ENDANGERED SPECIES RESEARCHEndang Species Res

Vol. 23: 133–147, 2014doi: 10.3354/esr00586

Published online February 28

INTRODUCTION

The North Atlantic right whale Eubalaena glacialiswas hunted nearly to extinction by 1000 yr of whalingthat ended in the early 1900s (Reeves et al. 2007).Now one of the world’s most endangered largewhales (Marine Mammal Commission 2008), the spe-cies currently occurs almost exclusively over the con-tinental shelf off the eastern USA and Canada. As oflate 2013, it was estimated to number about 500whales (www. narwc.org/ papers .php ? mc=3). The prin-cipal threats to its survival — vessel collisions andentanglement in fishing gear (Knowlton & Kraus2001, Moore et al. 2004, Knowlton et al. 2012, van derHoop et al. 2013) — are the main constraints to itsrecovery (Kraus et al. 2005, National Marine Fish-

eries Service 2005). From 1990 through 2012, morethan half of all dead right whales found stranded orfloating at sea (39 of 73) were attributable to ship col-lisions (n = 23) or entanglement (n = 16) (Knowlton &Kraus 2001, Moore et al. 2004, Marine MammalCommission 2013). With no apparent progress inreducing entanglement deaths (Knowlton et al. 2012,van der Hoop et al. 2013), reducing vessel collisionshas become even more important.

Several early studies indicated that reducing shipspeed in key right whale habitats could reduce vessel-related whale deaths. Knowlton et al. (1995) modeledhydrodynamic forces around ships traveling at differ-ent speeds and concluded that objects the size anddensity of a whale can be pulled towards hulls andpropellers of large ships with a force that increases as

© Inter-Research 2014 · www.int-res.com*Corresponding author: dlaist@mmc.gov

Effectiveness of mandatory vessel speed limits forprotecting North Atlantic right whales

David W. Laist1,*, Amy R. Knowlton2, Daniel Pendleton2

1Marine Mammal Commission, 4340 East-West Highway, Rm. 700, Bethesda, Maryland 20814, USA2New England Aquarium, 1 Central Wharf, Boston, Massachusetts 02110, USA

ABSTRACT: To reduce right whale Eubalaena glacialis deaths caused by ship collisions along theUS East Coast, a rule was implemented on 8 December 2008 requiring all vessels ≥65 feet (19.8 m)to travel 10 knots (18.5 km h−1) or less in 10 seasonal management areas (SMAs). To evaluate theeffectiveness of this rule, we plotted the locations of all right whale and humpback whaleMegaptera novaeangliae carcasses attributed to ship-strikes since December 1990 in US waters todetermine their proximity to SMAs. In the 18 yr pre-rule period, 13 of 15 (87%) right whales and12 of 26 (46%) humpback whales killed by ships were found inside later SMA boundaries orwithin 45 nmi (83 km) of their perimeters during later active dates. In the first 5 yr after the rulebecame effective, no ship-struck right whales were found inside or within 45 nmi of any activeSMA. This was nearly twice as long as the longest pre-rule period without discovery of a ship-struckcarcass in those areas during effective time periods. Based on the 18 yr pre-rule period, bootstrapresampling analyses revealed that the probability of finding no ship-struck whales in or nearSMAs during the first 5 yr post-rule period would be a statistically significant reduction in suchdeaths (p = 0.031). The results suggest the rule has been effective at reducing right whale deaths.We suggest enlarging SMAs to include additional parts of the right whale migratory corridor.

KEY WORDS: North Atlantic right whales · Humpback whales · Ship strikes · Conservation · Vessel speed limits

Resale or republication not permitted without written consent of the publisher

FREEREE ACCESSCCESS

Endang Species Res 23: 133–147, 2014

speeds increase above 10 knots. Clyne (1999) alsosimulated risks of collisions with vessels traveling atvarious speeds and found that collisions with the bowwere more likely when speeds increased above10 knots. Laist et al. (2001) examined accounts of acci-dental collisions with whales by vessels travelling atknown speeds and concluded that lethal collisionsincrease sharply between speeds of 10 to 14 knots(18.5 to 15.9 km h−1) and were rare at speeds below10 knots. Based on those findings the seasonal distri-bution of right whales, the location of ship-struck car-casses, and input from the shipping industry, Russellet al. (2001) recommended seasonal managementareas with 10 knot speed limits off major ports and inkey habitats along the eastern US coast. Assumingwhale deaths due to ships are strictly a function ofimpact force and vessel hydrodynamics, Vanderlaan& Taggart (2007) concluded that the greatest rate ofchange in the probability of lethal collisions wasbetween vessel speeds of 8.6 to 15 knots (15.9 to27.8 km h−1) and that the probability of death de -clined by 50% at speeds of <11.8 knots (21.9 km h−1).

Based largely on those findings and their own ana -lyses, the National Marine Fisheries Service (NMFS)adopted a rule to limit vessel speeds in key US rightwhale habitats as part of its ‘right whale ship-strikereduction strategy’ (NMFS 2008a). The rule becameeffective on 8 December 2008 for a 5 yr period (i.e.until 8 December 2013). Although in tended to protectright whales, the measure was also expected to pro-vide some protection to humpback whales Mega -ptera novaeangliae and other large whales whoseranges overlap with those of right whales (NMFS2008b). The rule requires all vessels 65 feet (19.8 m)or longer (also herein referred to as ‘ships’) to usespeeds of 10 knots or less when transiting 10 Sea-sonal Management Areas (SMAs) along the US EastCoast during periods of peak right whale occurrence(Fig. 1). The 10 SMAs comprise 6 that extend 20 nau-tical miles (nmi; 37 km) from shore, off major portsalong the species’ coastal migratory corridor betweensouthern New England and Georgia (effective 1November to 30 April); 3 in feeding areas off Massa-chusetts (i.e. Cape Cod Bay, effective 1 January to 15May; the Great South Channel, effective 1 April to 31July; and an area immediately east and north of CapeCod, effective 1 March to 30 April); and 1 in the coreof the species’ calving grounds off the southeasternUS coast of Georgia and Florida (effective 15 Novem-ber to 15 April).

