Biology of deep-water chondrichthyans: Introduction

1. Introduction

Approximately half of the known chondrichthyans (sharks,skates, rays, and chimaeras), 575 of 1207 species (47.6%, Table 1),live in the deep ocean (below 200 m), yet little is known of thebiology or life histories of most of these fishes (Kyne andSimpfendorfer, 2007). The limited information available fordeep-water chondrichthyans is compounded by their rarity, aswell as the prevalent uncertainty in the alpha taxonomy of deep-water species. Many species are known only from the typematerials, which are generally limited to nondestructive sampling,e.g., morphometrics, imaging (X-ray, MRI, CT scanning). Thus,research has been hindered by a lack of specimens available forinvestigation that requires destructive sampling or live specimens(e.g., life history, diet, telemetry). The need for more research anddissemination of information about deep-water chondrichthyanshas become imperative as fisheries worldwide continue to expandinto deeper waters and exploit deep-water stocks, usually in theabsence of data required for appropriate management (Moratoet al., 2006; Kyne and Simpfendorfer, 2010).

1.1. Fisheries effects

Until recent decades, much of the fishing effort for deep-waterchondrichthyans was localized and often artisanal, with limitedpopulation level effects. Contemporary fishing effort for deep-water sharks has been increasing worldwide, concentrating parti-cularly on species within the genera Centrophorus, Deania, andCentroscymnus (Kyne and Simpfendorfer, 2007, 2010; Moura et al.,2014). This escalation is usually initiated by collapses in near-shorefisheries or increases in ex-vessel price of shark meat and liver oil.The effects of fishery development on deep-water chondrichth-yans are magnified by the advent of more efficient fishingtechnology (e.g., automated longliners, larger trawl nets, high-resolution bathymetric imaging). Global increases in fishing effortfor deep-water species come in spite of recent data that indicatemany deep-water fishes have among the most conservative ofvertebrate life histories (i.e., slower growth, delayed maturity,lower fecundity; Simpfendorfer and Kyne, 2009). Such “K-selected” life histories render most deep-water species highlysusceptible to overexploitation and localized depletion, yet mostof the global exploitation occurs in the absence of requisite stockassessments or management plans (Kyne and Simpfendorfer,2010).

Many deepwater chondrichthyans are captured as bycatch infisheries targeting deep-water teleosts and crustaceans. Bycatchmortality, much of which is discarded, likely exceeds targeted

mortality of these taxa. Graham et al. (2001) documented declinesin relative abundances of more than 95% over 20 years for sixspecies of deep-water sharks captured as bycatch in trawl fisheriestargeting teleosts around southeastern Australia. Studies ofrebound potential for deep-water sharks are rare (Kyne andSimpfendorfer, 2010), yet have indicated a very low capacity torecover from population declines relative to shelf and pelagicspecies (Simpfendorfer and Kyne, 2009). More of these types ofstudies are needed to better document how populations of deep-water chondrichthyans respond to fishing mortality.

1.2. Life history

Deep-water sharks generally exhibit very conservative lifehistory parameters relative to shallower-dwelling species (Kyneand Simpfendorfer, 2007). Reproductive output is limited, markedby low fecundity and presumably long gestational periods (Kyneand Simpfendorfer, 2010) and may require extensive energeticinvestments to produce some of the largest ova known amongvertebrates (Guallart and Vicent, 2001; Cotton et al., 2015).Segregation by sex and maturity stage is common in deep-waterchondrichthyans (Yano and Tanaka, 1988; Wetherbee, 1996; Girardand Du Buit, 1999; Clarke et al., 2001; Jakobsdóttir, 2001;McLaughlin and Morrissey, 2005; Cotton et al., 2015), possiblynecessitating large migrations for mating.

Studies of age and growth of deep-water chondrichthyansindicate that most species examined exhibit high longevity andlow growth rates (summarized in Kyne and Simpfendorfer (2010)).Some species, however, have been shown to exhibit more moder-ate longevities and growth rates (e.g., Squalus blainville, Cannizzaroet al., 1995; Etmopterus spinax, Gennari and Scacco, 2007; Coelhoand Erzini, 2008; Amblyraja georgiana Francis and Ó Maolagáin,2005; Squalus cf. mitsukurii, Cotton et al., 2011).

1.3. Distribution and movement patterns

Due to the relative environmental homogeneity (temperature,salinity, light levels, pressure) of the deep ocean, boundaries tospecies distribution are less pronounced than for shallower dwell-ing species. Therefore, many deep-water chondrichthyans havebroad, often global, distributions, though species with limitedgeographic ranges, including endemics, are also commonlyreported (Compagno et al., 2005). Overall, the reported geographicranges of deep-water sharks may be underestimated as these areoften based on scant catch data and may simply reflect theprevailing inadequacy in deep-water sampling. A great deal ofinformation is available pertaining to regional distributions of

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Table 1Total number of extant chondrichthyan species by genus, compared with deep-water (DW) species. An annotated checklist of deep-water species compiled by Kyne andSimpfendorfer (2010) is compared with the present compilation (2014). New species described since Kyne and Simpfendorfer (2010) published their checklist are indicated.Differences in numbers of deep-water species per genus are indicated by bold format and are largely due to the addition of newly described species, with some differencesattributed to taxonomic revision (e.g. synonymy, revised generic assignment, etc.) or omission/inclusion in the previous compilation.

