abundance of giant grenadier may be even higher than indicated by the biomass estimates.

Depth distribution, sex composition, and size

The recent trawl surveys provide infor-mation on the depth distribution of giant grenadier in the EBS and GOA in terms of both biomass and CPUE (Figures 2 and 3). The basic survey design in each area used different stratification schemes for depth; for example, the EBS surveys were struc-

Table 4. Biomass estimates (mt) and associated 95% confidence bounds (mt), variances, and coefficients of variation (cv) for giant grenadier Albatrossia pectoralis in recent bottom trawl surveys in Alaska that sampled the upper continental slope.Source: the Alaska Fisheries Science Center’s “Racebase” trawl survey database, Oct. 2006, available from the U.S. National Marine Fisheries Service, Alaska Fisheries Science Center, RACE Division, 7600 Sand Point Way NE, Seattle WA 98115.

95% Conf. boundsRegion Year Biomass Lower Upper Variance cv (%)

Eastern Bering Sea 2002 426,397 344,922 507,871 1,659,519,194 9.6Eastern Bering Sea 2004 666,508 527,524 805,491 4,829,084,657 10.4Gulf of Alaska 1999 389,908 313,786 466,030 1,418,688,152 9.7Gulf of Alaska 2005 587,346 420,489 754,202 6,503,760,627 13.7

10 G. Walters, U.S. National Marine Fisheries Service, Alaska Fisheries Science Center, RACE Division, 7600 Sand Point Way NE, Seattle WA 98115. Personal communication. October 2004.


tured with 200–400 and 400–600 m strata, whereas the GOA surveys had 200–300 and 300–500 m strata. Unfortunately, this means depth results between surveys are not directly comparable. The EBS surveys showed a very low abundance of giant grenadier in depths under 400 m, relatively high abundance in 400–1,000 m, and a decline in 1,000–1,200 m. Highest CPUE was in 600–1,000 m. In the GOA, few giant grenadier were found un-der 300 m, and greatest biomass and CPUE were in the 500–700 m stratum. In particular, CPUE showed a marked peak at 500–700 m. The surveys in both areas generally showed a decline in the deepest strata sampled (1,000–

1,200 m in the EBS and 700–1,000 m in the GOA), which suggests that the surveys may have encompassed most of the population of giant grenadier. However, biomass and CPUE were still relatively high in these deep strata, and to what extent giant grenadier are distributed beyond these strata is unknown.

The trawl surveys showed that male and female giant grenadier were considerably different in their depth distribution, size, and population number. In both the EBS and the GOA, nearly all the fish at depths <500–600 m were female, whereas males became in-creasingly abundant in deeper water (Figure 4). In the EBS surveys, which extended to

Biomass (1,000s of metric tons)

2002 EBS

0 50 100 150 200 250

1000-1200

800-1000

600-800

400-600

200-400

2004 EBS

0 50 100 150 200 250

1000-1200

800-1000

600-800

400-600

200-400

1999 GOA

0 50 100 150 200 250

700-1000

500-700

300-500

200-300

100-200

2005 GOA

0 50 100 150 200 250

700-1000

500-700

300-500

200-300

100-200Dep

th s

trat

um

(m

)

Figure 2. Depth distribution of biomass estimates for giant grenadier Albatrossia pectoralis in recent bottom trawl surveys of the eastern Bering Sea (EBS) and Gulf of Alaska (GOA). (Depth strata shown for the EBS and GOA are not the same because each survey had a different strati-fication scheme for depth).

426 Clausen

CPUE (1,000s of kg per km squared)

2002 EBS

0 10 20 30 40

1000-1200

800-1000

600-800

400-600

200-400

2004 EBS

0 10 20 30 40

1000-1200

800-1000

600-800

400-600

200-400

1999 GOA

0 10 20 30 40

700-1000

500-700

300-500

200-300

100-200

2005 GOA

0 10 20 30 40

700-1000

500-700

300-500

200-300

100-200Dept

h st

ratu

m (m

)

Figure 3. Depth distribution of catch-per-unit-effort (CPUE) for giant grenadier Albatrossia pec-toralis in recent bottom trawl surveys of the eastern Bering Sea (EBS) and Gulf of Alaska (GOA). (Depth strata shown for the EBS and GOA are not the same because each survey had a different stratification scheme for depth).

deeper water than the GOA surveys, males predominated in the deepest stratum of 1,000–1,200. Female giant grenadier aver-aged much larger than males in each survey, and their population numbers were substan-tially greater (Figure 5). For example, in the 2004 EBS survey, females had a mean PAFL of 29.4 cm compared to a mean of only 24.1 cm for males. This difference is even greater than what would outwardly seem, because PAFL is a much shorter measurement relative to the fish’s size than usual length measure-ments such as fork length or total length. The 2004 EBS mean lengths translate to a weight

of 3.43 kg/fish for females versus 1.86 kg/fish for males, a difference of over 80% (based on the length-weight relationships that were presented previously). Overall in the EBS surveys, the population size of females was about three times greater than that of males (Figure 4; see histograms for “all depths”). In the GOA surveys, females were ∼4–6 times more abundant than males.

Similar to giant grenadier, females of many grenadier species are reported to be larger than males. For three out of four gren-adier species examined off the U.S. West Coast, maximum length of females was sub-


stantially larger than males (Stein and Pearcy 1982). Females of three grenadier species in the Mediterranean Sea were also found to be bigger than males (Massuti et al. 1995). Al-though it may be generally true that female grenadier are larger than males for most spe-cies, exceptions do occur. For example, male and female length compositions were very similar for both Pacific and popeye grena-dier in the 2002 and 2004 EBS trawl surveys (Hoff and Britt 2003, 2005).

Population size compositions for gi-

ant grenadier from the recent trawl surveys indicate that lengths of the fish were larger in the EBS compared to the GOA (Figure 5). In both the 2002 and 2004 EBS surveys, mean length for sexes combined was 28.1 cm PAFL, compared to 24.9 cm and 25.9 cm for sexes combined in the 1999 and 2005 GOA surveys, respectively. This difference in size between areas held true for both sexes, but in particular, a much greater percentage of the EBS population consisted of females over 30 cm in length.

Dep

th s

trat

um (m

)

Percent of population at each stratum

2004 EBS

24

59

35

15

4

0

76

41

65

85

96

100

0 20 40 60 80 100

all depths

1000-1200

800-1000

600-800

400-600

200-400

male female

2002 EBS

24

54

32

14

4

0

76

46

68

86

96

100

0 20 40 60 80 100

all depths

1000-1200

800-1000

600-800

400-600

200-400

male female

1999 GOA

22

34

24

3

0

0

78

66

76

97

100

0

0 20 40 60 80 100

all depths

701-1000

501-700

301-500

201-300

101-200

male female

2005 GOA

15

35

14

6

0

0

85

65

86

94

100

0

0 20 40 60 80 100

all depths

701-1000

501-700

301-500

201-300

101-200

male female

Figure 4. Sex distribution, by depth stratum, of the estimated population of giant grenadier Al-batrossia pectoralis in recent bottom trawl surveys of the eastern Bering Sea (EBS) and Gulf of Alaska (GOA). (Depth strata shown for the EBS and GOA are not the same because each survey had a different stratification scheme for depth).

428 Clausen

The GOA 1999 size compositions showed a relatively large number of very small fish less than 15 cm PAFL (Figure 5). Because giant grenadiers of this size are re-ported to be pelagic and not caught in bot-tom trawls (see previous section Life Histo-ry, Habitat, and Ecological Relationships), the occurrence of these fish in 1999 is of special interest. Survey haul records indi-cate that virtually all these small fish came from a single haul at a depth of 569 m in the Chirikof area (Figure 1). Therefore, the fish appear to be either a misidentification or coding error, or if correct, represent a highly anomalous event. This catch was the only substantial occurrence of giant grena-dier less than15 cm PAFL for any haul in the GOA trawl database. Misidentification is considered unlikely because several ex-perienced fishery scientists participated in

this survey, although it is possible the fish were popeye grenadier, which commonly are around 10 cm PAFL and can be taken in bottom trawls. If the identification was valid, a reasonable scenario is that the fish were caught in the deep midwater during retrieval of the net.