In addition to SMAs, the NMFS ship-strike reduc-tion strategy included new vessel routing measuresfor the port of Boston in Massachusetts and 3 ports in

the southeastern US right whale calving grounds,and established 2 other types of management areas:Dynamic Management Areas (DMAs) and a seasonal‘Area To Be Avoided’ (ATBA). DMAs are temporary15 d management areas established on short noticeto protect aggregations of 3 or more right whalesfound at unpredictable locations outside of activeSMAs. When DMA boundaries are announcedthrough customary maritime communication media(e.g. voice radio and local notices to mariners) shipsare asked, but not required, to limit speeds to 10 knotsor to steer clear of those areas. ATBAs, establishedunder the authority of coastal nations after approvalof the International Maritime Organization, are areaswhere ship operators are asked, but not required, toavoid transits. Such an area off Nova Scotia, Canada,has been shown to be effective at reducing the risk oflethal vessel strikes in right whale habitats (Vander-laan et al. 2008). The ATBA for right whale protectionlies principally within the boundary of the GreatSouth Channel SMA, east of the shipping lanes thatrun along that SMA’s western edge (Fig. 1). The newrouting measures: (1) narrowed and shifted the

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Fig. 1. Eubalaena glacialis. Locations and effective dates ofSeasonal Management Areas (SMAs) requiring 10 knot shipspeed limits after 8 December 2008 to protect North Atlantic

right whales

Laist et al.: Speed limits for right whales

east−west leg of track of vessel traffic separationlanes leading into Boston Harbor to reduce overlapwith right whale habitat in Cape Cod Bay (Silber etal. 2012a) and (2) recommended routes through CapeCod Bay and off the ports of Jacksonville, Fernand-ina, and Brunswick to minimize transit distancesthrough areas used least intensively by right whales(Lagueux et al. 2011).

Initially proposed in June 2006 (NMFS 2006), therule finally adopted in 2008 was subject to a pro-tracted review by high-level officials in the US gov-ernment. Concerned about its economic impactsand skeptical of the measure’s effectiveness, severalchanges were imposed on the action preferred bythe NMFS. In part, the width of SMAs along thespecies’ migratory corridor was reduced from 30 to20 nmi (55 to 37 km), and a sunset provision wasadded requiring the rule to expire 5 yr after itseffective date (i.e. 8 December 2013). During the5 yr period the NMFS was to evaluate effectivenessof the speed requirement for reducing whale deathsand decide whether to extend, modify, or allow itto lapse. Another required change was making the10 knot speed limit in DMAs voluntary instead ofmandatory. On 9 December 2013, the rule wasextended indefinitely subject to further review todetermine if dredged channels through SMAs shouldbe exempted from its provisions as requested bypetition (NMFS 2013).

After the 2008 rule was adopted, the NMFS devel-oped a plan to evaluate its effectiveness (Silber &Bettridge 2009). Based on the first 3 yr of post-ruleexperience, the NMFS examined vessel compliancerates and economic impacts using data from anAutomatic Identification System for ships (Silber &Bettridge 2012) and evaluated its biological effec-tiveness based on intervals between all documentedcollisions with large whales along the east coast 2 yrbefore the rules went into effect versus 2 yr after-wards (Pace 2011). From those analyses, the NMFSconcluded that biological data were not yet suffi-cient to reach statistically meaningful conclusions,but that „…there may be ‘a meager amount of evi-dence in support of a reduction in ship-strike deathsand serious injuries of large whales’“ (Silber & Bet-tridge 2012, p. iv).

Several other studies have investigated compliancewith the new speed restrictions in both SMAs (Silber& Bettridge 2010, Lagueux et al. 2011, Mueller et al.2011, Wiley et al. 2011) and DMAs (Asaro 2012, Sil-ber et al. 2012b). Initial compliance in SMAs waspoor, but improved after warnings began to be issuedin late 2009 and improved further after notices of vio-

lations with speed limits were issued in late 2010 (Sil-ber & Bettridge 2012). Most ships, however, reducedtheir speed to varying degrees, although not neces-sarily to 10 knots. Compliance in DMAs was verypoor. This result was similar to a voluntary requestasking vessels to travel at 10 knots off Southern Cal-ifornia to protect blue whales, which resulted inalmost no change in vessel speeds (McKenna et al.2012). Still other studies have recently provided fur-ther evidence that collision risks increase as vesselspeeds increase above 10 knots due to hydrodynamiceffects (Silber et al. 2010), and whale deaths are cor-related with vessels traveling at increasing speeds(Conn & Silber 2013).

The reason why slow speeds are thought to reducelethal collisions is subject to debate. Some suggest itis due solely to reduced impact and hydrodynamicforces (Vanderlaan & Taggart 2007, Vanderlaan et al.2009, Silber et al. 2010); others suggest it providesadded time for whales to avoid oncoming ships (Laistet al. 2001, Gende et al. 2011). Regardless of themechanism and its intuitive rationale for reducingspeed to reduce collision risks, the effectiveness ofspeed requirements remains poorly documented andis still subject to doubt by some. To further explorewhether speed restrictions have been effective atreducing lethal whale collisions, we examined infor-mation on known and possible ship-strike deaths ofright and humpback whales found in and near SMAsbefore and after the NMFS implemented its ruleslimiting ship speeds along the US East Coast.

Specifically, we examined the locations and discov-ery dates of all right whale and humpback whale car-casses attributed to ship strikes or un known causes todetermine their proximity to SMA boundaries andtheir occurrence relative to SMA effective datesbefore and after the rule went into effect on 8 Decem-ber 2008. We did not include fin whales because,unlike right whales and humpback whales, they canbe carried 1000s of kilometers into ports on the bowsof ships making it unclear where they were struck(Laist et al. 2001). We also did not consider otherlarge whales (i.e. sperm, blue, sei, or minke whales),because they occur infrequently in areas whereSMAs have been designated and be cause lethal col-lisions with those species along the US East Coasthave been rare over the past 25 yr (Laist et al. 2001).We hypothesized that the average annual tally ofright whale carcasses, and possibly also humpbackwhale carcasses, attributable or possibly attributableto ships discovered in or near SMA boundaries dur-ing SMA time frames would be lower after the ship-strike reduction rule went into effect.

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MATERIALS AND METHODS

We searched the National Marine Mammal Strand-ing Database maintained by the NMFS for records ofall known right whale and humpback whale deathsattributed to ship strikes along the eastern US andCanadian coasts after 8 December 1990. For rightwhales, we also examined the Right Whale Photo-identification Catalogue maintained by the NewEngland Aquarium for such deaths. Because theNMFS ship-strike reduction strategy is focused onUS waters, our analyses of SMA effectiveness usedonly records of dead whales found within the USExclusive Economic Zone. We sought records fromCanada (i.e. waters north and east of the Hague Linethat serves as the boundary between the US andCanadian Exclusive Economic Zones; Fig. 1), theonly other area where North Atlantic right whalesare known to have been killed by ships, to indicatewhat proportion of the ship-collision problem occursin US waters. For right whales, our study periodextended through 8 December 2013, the latest datefor which records were available from the RightWhale Photo-identification Catalogue. Because ofdelays in entering stranding data into the nationaldatabase, analyses of humpback whales extendedonly through 8 July 2011.