Order Family Genus Total # valid spp.(2014)

# of DW spp.(2010)

# new spp. described2009–2014

# of DW spp.(2014)

% of DW spp.within genus

Chimaeriformes Callorhinchidae Callorhinchus 3 0 0 0 0Chimaeridae Chimaera 14 11 3 14 100

Hydrolagus 25 21 1 25 100Rhinochimaeridae Harriotta 2 2 0 2 100

Neoharriotta 3 3 0 3 100Rhinochimaera 3 3 0 3 100

Hexanchiformes Chlamydoselachidae Chlamydoselachus 2 1 1 2 100Hexanchidae Heptranchias 1 1 0 1 100

Hexanchus 2 2 0 2 100Notorynchus 1 0 0 0 0

Squaliformes Centrophoridae Centrophorus 11 11 0 11 100Deania 4 4 0 4 100

Dalatiidae Dalatias 1 1 0 1 100Euprotomicroides 1 1 0 1 100Euprotomicrus 1 1 0 1 100Heteroscymnoides 1 1 0 1 100Isistius 2 2 0 2 100Mollisquama 1 1 0 1 100Squaliolus 2 2 0 2 100

Etmopteridae Aculeola 1 1 0 1 100Centroscyllium 7 7 0 7 100Etmopterus 37 32 3 37 100Trigonognathus 1 1 0 1 100

Oxynotidae Oxynotus 5 5 0 5 100Somniosidae Centroscymnus 2 2 0 2 100

Centroselachus 1 1 0 1 100Proscymnodon 2 2 0 2 100Scymnodalatias 4 3 0 4 100Scymnodon 1 1 0 1 100Somniosus 5 5 0 5 100Zameus 2 2 0 2 100

Squalidae Cirrhigaleus 3 3 0 3 100Squalus 25 22 1 22 88

Echinorhiniformes Echinorhinidae Echinorhinus 2 2 0 2 100

Pristiophoriformes Pristiophoridae Pliotrema 1 1 0 1 100Pristiophorus 7 2 2 4 57

Squatiniformes Squatinidae Squatina 22 7 1 8 36

Heterodontiformes Heterodontidae Heterodontus 9 1 0 0 0

Orectolobiformes Brachaeluridae Brachaelurus 2 0 0 0 0Ginglymostomatidae Ginglymostoma 1 0 0 0 0

Nebrius 1 0 0 0 0Pseudoginglymostoma 1 0 0 0 0

Hemiscylliidae Chiloscyllium 8 0 0 0 0Hemiscyllium 9 0 2 0 0

Orectolobidae Eucrossorhinus 1 0 0 0 0Orectolobus 10 0 1 0 0Sutorectus 1 0 0 0 0

Parascylliidae Cirrhoscyllium 3 1 0 1 33Parascyllium 5 1 0 1 20

Rhincodontidae Rhincodon 1 0 0 0 0Stegostomatidae Stegostoma 2 0 0 0 0

Lamniformes Alopiidae Alopias 3 1 0 1 33Cetorhinidae Cetorhinus 1 1 0 0 0Lamnidae Carcharodon 1 0 0 0 0

Isurus 2 0 0 0 0Lamna 2 0 0 0 0

Megachasmidae Megachasma 1 0 0 0 0Mitsukurinidae Mitsukurina 1 1 0 1 100Odontaspididae Carcharias 1 0 0 0 0

Odontaspis 2 2 0 2 100Pseudocarchariidae Pseudocarcharias 1 1 0 1 100

Carcharhiniformes Carcharhinidae Carcharhinus 34 1 1 2 6Galeocerdo 1 0 0 0 0Glyphis 5 0 1 0 0Isogomphodon 1 0 0 0 0Lamiopsis 2 0 0 0 0

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Table 1 (continued )

Order Family Genus Total # valid spp.(2014)

# of DW spp.(2010)

# new spp. described2009–2014

# of DW spp.(2014)

% of DW spp.within genus

Loxodon 1 0 0 0 0Nasolamia 1 0 0 0 0Negaprion 2 0 0 0 0Prionace 1 0 0 0 0Rhizoprionodon 7 0 0 0 0Scoliodon 2 0 0 0 0Triaenodon 1 0 0 0 0

Hemigaleidae Chaenogaleus 1 0 0 0 0Hemigaleus 2 0 0 0 0Hemipristis 1 0 0 0 0Paragaleus 4 0 0 0 0

Leptochariidae Leptocharias 1 0 0 0 0Pentanchidae Halaelurus 7 0 0 0 0

Holohalaelurus 5 5 0 5 100Pentanchus 1 1 0 1 100

Proscylliidae Ctenacis 1 0 0 0 0Eridacnis 3 3 0 3 100Proscyllium 3 0 0 0 0

Pseudotriakidae Gollum 2 1 1 2 100Planonasus 1 0 1 1 100Pseudotriakis 1 1 0 1 100

Scyliorhinidae Apristurus 37 35 2 37 100Asymbolus 9 2 0 3 33Atelomycterus 5 0 0 0 0Aulohalaelurus 2 0 0 0 0Bythaelurus 9 8 1 9 100Cephaloscyllium 18 11 1 13 72Cephalurus 1 1 0 1 100Figaro 2 2 0 2 100Galeus 17 16 0 16 94Haploblepharus 4 0 0 0 0Parmaturus 9 9 0 9 100Poroderma 2 0 0 0 0Schroederichthys 5 3 0 3 60Scyliorhinus 15 9 0 10 67

Sphyrnidae Eusphyra 1 0 0 0 0Sphyrna 8 0 1 0 0

Triakidae Furgaleus 1 0 0 0 0Galeorhinus 1 0 0 0 0Gogolia 1 0 0 0 0Hemitriakis 6 1 0 1 17Hypogaleus 1 0 0 0 0Iago 2 2 0 2 100Mustelus 28 3 1 4 14Scylliogaleus 1 0 0 0 0Triakis 5 0 0 0 0

Rajiformes Anacanthobatidae Anacanthobatis 5 5 0 5 100Cruriraja 8 7 1 8 100Indobatis 1 1 0 1 100Sinobatis 6 6 0 6 100