Relationship between size and depth

To investigate the relationship between size of the fish and depth, mean popula-tion size by depth stratum was determined for the recent EBS and GOA trawl surveys (Table 5). This analysis was done separately for males and females because of the large difference in depth distribution between the sexes and because the sexes differ sub-stantially in size. The results indicate a pro-nounced decline in mean size of females

Pop

ulat

ion

(mill

ions

)

Pre-anal fin length (cm)

0

2

4

6

8

10

10 20 30 40 50

male female

male mean = 23.8female mean = 29.5

2002 EBSTrawl Survey

02468

1012

10 20 30 40 50

male female


2004 EBSTrawl Survey

02468

1012

10 20 30 40 50

male female


1999 GOATrawl Survey

0

5

10

15

20

25

10 20 30 40 50

male female


2005 GOATrawl Survey

sexes combinedmean = 28.1

sexes combinedmean = 28.1

sexes combinedmean = 24.9 sexes combined

mean = 25.9

Figure 5. Estimated population size compositions for giant grenadier Albatrossia pectoralis in re-cent bottom trawl surveys of the eastern Bering Sea (EBS) and Gulf of Alaska (GOA). (EBS surveys covered depths of 200–1,200 m and GOA surveys covered depths of 200–1,000 m).


from shallow to deep. In each survey, aver-age female size was always largest in the shallowest stratum, whereas the smallest size was consistently in deeper water. In contrast to females, there did not appear to be any significant size trend by depth for males. These results for giant grenadier are contrary to the so-called “bigger-deeper” trend for groundfish, which is also termed “Heincke’s Law” in honor of the early 20th century biologist who first noted this phenomenon in the North Sea. This “law”

states that larger-sized fish tend to inhabit the deeper portions of the species’ depth range. Merrett and Haedrich (1997) provide a detailed discussion of the “bigger-deeper” trend as it relates to the distribution of deep-water fish. They note that the trend does indeed appear to hold true for many deep-water species, including some grenadiers, but there are also many exceptions. Based on the data in Table 5, it appears that giant grenadier in Alaska is one of those excep-tions.

Eastern Bering Sea

Depth Male Female Sexes combinedstratum (m) 2002 2004 2002 2004 2002 2004

200–400 - - 35.9 35.5 35.9 35.5400–600 22.6 22.3 31.4 30.1 31.0 29.9600–800 23.8 22.4 29.5 28.6 28.8 27.7800–1,000 23.9 23.9 28.6 28.8 27.1 27.11,000–1,200 23.9 25.2 26.2 30.8 25.0 27.5

Gulf of Alaska

Depth Male FemaleSexes combined

stratum (m) 1999 2005 1999 2005 1999 2005

201–300 - - 30.3 28.7 30.3 28.7301–500 25.4 24.7 28.7 26.9 28.6 26.8501–700a 23.0 23.3 25.1 25.9 25.9 25.5701–1,000 23.2 23.4 26.0 25.8 25.0 25.0

aOne haul in this stratum in 1999 that had an anomalously large catch of fish <15 cm PAFL was excluded from the data (see text for discussion).

Table 5. Mean estimated population size (cm), by depth stratum and sex, for giant grenadier Albatrossia pectoralis in recent bottom trawl surveys of the eastern Bering Sea and the Gulf of Alaska. Depth strata shown for the EBS and GOA are not the same because each survey had a different stratification scheme for depth. Dashes indicate no fish were caught.

430 Clausen

Ecological importance of giant grenadier

Results of the recent EBS and GOA trawl surveys emphasize the important ecological role of giant grenadier in Alaskan waters. In both the 2002 and 2004 EBS trawl surveys, gi-ant grenadier was by far the most abundant spe-cies and comprised about half the total biomass for all species at depths 200–1,000 m on the continental slope (Figure 6). Similarly, in the 1999 and 2005 GOA surveys, giant grenadier

was the most abundant slope species at depths 200–1,000 m and composed approximately one-third the total biomass in this stratum. The GOA surveys also covered the continental shelf, and among all species caught in the 1999 GOA survey on both the shelf and slope, giant grena-dier was ranked the fifth most abundant species in terms of CPUE, after arrowtooth flounder Atheresthes stomias, Pacific ocean perch Se-bastes alutus, walleye pollock Theragra chal-cogramma, and Pacific halibut Hippoglossus stenolepis (Britt and Martin 2001).

2002 EBS

Giantgrenadier

PopeyeArrowtooth

Otherspecies

36%

POP8%

46%

5%5%

2004 EBS

Giantgrenadier

Popeye

Arrowtooth

Otherspecies

27%

POP

9%

55%

1999 GOA

Giantgrenadier

Arrowtooth

Otherspecies

30%

POP 17%

33%

11%9%

2005 GOA

Giantgrenadier

Sablefish

Arrowtooth

Otherspecies 25%

POP 12%

32%

20%11%

Sablefish

Figure 6. Biomass estimates (%) of species caught in recent bottom trawl surveys of the eastern Bering Sea (EBS) and Gulf of Alaska (GOA) continental slope at depths 200–1,000 m. (Arrow-tooth = Arrowtooth flounder Atheresthes stomias, POP = Pacific ocean perch Sebastes alutus, Popeye = Popeye grenadier Coryphaenoides cinereus).Source: the Alaska Fisheries Science Center’s “Racebase” trawl survey database, October 2006, available from the U.S. National Marine Fisheries Service, Alaska Fisheries Science Center, RACE Division, 7600 Sand Point Way NE, Seattle WA 98115.

431The Giant Grenadier in Alaska Comparison of abundance between Alaska and the U.S. West Coast

The EBS and GOA trawl surveys re-sults for giant grenadier can be compared with those for another region of the north-east Pacific, the U.S. West Coast. The U.S. National Marine Fisheries Service conducts comprehensive bottom trawl surveys of the continental slope off the West Coast that are generally analogous to those off Alaska, al-though the details of the trawl gear and sta-tion pattern are somewhat different (Builder Ramsey et al. 2002; Keller et al. 2006). Area-swept estimates of biomass and mean CPUE are computed just as they are for the Alaska surveys. The West Coast trawl survey results indicate that giant grenadier is an important species on the slope in this region, but it does not dominate in the slope ecosystem as it does in Alaska. For example, whereas gi-ant grenadier was overwhelmingly the most abundant species on the slope of the EBS and GOA, it was ranked fourth in mean CPUE in the 2002 West Coast survey at depths of 550–1,280 m, after longspine thornyhead Se-bastolobus altivelis, Dover sole Microstomus pacificus, and Pacific grenadier (Keller et al. 2006). Overall mean CPUE for giant grena-dier at these depths in the 2002 West Coast survey was about 800 kg/km2 (Keller et al. 2006), as compared to mean CPUEs of about 10,000–15,000 kg/km2 for giant grenadier in depths of 501–1,000 m in the 1999 GOA survey (Britt and Martin 2001). Therefore, it appears that within the slope habitat at these depths, giant grenadier may be at least an or-der of magnitude more abundant in the GOA than off the U.S. West Coast.

