Deep-water Shark Research Articles

Eocene squalomorph sharks (Chondrichthyes, Elasmobranchii) from Antarctica

Rare remains of predominantly deep-water sharks of the families Hexanchidae, Squalidae, Dalatiidae, Centrophoridae, and Squatinidae are described from the Eocene La Meseta Formation, Seymour Island, Antarctic Peninsula, which has yielded the most abundant chondrichthyan assemblage from the Southern Hemisphere to date. Previously described representatives of Hexanchus sp., Squalus weltoni, Squalus woodburnei, Centrophorus sp., and Squatina sp. are confirmed and dental variations are documented. Although the teeth of Squatina sp. differ from other Palaeogene squatinid species, we refrain from introducing a new species. A new dalatiid taxon, Eodalatias austrinalis gen. et sp. nov. is described. This new material not only increases the diversity of Eocene Antarctic elasmobranchs but also allows assuming that favourable deep-water habitats were available in the Eocene Antarctic Ocean off Antarctica in the Eocene. The occurrences of deep-water inhabitants in shallow, near-coastal waters of the Antarctic Peninsula agrees well with extant distribution patterns.

Population genetics of the deep-sea bluntnose sixgill shark, Hexanchus griseus, revealing spatial genetic heterogeneity

Hexanchus griseus is a globally distributed deep-water shark species. It inhabits tropical and temperate waters throughout the world, including the Mediterranean Sea where it is by-caught by small-scale fisheries in the region. In this study, we analysed the genetic variation of H. griseus specimens collected from different areas within and outside the Mediterranean region, to assess its genetic connectivity. The mitochondrial DNA (mtDNA) sequence analysed in this study ranged from cytochrome b to 16S rRNA genes including the control region, the 12S rRNA gene and the interspersed tRNA genes in the region, covering a total of 3731 to 3914 nucleotides. Results have shown that this species exhibits geographically distinct maternal lineages, indicating population structure along geographical ranges. These findings reveal population subdivisions not only between the Pacific Ocean and the Atlantic Ocean, but also within the oceans and on a smaller scale within the Mediterranean Sea. This highlights the need to consider each population subdivision separately when designing management plans for the conservation of this species.

Polar compounds preclude mathematical lipid correction of carbon stable isotopes in deep-water sharks

Lipids affect stable isotope values generated for marine fishes, however these effects remain poorly described for many extant shark taxa, especially deep-sea species. Here, we report the effects of lipid extraction (LE) on δ13C, δ15N, and C:N values of seven deep-sea sharks, generate novel mathematical normalizations for δ13C based on the relationship between bulk and lipid extracted values (δ13CBulk and δ13CLE) and examine whether common normalized correction models provide a robust method for addressing lipid-biasing effects in two species, the Cuban dogfish (Squalus cubensis; n=20), and Greenland shark (Somniosus microcephalus; n=24). LE generally resulted in enrichment of 13C and 15N, but produced variable effects on C:N across all species. Novel mathematical normalizations for δ13C were derived from the pooled shark community, and a single species-specific correction was generated for the Cuban dogfish, but could not be determined for the Greenland shark. Four common lipid correction models used for teleosts, failed to accurately predict δ13C values statistically similar to δ13CLE, in both Cuban dogfish and Greenland sharks, likely due to the confounding effects of lipids and urea on C:N. These observations suggest that chemical lipid extraction should be a mandatory procedure prior to interpreting stable isotope data for deep-sea sharks, at least for those species where lipid effects are large.

First southeastern Atlantic record of the false catshark, Pseudotriakis microdon (Carcharhiniformes: Pseudotriakidae)

The false catshark, Pseudotriakis microdon, is a large-bodied, poorly known deepwater shark, with a global distribution, except for the eastern Pacific and South Atlantic oceans. Here we report the first record of the false catshark from the southeastern Atlantic. The specimen, estimated to be approximately 290 cm in total length, was observed via an unmanned submersible 700 m depth off the western slope of Valdivia Seamount (26.2° S, 6.3° E).

Isopods present on deep-water sharks Squalus cubensis and Heptranchias perlo from The Bahamas

Isopods are micropredators of deep-water sharks; however, their associations are poorly described in the scientific literature. We present the association of three isopod genera Aega sp., Aegaphales sp., and Cirolana sp. with two species of deep-sea shark, the Cuban dogfish (Squalus cubensis) and the sharpnose sevengill (Heptranchias perlo). Although limited conclusions can be drawn from this observation, it provides a novel association of micropredatory isopods with two poorly studied species of deep-water shark.