Arhynchobatidae Arhynchobatis 1 1 0 1 100Atlantoraja 3 0 0 0 0Bathyraja 53 47 2 53 100Brochiraja 8 6 2 8 100Insentiraja 2 2 0 2 100Irolita 2 0 0 0 0Notoraja 11 6 5 11 100Pavoraja 6 6 0 6 100Psammobatis 8 1 0 2 25Pseudoraja 1 1 0 1 100Rhinoraja 3 4 0 3 100Rioraja 1 0 0 0 0Sympterygia 4 0 0 0 0

Rajidae Amblyraja 10 10 0 10 100Beringraja 2 0 0 0 0Breviraja 7 6 0 7 100Dactylobatus 2 2 0 2 100Dipturus 48 37 1 39 81Fenestraja 8 8 0 8 100Gurgesiella 3 3 0 3 100Hongeo 1 0 0 0 0Leucoraja 15 10 0 12 80Malacoraja 4 4 0 4 100Neoraja 5 5 0 5 100

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deep-water chondrichthyans in the form of catch records, rangeextensions, field guides, etc. Very few studies have compiled thesedata sources over global scales to better document the full extentof species distributions and spatial segregations (e.g., Moura et al.,2014). Technological advances in telemetry may be used to addressinformational gaps pertaining to distributions of deep-waterspecies (Rodríguez-Cabello and Sánchez, 2014; Comfort andWeng, 2015; Campana et al., 2015; Daley et al., 2015).

Deep-water chondrichthyans occupy many different habitats inthe deep ocean. Demersal species inhabit the continental shelfbreak and slope habitats, whereas species such as Isistius spp. andPteroplatytrygon violacea are found in bathypelagic and mesope-lagic habitats by day and the epipelagic zone by night. Deep-waterchondrichthyans are absent from abyssal habitats possibly due toenergetic limitations of buoyancy control (Priede et al., 2006),dietary limitation of trimethylamine N-oxide (TMAO) required for

Table 1 (continued )

Order Family Genus Total # valid spp.(2014)

# of DW spp.(2010)

# new spp. described2009–2014

# of DW spp.(2014)

% of DW spp.within genus

Okamejei 15 3 2 4 27Raja 27 9 0 7 26Rajella 18 16 1 18 100Rostroraja 1 1 0 1 100Spiniraja 1 0 0 0 0Zearaja 3 2 0 2 67

Torpediniformes Hypnidae Hypnos 1 0 0 0 0Narcinidae Benthobatis 4 4 0 4 100

Diplobatis 4 0 0 0 0Discopyge 2 0 0 0 0Narcine 21 3 0 3 14

Narkidae Crassinarke 1 0 0 0 0Electrolux 1 0 0 0 0Heteronarce 4 2 0 3 75Narke 3 0 0 0 0Temera 1 0 0 0 0Typhlonarke 2 2 0 2 100

Platyrhinidae Platyrhina 3 0 2 0 0Platyrhinoidis 1 0 0 0 0

Torpedinidae Tetronarce 2 0 0 0 0Torpedo 21 7 0 5 24

Rhinopristiformes Pristidae Anoxypristis 1 0 0 0 0Pristis 4 0 0 0 0

Rhinobatidae Aptychotrema 3 0 0 0 0Glaucostegus 5 0 0 0 0Rhina 1 0 0 0 0Rhinobatos 34 1 0 1 3Rhynchobatus 7 0 2 0 0Trygonorrhina 3 0 0 0 0Zanobatus 1 0 0 0 0Zapteryx 3 0 0 0 0

Myliobatiformes Dasyatidae Dasyatis 42 1 1 2 5Heliotrygon 2 0 2 0 0Himantura 30 0 3 0 0Neotrygon 6 0 1 0 0Pastinachus 6 0 2 0 0Pteroplatytrygon 1 0 0 0 0Taeniura 2 0 0 0 0Taeniurops 1 0 0 0 0Urogymnus 1 0 0 0 0

Gymnuridae Gymnura 14 0 0 0 0Hexatrygonidae Hexatrygon 1 1 0 1 100Myliobatidae Aetobatus 4 0 1 0 0

Aetomylaeus 4 0 0 0 0Manta 2 0 0 0 0Mobula 10 0 0 0 0Myliobatis 12 0 1 1 8Pteromylaeus 2 0 0 0 0Rhinoptera 10 0 0 0 0

Plesiobatidae Plesiobatis 1 1 0 1 100Potamotrygonidae Paratrygon 1 0 0 0 0

Plesiotrygon 2 0 1 0 0Potamotrygon 22 0 5 0 0

Urolophidae Trygonoptera 6 0 0 0 0Urolophus 22 2 0 7 32

Urotrygonidae Urobatis 6 0 0 0 0Urotrygon 13 0 0 0 0

TOTAL 1207 523 60a 575b x̄¼42.1%

a 50% of new spp. described 2009–2014 are deep-water.b 47.6% of total spp. are deep-water.

Editorial / Deep-Sea Research II 115 (2015) 1–104

stabilizing proteins in the presence of high urea concentrations(Laxson et al., 2009), or trophic limitations (Musick and Cotton,2015).

Telemetry studies have been conducted for only a few deep-water species (Kyne and Simpfendorfer, 2010), with some studiesrevealing diel vertical migrations (Grubbs and Kraus, 2010,Comfort and Weng, 2015; Daley et al., 2015).

Studies of population structure (Chevolot et al., 2007;Veríssimo et al., 2011, 2012) and species distributions (Mouraet al., 2014) have demonstrated wide geographic ranges and highdispersal potential for some species. Such information can be usedto inform fisheries management models as geographically limitedfishing effort may have wide-ranging effects on deep-waterspecies. In the absence of studies like these, it will be impossibleto predict population growth trajectories or assess the full effect offishing mortality on exploited species.