We also searched for records of all right whaledeaths after 8 December 1990 that were attributed tounknown causes, because some of those whales mayhave been killed by ship strikes (e.g. some whaleswere documented floating offshore, but were not ex-amined closely). We selected 8 December 1990 as thestart of our study period because: (1) that date gener-ally corresponds with the time when East Coast car-cass recovery efforts for right whales were expandedand ne cropsy teams began flensing carcasses to thebone to look for internal ship-collision injuries not al-ways apparent externally, and (2) it was statisticallyconvenient to use the same day and month as the 8December 2008 effective date for the NMFS rule.Data recorded for each dead whale in the nationalstranding database include the date, latitude and lon-gitude, and general description of where the carcasswas first seen; the cause of death, if it can be deter-mined; the whale’s decomposition state; and a sum-mary of necropsy results (if conducted) or other find-ings explaining the assigned cause of death. Whenthose data for right whales were missing, supplemen-tal information was ob tained when available from theRight Whale Photo-identification Catalogue.

Carcass locations were mapped using ArcGIS Ver-sion 10.0. SMA boundaries were added using coor -

dinates available from the NMFS. Separate mapsshowing carcass discovery locations before and afterthe rule went into effect on 8 December 2008 wereprepared for right whales killed by ships and for rightwhales that died of unknown causes that might haveinvolved ship collisions. To identify carcasses ofwhales possibly killed by ships, we narrowed the listof carcasses attributed to unknown causes by elimi-nating those that were thoroughly necropsied andhad no signs of ship-collision injuries. We also pre-pared a map for humpback whales, but only fordeaths attributed to ship strikes; 275 humpbackwhale carcasses attributed to unknown causes werenot plotted. Much less effort is made to retrieve andnecropsy dead humpback whales than right whales;thus, unlike the situation for right whales, almost norecords of humpback whales could be ruled out aspossibly being collision related. Because of the largenumber of humpback whale carcasses attributedto unknown causes and the inability to exclude anythat were clearly not caused by ship collisions, weconcluded that for this species it would not be possi-ble to distinguish meaningful trends relative to shipcollisions and implementation of SMAs from suchcarcasses.

From plotted locations we identified all right whalecarcasses attributed to ship strikes and to unknowncauses potentially involving ship strikes found insideSMA boundaries during effective time frames beforeand after the ship-strike reduction rule went intoeffect. For all other right whale carcasses in USwaters, we calculated their distance to the nearestSMA boundary. To account for carcasses that mayhave drifted outside SMA boundaries after whaleswere struck and before they were found dead, weconsidered any carcasses inside SMAs or within 45nmi (74 km) of SMA boundaries during their activetime frames (hereafter referred to as ‘in or near activeSMAs’) to be potential victims of collisions insideSMA boundaries. We did the same for humpbackwhale carcasses, but only for those attributed to shipstrikes. We then calculated the average annual num-ber of ship-struck carcasses found in or near activeSMAs for each species during the 18 yr pre-ruleperiod and for post-rule periods of 5.0 yr (1826 d) forright whales and 2.5 yr (942 d) for humpback whales(i.e. the latest dates for which data were available).

The drift distance of 45 nmi was based on estimatesof carcass degradation and drift rates. Almost allright whale deaths attributed to ship collisions in thisstudy were found moderately decomposed (Code 3)or fresher according to the 5 category ranking system(with Code 5 representing the most degraded) used

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to describe carcass degradation states (Geraci &Lounsbury 2005). We estimated it would take a max-imum of 6 d for a right whale carcass to become mod-erately decomposed. This was based on a right whalenamed Staccato (Catalogue No. 1014) that was pho-tographed alive and uninjured on 15 April 1999 andnext seen 5 d later floating dead off Cape Cod, Mas-sachusetts, after being struck by a ship. Its carcasswas towed ashore the day it was sighted and it wasnecropsied the following day (i.e. 21 April), at whichtime it was re corded as being moderately decom-posed (i.e. Code 3). Although carcass degradationcan proceed at different rates depending on temper-ature, because right whales along the US East Coastalmost always occur in cool water similar to tempera-tures in Cape Cod Bay in April, we considered theApril 1999 case to be the best available estimate ofthe time needed for a right whale to degrade to aCode 3 condition.

Average carcass drift rate was estimated from thedistances of movements reported for 5 right whalecarcasses seen drifting in US waters and later re -sighted at another location. These carcasses werefirst seen floating on the following dates: 3 Septem-ber 2002, 6 September 2002, 7 February 2004, 27June 2010, and 2 March 2012. Coordinates for initialand resighting locations documented drift distancesof at least 77 nmi (143 km) in 22 d, 112 nmi (204 km)in 8 d, 54 nmi (100 km) in 2 d, 21 nmi (39 km) in 3 d,and 27 nmi (50 km) in 5 d, respectively, giving anaverage drift distance of 7.3 nmi (13.5 km) per day or43.8 nmi (81.1 km) in 6 d, which we rounded off to45 nmi (83.3 km) for mapping convenience. Althoughthese records do not reflect all possible conditionsthat could influence carcass drift rates, they reflect atleast some range of conditions in different seasonsand areas and are the best available data at this time.

We conducted a bootstrap resampling analysis(Efron & Tibshirani 1993) to test the hypothesis thatthe average annual number of ship-struck whale car-casses found after the speed rule went into effectwould be less than the average number during the18 yr before the speed rule went into effect. Thishypothesis was tested separately for right whale car-casses found in or near active SMAs and for rightwhale carcasses found >45 nmi from SMAs (Table 1).We did the same for ship-struck humpback whalecarcasses. For right whales, annual carcass totalsfrom the 18 yr pre-rule period were resampled onemillion times, with each sample consisting of a ran-dom selection of 5 annual carcass totals to match thenumber of years in the post-rule period. After eachannual total was selected, it was returned to the pool

of eligible years so that each draw in a 5 yr samplehad 18 annual totals from which to select (i.e. randomselection with replacement). We followed the sameprocedure for humpback whales, but had only 2.5 yrof post-rule data. Therefore, each bootstrap samplefor humpback whales consisted of a random selectionof 3 annual pre-rule carcass totals. The mean of eachbootstrap sample was calculated, and those valueswere sorted in ascending order. The limits of theupper 95% of values were used as the confidenceinterval. The percentage of mean values less than thelower bound constituted the p-value.