Trophic ecology of small deepwater lanternsharks (Etmopterus spinax and Etmopterus pusillus) from the south Portuguese coast

Event Abstract Back to Event Trophic ecology of small deepwater lanternsharks (Etmopterus spinax and Etmopterus pusillus) from the south Portuguese coast Laura Nuño-Muñoz1*, Rui P. Vieira1, 2*, Maria E. Costa1* and Jorge M. Gonçalves1* 1 PhD Student, CCMAR—Centre of Marine Sciences, Universidade do Algarve, Faro, Portugal, Portugal 2 University of Southampton, Ocean and Earth Science, United Kingdom In order to understand dynamics of marine food webs it is important to test relevant hypotheses on predator–prey interactions by studying basic biological data. The knowledge on functional ecology of top predators is crucial to perceive their ecological role, particularly in the context of changes in communities under human-induced pressures. Lanternsharks are commonly caught as bycatch from crustacean bottom trawl fishing in the southern Portuguese coast; studying feeding habits of these species is essential to reach a better knowledge on their behaviour and trophic ecology. Feeding habits of two small deepwater lanternsharks, Etmopterus spinax (Linnaeus, 1758) and Etmopterus pusillus (Lowe, 1839), was investigated. The stomach contents of 173 E. spinax and 58 E. pusillus individuals were analysed. Results indicated some degree of trophic overlap in the diet of these two deepwater sharks, both showing low diversity, richness and evenness of prey species in their stomach contents. Etmopterus spinax has a preference for crustaceans (mainly decapods), followed by teleost fishes and cephalopods as accessory prey, while fish, crustaceans and cephalopods constituted the main food items of E. pusillus. No significant differences were found between sexes for both species, but our results suggest ontogenetic and seasonal changes in E. pusillus diet; both species shared the same trophic level (TL = 3.8 for E. spinax and TL = 4.1 for E. pusillus). Our work is a valid contribution for the evaluation of the trophic relationships of two deepwater shark species from the Portuguese south coast and a common component of the crustacean trawl fishery in the region. Studying their biology and gathering information about their suitable habitats may be an important step towards the conservation of highly vulnerable species. Acknowledgements We would like to thank to Isidoro Costa, Pedro Monteiro, Carlos Afonso, Luís Bentes and Frederico Oliveira for helping during lab work. R. P. Vieira is supported by the doctoral grant from the Portuguese Science Foundation (SFRH/BD/84030/2012). Keywords: Lanternshark, trophic ecology, Crustacean fisheries, South Portugal, deep sea Conference: IMMR | International Meeting on Marine Research 2016, Peniche, Portugal, 14 Jul - 15 Jul, 2016. Presentation Type: Poster presentation Topic: Fisheries and Management Citation: Nuño-Muñoz L, Vieira RP, Costa ME and Gonçalves JM (2016). Trophic ecology of small deepwater lanternsharks (Etmopterus spinax and Etmopterus pusillus) from the south Portuguese coast. Front. Mar. Sci. Conference Abstract: IMMR | International Meeting on Marine Research 2016. doi: 10.3389/conf.FMARS.2016.04.00023 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 04 Jun 2016; Published Online: 13 Jul 2016. * Correspondence: Miss. Laura Nuño-Muñoz, PhD Student, CCMAR—Centre of Marine Sciences, Universidade do Algarve, Faro, Portugal, Faro, Portugal, arualnm7@gmail.com Mr. Rui P Vieira, PhD Student, CCMAR—Centre of Marine Sciences, Universidade do Algarve, Faro, Portugal, Faro, Portugal, rui.vieira@cefas.co.uk PhD. Maria E Costa, PhD Student, CCMAR—Centre of Marine Sciences, Universidade do Algarve, Faro, Portugal, Faro, Portugal, esmeraldacosta@sapo.pt Dr. Jorge M Gonçalves, PhD Student, CCMAR—Centre of Marine Sciences, Universidade do Algarve, Faro, Portugal, Faro, Portugal, jgoncal@ualg.pt Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Laura Nuño-Muñoz Rui P Vieira Maria E Costa Jorge M Gonçalves Google Laura Nuño-Muñoz Rui P Vieira Maria E Costa Jorge M Gonçalves Google Scholar Laura Nuño-Muñoz Rui P Vieira Maria E Costa Jorge M Gonçalves PubMed Laura Nuño-Muñoz Rui P Vieira Maria E Costa Jorge M Gonçalves Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.