Longline surveys

Longline survey methods

Longline surveys of the continental slope off Alaska have been conducted annu-

ally since 1979 (Hanselman et al. 2006). The primary purpose of the surveys is to assess abundance of sablefish, which is an impor-tant commercial species caught on the slope in Alaska, but giant grenadier are also caught in large numbers. Standardized longline sta-tions are fished in the survey each summer along the slope throughout the GOA, and in the years since 1996 have also covered either the EBS or the AI. A total of 45 stations is fished in the GOA, 16 in the EBS, and 14 in the AI, and the same stations are repeat-ed from year to year. One station is fished per day with 7,200 baited hooks attached at regular intervals to a groundline 8.6 nautical miles in length. The standard depth sampled at each station is 201–1,000 m, although be-cause of bottom topography sometimes this entire range cannot be covered at a station. Standard bait used is chopped Atlantic squid Illex illecebrosus. (See Rutecki et al. (1997) for details on survey gear and methodology). An index of relative biomass, called the “rela-tive population weight” (RPW), is computed for all the major species caught in the survey. However, RPW values for giant grenadier are only available for the years since 1990.11 The analytical methods for determining RPW are described by Sigler and Zenger (1989), and it should be noted that although RPW is an in-dex of biomass, it is actually a unit-less value. Other measures of giant grenadier abundance in the surveys have been computed for the years 1979–1989, including catch-per-unit-effort values and an index of abundance by number, called “relative population number.” These data for the surveys before 1990 are presented in Sasaki and Teshima (1988) and Zenger and Sigler (1992), but will not be dis-cussed in this report.

In the GOA and AI, the longline gear used in the surveys is able to sample a high 11 C. Lunsford, U .S. National Marine Fisheries Service, Alaska Fisheries Science Center, Auke Bay Laboratories, 17109 Pt. Lena Loop Rd., Juneau, AK 99801. Personal communication. July 2004.

432 Clausen

proportion of the steep and rocky habitat that characterizes the slope in these regions. This is in contrast to the bottom trawls used on the trawl surveys, which are often limited to fish-ing on relatively smooth substrate. Because of this difference, the longline surveys may do a better job of monitoring abundance of giant grenadier on the slope, although they do not provide estimates of absolute biomass.

Abundance trends and regional differences in abundance

The RPWs provide a standardized time series of annual abundance for giant grenadier in the GOA for the period 1990–2006 and an intermittent series in the AI and EBS (Table 6). The survey was expanded from the GOA into the AI in 1996 and to the EBS in 1997, but these latter two regions have only been sampled in alternating years. Therefore, the time series is much less complete for the AI and EBS. In the GOA, definitive trends in RPW are difficult to discern. Generally, however, RPW decreased in the first three years to a low of 800,000, then increased to a high in 1997 of 1,420,000, and finally diminished again to a low of 900,000 in 2004. Although Sigler and Fujioka (1988) have used the bootstrap method to analyze changes in the survey’s RPWs for sablefish, no corresponding analysis has been done to de-termine whether the trends in giant grenadier RPW are statistically valid. The RPW values in Table 6 also indicate that giant grenadier are particularly abundant in the AI; in all years the AI was sampled, RPWs in this region were greater than those in the GOA, even though the area of potential habitat on the slope for depths 201–1,000 m is approximately 75% larger in the GOA (Sasaki 1985).

Giant grenadier catch rates in the surveys can be used to examine the geographic distri-bution of abundance in more detail (Table 7). Highest catch rates are seen in the eastern AI, the Shumagin and Chirikof areas in the GOA, and Bering areas 3 and 4, which are located

NW of the Pribilof Islands (see Figure 1 for the location of these areas). The catch rates also provide evidence for the extreme abun-dance of giant grenadier in these areas. For ex-ample, in the SE Aleutians and Shumagin ar-eas, giant grenadier were caught on over 25% of the hooks that were set. In the GOA, there appears to be a definite decline in catch rates as one progresses from the west (Shumagin area) to the east (Southeastern area). The 1999 and 2005 GOA trawl surveys also showed a similar trend and found very low catch rates and biomass estimates for giant grenadier in the eastern GOA (Britt and Martin 2001; Foot-note12).

Size composition

Population size compositions for giant grenadier in the EBS and eastern AI regions (Figures 7 and 8) were consistently larger than those in the GOA (Figure 9) for any given sur-vey year. This difference in size between the EBS and the GOA agrees with that found in the recent trawl surveys of these two regions, which were discussed previously. The size dis-tributions of the longline surveys in the EBS tend to be spread over more lengths and in-clude more large fish >35 cm PAFL. All three regions have shown a general decline in size since about 2000, with recent surveys (2005 for the GOA and EBS and 2006 for the eastern AI) showing the smallest mean length for any year in the time series. In particular, the GOA distribution became skewed toward smaller fish in recent years, and mean length declined from 30.9 cm in 2000 to 27.9 cm in 2005. How-ever, this declining trend in the GOA ended in 2006, when mean length increased to 28.5 cm. Further analysis is needed to understand the

12 Unpublished data for 2005 GOA trawl survey in NMFS Alaska Fisheries Science Center’s “Racebase” trawl survey database, October 2005. U.S. National Marine Fisheries Service, Alaska Fisheries Science Center, RACE Division, 7600 Sand Point Way NE, Seattle WA 98115.


Year Eastern Bering Sea Aleutian Islands Gulf of Alaska

1990 - - 1,069,723

1991 - - 959,567

1992 - - 805,356

1993 - - 1,148,754

1994 - - 1,133,409

1995 - - 1,402,019

1996 - 1,281,800 1,251,843

1997 840,693 - 1,418,428

1998 - 1,348,632 1,185,404

1999 632,379 - 1,277,141

2000 - 1,743,203 1,230,161

2001 431,114 - 1,198,183

2002 - 1,760,703 1,011,721

2003 592,467 - 1,194,939

2004 - 1,662,371 903,906

2005 771,441 - 943,662

2006 - 1,991,259 963,947

mean 653,619 1,631,328 1,123,421

Table 6. Giant grenadier Albatrossia pectoralis relative population weight, by region, in longline surveys of the upper continental slope in Alaska, 1990–2006. Depths covered were 201–1,000 m, and dashes indicate years that the eastern Bering Sea or Aleutian Islands were not surveyed. Gulf of Alaska values include data only for the upper continental slope and do not include con-tinental shelf gullies sampled in the surveys.Source: C. Lunsford, U.S. National Marine Fisheries Service, Alaska Fisheries Science Center, Auke Bay Laboratories, 17109 Pt. Lena Loop Rd., Juneau, AK 99801. Personal communication, Oct. 2006.

434 Clausen

reasons for the declines, i.e., if the declines were due to fewer large fish, more small fish, or a combination of these two factors.

A comparison between Figure 5 (size compositions for the EBS and GOA trawl surveys) and Figures 7 and 9 (size composi-tions for the EBS and GOA longline surveys) reveals that the size distributions were con-siderably smaller for giant grenadier in the trawl surveys. For example, mean length for combined sexes in the 1999 GOA trawl sur-vey was 24.9 cm PAFL, whereas it was 30.4 cm in that year’s GOA longline survey. As discussed previously, the 1999 trawl survey caught some unusually small giant grenadier under 15 cm PAFL, which may make it rath-

er anomalous for comparisons. However, if these small fish are excluded from the size compositions, mean population size for the 1999 trawl survey is then 26.4 cm, which is still much less than the 30.4 cm mean length in that year’s GOA longline survey. Simi-larly, giant grenadier populations in the 2002 and 2004 EBS trawl surveys averaged 28.1 cm, versus an average of 32.4 cm in the 2003 EBS longline survey. These data indicate that there is a substantial difference in the size se-lectivity between the gear types used in each survey. It appears that the longline surveys are not sampling many of the smaller giant grenadier less than ∼25 cm PAFL that are taken in the trawl surveys.

Table 7. Giant grenadier Albatrossia pectoralis mean catch rates (no/100 hooks), by area (as shown in Fig. 1), in longline surveys of the continental slope in Alaska, 1990–2006 at depths 201–1,000 m (For actual years surveyed in the eastern Bering Sea, Aleutian Islands, and Gulf of Alaska, see Table 6; data are not available for the NW and SW Aleutians). Source: C. Lunsford, U.S. National Marine Fisheries Service, Alaska Fisheries Science Center, Auke Bay Laboratories, 17109 Pt. Lena Loop Rd., Juneau, AK 99801. Personal communication, Oct. 2006.