To investigate the hypothetical probability of dis-covering ship-struck right whale carcasses in or nearSMAs in the sixth post-rule year, we did an addi-tional bootstrap resampling as described above, butdrew 6 values instead of 5 from the pool of 18 pre-rule annual ship-strike carcass totals in or nearSMAs. From those samples we calculated the pro -bability of discovering zero whales in the first 5 yr,followed by discovering ≤1 and ≤2 carcasses in thesixth year. We considered only 0, 1, or 2 carcass discoveries because these were the only valuesobserved in any given year during the pre-ruleperiod and, thus, were the only values possible inthe bootstrap samples.

We also compared maximum waiting times be tweendiscovery of ship-struck right whale and humpbackwhale carcasses found in or near active SMAs duringpre- and post-rule periods to determine the extentto which intervals between recorded ship-collisiondeaths differed.

RESULTS

Over the entire study period, 23 of 72 confirmedright whale deaths (31.9%) were attributed to shipcollisions. Three-fourths of those deaths were in USwaters (17 deaths including 15 pre-rule and 2 post-rule) and one-fourth (6 deaths) were in Canadianwaters (Table 1, Fig. 2). During the 18 yr pre-ruleperiod, 10 of the 15 carcasses in US waters wereinside SMAs, and 3 others were within 45 nmi ofSMA boundaries (including 2 within just 6 nmi) dur-ing later SMA active dates. Together, those 13 car-casses comprised 87% of all known ship-strikedeaths (Table 2) in US waters during the pre-ruleperiod for an average carcass discovery rate of 0.72right whales yr−1 in or near active SMAs.

The decomposition state of all ship-struck rightwhale carcasses found in or near later SMA bound-aries in the pre-rule period was moderate or fresher,

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suggesting they may have drifted up to 45 nmi be -tween the time of death and carcass discovery. The 3longest waiting times between finding such car-casses in the pre-rule period were 2.8 yr (i.e. 1057 dbetween 17 March 2001 and 7 February 2004), 2.2 yr(i.e. 785 d between 6 December 1993 and 30 January1996), and 1.9 yr (i.e. 709 d between 30 December2006 and 8 December 2008). Only 2 pre-rule shipstrikes were found outside the potential reach ofeventual SMA protection provisions; both wereinside or within 45 nmi of SMA boundaries, but werediscovered 7 wk or more outside later SMA activedates. During the first 5.0 post-rule years, no ship-struck right whales were found in or near any activeSMAs, giving a carcass discovery rate of 0 yr−1. Dur-ing that period, 2 ship-struck right whales werefound in US waters; both were found within theactive dates of the nearest SMA, but were >45 nmiaway from the nearest SMA boundary (one 47 nmiaway in Code 4 condition, the other 112 nmi away inCode 3 condition).

Thirty-three right whale deaths were attributed tounknown causes over the entire study period; 29 inUS waters and 4 in Canadian. Eight of the 29 in USwaters were recovered in moderate to fresh condition(mostly neonates) and were ruled out as possibleship-collision victims based on necropsy results that

found no evidence of collision injuries. Therefore, 25of all mortalities attributed to unknown cause mighthave been due to ship strikes; 21 in US waters (14pre-rule and 7 post-rule) and 4 in Canadian waters(Table 3, Fig. 3). During the 18 yr pre-rule period, 8 ofthe 14 possible ship-strike carcasses in US waters(57.1%) were found either inside (n = 5) or within45 nmi (n = 3) of SMA boundaries during their latereffective dates for an annual pre-rule discovery rateof 0.44 right whale carcasses yr−1 in or near activeSMAs. During the first 5.0 yr after the rule’s effectivedate, 4 of 7 carcasses (57.1%) found in US watersattributed to unknown causes that may have in cludedship strikes were inside (n = 1) or within 45 nmi(n = 3) of active SMAs for an average discovery rateof 0.80 carcasses yr−1 (Table 2).

Over the entire study period, 32 humpback whaleship-strike deaths were discovered. They were all inUS waters (Table 4, Fig. 4) and included 26 duringpre-rule years and 6 during the first 2.5 post-ruleyears. During the pre-rule period 12 of 26 ship-struckhumpback whales (46%) were found inside (n = 6) orwithin 45 nmi (n = 6) of SMA boundaries during laterSMA effective dates, giving a discovery rate of 0.66carcasses yr−1 (Table 4). The longest waiting time be -tween finding at least one such carcass in pre-ruleyears was 5.6 yr (i.e. 2064 d between 14 April 1992

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Date (mm/dd/yy) Nearest SMA Inside SMA Inside SMA Distance from SMA Decomp. dates? boundary? (nmi/km) code

Pre-rule03/12/91a Calving grounds SMA Yes Yes 0 301/05/93a Calving grounds SMA Yes Yes 0 112/06/93a Chesapeake Bay SMA Yes No 2.6/4.8 Unk01/30/96a Calving grounds SMA Yes Yes 0 303/09/96a Cape Cod Bay SMA Yes Yes 0 Unk04/20/99a Cape Cod Bay SMA Yes Yes 0 303/17/01a Delaware Bay SMA Yes No 36/66.7 306/18/01 New York Harbor SMA No Yes 0 308/22/02 Delaware Bay SMA No No 15.4/28.5 402/07/04a Chesapeake Bay SMA Yes Yes 0 311/17/04a Chesapeake Bay SMA Yes Yes 0 301/12/05a Calving grounds SMA Yes Yes 0 204/28/05a Outer Cape Cod SMA Yes No 5.9/10.9 301/10/06a Calving grounds SMA Yes Yes 0 212/30/06a Calving grounds SMA Yes Yes 0 3

Post-rule07/02/10 Great South Channel SMA Yes No 112/207 303/27/11 Chesapeake Bay SMA Yes No 47/86 4

aCarcass found in or within 45 nmi (83 km) of SMA boundaries during active time frames

Table 1. Eubalaena glacialis. Date and distance from Seasonal Management Areas (SMAs) of all North Atlantic right whalecarcasses attributed to ship collisions along the US East Coast: 1 January 1990 to 8 December 2013, before (pre-rule) and after(post-rule) the SMA implementation on 8 December 2008. Decomposition (Decomp.) codes — 1: alive; 2: fresh; 3: moderate

decomposition; 4: advanced decomposition; Unk: unknown condition; nmi: nautical mile

Laist et al.: Speed limits for right whales

and 10 December 1997), 2.9 yr (i.e. 1090 d between10 December 1997 and 4 December 2000), and 2.8 yr(i.e. 1045 d between 8 February 2002 and 19 Decem-ber 2004). During the 2.5 yr (912 d) post-rule period,no ship-struck humpback whales were found insideactive SMAs, but 2 were within 45 nmi of activeSMAs, giving a post-rule discovery rate of 0.80humpback whale carcasses yr−1.