The diversity, distribution and status of deep-water elasmobranchs in the Rockall Trough, north-east Atlantic Ocean.

Data from a scientific deep-water trawl fisheries survey in the north-east Atlantic were analysed to determine the spatial and bathymetric distribution of elasmobranch species and assess the change in relative abundance over the period 1998-2013. During this period, commercial fisheries for deep-water sharks went from being entirely unregulated, to being briefly managed, to being completely prohibited. A total of 22 species of shark and 10 species of skate were recorded between depths of 300 and 2030 m. All showed strong species-specific depth-related trends in abundance. Out of the 11 more common species, five showed no change in relative abundance over time, two (Centrophorus squamosus and Centroselachus crepidater) declined significantly and four increased in relative abundance (Apristurus aphyodes, Apristurus microps, Galeus melastomus and Deania calcea). Assuming these populations were depleted by fisheries in the past, the current data do not suggest there has been an overall recovery. Positive signs for some species in the most recent years suggest movement or recruitment back into the area; however, it is of concern that two species continued to decline. There is a continued need to have precautionary management of these elasmobranch species, and the current ban on landing these species in European waters remains appropriate.

Distribution and comments on the morphology of Centroscymnus owstonii Garman, 1906 (Squaliformes: Somniosidae), with focus on its occurrence in the Indian Ocean

The Roughskin Dogfish Centroscymnus owstonii is one of the most widespread deepwater shark species, but its global distribution is mostly based on patchy records. In this study, C. owstonii was reinvestigated with focus on its poorly known distribution in the western and eastern Indian Ocean. Previous records of the species from the Seychelles, which, for decades, were considered to be of a different species, were verified in this study. Furthermore, the first records from off Reunion Island, Madagascar, and Indonesia are provided, including the smallest free-swimming specimen of the species described in detail to date. Based on these specimens, a description of C. owstonii is given with updated and extended morphometric data, photographic documentation and scanning electron microscopy (SEM) images of dermal denticles. Additionally, specimens from the Indian Ocean are compared with specimens from the Pacific and Atlantic Oceans. For the Pacific Ocean, the first record from the central western North Pacific is provided from the Hawaiian-Emperor seamount chain. This record also represents the most open ocean known occurrence of C. owstonii.

Comparison of life histories of two deep-water sharks from eastern Australia: the piked spurdog and the Philippine spurdog

Deep-water sharks have low biological productivity and are vulnerable to exploitation with species-specific regional life history required to enable effective management. The present study describes the life history of two squalids collected from Australia: (1) the piked spurdog (Squalus megalops) from the tropical Great Barrier Reef; and (2) the Philippine spurdog (S. montalbani) from New South Wales. Maximum observed ages for males and females were 18 and 25 years for S. megalops and 28 and 27 years for S. montalbani. Multiple growth models were all well supported and indicated very slow growth rates for both species. The tropical S. megalops population was smaller and older at maturity than previously reported temperate populations. Males were mature at 352-mm stretched total length (LST) and 12.6 years, whereas females were mature at 422mm LST and 19.1 years. Squalus montalbani males were mature at 700mm LST and 21.8 years, whereas females were mature at 800mm LST and 26 years. Fecundity was lower for S. megalops than S. montalbani with two to three compared with nine to 16 embryos. Both species have a conservative life history, although in the event of overfishing the longer-lived, later-maturing and deeper-dwelling S. montalbani is likely to take longer to recover than S. megalops.

A Novel Use of near Infrared Spectroscopy: Ageing Deepwater Sharks

To age sharks, the growth bands in the shark vertebrae (like the rings in a tree) or on the spines in front of each dorsal fin (which only some sharks have) are manually counted using a microscope. This is time-consuming and is only possible on dead animals. NIR spectroscopy is shown to be able to detect age in dorsal fin spines of sharks and hand-held NIR spectroscopy units could potentially be used for ageing of sharks in the field, at sea, using a hand-held unit to scan the fin spine on a live animal.