MeanArea catch rate

Eastern Bering SeaBering 4 19.1Bering 3 23.9Bering 2 8.6Bering 1 1.3Aleutian IslandsNE Aleutians 20.2SE Aleutians 25.6Gulf of AlaskaShumagin 25.8Chirikof 21.5Kodiak 12.1W Yakutat 6.3E Yakutat 3.6Southeastern 3.1



0

5

10

15

10 20 30 40 50

Eastern Bering Sea 1997

mean = 31.7

0

5

10

15

10 20 30 40 50


mean = 31.0

0

5

10

15

10 20 30 40 50


mean = 33.1

0

5

10

15

10 20 30 40 50


mean = 32.4

0

5

10

15

10 20 30 40 50


mean = 30.6

Figure 7. Estimated population size compositions for giant grenadier Albatrossia pectoralis in the 1997–2005 longline surveys of the eastern Bering Sea.

436 ClausenPe

rcen

t


0

5

10

15

10 20 30 40 50

Eastern Aleutians 1996

mean = 31.9

0

5

10

15

10 20 30 40 50


mean = 31

0

5

10

15

10 20 30 40 50


mean = 32.1

0

5

10

15

10 20 30 40 50


mean = 32.4

0

5

10

15

10 20 30 40 50


mean = 30.4

0

5

10

15

10 20 30 40 50


mean = 31.9

0

5

10

15

10 20 30 40 50


mean = 30.0

Figure 8. Estimated population size compositions for giant grenadier Albatrossia pectoralis in the 1996–2006 longline surveys of the eastern Aleutian Islands (area of the Aleutian Islands east of 180o longitude). (Size composition data are not available for the western Aleutian Islands).

437The Giant Grenadier in AlaskaPe

rcen

t


0

5

10

15

10 20 30 40 50

1992mean = 30.6

0

5

10

15

10 20 30 40 50

1999mean = 30.4

0

5

10

15

10 20 30 40 50

1998mean = 30.1

0

5

10

15

10 20 30 40 50

1997mean = 30.6

0

5

10

15

10 20 30 40 50

1996mean = 30.8

0

5

10

15

10 20 30 40 50

1993mean = 30.8

0

5

10

15

10 20 30 40 50

1994mean = 31.1

0

5

10

15

10 20 30 40 50

1995mean = 30.6

Gulf of Alaska

Gulf of Alaska

Gulf of Alaska

Gulf of Alaska

Gulf of Alaska

Gulf of Alaska

Gulf of Alaska

Gulf of Alaska

Figure 9. Estimated population size compositions for giant grenadier Albatrossia pectoralis in the 1992–2006 longline surveys of the Gulf of Alaska.

438 ClausenPe

rcen

t


0

5

10

15

10 20 30 40 50

2000mean = 30.9

0

5

10

15

10 20 30 40 50

2004mean = 29.1

0

5

10

15

10 20 30 40 50

2005mean = 27.9

0

5

10

15

10 20 30 40 50

2001mean = 29.7

0

5

10

15

10 20 30 40 50

2002mean = 29.7

0

5

10

15

10 20 30 40 50

2003mean = 29.2

Gulf of Alaska

Gulf of Alaska

Gulf of Alaska

Gulf of Alaska

Gulf of Alaska

Gulf of Alaska

0

5

10

15

10 20 30 40 50

2006mean = 28.5

Gulf of Alaska

Figure 9. Continued

439The Giant Grenadier in Alaska Sex and depth distribution

Information on sex distribution of giant grenadier caught in the longline survey was collected only in 2006 (Table 8). Results show that females were the overwhelming majority of the catch, comprising 97% of the fish sam-pled in the GOA and 94% in the eastern AI. Females especially predominated in depths shallower than 800 m. Because these are the depths in which the longline fishery operates, this strongly suggests that most of the commer-cial catch of giant grenadier is female. (Previ-ously, there has been no information on either the sex or size composition of giant grenadier caught in Alaskan longline fisheries because observers have not conducted detailed sam-pling for these fish. However, in 2007, observ-ers on commercial longline vessels have been requested to begin collecting these data for giant grenadier). Similar to the trawl surveys, there was a trend toward an increased number of males in progressively deeper strata, and the largest percentage of males was in the deepest stratum in both surveys (compare Table 8 with Figure 4). These results imply that much of the male population may reside in depths >1,000–1,200 m that are not covered by the surveys, at

least during the summer period when the sur-veys take place. Also, the percentage of males caught in the 2006 longline survey was much lower than the percentages found in the trawl surveys. This is not surprising due to the fact that males average significantly smaller than females (Figure 5), and the longline gear ap-pears to select for larger fish.

Depth distributions of giant grenadier RPW for the EBS and AI in longline surveys since 2002 have been somewhat variable (Fig-ures 10 and 11). In three of the five longline surveys in these regions, RPW showed a sub-stantial decline in the deepest stratum (801–1,000 m). For these three surveys (2002 and 2004 in the AI and 2003 in the EBS), the results suggest that the surveys may have covered a major portion of the biomass distribution of giant grenadier. However, the 2005 EBS and the 2006 AI surveys were different, as they in-dicated the highest RPW was at 601–1,000 m and that additional sampling needs to be done in deeper waters to cover more of the depth range of giant grenadier.

In contrast to the EBS and AI, the depth distribution of RPW since 2002 for giant grenadier in the GOA was very similar in each of the last five longline surveys (Figure 12).

Perc

ent


0

5

10

15

10 20 30 40 50

2000mean = 30.9

0

5

10

15

10 20 30 40 50

2004mean = 29.1

0

5

10

15

10 20 30 40 50

2005mean = 27.9

0

5

10

15

10 20 30 40 50

2001mean = 29.7

0

5

10

15

10 20 30 40 50

2002mean = 29.7

0

5

10

15

10 20 30 40 50

2003mean = 29.2

Gulf of Alaska

Gulf of Alaska

Gulf of Alaska

Gulf of Alaska

Gulf of Alaska

Gulf of Alaska

0

5

10

15

10 20 30 40 50

2006mean = 28.5

Gulf of Alaska

Table 8. Sex distribution, by depth stratum, of giant grenadier Albatrossia pectoralis sampled in the 2006 longline survey in Alaska. Source: C. Lunsford, U.S. National Marine Fisheries Service, Alaska Fisheries Science Center, Auke Bay Laboratories, 17109 Pt. Lena Loop Rd., Juneau AK 99801. Personal communication, Oct. 2006.

Eastern Aleutian Islands Gulf of AlaskaDepth No. fish Percent Percent No. fish Percent Percentstratum (m) sampled male female Sampled male female

201–300 5 0.0 100.0 176 0.0 100.0301–400 134 0.0 100.0 1,097 0.5 99.5401–600 824 1.2 98.8 1,970 1.5 98.5601–800 684 5.8 94.2 1,876 3.8 96.2801–1000 278 24.8 75.2 871 10.1 89.9All depths 1,925 6.2 93.8 5,990 3.2 96.8

440 Clausen

Relative population weight (1,000's)

Dep

th s

trat

um (m

)

0 50 100 150 200 250 300

801-1000

601-800

401-600

301-400

201-300

101-200 2003 Bering Sea Longline Survey

0 50 100 150 200 250 300

801-1000

601-800

401-600

301-400

201-300

101-200 2005 Bering Sea Longline Survey

Figure 10. Depth distribution of giant grenadier Albatrossia pectoralis relative population weight in the 2003 and 2005 longline surveys of the eastern Bering Sea.

RPW was relatively high for each of the three deepest strata sampled in these surveys: 401–600 m, 601–800 m, and 801–1,000 m, with the peak at 801–1,000 m in all years except 2006. These data indicate that additional sampling needs to be done in the GOA at depths over 1,000 m to determine where the abundance of giant grenadier begins to decline. The data also suggest that an unknown and perhaps signifi-cant portion of the giant grenadier population in the GOA may reside in depths beyond 1,000 m that are not currently surveyed. These depth results are similar to those depicted in Figure 2 for the 1999 GOA trawl survey, which also showed a large biomass of giant grenadier ex-tending to at least 1,000 m. The GOA long-line depth distributions, however, are different than those seen in the 2005 GOA trawl survey,

which indicated a considerable decline in bio-mass at depths over 700 m.