From our bootstrap resampling analysis, the upper95% confidence interval around the annual pre-rulemean number of right whale ship-strike deaths in ornear SMAs (0.72 carcasses yr−1) was 0.2 to 2.0 (Fig. 5).As of 5.0 yr after the rule’s adoption, the post-ruleannual mean number of ship-strike deaths in or nearSMAs was 0. The probability of a 5 yr post-rule car-cass discovery rate of 0 is significantly lower (p =0.031) than the pre-rule mean. An additional boot-strap resampling analysis was conducted to estimatethe probabilities of finding 0, ≤1, or ≤2 carcasses in

the sixth post-year rule after 5 consecutive years ofno deaths. Those probabilities were estimated to bep = 0.012, p = 0.024, and p = 0.031, respectively.

We found no other significant or borderline signifi-cant differences between pre- and post-rule carcassdiscovery rates. For right whales, there were noapparent differences for (1) ship-struck carcassesfound >45 nmi from active SMAs (p = 0.99) or (2) car-casses attributed to unknown causes that might haveincluded ship strikes either in or near active SMAs(p = 0.92) or beyond 45 nmi of the nearest active SMA(p = 0.87). For humpback whales, there was no signif-icant difference in discovery rates for ship-struck car-casses either within or near active SMAs (p = 0.68) orbeyond 45 nmi of the nearest active SMAs (p = 0.85).

DISCUSSION

Right whales

Results of this study indicate that the locations andtime frames of SMAs were well-chosen to protectNorth Atlantic right whales from ship strikes. Duringthe 18 yr before SMAs were implemented, 87% (13of 15) of all right whales known to have been killedby ships in US waters were found inside or within45 nmi of SMAs during later SMA effective dates.Indeed, most of those carcasses (i.e. 12 of 15 or 80%)were inside or within 6 nmi of SMA boundaries. Ittherefore appears that most right whales killed byships before December 2008 were found in or near

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Fig. 2. Eubalaena glacialis. Locations and dates where allNorth Atlantic right whales killed by ships were found be-fore and after Seasonal Management Areas (SMAs) were es-tablished on 8 December 2008. *: carcass found in or within45 nmi (83 km) of SMA boundaries during active timeframes; J: carcass locations during pre-rule years, 1990 to2008; M: carcass locations during post-rule years, 9 Decem-

ber 2008 through 8 December 2013

Pre- Post- rule rule

Right whales — ship strikesInside or within 45 nmi of SMA boundaries 13 0Beyond 45 nmi of nearest SMA 2 2

Right whales — unknown causeInside or within 45 nmi of SMA boundaries 8 4Beyond 45 nmi of nearest SMA 6 3

Humpback whales — ship strikesInside or within 45 nmi of SMA boundaries 12 2Beyond 45 nmi of nearest SMA 14 4

Table 2. Eubalaena glacialis, Megaptera novaeangliae. Num-ber of known right whale and humpback whale deaths alongthe US East Coast attributed to ship strikes and unknowncauses, possibly including ship strikes, inside or within45 nmi of active Seasonal Management Area (SMA) bound-aries or beyond 45 nmi of SMA boundaries, before and afterthe SMA implementation on 8 December 2008 (i.e. 8 Decem-ber 1990 through 8 December 2013 for right whales and

through 8 June 2011 for humpback whales)

Endang Species Res 23: 133–147, 2014

areas where SMAs were later established and alsoduring their eventual effective dates.

The results also suggest that SMAs have effectivelyreduced the number of whale deaths due to ships.Average annual discovery rates of ship-struck rightwhale carcasses in or near active SMAs declined sig-nificantly from 0.72 to 0 carcasses yr−1 for at least thefirst 5.0 yr after the rule went into effect. This meas-ure of reduction is likely to be conservative giventhat estimates of the size of the North Atlantic rightwhale population increased over the study periodfrom about 295 whales in 1992 (Knowlton et al. 1994)to about 500 whales in 2013, with the addition ofabout 80 whales from 2008 through 2013 (New Eng-land Aquarium unpubl. data). Thus, the number ofwhales available to be struck has increased in post-rule years. In addition, the 5.0 yr post-rule periodduring which no ship-struck right whales carcasswere discovered in or near any acitve SMAs is almosttwice as long as the longest gap (i.e. 2.8 yr) betweensuch discoveries during the pre-rule period.

These results are encouraging, but require alonger time period to confirm if the apparent effec-

tiveness holds up over time. The recommendedrouting changes off Boston, the new recommendedroutes in Cape Cod Bay and the southeastern UScalving grounds, and new ATBA also may havecontributed to the apparent reduction in rightwhale ship-strike deaths by directing trafficthrough habitats used somewhat less frequently bywhales. For example, a 58% reduction in collisionrisks was predicted by shifting a segment of theBoston shipping lanes (www. scimaps. org/ maps/map/ realigning_ the_ bosto_88/), and Fonnesbeck etal. (2008) predicted as much as a 44% reductionwith new shipping lanes through the calvinggrounds. However, the new routes must still crosskey right whale habitats, and no useful routingalternatives exist for mid-Atlantic ports along theright whale’s coastal migratory corridor, wherenearly half of all vessel-related right whale deathshave been discovered. Thus, although there shouldbe some uncertain amount of risk reduction fromnew routes now in place, we believe speed restric-tions are likely to be a more important factor inreducing collision risks along the US East Coast.

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Date (mm/dd/yy) Nearest SMA Inside SMA Inside SMA Distance from SMA Decomp. dates? boundary? (nmi/km) code

Pre-rule01/15/93 Calving grounds SMA Yes No 62/115 Unk12/06/93a Chesapeake Bay SMA Yes No 1.2/2.2 Unk02/08/96a Calving grounds SMA Yes Yes 0 402/19/96a Calving grounds SMA Yes Yes 0 310/07/98 Chesapeake Bay SMA No No 8.5/15.7 401/19/00a Block Island Sound SMA Yes Yes 0 Unk01/27/01a Calving grounds SMA Yes No 15/28 Unk03/17/01a NC-GA Coast SMA Yes No 3/5.6 406/10/02a Great South Channel SMA Yes Yes 0 409/03/02 Chesapeake Bay SMA No No 38/70.3 309/06/02 Chesapeake Bay SMA No No 65/120.3 412/09/04 Great South Channel SMA No No 38/70.3 Unk01/09/05 Great South Channel SMA No No 21/38.9 402/14/08a Calving grounds SMA Yes Yes 0 4

Post-rule02/17/09a Calving grounds SMA Yes Yes 0 302/25/09 Great South Channel SMA No Yes 0 308/18/09 New York Harbor SMA No No 44/81.5 412/19/09 Great South Channel SMA No No 6.1/11.3 202/19/11a NC-GA SMA Yes No 34/63.0 403/17/11a Delaware Bay SMA Yes No 40/74.1 303/02/12a Race Point SMA Yes No 24/44.5 3

aCarcass found in or within 45 nmi (83 km) of SMA boundaries during active time frames