1.4. Trophic ecology

Deep-water chondrichthyans occupy trophic guilds rangingfrom specialized to generalist predators with diets that reveal ahigh degree of connectivity with pelagic, mesopelagic, and benthicecosystems (Kyne and Simpfendorfer, 2010). Some shark speciesprimarily feed on teleosts, whereas others specialize on crusta-ceans or cephalopods. A few species have been shown to scavengemarine mammals, while others (e.g., Isistius spp.) are known toparasitize pelagic fishes and cetaceans. Skates and holocephalansprimarily consume crustaceans and secondarily consume teleosts.With large migrations suggested by some authors (Veríssimo et al.,2011, 2012; Cotton et al., 2015) and demonstrated in recenttelemetry studies (Campana et al., 2015; Rodríguez-Cabello andSánchez, 2014) these species may act as vectors of microbial andbiogeochemical transport over long distances.

1.5. Environmental contaminants

Deep-water chondrichthyans have shown elevated levels ofmercury in multiple studies from various regions (Hornung et al.,1993; Pethybridge et al., 2010; Newman et al., 2011). It is unknownwhether appropriate species-specific consumption advisories existin countries where deep-water chondrichthyans are consumed.Although several studies assessing bioaccumulation of methylmer-cury in deep-water sharks are in progress (D. Grubbs, unpublisheddata), more research is needed to fully assess the levels ofexposure to environmental contaminants for deep-water chon-drichthyans, particularly in those countries where they are con-sumed. Studies of other environmental contaminants in deep-water chondrichthyan tissues (e.g., PCB's, DDT, HCB, dioxins, flameretardants) have also indicated elevated levels in these species(Serrano et al., 2000; Storelli and Marcotrigiano, 2001; Fisk et al.,

2002; Storelli et al., 2005; Strid et al., 2007, 2013; Corsolini et al.,2014).

Following the 2010 Deepwater Horizon oil spill in the Gulf ofMexico, which occurred at a depth of over 1500 m, information ontaxonomy, biology, and ecology for deep-water chondrichthyanswas lacking for those species potentially affected. Thus an accurateassessment of toxicant exposure and recovery was hindered by theabsence of pre-spill biological data, as well as the low taxonomicresolution that confounded research efforts following the spill. Ashuman influence and exploitation of natural resources for foodand energy expand deeper into the sea, disasters such as theDeepwater Horizon oil spill highlight the importance of studyingdeep-water communities.

2. Rationale

The IUCN Shark Specialist Group (SSG) defines deep-waterchondrichthyans as those “whose distribution is predominantly at,are restricted to, or spend the majority of their lifecycle at, depthsbelow 200 m” (Kyne and Simpfendorfer, 2007). As predators oftenoccupying the highest trophic levels in deep-sea ecosystems (Musickand Cotton, 2015), these species serve vital functions in deep oceancommunities. Deep-water chondrichthyans have unique life historycharacteristics and evolutionary adaptations, and consequentlyrequire special management considerations relative to theirshallower-dwelling counterparts. Traditional management pract-ices and harvest targets may not be appropriate for these species.Consequently, there is a pressing need for more information aboutthe ecology and biology of these species to better understand theroles of chondrichthyans in the world's largest ecosystem, the deepsea. With this rationale in mind, the symposium “Biology of Deep-Water Chondrichthyans” was proposed as a contribution to the 28thAnnual Meeting (2012) of the American Elasmobranch Society inVancouver, British Columbia.

Although other scientific societies have held numerous sympo-sia focused on deep-water fishes, only the International Congresson the Biology of Fish (2002), and the Food and AgricultureOrganization of the United Nations (FAO) “Deep Sea 2003” meet-ings have held symposia focused exclusively on deep-waterchondrichthyan research. In 2008 the American Fisheries Societyheld a symposium at their annual meeting in Ottawa, Canada,entitled “Global Management of Squaloid Sharks – Protection andEnhancement of Regional Fisheries in Light of Global ConservationInitiatives.” Composed almost exclusively of management-themedpresentations about Squalus acanthias, a shelf-dwelling dogfish,this symposium was primarily focused on the pending decision tooffer a CITES listing to this species (Gallucci et al., 2009). Deep-water squaloids were the focus of only two presentations in thatsymposium. “Biology of Deep-Water Chondrichthyans”, we soughtto provide a forum for presentations that highlight many of thelesser-known deep-water chondrichthyans, as these species arelargely underrepresented in the literature (Table 2).

The “Biology of Deep-Water Chondrichthyans” symposium soli-cited presentations that highlight the extensive volume of newinformation available for this unique group of fishes and selectedcontributions were published through this special issue of Deep-SeaResearch II. Additionally, the symposium facilitated the formation ofnetworks of deep-water chondrichthyan researchers working withinthe sub-disciplines of taxonomy, telemetry, trophic ecology, age andgrowth, biogeography, ecotoxicology, physiology, reproductive biol-ogy, and population genetics. Hence, this symposium provided atimely update to the current status of deep-water chondrichthyanresearch and fostered many collaborative projects among research-ers so that the global research community may be informed of the

Table 2Numbers of citations in the literature for any chondrichthyan species compared tothose for deep-water species (DW), using various common databases. The year ofthe earliest citation for each search is given in parentheses.

Database # of papersAll species

# of papersDW species

% papers forDW taxa

Web of Science 65,910 (1872) 8708 (1875) 13.2ProQuest (any citation) 189,059 (1743) 6343 (1839) 3.4ProQuest (peer-reviewed only) 49,810 (1820) 3605 (1847) 7.2ASFAa (any citation) 10,975 (1923) 2016 (1932) 18.4ASFAa (peer-reviewed only) 5927 (1935) 1001 (1935) 16.9

a Aquatic Science & Fisheries Abstracts (ASFA) 1: Biological Sciences & LivingResources.