Competition for hooks in the longline survey

A possible factor that may have influ-enced the survey’s catch rates for giant gren-adier is competition among species for baited hooks. Zenger and Sigler (1992) suggested that giant grenadier may be out-competed on the longline by more energetic fish such as sablefish. If sablefish are more quickly at-tracted to and caught on the hooks, or are able to drive away giant grenadier when both spe-cies are competing for the hooks, the survey’s catch rates for giant grenadier would not be a true indicator of their abundance. This could



Dep

th st

ratu

m (m

)

0 100 200 300 400 500 600

801-1000

601-800

401-600

301-400

201-300

101-200 2002 Aleutians Longline Survey

0 100 200 300 400 500 600

801-1000

601-800

401-600

301-400

201-300


0 100 200 300 400 500 600

801-1000

601-800

401-600

301-400

201-300


Figure 11. Depth distribution of giant grenadier Albatrossia pectoralis relative population weight in the 2002, 2004, and 2006 longline surveys of the eastern Aleutian Islands (area of the Aleu-tian Islands east of 180o longitude). (Data on depth distribution are not available for the western Aleutian Islands).

442 ClausenD

epth

stra

tum

(m)


0 100 200 300 400

801-1000

601-800

401-600

301-400

201-300

101-200

0 100 200 300 400

801-1000

601-800

401-600

301-400

201-300

101-200 2003 GOA Longline Survey

0 100 200 300 400

801-1000

601-800

401-600

301-400

201-300

101-200

0 100 200 300 400

801-1000

601-800

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101-200

2004 GOA Longline Survey

0 100 200 300 400

801-1000

601-800

401-600

301-400

201-300

101-200 2006 GOA Longline Survey2002 GOA Longline Survey

Figure 12. Depth distribution of giant grenadier Albatrossia pectoralis relative population weight in the 2002–2006 longline surveys of the Gulf Alaska (GOA).

2005 GOA Longline Survey


be a partial explanation for the survey’s high catch rates of giant grenadier in the EBS and eastern AI, as the relatively low abundance of sablefish in these two regions could result in a greater number of unoccupied hooks avail-able for catching giant grenadier. Similarly, it could also explain the large RPW values for giant grenadier in the deep 801–1,000 m stratum in the GOA surveys and in some of the AI and EBS surveys because the relative-ly low abundance of sablefish in this stratum may allow more giant grenadier to be caught. To investigate the problem of possible com-petition for hooks in the longline survey, ad-ditional analysis and possibly experimental studies are needed.

Discussion of Possible

Overfishing of Giant Grenadier in Alaska

Although currently there is no directed fishing for giant grenadier in Alaska, the esti-mated catch of these fish taken as bycatch in other fisheries (Table 1) may be large enough to raise concerns from a conservation stand-point, for at least three reasons:

a) All the giant grenadier caught are dis-carded, and none of these survive because the fish cannot withstand the pressure change caused by retrieval to the surface.

b) There have been several recent studies that indicate deep-sea fish such as grenadiers appear to be especially susceptible to overfish-ing, which suggests fishery managers need to exercise particular caution when setting catch levels for these fish. One study in the NW At-lantic examined the relative abundance over a 20 year period of five deep-water species that were taken in target fisheries or as by-catch, and abundance of all five progressively declined to the point that each could be con-sidered “critically endangered” (Devine et al. 2006). Two of these species were grenadiers.

The depletion of one of these grenadiers, the roundnose grenadier Coryphaenoides rupes-tris, has also been documented by Atkinson (1995). In the early years of the fishery for this species, catches were as high as 75,000 mt, but landings quickly declined in later years even though exploitation was only moderate. Roundnose grenadier stocks appear to have become depleted with little sign of recovery. The particular vulnerability of deep-sea fish such as grenadiers to overfishing is likely due to the life history traits they have evolved in response to living in the relatively unproduc-tive environment of the deep ocean. These traits may include longevity, slow growth, low fecundity, late maturation, low metabolic rates, and not spawning in some years (Mer-rett and Haedrich 1997; Koslow et al. 2000; Drazen 2008, this volume). All these char-acteristics imply that the replenishment rate for these fish could be less than recruitment if they are subject to fishing pressure.

c) Because the sablefish and Greenland halibut fisheries operate at depths where female giant grenadier greatly outnumber males, the vast majority of the giant grena-dier catch is female. Disproportionate remov-al of females by the fishery clearly reduces the spawning potential of the stocks and could put them at greater risk of overfishing if catches were sufficiently large.

Thus, for all these reasons, examination of possible overfishing of giant grenadiers is warranted.

Relatively little information is available on the population dynamics of giant grena-dier for use in determining possible over-fishing. The only modern age determination study for giant grenadier produced uncer-tain results, although it indicated that giant grenadier appear to be relatively long-lived and may have a maximum age of ∼56 years. Due to this uncertainty, age-structured mod-eling is not possible to help determine if giant

444 Clausen

grenadier have been overfished. For data-de-ficient fish populations such as giant grena-dier, one way to estimate overfishing levels and appropriately conservative harvest levels relies on use of just two population param-eters: the natural mortality rate M and an esti-mate of biomass B (Quinn and Deriso 1999). In Federal waters of Alaska, the NPFMC has adopted prescribed overfishing and harvest levels for species whose only information is M and B (Witherell and Ianelli 1997). These definitions are: 1) overfishing (OFL): OFL = M × B, and 2) harvest levels (i.e., accept-able biological catch (ABC)): ABC ≤ (0.75 × OFL). Estimates of both biomass and natural mortality are available for giant grenadier in Alaska and have been presented in this re-port, so this methodology can be applied to these fish.

There have been various biomass esti-mates for giant grenadier in each of the three major management regions for groundfish in Alaska (Table 3), and a decision must be made as to which of these estimates are most appropriate for the OFL and ABC computa-tions. For the EBS and the GOA, I chose to use the mean of the two recent surveys in each region (2002 and 2004 in the EBS, and 1999 and 2005 in the GOA) as the best esti-mates available for the computations of OFL and ABC. These values are: 546,453 mt for EBS, and 488,627 mt for GOA.

Because no trawl surveys in the AI since 1986 have sampled deeper waters where most giant grenadier biomass is found, I recom-mend an indirect method for determining a more up-to-date biomass in this region. This method is based on using a combination of longline survey RPW values and trawl sur-vey biomass estimates to compute biomass estimates for the AI. Since 1996 and 1997 when the longline survey first sampled the AI and the EBS, mean RPW values for each region (1,631,328 and 653,619, respectively; Table 6) indicate that the biomass of giant grenadier in the AI is approximately 2.50

times greater than in the EBS. If this ratio of 2.50 is then applied as an adjustment factor to the mean EBS trawl survey biomass in 2002 and 2004 of 546,453 mt, an indirect biomass estimate of 1,363,858 mt can be computed for the AI. Similarly, an alternative indirect biomass can be computed for the AI which is based on survey data from the AI and GOA, rather than from the AI and EBS. Us-ing a procedure identical to that above, the mean longline RPW for giant grenadier in the years 1996–2006 is 1,631,328 in the AI and 1,143,576 in the GOA, which equals a ratio of 1.43. Using this ratio as an adjustment fac-tor for the trawl survey’s mean GOA biomass for 1999 and 2005 of 488,627 mt yields an indirect biomass estimate of 697,034 mt for the AI.