Table 3. Eubalaena glacialis. Date and distance from Seasonal Management Areas (SMAs) of all North Atlantic right whalecarcasses attributed to unknown causes, possibly including ship strikes, along the US East Coast: 1 January 1990 to 8 Decem-ber 2013, before (pre-rule) and after (post-rule) the SMA implementation on 8 December 2008. Decomposition (Decomp.)codes — 1: alive; 2: fresh; 3: moderate decomposition; 4: advanced decomposition; Unk: unknown condition; NC: North

Carolina; GA: Georgia

Laist et al.: Speed limits for right whales

We found no indication that SMAs have reducedthe number of right whale deaths attributed to un-known causes. The percentages of such deaths in ornear active SMAs in the pre-rule (57.1%, 8 of 14) andpost-rule (57.1%, 4 of 7) periods were identical, andthe average annual carcass recovery rate actually in-creased from 0.44 to 0.80 carcasses yr−1 during thepost-rule period. The most parsimonious interpreta-tions for the increase in deaths due to unknowncauses are that (1) all or most right whale deaths thatmay have been attributed to unknown causes butwere actually due to ship strikes occurred >45 nmifrom the nearest active SMA, (2) most right whaledeaths attributed to unknown causes were not causedby ship collisions, and the increase reflects stochasticvariability. As indicated below, an example of the firstpossibility may be the cluster of 4 carcasses attributedto un known causes found in the southern GreatSouth Channel area in winter. This is an area with

high ship traffic and limited winter survey effort. Thesecond possibility has some support from past experi-ence. During a 4 yr period between 1993 and 1996,the annual discovery rate for right whale carcassesattributed to unknown causes in or near later activeSMAs was 0.75 car casses yr−1 (3 of 4 carcasses),which approaches the post-rule rate of 0.80 (Table 3).

Other studies have found little or no evidence thatrecent management measures have reduced vessel-related right whale deaths along the US East Coast.Analyses to date, however, have been too broad inscope, or involved time frames ill-suited for assessingeffectiveness of the SMA network. For example, vander Hoop et al. (2013) found no noticeable reductionin large whale vessel- and entanglement-relateddeaths from 2003 through 2009 (when a number ofmanagement actions were implemented, includingoutreach efforts to advise mariners of collision risks),compared to earlier years. That study, however, wasnot designed to assess the effectiveness of site-spe-cific measures or specifically of SMA vessel-speedrestrictions. In particular, it included only 1 yr of dataafter SMAs were established.

Similarly, Pace (2011) found no significant reduc-tion in ship-collision deaths after the rule went intoeffect. However, his analysis was based on only 2 yrof post-rule data, measured intervals between colli-sions involving all species of large whales (i.e. hump-back, right, fin, and sei whales), considered all typesof vessels (including those <65 ft in length that arenot subject to regulation), and included all US andCanadian waters (including those not near SMAs).Furthermore, it did not distinguish between colli-sions inside versus outside SMA time frames. In con-trast, our ana lysis focuses on those collisions mostlikely to have occurred within SMA boundaries, dur-ing effective dates, on the species of greatest concern(i.e. right whales), and on the vessels most likely tohave been subject to management (i.e. all carcassesconsidered in this analysis had large wounds or con-tusions indicative of collisions with vessels that likelywere >65 feet long). Therefore, we believe this ana -lysis provides a more direct and useful measure ofthe rule’s effectiveness for right whales.

Humpback whales

Our results suggest that SMAs have not provided asignificant benefit for humpback whales. Whereas87% of all ship-struck right whales were found in ornear SMAs during effective dates in the pre-ruleperiod, less than half (46%) of all such humpback

141

Fig. 3. Eubalaena glacialis. Locations and dates where allNorth Atlantic right whales killed by unknown causes, pos-sibly including ship strikes, were found before and afterSeasonal Management Areas (SMAs) were established on 8December 2008. *: carcass found in or within 45 nmi (83 km)of SMA boundaries during active time frames; J: carcass locations during pre-rule years, 1990 to 2008; M: carcass lo-cations during post-rule years, 9 December 2008 through

8 December 2013

Endang Species Res 23: 133–147, 2014

whales were in or near those areas during activedates. However, it is notable that 12 of the other 15pre-rule humpback whales killed by ships werefound in or near SMA boundaries, but were outsideof SMA active dates (Table 5). This pattern persistedin post-rule years when all 6 of the ship-struck hump-back whale carcasses were found in or near SMAboundaries, but only 2 were within their active dates.Thus, it would seem that SMAs could be beneficialfor humpback whales if their effective dates wereexpanded to better reflect the timing of their sea-sonal occurrence in SMA boundaries. The occur-rence of humpback whale collisions outside of activedates is understandable given that SMA time frameswere developed specifically for right whale protection.

Uncertainties in the time and location of collisions

In addition to constraints due to the small samplesize of ship-struck carcasses on the statistical powerof our analyses, 2 other limitations led to uncertain-ties: (1) the precise dates of collisions and (2) the pre-cise locations of collisions relative to SMA dates andboundaries. Because the length of time between acollision and the discovery of collision-related car-casses is unknown and variable, there is some uncer-tainty about whether those whales were struck dur-ing SMA active dates. In most cases, we believecarcass discovery dates can be related with reason-able accuracy to active SMA dates. All ship-struckright whale carcasses found in or near SMAs during

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Date (mm/dd/yy) Nearest SMA Inside SMA Inside SMA Distance from SMA Decomp. dates? boundary? (nmi/km) code

Pre-rule11/08/91a New York Harbor SMA Yes No 22.6/41.9 Unk02/14/92a Chesapeake Bay SMA Yes Yes 0 304/16/92a Delaware Bay SMA Yes No 22.7/42.0 406/04/95 Chesapeake Bay SMA No No 0.1/0.2 305/09/96 Delaware Bay SMA No No 0.5/0.9 311/03/96a Chesapeake Bay SMA Yes No 42.9/79.5 312/10/97a Morehead City SMA Yes Yes 0 312/04/00a Morehead City SMA Yes Yes 0 01/25/01 Chesapeake Bay SMA Yes No 51.6/95.6 204/08/01a NC-GA Coast SMA Yes Yes 0 207/29/01 New York Harbor SMA No No 6.8/12.6 308/18/01 Delaware Bay SMA No No 22.5/41.7 210/01/01 Cape Cod Bay SMA No Yes 0 302/08/02a Chesapeake Bay SMA Yes No 4.8/8.9 Unk05/30/02 Race Point SMA No No 51.7/95.7 308/01/02 New York Harbor SMA No No 0 406/06/03 Chesapeake Bay SMA No No 4.6/8.5 2-312/19/04a Delaware Bay SMA Yes Yes 0 301/09/06a NC-GA Coast SMA Yes Yes 0 303/17/06a Chesapeake Bay SMA Yes No 1.5/2.8 309/27/06 Delaware Bay SMA No Yes 0 410/15/06 Delaware Bay SMA No No 6.2/11.5 405/10/07 Chesapeake Bay SMA No No 21.6/40.0 405/13/07 Race Point SMA No No 9.2/17.0 406/24/07 Race Point SMA No Yes 0 311/04/08a Delaware Bay SMA Yes No 20.1/37.2 2