Trophic interactions of common elasmobranchs in deep-sea communities of the Gulf of Mexico revealed through stable isotope and stomach content analysis

Deep-water sharks are abundant and widely distributed in the northern and eastern Gulf of Mexico. As mid- and upper-level consumers that can range widely, sharks likely are important components of deep-sea communities and their trophic interactions may serve as system-wide baselines that could be used to monitor the overall health of these communities. We investigated the trophic interactions of deep-sea sharks using a combination of stable isotope (δ13C and δ15N) and stomach content analyses. Two hundred thirty-two muscle samples were collected from elasmobranchs captured off the bottom at depths between 200 and 1100m along the northern slope (NGS) and the west Florida slope (WFS) of the Gulf of Mexico during 2011 and 2012. Although we detected some spatial, temporal, and interspecific variation in apparent trophic positions based on stable isotopes, there was considerable isotopic overlap among species, between locations, and through time. Overall δ15N values in the NGS region were higher than in the WFS. The δ15N values also increased between April 2011 and 2012 in the NGS, but not the WFS, within Squalus cf. mitsukurii. We found that stable isotope values of S. cf. mitsukurii, the most commonly captured elasmobranch, varied between sample regions, through time, and also with sex and size. Stomach content analysis (n=105) suggested relatively similar diets at the level of broad taxonomic categories of prey among the taxa with sufficient sample sizes. We did not detect a relationship between body size and relative trophic levels inferred from δ15N, but patterns within several species suggest increasing trophic levels with increasing size. Both δ13C and δ15N values suggest a substantial degree of overlap among most deep-water shark species. This study provides the first characterization of the trophic interactions of deep-sea sharks in the Gulf of Mexico and establishes system baselines for future investigations.

The utility of near infrared spectroscopy for age estimation of deepwater sharks

Reliable age information is vital for effective fisheries management, yet age determinations are absent for many deepwater sharks as they cannot be aged using traditional methods of growth bands counts. An alternative approach to ageing using near infrared spectroscopy (NIRS) was investigated using dorsal fin spines, vertebrae and fin clips of three species of deepwater sharks. Ages were successfully estimated for the two dogfish, Squalus megalops and Squalus montalbani, and NIRS spectra were correlated with body size in the catshark, Asymbolus pallidus. Correlations between estimated-ages of the dogfish dorsal fin spines and their NIRS spectra were good, with S. megalops R2=0.82 and S. montalbani R2=0.73. NIRS spectra from S. megalops vertebrae and fin clips that have no visible growth bands were correlated with estimated-ages, with R2=0.89 and 0.76, respectively. NIRS has the capacity to non-lethally estimate ages from fin spines and fin clips, and thus could significantly reduce the numbers of sharks that need to be lethally sampled for ageing studies. The detection of ageing materials by NIRS in poorly calcified deepwater shark vertebrae could potentially enable ageing of this group of sharks that are vulnerable to exploitation.

Is Centrophorus squamosus a highly migratory deep-water shark?

Deep-water sharks are considered highly vulnerable species due to their life characteristics and very low recovery capacity against overfishing. However, there is still limited information on the ecology or population connectivity of these species. The aim of this study was to investigate if the species Centrophorus squamosus could make long displacements and thus confirm the existence of connectivity between different deep-water areas. In addition, the study was the first attempt to use tagging techniques on deep-water sharks, since it has never been undertaken before. Five C. squamosus were tagged with satellite tags (PAT) in the El Cachucho Marine Protected Area (Le Danois Bank) located in waters of the North of Spain, Cantabrian Sea (NE Atlantic). Data from four of these tags were recovered. One of the sharks travelled approximately 287nm toward the north east (French continental shelf) hypothetically following the continental slope at a mean depth of 901±109m for 45 days. Two other sharks spent almost 4 months traveling, in which time they moved 143 and 168nm, respectively, to the west (Galician coast). Finally, another leafscale gulper shark travelled to the NW (Porcupine Bank) during a period of 3 months at a mean depth of 940±132m. Depth and temperature preferences for all the sharks are discussed. Minimum and maximum depths recorded were 496 and 1848m, respectively. The temperature range was between 6.2 and 11.4°C, but the mean temperature was approximately 9.9±0.7°C. The sharks made large vertical displacements throughout the water column with a mean daily depth range of 345±27m. These preliminary results support the suggestion of a whole population in the NE Atlantic and confirm the capacity of this species to travel long distances.