The two indirect biomass estimates for the AI differ greatly in value, and selecting which to use in the determinations of OFL and ABC has a substantial effect on the re-sults. Clearly, the difference is large enough that it indicates uncertainty concerning these estimates. The 1.4 million mt estimate (based on data from the AI and EBS surveys) may be more accurate because both the longline and trawl surveys in the GOA do not sample the abundance of giant grenadier as well as their corresponding surveys in the EBS. In par-ticular, longline survey catch rates for giant grenadier in the GOA are likely affected by the fact that sablefish are very abundant there and may out-compete giant grenadiers for the hooks, which may introduce a bias into the survey results in this region for grenadier. In contrast, sablefish abundance is relatively low in both the EBS and AI, which may re-sult in better and more comparable longline survey data for giant grenadier in these areas. To a lesser degree, GOA trawl surveys may also be hindered in their determination of gi-ant grenadier abundance compared to trawl surveys in the EBS because of the more dif-ficult trawling conditions along the slope in the GOA.


In addition to biomass, the NPFMC’s other required parameter for computations of OFL and ABC for a species such as gi-ant grenadier is an estimate of the natural mortality rate. As discussed previously, a natural mortality estimate for giant grena-dier of 0.074 can be determined based on the maximum age of 56 years in Burton’s (1999) age study. However, this study did not find a reasonable fit of von Bertalanffy parameters to the age data, which is indica-tive of extremely variable and uncertain re-sults. Hoenig’s (1983) method, which was used to determine the mortality estimate, is quite sensitive to the maximum age used in its estimation of mortality. Consequently, if the true maximum age is substantially different than the age of 56 years reported by Burton (1999), the mortality estimate of 0.074 may not be accurate. For example, several other grenadier species have maxi-mum reported ages of 60–70+ years (Mer-rett and Haedrich 1997; Matsui et al. 1990; Andrews et al. 1999), and if giant grenadier grow to this age, Hoenig’s method would yield a significantly lower estimate of mor-tality. Therefore, in addition to the mortality estimate of 0.074, it may also be appropri-ate to use an alternative, proxy estimate of natural mortality for giant grenadier in the OFL and ABC determinations. A suggested proxy natural mortality rate is 0.057 that has been estimated for Pacific grenadier (Clausen and Gaichas 2004). Similar to the mortality rate that was computed for giant grenadier, this value was also determined using Hoenig’s method, but it was based on an age determination study that resulted in successful von Bertalanffy growth equa-tions (Andrews et al. 1999).

A summary of OFL and ABC computa-tions based on these estimates of biomass and mortality is shown in Table 9. Table 9a presents a less-conservative approach to these calculations because it uses the higher biomass estimate for the AI of ∼1.4

million mt and also uses the higher natural mortality of 0.074 that was determined for giant grenadier. In contrast, Table 9b pres-ents a more conservative and risk-averse approach in which the lower biomass esti-mate for the AI of ∼700,00 mt and the proxy natural mortality of 0.057 are used. Results for both approaches indicate that overfish-ing of giant grenadier is not presently oc-curring in Alaska, despite the reasons for concern that were discussed previously. For the less-conservative approach in Table 9a, the OFLs and ABCs are much greater than mean catch for the years 1997–2005. This is especially true in the EBS and AI, where even the ABCs are at least an order of mag-nitude greater than the mean catches. The more conservative, risk-averse approach in Table 9b shows values of OFL and ABC that are substantially lower than those in Table 9b, especially for the AI where the biomass estimate is much less. However, despite these lower values, the OFLs and ABCs are still much larger than the mean catch. Therefore, both approaches indicate that the biomass of giant grenadier in Alas-ka appears to be so high that it has been able to support the catches that have been taken in recent years.

The OFLs and ABCs in Table 9 for gi-ant grenadier in the EBS and AI are so large relative to the mean catch that it appears catches could increase substantially in these areas without endangering the stocks. The ratio of OFLs and ABCs to mean catch is much smaller in the GOA, where more giant grenadier are caught than in the EBS and AI, but not so low as to indicate that overfishing is currently a problem in this area. However, because of the special con-cerns for susceptibility of giant grenadier to overharvest, fishery managers may want to err on the side of caution and ensure that a large increase in the GOA catch does not occur until better information is available on natural mortality, biomass, and age.

446 Clausen

a.

HigherHigher natural OFL ABC mean

Area biomass mortality M definition OFL definition ABC catch

EBS 546,453 0.074 biom × M 40,437 OFL × 0.75 30,328 3,154AI 1,363,858 0.074 biom × M 100,925 OFL × 0.75 75,694 2,358GOA 488,627 0.074 biom × M 36,158 OFL × 0.75 27,119 10,903Total 2,398,938 177,521 133,141 16,416

Note: a less conservative approach in which computations are based on a higher estimate of biomass in the AI and on a natural mortality rate of 0.074 for giant grenadier.

b.

LowerLower natural OFL ABC mean

Area biomass mortality M definition OFL definition ABC catch

EBS 546,453 0.057 biom × M 31,148 OFL × 0.75 23,361 3,154AI 697,034 0.057 biom × M 39,731 OFL × 0.75 29,798 2,358GOA 488,627 0.057 biom × M 27,852 OFL × 0.75 20,889 10,903Total 1,732,114 98,730 74,048 16,416

Note: a more conservative approach in which computations are based on a lower estimate of biomass in the AI and on a proxy natural mortality rate of 0.057 for giant grenadier. The proxy rate is the mortality rate for Pacific grenadier.

Table 9. Computations of overfishing levels (OFL) and acceptable biological catch (ABC) for gi-ant grenadier Albatrossia pectoralis in the eastern Bering Sea (EBS), Aleutian Islands (AI), and Gulf of Alaska (GOA). For comparison, the mean estimated catch of giant grenadier for the years 1997–2005 is also shown. (Biomass, OFL, ABC, and mean catch are in metric tons).

447The Giant Grenadier in Alaska Summary

Little information is available on the gi-ant grenadier in Alaska, although this fish is an important species inhabiting the Alas-kan continental slope. This study examined fishery and survey data on giant grenadier in Alaska from three major areas, the eastern Bering Sea (EBS), Aleutian Islands (AI), and the Gulf of Alaska (GOA), to determine catch levels, abundance and distribution, ecological importance, size, and whether overfishing of this species has occurred. The study also provided a summary of existing literature on giant grenadier from Alaska and other areas.

Official catch statistics have not been col-lected, but catches for the years 1997–2005 can be estimated based largely on data from observers on commercial vessels. Annual catch estimates in Alaska for this period aver-aged ∼16,000 mt and ranged between 11,000 and 21,000 mt. The catch is mostly taken in the GOA, followed by the EBS and then the AI. Except for two extremely small explorato-ry fishing efforts, all the giant grenadier catch has been taken as bycatch, predominantly in longline fisheries for sablefish and Greenland halibut. This bycatch is all discarded, and none of the discards survive because the fish are not able to survive the pressure change when brought to the surface.

Survey information on giant grenadier in Alaska comes from comprehensive bottom trawl and longline surveys of the continental slope. Both survey types indicate that giant grenadier are extremely abundant on the slope at depths of 300–1,000 m. The trawl surveys have been too intermittent to show trends in abundance, but biomass estimates as high as 667,000 mt in the EBS and 587,000 mt in the GOA have been found in recent years. The trawl surveys in particular demonstrate the ecological importance of giant grenadier in the slope environment. In both the EBS and the GOA, giant grenadier are by far the most

abundant species on the slope at depths of 200–1,000 m. In recent surveys of the EBS at these depths, they comprised about half the total biomass of all species, and in the GOA, they comprised about one third the biomass in depths 200–1,000 m. The longline surveys provide estimates of relative biomass only, but in contrast to the trawl surveys, they sam-ple the GOA slope annually, and since 1996, the AI and EBS slopes biennially. The long-line surveys in the GOA generally showed an increasing trend from 1992 to 1997 and then somewhat of a decrease in subsequent years. However, interpretation of abundance trends for giant grenadier in the longline surveys is difficult, especially because competition for hooks with sablefish may have an effect on catch rates. Both survey types show relative-ly high catch rates of giant grenadier in the deepest strata sampled, which indicates that an unknown and possible significant portion of the population may reside in deeper waters that have not been sampled.