Editorial / Deep-Sea Research II 115 (2015) 1–10 5

latest developments and fisheries managers can better formulatemanagement plans and conservation efforts where appropriate.

3. Taxonomic diversity

As of this reporting, there were 1207 extant chondrichthyanspecies, 575 (47.6%) of which were classified as “deep-water”according to the previously stated IUCN SSG definition (Table 1,Appendix B). Expressed as the unweighted, mean percent compo-sition per genus, deep-water species composed 42.1% of chon-drichthyan genera. Distribution of deep-water species acrossgenera was highly skewed. Of the 197 chondrichthyan genera, 98(49.7%) contained no deep-water species and 72 (36.5%) werecomposed exclusively of deep-water taxa, with the remaining 27(13.7%) genera containing intermediate values of deep-waterspecies composition (Table 1). Species compositions were some-what less skewed at the family level, with 20 families (36.4%)containing no deep-water species; 14 families (25.4%) with exclu-sively deep-water taxa, and 21 families (38.2%) with intermediatedeep-water species compositions. At the ordinal level, deep-waterspecies were more evenly represented across orders, with 1 ordercontaining no deep-water species (7.1%), 1 order (7.1%) with

exclusively deep-water taxa, and 12 orders (85.7%) with inter-mediate deep-water species compositions.

4. Relative literature coverage

A survey of the literature (Appendix A) revealed a dispropor-tionately low percentage of publications pertaining to deep-waterchondrichthyans relative to all other chondrichthyan species(Table 2). This disproportionality is evident across all yearssurveyed (Fig. 1) in queries of primary literature, as well as thoseof all reference sources (Table 2). However, the proportion ofliterature devoted to deep-water taxa has been increasing inrecent years. This is in part related to a recent increase in thenumber of new taxonomic descriptions of deep-water species. Forexample, Kyne and Simpfendorfer (2007) reported that more than20% of the known species of deep-water chondrichthyans wereundescribed. Many of these taxa have now been formallydescribed. Of the �230 species of chondrichthyans that weredescribed between 2000 and 2014, 65% of them were deep-watertaxa (Pollerspöck, 2014).

Most of the published literature on deep-water chondrichthyantaxa is either taxonomic in nature (e.g., descriptions or revisions)or biodiversity-focused (e.g. catch records, species inventories,

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Fig. 1. Numbers of peer-reviewed publications by decade that cover any chondrichthyan species (gray bars) and deep-water chondrichthyan species (black bars), using thedatabases ProQuest (A, raw data; B, log-transformed data) and Aquatic Science & Fisheries Abstracts (ASFA) 1: Biological Sciences & Living Resources (C, raw data; D,log-transformed data).

Editorial / Deep-Sea Research II 115 (2015) 1–106

field guides, etc.), with basic ecology for most species almostentirely unstudied. For example, Pollerspöck (2014) compiled theliterature pertaining to Oxynotus paradoxus, yielding 32 papers, allof which focus on taxonomy or biodiversity. Hence, although manypapers have been published for O. paradoxus, basic biology orecology of the species remains almost entirely unknown (Soldoand Freitas, 2009). Simpfendorfer and Kyne (2009) reported thatlife history data sufficient to estimate production potential wereavailable for only 2.5% of deep-water chondrichthyan species.However, due to the recent increase in life history research onthese taxa, particularly the deep-water skates, Rigby andSimpfendorfer (2015), report life history data are now availablefor nearly 7% of deep-water species. This highlights the recentincrease in published data for deep-sea chondrichthyans but alsopoints to the need for additional effort.

One of the primary obstacles to deep-water chondrichthyanresearch is the difficulty involved in observing, sampling, orcollecting these species. The expense and logistics required tostudy deep-water taxa is usually exponentially higher than that ofcoastal or pelagic species (Gage and Tyler, 1991; Merrett andHaedrich, 1997). This disparity will likely continue to hamperfuture research efforts for deep-water chondrichthyans.

5. Outcomes

The "Biology of Deep-Water Chondrichthyans" symposiumincluded 26 presenters (20 oral and 6 posters) from 9 countries.This special issue of Deep-Sea Research II includes 14 contributedpapers from the symposium, covering topics ranging from taxon-omy (Straube et al., 2015; Weigmann et al., 2015), biodiversity(Brooks et al., 2015), trophic ecology (Churchill et al., 2015a,2015b; Musick and Cotton, 2015), life history and demographics(Coelho et al., 2015; Cotton et al., 2015; King and McPhie, 2015;Rigby and Simpfendorfer, 2015), and behavior (Campana et al.,2015; Comfort and Weng, 2015; Daley et al., 2015).

The information presented herein will alert research andmanagement communities of the volume of new informationavailable on this unique group of fishes. Additionally, participatingresearchers had the opportunity to interact with and establishnew colleagues and collaborators working within various sub-disciplines of deep-water chondrichthyan research.

In conjunction with the symposium, a taxonomy workshopfocused on gulper sharks (Centrophorus spp.) was offered tosymposium attendants. This workshop facilitated multiple colla-borative studies and two published manuscripts aimed at resol-ving the problematic alpha taxonomy within the genusCentrophorus (White et al., 2013; Veríssimo et al., 2014). Moretaxonomic studies focused on Centrophorus and Deania spp. arecurrently underway (S. Tanaka, W. White, personal communica-tion). The products of this workshop will reduce taxonomicconfusion and redundancy in the literature, thus benefiting futurestudies of these species.