On the Origin of a Novel Parasitic-Feeding Mode within Suspension-Feeding Barnacles

In his monograph on Cirripedia from 1851, Darwin pointed to a highly unusual, plateless, and most likely parasitic barnacle of uncertain phylogenetic affinity. Darwin's barnacle was Anelasma squalicola, found on deep-water sharks of the family Etmopteridae, or lantern sharks. The barnacle is uncommon and is therefore rarely studied. Recent observations by us have shown that they occur at an unusually high prevalence on the velvet belly lantern shark, Etmopterus spinax, in restricted fjord areas of western Norway. A phylogenetic analysis based on ribosomal DNA data (16S, 18S, and 28S) from 99 selected barnacle species, including all available pedunculate barnacle sequences from GenBank, shows that A. squalicola is most closely related (sister taxon) to the pedunculate barnacle Capitulum mitella. Both C. mitella and species of Pollicipes, situated one node higher in the tree, are conventional suspension feeders from the rocky intertidal. Our phylogenetic analysis now makes it possible to establish morphological homologies between A. squalicola and its sister taxon and provides the evolutionary framework to explain the unprecedented transition from a filter-feeding barnacle to a parasitic mode of life.

Large-scale distribution of three deep-water squaloid sharks: Integrating data on sex, maturity and environment

Deep-water sharks exhibit species-specific reproductive strategies, which include segregation by sex, size and reproductive stage. However, due to the wide spatial distribution of most species, available information, usually collected at a regional scale, is usually not adequate to infer species reproductive spatial dynamics. This study draws together information on the distribution of reproductive stages of three species of squaliform sharks: Portuguese dogfish Centroscymnus coelolepis (Somniosidae), leafscale gulper shark Centrophorus squamosus (Centrophoridae) and birdbeak dogfish Deania calcea (Centrophoridae), gathering data from several geographical areas from the Atlantic, Indian and Pacific Oceans. For each species we analysed the sex ratio and the spatial patterns of reproductive stages within regions, considering the influence of geographical area, depth, season, temperature and salinity. The combination of statistical methods used in this study successfully identified a number of life history patterns which reflect different use of habitats by sex and life cycle stage. Pregnant females of the three species are spatially segregated, inhabiting shallower and/or warmer waters. In the case of the leafscale gulper shark this segregation might be associated with large scale migrations. In contrast, in Portuguese dogfish all adult maturity stages occur in the same geographical area. Pregnant female birdbeak dogfish were rare in all samples. Larger immature specimens of all the three species distribute deeper than the remaining maturity stages in most of the regions analysed. Mature males of leafscale gulper shark and birdbeak dogfish were more broadly distributed than mature females, supporting the possibility of sex-biased dispersal. Neonates and small sized specimens were scarce in the Northeast Atlantic potentially explained by their concentration in nurseries, and/or by gear selectivity. Management measures will benefit from considering the geographic scale of demographic variation between species. However, standardized collaborative approaches will be needed for comprehensive assessment.

Fossil Chondrichthyes from the central eastern Pacific Ocean and their paleoceanographic significance

The study of the chondrichthyan fauna from the Angostura, Onzole, Canoa and Jama formations, in the Neogene of Bordón and Manabí basins, Ecuador, reveals the presence of 30 taxa, including the deep water shark †Chlamydoselachus landinii sp. nov. The assemblages are dominated by tropical shallow and deep water chondrichthyans, suggesting paleoenvironments associated with a short platform shelf bordering a deep margin. These assemblages are the most diverse shark and ray association known from the Tropical Central Eastern Pacific Ocean in the South American coastal basin, and provide new information on the paleoecology and paleodiversity of Neogene chondrichthyans.

Endohelminth parasites of the leafscale gulper shark, Centrophorus squamosus (Bonnaterre, 1788) (Squaliformes:Centrophoridae) off Madeira Archipelago

The endohelminth parasite fauna of a deep water shark, the leafscale gulper shark, Centrophorus squamosus, examined from Madeiran waters, from September 2009 to January 2010, consisted of larval and juvenile cestodes of two orders, namely Trypanorhyncha and Tetraphyllidea, and L3 stages of Anisakis spp. Infection with Anisakis spp. could be due to the shark's opportunistic feeding on squids and black-scabbard fish, Aphanopus carbo, which is heavily parasitized by Anisakis spp. in Madeira waters. The occurrence of larval and juvenile cestodes only, in this shark, suggests that the leafscale gulper shark features as a paratenic or a dead-end host for the parasites.