Longline survey catch rates consistent-ly indicate that greatest abundance of giant grenadier in Alaska is in the western Gulf of Alaska, eastern Aleutian Islands, and in some areas of the Bering Sea. There appears to be a progressive decline in abundance of the fish in the GOA from west to east. This is sup-ported by trawl survey results, which also show giant grenadier are much less abundant in the eastern GOA. A comparison between trawl surveys in Alaska and off the U.S. West Coast indicates that relative abundance of gi-ant grenadier on the slope may be ten times or more higher in Alaska.

Longline and trawl surveys both indicate that giant grenadier in the EBS are consis-tently larger than in the GOA. The longline surveys also indicate that fish from the AI are similar in size to those in the EBS. Gi-ant grenadier caught on longlines averaged significantly larger than those caught with trawls, apparently because of size selectivity of longline gear (longline catches comprised

448 Clausen

relatively few fish less than 25 cm PAFL). Trawl data show that females average sig-nificantly larger than males.

Male and female giant grenadier have different depth distributions. Both survey types show females greatly predominate in depths <700–800 m, and males become increasing abundant in deeper water. This sexual separation by depth has important fishery implications because nearly all the commercial catch is thought to occur in depths <800 m, which means the catch is disproportionately female. Giant grenadier did not show evidence of the so-called “big-ger-deeper” trend, in which the size of many groundfish species on the slope increases with depth. On the contrary, mean size of female giant grenadier in the trawl surveys was largest in shallower water, and declined in deeper water.

Even though there is no directed fishing for giant grenadier and the catches appear to be relatively modest, giant grenadier may be especially susceptible to overfishing for a number of reasons. These include their discard mortality rate of 100%, the dispro-portionate catch of females, and the docu-mented general vulnerability of many deep-sea fish species to overfishing because of their peculiar life history traits. An analysis was conducted to determine if overfishing has occurred for giant grenadier in Alaska. This analysis was based on using estimates of biomass and natural mortality for giant grenadier to compute levels of overfish-ing and Acceptable Biological Catch. Re-sults indicated that catches have been much less that the computed overfishing levels. Therefore, the biomass of giant grenadier in Alaska appears to be sufficiently high that it has been able to support the catches that have been taken. Higher catches could prob-ably be taken in the EBS and AI, but fishery managers may want to exercise caution if catches increase in the GOA.

References

Allen, M. J., and G. B. Smith. 1988. Atlas and zooge-ography of common fishes in the Bering Sea and northeastern Pacific. NOAA Technical Report NMFS 66.

Ambrose, D. A. 1996. Macrouridae: grenadiers. Pages 483–499 in H. G. Moser, editor. The early stages of fishes in the California Current region. CAL-COFI Atlas No. 33. California Cooperative Oce-anic Fisheries Investigations, La Jolla, California.

Andrews, A. H., G. M. Cailliet, and K. H. Coale. 1999. Age and growth of Pacific grenadier (Co-ryphaenoides acrolepis) with age estimate valida-tion using an improved radiometric ageing tech-nique. Canadian Journal of Fisheries and Aquatic Sciences 56:1339–1350.

Atkinson, D. B. 1995. The biology and fishery of roundnose grenadier (Coryphaenoides rupestris Gunnerus, 1765) in the northwest Atlantic. Pages 51–112 in A. G. Hopper, editor. Deep water fisher-ies of the North Atlantic slope. Kluwer Academic Publishers, Dordrecht, Netherlands.

Bakkala, R. G., W. A. Karp, G. F. Walters, T. Sasaki, M. T. Wilson, T. M. Sample, A. M. Shimada, D. Adams, and C. E. Armistead. 1992. Distribu-tion, abundance, and biological characteristics of groundfish in the eastern Bering Sea based on results of U.S.–Japan bottom trawl and midwater surveys during June–September 1988. U.S. De-partment of Commerce, NOAA Technical. Memo-randum NMFS F/NWC-213.

Britt, L. L., and M. H. Martin. 2001. Data report: 1999 Gulf of Alaska bottom trawl survey. U.S. Depart-ment of Commerce, NOAA Technical Memoran-dum NMFS-AFSC-121.

Builder Ramsey, T., T. A. Turk, E. L. Fruh, J. R. Wal-lace, B. H. Horness, A. J. Cook, K. L. Bosley, D. J. Kamikawa, L. C. Hufnagle, and K. Piner. 2002. The 1999 Northwest Fisheries Science Center Pacific West Coast upper continental slope trawl survey of groundfish resources off Washington, Oregon, and California: estimates of distribution, abundance, and length composition. U.S. Depart-ment of Commerce, NOAA Technical Memoran-dum NMFS-NWFSC-55.

Burton, E. J. 1999. Radiometric age determination of the giant grenadier (Albatrossia pectoralis) using 210Pb:226Ra disequilibria. Master’s thesis, San Fran-cisco State University, San Francisco, California.

Busby, M. S. 2005. An unusual macrourid larva (Gadi-formes) from San Juan Island, Washington, USA. Ichthyological Research 52:86–89.


Clausen, D. M., and S. Gaichas. 2004. Grenadiers in Alaska. Pages 168–186 in J. Boldt, editor. Ecosys-tem considerations for 2005. North Pacific Fisher-ies Management Council, Anchorage, Alaska.

Clausen, D. M., and S. Gaichas. 2005. Grenadiers in Alaska. Pages 179–201 in J. Boldt, editor. Ecosys-tem considerations for 2006. North Pacific Fisher-ies Management Council, Anchorage, Alaska.

Crapo, C., B. Himelbloom, R. Pfutzenreuter, and C. Lee. 1999a. Causes for soft flesh in giant grenadier (Albatrossia pectoralis) fillets. Journal of Aquatic Food Product Technology 8(3):55–68.

Crapo, C., B. Himelbloom, R. Pfutzenreuter, and C. Lee. 1999b. Texture modification processes for giant grenadier (Albatrossia pectoralis) fillets. Journal of Aquatic Food Product Technology 8(4):27–41.

Devine, J. A., K. D. Baker, and R. L. Haedrich. 2006. Deep-sea fishes qualify as endangered. Nature (London) 439:29.

Drazen, J. C., T. W. Buckley, and G. R. Hoff. 2001. The feeding habits of slope dwelling macrourid fishes in the eastern North Pacific. Deep-Sea Research I 48:909–935.

Drazen, J. C. 2008. Energetics of grenadier fishes. Pages 203–223 in A. M. Orlov and T. Iwamoto, editors. Grenadiers of the world oceans: biology, stock assessment, and fisheries. American Fisher-ies Society, Symposium 63, Bethesda, Maryland.

Endo, H., M. Yabe, and K. Amaoka. 1993. Occur-rence of the macrourid alevins genera Albatros-sia and Coryphaenoides in the northern North Pacific Ocean. Japanese Journal of Ichthyology 40(2):219–226.

Gaichas, S. 2002. Squid and other species in the Bering Sea and Aleutian Islands. Pages 669–699 in Stock assessment and fishery evaluation report for the groundfish resources of the Bering Sea/Aleutian Islands regions. North Pacific Fisheries Manage-ment Council, Anchorage, Alaska.

Goddard, P., and M. Zimmermann. 1993. Distribu-tion, abundance, and biological characteristics of groundfish in the eastern Bering Sea based on results of U.S. bottom trawl surveys during June-September 1991. AFSC Processed Report 93–15. Alaska Fisheries Science Center, Seattle.

Hanselman, D. H., C. R. Lunsford, J. T. Fujioka, and C. J. Rodgveller. 2006. Alaska sablefish assessment for 2007. Pages 341–428 in Stock assessment and fishery evaluation report for the groundfish resources of the Bering Sea/Aleutian Islands re-gions. North Pacific Fisheries Management Coun-cil, Anchorage, Alaska.

Hoenig, J. M. 1983. Empirical use of longevity data to

estimate mortality rates. Fishery Bulletin 82(1): 898–902.