Post-rule07/27/09 New York Harbor SMA No Yes 0 303/13/10a Delaware Bay SMA Yes No 12.8/23.7 306/10/10 New York Harbor SMA No No 0.1/0.2 307/04/10 Delaware Bay SMA No No 12.0/22.2 403/07/11a Morehead City SMA Yes No 15/27.8 105/28/11 New York Harbor No No 23.9/44.3 4

aCarcass found in or within 45 nmi (83 km) of SMA boundaries during active time frames

Table 4. Megaptera novaeangliae. Date and distance from Seasonal Management Areas (SMAs) of all humpback whale car-casses attributed to ship strikes along the US East Coast: 1 January 1990 to 8 June 2011, before (pre-rule) and after (post-rule)the SMA implementation on 8 December 2008. Decomposition (Decomp.) codes — 1: alive; 2: fresh; 3: moderate decomposition;

4: advanced decomposition; Unk: unknown condition; NC: North Carolina; GA: Georgia

Laist et al.: Speed limits for right whales

pre-rule years with information on their decomposi-tion state (i.e. 11 of 13) were moderately decomposed(Code 3) or fresher. Similarly, all but 1 ship-struckhumpback whale found in or near SMAs with infor-mation on decomposition condition (7 of 8) wereCode 3 or fresher. As noted above, right whale car-casses can degrade to a Code 3 condition within aweek or less. Because most right whale carcassesattributed to ship strikes along the US East Coasthave involved massive injuries, such as fracturedskulls or vertebrae, severed tail stocks, and long,deep propeller wounds (Moore et al. 2004), it seemsreasonable to assume that most victims die within aday or 2, if not hours, of being hit. By adding thosepre- and post-mortem times together, it seems likelythat most ship-collision deaths reported in this studyoccurred no more than about 7 to 8 d before the dis-covery dates. Only 1 ship-struck whale found in ornear an SMA was found <9 d after the beginning or

end dates of the nearest active SMA (i.e. a humpbackwhale with no information on its decomposition statewas found 8 d after the start of the nearest SMA22.6 nmi away). Thus, it seems reasonable to believethat most, if not all, carcasses considered to havebeen struck in or near SMAs during active SMAdates were in fact struck during those periods.

Far less clear is whether ship-strike victims foundin or near SMA boundaries were in fact struck withinSMA boundaries. Complicating factors include thepossibility of whales swimming some distance afterbeing struck and before they die and drift an addi-tional distance from collision locations. Because ofthose possibilities, some dead whales discovered out-side SMA boundaries may have been struck insideSMA boundaries and vice versa. In general, it seemsunlikely that lethally struck whales would swim longdistances after being hit. Even if whales do not dieinstantly or within a few hours, massive injuries typi-cal of collision deaths are likely to leave them mori-bund or highly immobile. Transport of moribund ordead whales by wind and currents is more difficult togauge. As noted above, resighted right whale car-casses drifted an average of 7 nmi d−1, and 1 drifted112 nmi (204 km) in 8 d, for an average of 14 nmi(26 km) d−1. Thus, it is possible that some ship-struckcarcasses could have drifted into SMAs from adja-

143

Fig. 4. Megaptera novaeangliae. Locations and dates whereall humpback whales killed by ships were found before andafter Seasonal Management Areas (SMAs) were establishedon 8 December 2008. *: carcass found in or within 45 nmi(83 km) of SMA boundaries during active time frames; J:carcass locations during pre-rule years, 1990 to 2008; M: car-cass locations during post-rule years, 9 December 2008

through 8 June 2013

0 1 2 3 4 5 6 7 8 9 100

0.05

0.1

0.15

0.2

Pro

bab

ility

Number of right whale carcasses found in or near SMAs

Fig. 5. Eubalaena glacialis. Probabilities of finding 0 to 10right whale carcasses in or near Seasonal Management Ar-eas (SMAs) over the 5 yr post-rule period (8 December 2008to 8 December 2013) based on bootstrap resampling of dis-covery records during the 18 yr pre-rule period (8 December1990 to 7 December 2008). Dark gray bars show probabili-ties of 5 yr totals assuming whales could be found in anyyear during the 5 yr period; light gray bars show probabili-ties assuming no whales were found in years 1 to 5 and 0, ≤1,or ≤2 whales were found in Year 6; gray dashed line showsthe annual mean pre-rule discovery rate of 0.72 (equivalent

to 3.6 carcasses over 5 yr)

Endang Species Res 23: 133–147, 2014

cent areas. Indeed, given that 5 of 8 right whale car-casses found inside SMA boundaries during pre-ruleyears were moderately decomposed, it would seemlikely that at least some drifted 45 nmi before beingfound, which could have put them outside but nearSMA boundaries.

A detailed analysis of carcass drift for ship-strikevictims found in the past was beyond the scope of thisstudy. To improve understanding of where ship-strike victims are actually struck relative to SMAboundaries in the future, we recommend conductinga retrospective drift analysis as a routine part ofinvestigations for future ship-struck right whale car-casses. Where possible, estimates should be madeduring necropsies of the time between death and thediscovery of all carcasses attributed to ship strikes.That time span should then be used to trace the pos-sible drift path back to a predicted location at thetime of death based on prevailing winds and currentsover that period.

Despite uncertainty about precisely where pastship-strike victims were struck, the pattern of carcassrecovery shown in Fig. 2 strongly suggests thatnearly 90% of all right whale deaths attributed toship strikes in US waters since 8 December 1990 andbefore the rule became effective were struck in ornear SMAs during the periods in which these were ineffect. The possibility that some of those whales werestruck in waters adjacent to SMA boundaries under-scores the importance of expanding SMA boundariesalong the species’ migratory corridor (i.e. from Geor-gia to New York) to the 30 nmi limit originally pro-posed by the NMFS based on its past assessment ofthe width of the right whale migratory corridor andrelevant new information. In addition, we recom-mend that further studies be undertaken to betterdefine the distances from shore that most rightwhales travel during their migrations in spring andfall between Georgia and New York.