Assessment of radiometric dating for age validation of deep-water dogfish (Order: Squaliformes) finspines

Vertebrae of most deep-water sharks are too poorly calcified to record visible growth bands and therefore are not useful for age determination. Most dogfish species (Order: Squaliformes) possess dorsal finspines and several recent studies have shown that these structures offer potential for age determination. Age validation should be central to any age determination study, yet to date no age and growth study of deep-water sharks has included a complete validation of age estimates. In this study we sought to age two deep-water dogfish species by analyzing 210Pb and 226Ra incorporated into the internal dentin of the finspines. These radiometric age estimates were compared with counts of internal growth bands observed in the finspines. A pilot study indicated that dorsal finspines of Centroselachus crepidater are too small and thus offer insufficient mass for the radiometric techniques employed in this study. For ageing larger finspines of Centrophorus squamosus, the lead–radium disequilibria method (ingrowth of 210Pb from 226Ra) was found to be inapplicable due to exogenous uptake of 210Pb in the finspine. Therefore, to approximate age, we measured the decay of 210Pb within the dentin material at the tip of the finspine (formed in utero), relative to the terminal material at the base of the finspine. Results with this method proved to be inconsistent and did not yield reliable age estimates. Hence the use of 210Pb and 226Ra for radiometric age determination and validation using dorsal finspines from these deep-water dogfishes was deemed unsuccessful. This outcome was likely due to violations of the consistent, life-long isotopic uptake assumption as well as the provision that the finspine must function as a closed system for these radioisotopes. Future improvements in analytical precision will allow for smaller samples to be analyzed, potentially yielding a better understanding of the fate of these radioisotopes within finspine dentin throughout the life of the shark.

Editorial: Management and monitoring of deep-sea fisheries and stocks

The management and monitoring of deep-sea fisheries and stocks is challenging due to the diversity of life histories in exploited stocks and sparseness of biological knowledge about certain species. Moreover, these issues are often combined with a relative shortage of suitable data. The FAO defines deep-sea fisheries as those exploiting species that can only sustain low exploitation rates (FAO 2009). In the European Union (EU) deep-sea fisheries are covered by council regulation No. 2347/2002 on “establishing specific access requirements and associated conditions applicable to fishing for deepsea stocks", which lists 24 species, including many deepwater sharks. Other definitions are used in other jurisdictions around the world. The papers presented in this special issue address a number of questions relevant to assess deepwater stocks and moving towards an ecosystem approach to the management of European deepwater fisheries. The underlying research was carried out in the EU-funded Deepfishman project, “Management and Monitoring of Deep-sea Fisheries and Stocks” (Grant agreement No. 227390), which was conducted from 2009 to 2012. These papers complement a number of recently published studies on deepwater stocks and fisheries, many of which were part of the same project. A recent review of deepwater stocks and their management worldwide concluded that, although deepwater fisheries in different regions might exploit the same species, case-specific monitoring and management strategies are often necessary (Large et al. 2013). Furthermore, Edwards et al. (2012) suggested that, although a range of approaches exist for deepwater stock assessment, from very simple to more sophisticated and informative, some methodological developments are still required. A recent example of such a development is the statistical catch-at-age model, which was used to assess the recruitment strength of the beaked redfish, Sebastes mentella in the Barents Sea (Planque et al. 2012). Another statistical catch-atage model was developed to provide estimates of total mortality and abundance of blue ling, Molva dypterygia, to the west of the British Isles (Trenkel et al. 2012). This model makes stock assessments possible using only fishery-dependent data

Spatial overlap between the leafscale gulper shark and the black scabbardfish off Portugal

Information about the spatial distribution of bycatch species and their spatial overlap with the target species is essential for fisheries management. The present study used fishery-dependent data (vessel monitoring systems, logbooks and official daily landings) to study the spatial distribution and overlap between black scabbardfish Aphanopus carbo and leafscale gulper shark Centrophorus squamosus taken by the longline fishery operating off mainland Portugal. The geostatistical method kriging was applied to estimate the distribution of the leafscale gulper shark in relation to black scabbardfish and thus assess the impact of the fishery on the leafscale gulper shark. Results indicate that in fishing grounds where the black scabbardfish is more abundant, the relative occurrence of deepwater sharks is reduced. These findings have implications for alternative management measures to be adopted in this particular fishery, particularly where it concerns the minimization of deepwater shark bycatch.