Hoff, G. R., and L. L. Britt. 2003. The 2002 eastern Ber-ing Sea upper continental slope survey of ground-fish and invertebrate resources. U.S. Department of Commerce, NOAA Technical Memorandum NMFS-AFSC-141.

Hoff, G. R., and L. L. Britt. 2005. Results of the 2004 eastern Bering Sea upper continental slope sur-vey of groundfish and invertebrate resources. U.S. Department of Commerce, NOAA Techni-cal Memorandum NMFS-AFSC-156.

Iwamoto, T., and Y. I. Sazonov. 1988. A review of the southeastern Pacific Coryphaenoides (sensu lato) (Pisces, Gadiformes, Macrouridae). Proceedings of the California Academy of Sciences 45(3):35–81.

Iwamoto, T., and D. L. Stein. 1974. A systematic review of the rattail fishes (Macrouridae: Gad-iformes) from Oregon and adjacent waters. Oc-casional Papers of the California Academy of Sciences 111:1–79.

Keller, A. A., B. H. Horness, V. J. Tuttle, J. R. Wallace, V. H. Simon, E. L. Fruh, K. L. Bosley, and D. J. Kami-kawa. 2006. The 2002 U.S. West Coast upper con-tinental slope trawl survey of groundfish resources off Washington, Oregon, and California: estimates of distribution, abundance, and length composition. U.S. Department of Commerce, NOAA Technical Memorandum NMFS-NWFSC-75.

Koslow, J. A., G. W. Boehlert, J. D. M. Gordon, R. L. Haedrich, P. Lorance, and N. Parin. 2000. Conti-nental slope and deep-sea fisheries: implications for a fragile ecosystem. ICES Journal of Marine Science 57:548–557.

Maloney, N. E. 2004. Sablefish, Anoplopoma fimbria, populations on Gulf of Alaska seamounts. Marine Fisheries Review 66(3):1–12.

Massuti, E., Morales-Nin, B., and C. Stefanescu. 1995. Distribution and biology of five grenadier fish (Pisces: Macrouridae) from the upper and middle slope of the northwestern Mediterranean. Deep-Sea Research I 42(3):307–330.

Matsui, T., S. Kato, and S. E. Smith. 1990. Biology and potential use of Pacific grenadier, Coryphaenoides acrolepis, off California. Marine Fisheries Review 52(3):1–17.

Mecklenburg, C. W., T. A. Mecklenburg, and L. K. Thorsteinson. 2002. Fishes of Alaska. American Fisheries Society, Bethesda, Maryland.

Merrett, N. R. and R. L. Haedrich. 1997. Deep-sea demersal fish and fisheries. Chapman and Hall, London.

Morita, T. 1999. Molecular phylogenetic relationships

450 Clausen

of the deep-sea fish genus Coryphaenoides (Gadi-formes: Macrouridae) based on mitochondrial DNA. Molecular Phylogenetics and Evolution 13(3):447–454.

Novikov, N. P. 1970. Biology of Chalinura pectora-lis in the North Pacific. Pages 304–331 in P. A. Moiseev, editor. Soviet fisheries investigations in the northeastern Pacific, Part V. Proceedings of the All-Union Scientific Research Institute of Marine Fisheries and Oceanography (VNIRO), volume 70—Proceedings of the Pacific Scientific Research Institute of Fisheries and Oceanography (TINRO), Russia, volume 72. (in Russian, trans-lated by Israel Program for Scientific Translations, Jerusalem, 1972).

Orlov, A. M., and S. I. Moiseev. 1999. Some biological features of Pacific sleeper shark, Somniosus paci-ficus (Bigelow et Schroeder 1944) (Squalidae), in the northwestern Pacific Ocean. Oceanological Studies 8(1–2):3–16.

Pakhorukov, N. P. 2005. Behavior and distribution of bottom and near-bottom fish on the Emperor Sea-mount chain (the Pacific Ocean). Journal of Ich-thyology 45(1):103–110.

Quinn, T. J., II, and R. B. Deriso. 1999. Quantitative fish dynamics. Oxford University Press, New York.

Ronholt, L. L., K. Teshima, and D. W. Kessler. 1994. The groundfish resources of the Aleutian Islands region and southern Bering Sea 1980, 1983, and 1986. U.S. Department of Commerce, NOAA Technical Memorandum NMFS-AFSC-31.

Rutecki, T. L., M. F. Sigler, and H. H. Zenger. 1997. Data report: National Marine Fisheries Service longline surveys, 1991–96. U.S. Department of Commerce, NOAA Technical Memorandum NMFS-AFSC-83.

Sasaki, T. 1985. Studies on the sablefish resources in the north Pacific Ocean. Bulletin of the Far Seas Fisheries Research Laboratory 22:1–107.

Sasaki, T., and K. Teshima. 1988. Data report on abun-dance indices of flatfishes, rockfishes, shortspine thornyhead, and grenadiers based on the results from Japan–U.S. joint longline surveys, 1979–87. Document submitted to the Annual Meeting of the International North Pacific Fisheries Com-mission, Tokyo, Japan, 1988 October. Fisheries Agency of Japan, Far Seas Fisheries Research Laboratory, Shimizu, Japan.

Sigler, M. F., and J. T. Fujioka. 1988. Evaluation of variability in sablefish, Anoplopoma fimbria, abundance indices in the Gulf of Alaska using

the bootstrap method. Fishery Bulletin 86(3): 445–452.

Sigler, M. F., and H. H. Zenger. 1989. Assessment of Gulf of Alaska sablefish and other groundfish species based on the domestic longline survey, 1987. U.S. Department of Commerce, NOAA Technical Memorandum NMFS F/NWC-169.

Tuponogov, V. N. 1997. Seasonal migrations of the grenadier Coryphaenoides pectoralis in the Sea of Okhotsk and contiguous waters. Russian Journal of Marine Biology 23(6):314–321.

Wakabayashi, K., R. G. Bakkala, and M. S. Alton. 1985. Methods of the U.S.–Japan demersal trawl surveys. Pages 7–29 in R. G. Bakkala and K. Wak-abayashi, editors. Results of cooperative U.S.-Ja-pan groundfish investigations in the Bering Sea during May–August 1979. Bulletin of the Interna-tional North Pacific Fisheries Commission 44.

Walker, W. A., J. G. Mead, and R. L. Brownell, Jr. 2002. Diets of Baird’s beaked whales, Berardius bairdii, in the southern Sea of Okhotsk and off the Pacific coast of Honshu, Japan. Marine Mammal Science 18(4):902–919.

Wilson, R. R. 1994. Interrelationships of the subgenera of Coryphaenoides (Gadiformes: Macrouridae): comparison of protein electrophoresis and peptide mapping. Copeia 1994(1):42–50.

Wilson, R. R., and P. Attia. 2003. Interrelationships of the subgenera of Coryphaenoides (Teleostei: Gadiformes: Macrouridae): synthesis of allozyme, peptide mapping, and DNA sequence data. Molec-ular Phylogenetics and Evolution 27:343–347.

Witherell, D., and J. Ianelli. 1997. A guide to stock assessment of Bering Sea and Aleutian Islands groundfish. North Pacific Fisheries Management Council, Anchorage, Alaska.

Yang, M-S. 2003. Food habits of the important ground-fishes in the Aleutian Islands in 1994 and 1997. AFSC Processed Report 2003–07. Alaska Fisher-ies Science Center, Seattle, Washington.

Yang, M-S., K. Dodd, R. Hibpshman, and A. White-house. 2006. Food habits of groundfishes in the Gulf of Alaska in 1999 and 2001. U.S. Department of Commerce, NOAA Technical Memorandum NMFS-AFSC-164.

Zenger, H. H., and M. F. Sigler. 1992. Relative abun-dance of Gulf of Alaska sablefish and other groundfish species based on National Marine Fisheries Service longline surveys, 1988–90. U.S. Department of Commerce, NOAA Technical Memorandum NMFS F/NWC-216.

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