6. Closing

As the world's largest professional society engaged in chon-drichthyan research, the American Elasmobranch Society provideda logical forum for a symposium covering the biology of deep-water chondrichthyans. Conservation efforts focused on these taxahave historically been plagued by a dearth of biological andecological data and the information presented herein will greatlyassist future research, conservation, and management efforts. Asthe global community of deep-water chondrichthyan researcherscontinues to grow, the exchange of ideas and presentation of

research, both at the symposium in Vancouver and in this specialissue of Deep-Sea Research II, will be a lasting contribution to theresearch community at large.

Acknowledgments

We give special recognition to Jack Musick for fostering ourstrong interest in chondrichthyan research, particularly related todeep-water taxa. Austin Heil assisted with construction of Booleansearch strings. The assistance of additional moderators Ana Ver-íssimo and Dave Ebert was greatly appreciated. We thank MattKolmann who helped to organize the Centrophorus taxonomyworkshop, as well as all the participants who gave up theirconference lunch break to contribute to the workshop. The authorsespecially appreciate the time and effort spent by dozens ofreviewers for the manuscripts herein, as well as “stand-in” editorsJeff Carrier and Colin Simpfendorfer who handled the review ofthis manuscript as well as another by the lead author. The authorswould like to thank the AES Grant Fund Committee for supportingthis symposium. The lead author's role in participation andorganization of this symposium was funded in part through theDepartment of Education Title VII Award P382G090003.

Appendix A. Literature review methods

Using a complex Boolean search string to include all chon-drichthyan taxa (Appendix A.1) we used three common databases(Web of Science, ProQuest, and Aquatic Science & Fisheries Abstracts(ASFA) 1: Biological Sciences & Living Resources) to determine thenumber of papers published on these taxa. This search string wasprimarily composed of a list of all valid chondrichthyan genera,except for a few generic names that have multiple meanings(Chimaera, Torpedo, Electrolux, Figaro, Iago, Gollum) and thus wouldhave generated extraneous results. For these genera, we includedeach species name in quotes (e.g. “Chimaera monstrosa”) in theBoolean search string (Appendix A.1). Doing so ensured that onlythose references with the exact phrase (Genus WITH species) wouldbe included in the query.

Similarly, we used a complex Boolean search string (Appendix A.2)to query the same databases and determine the number of paperspublished on deep-water chondrichthyans. For those genera com-posed entirely of deep-water taxa (Table 1), the genus name was usedto include all species within. For all others, the species name wasincluded in quotes as before.

Results of the queries above were used to plot the number ofpublications by decade related to any chondrichthyan speciesversus those related to deep-water taxa. These data were plottedraw to illustrate the recent exponential increase in papers devotedto chondrichthyan research, as well as log-transformed to illus-trate the relative contribution of those papers devoted to deep-water chondrichthyans over time.

Appendix A.1: Boolean search string for all chondrichthyan taxa

Harriotta or Callorhinchus or Neoharriotta or Rhinochimaera or“Chimaera argiloba” or “Chimaera bahamaensis” or “Chimaeracubana” or “Chimaera fulva” or “Chimaera jordani” or “Chimaeralignaria” or “Chimaera macrospina” or “Chimaera monstrosa” or“Chimaera notafricana” or “Chimaera obscura” or “Chimaeraopalescens” or “Chimaera owstoni” or “Chimaera panthera” or“Chimaera phantasma” or Hydrolagus or Chlamydoselachus orHeptranchias or Hexanchus or Notorynchus or Echinorhinus orCirrhigaleus or Squalus or Centrophorus or Deania or Aculeola orCentroscyllium or Etmopterus or Miroscyllium or Trigonognathus

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or Centroscymnus or Centroselachus or Proscymnodon or Scym-nodalatias or Scymnodon or Somniosus or Zameus or Oxynotus orDalatias or Euprotomicroides or Euprotomicrus or Heteroscym-noides or Isistius or Mollisquama or Squaliolus or Squatina orPliotrema or Pristiophorus or Anoxypristis or Pristis or Rhina orRhynchobatus or Aptychotrema or Glaucostegus or Rhinobatos orTrygonorrhina or Zapteryx or Platyrhina or Platyrhinoidis orZanobatus or Benthobatis or Diplobatis or Discopyge or Narcineor Crassinarke or “Electrolux addisoni” or Heteronarce or Narke orTemera or Typhlonarke or Tetronarce or Hypnos or “Torpedoadenensis” or “Torpedo alexandrinsis” or “Torpedo andersoni” or“Torpedo bauchotae” or “Torpedo californica” or “Torpedo fair-childi” or “Torpedo fuscomaculata” or “Torpedo mackayana” or“Torpedo macneilli” or “Torpedo marmorata” or “Torpedo micro-discus” or “Torpedo nobiliana” or “Torpedo panthera” or “Torpedoperuana” or “Torpedo puelcha” or “Torpedo semipelagica” or“Torpedo sinuspersici” or “Torpedo suessii” or “Torpedo torpedo”or “Torpedo tremens” or “Torpedo zugmayeri” or Arhynchobatis orAtlantoraja or Bathyraja or Brochiraja or Irolita or Insentiraja orNotoraja or Pavoraja or Psammobatis or Pseudoraja or Rhinoraja orSympterygia or Amblyraja or Beringraja or Breviraja or Dactyloba-tus or Dipturus or Fenestraja or Gurgesiella or Hongeo or Leucorajaor Malacoraja or Neoraja or Okamejei or Raja or Rajella or Riorajaor Rostroraja or Spiniraja or Zearaja or Anacanthobatis or Crurirajaor Indobatis or Sinobatis or Plesiobatis or Trygonoptera or Urolo-phus or Urobatis or Urotrygon or Hexatrygon or Paratrygon orPlesiotrygon or Potamotrygon or Heliotrygon or Himantura orNeotrygon or Dasyatis or Pastinachus or Pteroplatytrygon orTaeniura or Taeniurops or Urogymnus or Aetoplatea or Gymnuraor Aetobatus or Aetomylaeus or Myliobatis or Pteromylaeus orRhinoptera or Manta or Mobula or Heterodontus or Cirrhoscylliumor Parascyllium or Brachaelurus or Heteroscyllium or Eucrossorhi-nus or Orectolobus or Sutorectus or Chiloscyllium or Hemiscylliumor Ginglymostoma or Nebrius or Pseudoginglymostoma or Stegos-toma or Rhincodon or Carcharias or Odontaspis or Pseudocarchar-ias or Mitsukurina or Megachasma or Alopias or Cetorhinus orCarcharodon or Isurus or Lamna or Apristurus or Asymbolus orAtelomycterus or Aulohalaelurus or Bythaelurus or Cephaloscyl-lium or Cephalurus or “Figaro boardmani” or “Figaro striatus” orGaleus or Halaelurus or Haploblepharus or Holohalaelurus orParmaturus or Pentanchus or Poroderma or Schroederichthys orScyliorhinus or Ctenacis or Eridacnis or Proscyllium or “Gollumattenuatus” or “Gollum suluensis” or Planonasus or Pseudotriakisor Leptocharias or Furgaleus or Galeorhinus or Gogolia or Hemi-triakis or Hemipristis or Hypogaleus or “Iago garricki” or “Iagoomanensis” or Mustelus or Scylliogaleus or Triakis or Chaenoga-leus or Hemigaleus or Paragaleus or Carcharhinus or Galeocerdo orGlyphis or Isogomphodon or Lamiopsis or Loxodon or Nasolamiaor Negaprion or Prionace or Rhizoprionodon or Scoliodon orTriaenodon or Eusphyra or Sphyrna