SMA boundaries

With half of all known right whale deaths in USwaters since 1990 due to ship strikes found along thespecies’ migratory corridor — which is thought toextend to approximately 30 nmi from shore (Schick2009, Keller et al. 2012) — failure to include watersbetween 20 and 30 nmi in SMA boundaries leaves apotentially significant gap in protection of rightwhales from ship collisions. Its lack of inclusion alsocomplicates evaluations of SMA effectiveness. Withcurrent SMA boundaries along the migratory corri-

dor set as 20 nmi arcs around port entrances, it is pos-sible that vessels entering or leaving port may hitwhales in the offshore third of the species’ presumedmigratory corridor (i.e. 20 to 30 nmi from shore),where speed limits do not apply. Those carcassesmay drift into SMAs and be assumed incorrectly tohave been struck by ships complying with speedrestrictions inside an SMA. Also, because carcassdetection and retrieval becomes more difficult as dis-tance from shore increases, whales struck and killedin this offshore zone that do not drift towards shoremay be underestimated.

To more rigorously protect right whales and reduceuncertainty about whether ship-strike victims arestruck just beyond SMA boundaries where speedrestrictions do not apply, we recommend that (1) theboundaries of the SMAs along the species’ migratorycorridor be extended to 30 nmi from shore, as initiallyproposed by the NMFS; (2) the configuration ofSMAs be modified from an arc to a rectangle, withboundaries extending perpendicular from the pointswhere current SMA perimeters intersect with landout to 30 nmi offshore, to cover a greater portion ofvessel tracks across core migratory areas; and (3)SMAs be made effective indefinitely, with a viewtowards retaining them unless further analysesdemonstrate they are ineffective or should be modi-fied. Changing SMA boundaries along the migratorycorridor from arcs to rectangles that extend 20 (or 30)nmi from shore would increase their size by about25%. This change would increase the probabilitythat ships entering or leaving port along routes thatare not perpendicular to the coast would travel atspeeds safe for whales when transiting areas wheremigrating whales are most likely to be encountered.

It is also interesting that several right whale deathsdue to unknown causes, possibly including shipstrikes, were found offshore at distances and/or attimes of the year when retrieval was more difficult. Inthis regard, 4 of 15 right whale deaths of unknowncause were clustered in or near the southern tip ofthe Great South Channel SMA from Decemberthrough February, when that SMA was not in effect(Fig. 2). Those deaths, which occurred at a time ofyear with poor weather conditions and where carcassretrieval is very difficult, lie near an area where sev-eral heavily used vessel traffic corridors intersect(Ward-Geiger et al. 2005). That area may, therefore,be an additional site where ship collision risks arehigh and where the designation of an SMA should beconsidered. In general, carcasses are less likely to befound farther offshore, because of reduced surveyeffort. We do not, however, believe this bias would

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Laist et al.: Speed limits for right whales

alter our conclusions, because, with the exception ofwaters in the Gulf of Maine, right whale occurrenceis believed to decrease in waters beyond 30 nmi fromshore. In addition, those areas were not subject toregulation either before or after the rules went intoeffect, and thus right whale occurrence in or nearSMAs should not differ in either period. The whales’distance from shore may also make it less likely theywould drift into SMAs.

CONCLUSIONS

Analyses of the locations where ship-struck whalecarcasses are found provide useful methods for eval-uating the biological effectiveness of SMAs estab-lished to protect North Atlantic right whales. Theoverall pattern of carcass discovery locations shownin Fig. 2 strongly suggests that a large majority ofship-collision victims found in pre-rule years werestruck by ships entering and leaving ports where the10 SMAs were later designated and also on datesthat coincided with periods in which the later SMAswere in effect. The increased waiting time betweendiscovery of ship collisions in or near active SMAsafter the December 2008 implementation (i.e. 5.0 yras of the date of this analysis) also suggests that theseasonal 10 knot speed limit has been effective,although additional time is needed to confirm long-term trends. When the rule was adopted, it wasthought it would also benefit humpback whales, butthere is no evidence from this analysis that this hasbeen true. Numerous collisions involving humpbackwhales were found within or near SMA boundaries,but most were not during active SMA dates.

Based on these results, speed restrictions and theexisting SMAs are tools that should be kept in placeindefinitely. Dredged channels passing throughSMAs should not be exempted from restrictions, asrequested by petition, because whales must travelacross those channels and are at no less risk of beingstruck in those channels. The rules appear to havebeen effective and remain necessary to prevent ship-related right whale deaths. However, to better coverareas where right whales are at greatest risk, SMAboundaries along the right whale migratory corridorshould be extended from 20 to 30 nmi from shore, asoriginally proposed by the NMFS. In addition, con-sideration should be given to: (1) changing the con-figuration of SMA boundaries off ports inmid-Atlantic states from arcs to rectangles, to betterprotect whales migrating farther offshore; (2) estab-lishing a new winter SMA along a segment of desig-

nated shipping lanes south of the Great South Chan-nel SMA, where 4 unretrieved right whale carcassespossibly struck by ships were found in the months ofDecember through February; and (3) extending thedates of SMAs, to better cover times when humpbackwhales are likely to occur in SMA boundaries. Giventhe apparent effectiveness of reduced speed limitsand experience indicating a lack of compliance withvoluntary requests to use reduced speeds (McKennaet al. 2012, Silber et al. 2012b), we also recommendthat speed limits in short-term DMA zones be mademandatory, rather than voluntary, to protect periodicright whale aggregations found outside of activeSMAs. Our study provides encouraging evidencethat 10 knot speed restrictions are effective for reduc-ing vessel-related right whale deaths. Such restric-tions should be considered as an option for mitigatingvessel strikes of large whales in other parts of theworld where this problem is considered significant.

Acknowledgements. We thank Mendy Garron and AllisonHenry of the National Marine Fisheries Service for search-ing the National Marine Mammal Strandings database. Wealso thank Brooke Wikgren of the New England Aquariumfor plotting those records on a study area map, calculatingdistances of carcasses from SMA boundaries, and preparingthe figures in this paper. Peter Thomas, Michael Tlusty, and4 anonymous reviewers also provided constructive com-ments on various drafts for which we are very grateful. Wealso acknowledge and thank all the necropsy team leadersand stranding program participants whose hard work wasessential in creating this valuable database.

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Editorial responsibility: Simon Goldsworthy, West Beach, Australia

Submitted: December 4, 2012; Accepted: January 23, 2014Proofs received from author(s): February 21, 2014