Note: Some generic names (Chimaera, Torpedo, Electrolux, Fig-aro, Iago, Gollum) returned an excessive number of unrelatedsearch results. Therefore, we included full Latin names of eachspecies within those genera in the search string above.

Appendix A.2: Boolean search string for deep-water chondrichthyantaxa

Harriotta or Neoharriotta or Rhinochimaera or “Chimaeraargiloba” or “Chimaera bahamaensis” or “Chimaera cubana” or“Chimaera fulva” or “Chimaera jordani” or “Chimaera lignaria” or“Chimaera macrospina” or “Chimaera monstrosa” or “Chimaeranotafricana” or “Chimaera obscura” or “Chimaera opalescens” or“Chimaera owstoni” or “Chimaera panthera” or “Chimaera phan-tasma” or Hydrolagus or Chlamydoselachus or Heptranchias orHexanchus or Echinorhinus or Cirrhigaleus or “Squalus albifrons”

or “Squalus altipinnis” or “Squalus blainville” or “Squalus brevir-ostris” or “Squalus bucephalus” or “Squalus chloroculus” or “Squa-lus crassispinus” or “Squalus cubensis” or “Squalus edmundsi” or“Squalus grahami” or “Squalus griffini” or “Squalus hemipinnis” or“Squalus japonicus” or “Squalus lalannei” or “Squalus megalops” or“Squalus melanurus” or “Squalus mitsukurii” or “Squalus montal-bani” or “Squalus nasutus” or “Squalus notocaudatus” or “Squalusrancureli” or “Squalus raoulensis” or Centrophorus or Deania orAculeola or Centroscyllium or Etmopterus or Miroscyllium orTrigonognathus or Centroscymnus or Centroselachus or Proscym-nodon or Scymnodalatias or Scymnodon or Somniosus or Zameusor Oxynotus or Dalatias or Euprotomicroides or Euprotomicrus orHeteroscymnoides or Isistius or Mollisquama or Squaliolus or“Squatina aculeata” or “Squatina africana” or “Squatina albipunc-tata” or “Squatina argentina” or “Squatina caillieti” or “Squatinaformosa” or “Squatina pseudocellata” or “Squatina tergocellata” orPliotrema or “Pristiophorus delicatus” or “Pristiophorus lanae” or“Pristiophorus nancyae” or “Pristiophorus schroederi” or “Rhino-batos variegatus” or Benthobatis or “Narcine lasti” or “Narcinenelsoni” or “Narcine tasmaniensis” or “Heteronarce garmani” or“Heteronarce mollis” or “Heteronarce prabhui” or Typhlonarke or“Torpedo fairchildi” or “Torpedo macneilli” or “Torpedo microdis-cus” or “Torpedo nobiliana” or “Torpedo puelcha” or Arhynchoba-tis or Bathyraja or Brochiraja or Insentiraja or Notoraja or Pavorajaor “Psammobatis rudis” or “Psammobatis scobina” or Pseudorajaor Rhinoraja or Amblyraja or Breviraja or Dactylobatus or “Dip-turus acrobellus” or “Dipturus amphispinus” or “Dipturus apricus”or “Dipturus batis” or “Dipturus bullisi” or “Dipturus campbelli” or“Dipturus canutus” or “Dipturus cerva” or “Dipturus crosnieri” or“Dipturus diehli” or “Dipturus doutrei” or “Dipturus endeavouri”or “Dipturus garricki” or “Dipturus gigasa” or “Dipturus grahami”or “Dipturus gudgeri” or “Dipturus healdi” or “Dipturus innomi-natus” or “Dipturus johannisdavesi” or “Dipturus laevis” or “Dip-turus lanceorostratus” or “Dipturus leptocaudus” or “Raja lintea”or “Dipturus macrocauda” or “Dipturus melanospilus” or “Dipturusmennii” or “Dipturus nidarosiensis” or “Dipturus oculus” or“Dipturus olseni” or “Dipturus oregoni” or “Dipturus oxyrhynchus”or “Dipturus polyommata” or “Dipturus pullopunctata” or “Dip-turus queenslandicus” or “Dipturus springeri” or “Dipturus ste-norhynchus” or “Dipturus teevani” or “Dipturus tengu” or“Dipturus trachydermus” or “Dipturus wengi” or Fenestraja orGurgesiella or “Leucoraja caribbaea” or “Leucoraja circularis” or“Leucoraja compagnoi” or “Leucoraja fullonica” or “Leucorajagarmani” or “Leucoraja lentiginosa” or “Leucoraja leucosticte” or“Leucoraja melitensis” or “Leucoraja naevus” or “Leucoraja pristis-pina” or “Leucoraja wallacei” or “Leucoraja yucatanensis” orMalacoraja or Neoraja or “Okamejei arafurensis” or “Okamejeiheemstrai” or “Okamejei leptoura” or “Okamejei philipi” or “Rajaafricana” or “Raja bahamensis” or “Raja inornata” or “Raja mon-tagui” or “Raja polystigma” or “Raja rhina” or “Raja straeleni” orRajella or Rostroraja or “Zearaja chilensis” or “Zearaja nasutus” orAnacanthobatis or Cruriraja or Indobatis or Sinobatis or Plesiobatisor “Urolophus deforgesi” or “Urolophus expansus” or “Urolophuskaianus” or “Urolophus mitosis” or “Urolophus neocaledoniensis”or “Urolophus papilio” or “Urolophus piperatus” or Hexatrygon or“Dasyatis brevicaudata” or “Dasyatis multispinosa” or “Myliobatishamlyni” or “Cirrhoscyllium japonicum” or “Parascyllium sparsi-maculatum” or Odontaspis or Mitsukurina or Pseudocarcharias or“Alopias superciliosus” or Apristurus or “Asymbolus galacticus” or“Asymbolus pallidus” or “Asymbolus rubiginosus” or Bythaelurusor “Cephaloscyllium albipinnum” or “Cephaloscyllium cooki” or“Cephaloscyllium fasciatum” or “Cephaloscyllium formosanum” or“Cephaloscyllium hiscosellum” or “Cephaloscyllium isabellum” or“Cephaloscyllium signourum” or “Cephaloscyllium silasi” or“Cephaloscyllium speccum” or “Cephaloscyllium stevensi” or“Cephaloscyllium sufflans” or “Cephaloscyllium variegatum” or

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“Cephaloscyllium zebrum” or Cephalurus or “Figaro boardmani” or“Figaro striatus” or “Galeus antillensis” or “Galeus arae” or “Galeusatlanticus” or “Galeus cadenati” or “Galeus eastmani” or “Galeusgracilis” or “Galeus longirostris” or “Galeus melastomus” or“Galeus mincaronei” or “Galeus marinus” or “Galeus nipponensis”or “Galeus piperatus” or “Galeus polli” or “Galeus priapus” or“Galeus schultzi” or “Galeus springeri” or Holohalaelurus orParmaturus or Pentanchus or “Schroederichthys maculatus” or“Schroederichthys saurisqualus” or “Schroederichthys tenuis” or“Scyliorhinus boa” or “Scyliorhinus capensis” or “Scyliorhinuscervigoni” or “Scyliorhinus comoroensis” or “Scyliorhinus haeck-elii” or “Scyliorhinus hesperius” or “Scyliorhinus meadi” or “Scy-liorhinus retifer” or “Scyliorhinus tokubee” or “Scyliorhinus torrei”or Eridacnis or “Gollum attenuatus” or “Gollum suluensis” orPlanonasus or Pseudotriakis or “Hemitriakis abdita” or “Iagogarricki” or “Iago omanensis” or “Mustelus canis insularis” or“Mustelus mangalorensis” or “Mustelus stevensi” or “Musteluswalkeri” or “Carcharhinus altimus” or “Carcharhinus signatus”

Appendix B. Methods used to determine depths and compilethe list of extant chondrichthyan taxa (Table 1):

Table 1 was based on an annotated list of deep-water chon-drichthyans compiled by Kyne and Simpfendorfer (2010), butincluded new species described since that list was compiled(2009–2014). Reported depth ranges were used to determinewhether species was considered “deep-water” (as defined by theIUCN Shark Specialist Group), primarily based on compiled,species-specific data from the bibliographic database Shark-References.com (www.shark-references.com; Pollerspöck, 2014).In cases where no depth data were reported by Pollerspöck(2014), other resources were consulted, generally in decreasingpreference of consultation: IUCN Red List of Threatened Speciesassessments (www.iucnredlist.org), FishBase (www.fishbase.org)(Froese and Pauly, 2014), field guides (Compagno et al., 2005; Lastand Stevens, 2009; Castro, 2011), primary literature. For a fewspecies, no depth range was stated in any of these sources,therefore those species were assigned to the majority of the genusas either “deep-water” or not. Taxonomic validity of each specieswas verified primarily using Eschmeyer's Catalog of Fishes (www.calacademy.org/scientists/projects/catalog-of-fishes; Eschmeyerand Fong, 2014) and for select taxa, the Chondrichthyan Tree ofLife (sharksrays.org). Systematic placement of genera mostlyfollowed the Chondrichthyan Tree of Life.

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C.F. Cotton n

Department of Natural Sciences, Savannah State University, 3219College St., Box 20600, Savannah, GA 31404, USA

E-mail address: ccotton@fsu.edu

R.D. GrubbsFlorida State University Coastal & Marine Laboratory, Florida State

University, 3618 Coastal Highway 98, St. Teresa, FL 32358, USA

Available online 9 March 2015

n Corresponding author at: Florida State University Coastal & Marine Laboratory,3618 Coastal Highway 98, St. Teresa, FL 32358, USA. Tel.: þ1 850 697 4092;fax: þ1 850 697 3822.

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