Deep-water Shark Research Articles

Shedding light on the deep: The case of the velvet belly lanternshark in the North Aegean Sea.

Main biological features were assessed for the first time in the deep-water shark Etmopterus spinax from Hellenic waters by examining 150 individuals caught incidentally in the bottom-trawl commercial fishery off Skyros island. Females outnumbered males and the overall sex ratio was 1.38:1. Females ranged from 122 to 311 mm in total length (LT ) and males from 129 to 270 mm LT , both exhibiting positive allometric growth. Total length-total mass relationships and frequency distributions did not show significant differences between females and males. Sexual dimorphism was not either found by analysing 56 different morphological characteristics. The effect of sex and season was more prominent on the gonadosomatic and hepatosomatic indices compared to the relative condition factor. Most of the individuals were sexually immature, with two specimens classified as mature, one gravid female reaching 311 mm LT with undeveloped gonads and enlarged uteri with embryos, and one male reaching 270 mm LT with enlarged gonads and rigid claspers with hooks. The present study highlights the importance of the sampling location as a breeding and nursery ground for E. spinax in the eastern Mediterranean Sea that should be taken into account for the species' conservation considering its intrinsic characteristics, which make it vulnerable to fishing pressure.

Bioluminescence of the Largest Luminous Vertebrate, the Kitefin Shark, Dalatias licha: First Insights and Comparative Aspects

Bioluminescence has often been seen as a spectacular yet uncommon event at sea but considering the vastness of the deep sea and the occurrence of luminous organisms in this zone, it is now more and more obvious that producing light at depth must play an important role structuring the biggest ecosystem on our planet. Three species of deepwater sharks (Dalatias licha,Etmopterus lucifer, andEtmopterus granulosus) were collected from the Chatham Rise, off New Zealand, and for the first time, we documented their luminescence. Comparison of glowing shark pictures, combined with histological description of light organs and hormonal control analysis, highlight the evolutive conservation of the bioluminescence process within Dalatiidae and Etmopteridae. A special emphasis is placed on the luminescence ofD. licha, the largest known luminous vertebrate. This first experimental study of three luminous shark species from New Zealand provides an insight into the diversity of shark bioluminescence and highlights the need for more research to help understand these unusual deep-sea inhabitants: the glowing sharks.

Dietary fatty acid analyses of the squid Idioteuthis cordiformis: further evidence for predation on deepwater sharks

Idioteuthis cordiformis is the largest deepwater mastigoteuthid squid in the southern Pacific Ocean. Signature fatty acid (FA) and lipid class analysis was carried out on the digestive gland, fins and caecum oil of 18 individuals of I. cordiformis caught in the waters off southern Australia during late 2004. Lipid classes varied between the tissues and oil samples, with sex not being an important factor. The presence of hydrocarbons within the digestive gland and caecum was noteworthy, as high proportions of this lipid class are generally only common in the livers of many deepwater sharks. Monounsaturated FAs dominated the digestive gland and caecum oil, while the fin had high values of both saturated and polyunsaturated FAs. FA profiles of I. cordiformis were compared to profiles of potential prey species (sharks, small and large fish, crustaceans and squid) using Bray-Curtis similarity coefficients. Analysis of the digestive gland and caecum oil FA profiles revealed a close match with the following prey: myctophids (Lampanyctodes australis, Electrona paucirastra, Symbolophorus barnardi), the dragon fish Stomias boa, the smooth oreo Pseudocyttus maculatus and the deepwater sharks Etmopterus baxter, Dalatias licha, Centroselachus crepidater, Centroscymnus coelopsis and Centrophorus zeehaani. The fin FA profile did not match closely to any potential prey and was most similar to other squid mantle tissue. Based on the results of this study, I. cordiformis has a broad diet spectrum of teleost fish and deepwater sharks and occupies a high trophic position.

Preliminary age and growth of the deep-water goblin shark Mitsukurina owstoni (Jordan, 1898)

Owing to poorly mineralising structures, ageing deep-water elasmobranchs requires unconventional techniques. The aim of the present study was to develop an ageing method for the goblin shark Mitsukurina owstoni (Jordan, 1898) using Alcian blue staining of the vertebral column. One vertebral centrum from a male individual measuring 315.2-cm total length (TL) was aged with a minimum age of 27 years. Using a Bayesian von Bertalanffy growth model informed by back-calculated length at age, a literature search of maximum male TL, the TL of the smallest free-swimming individuals and informative priors, we estimated males grow to 374cm TL, mature at 16 years and live up to 60 years. Our results provide useful life history information, with the aim of elucidating the cryptic biology of this deep-water shark.

Squalus shiraii sp. nov. (Squaliformes, Squalidae), a new species of dogfish shark from Japan with regional nominal species revisited

A new species of deep-water dogfish shark, Squalus shiraiisp. nov., is described herein as endemic to the tropical waters off Southern Japan. This species has been largely misidentified with S. mitsukurii. However, morphological, meristic and morphometric evidence support it to be a separate and undescribed species. Squalus shiraiisp. nov. differs from this species by having body brown in colour dorsally, caudal fin with ventral and dorsal tips markedly tapered and broadly white, dermal denticles uniscuspidate and lanceolate and larger number of precaudal (91–94) and total vertebrae (120–123) (vs. body dark grey to black; caudal fin with ventral and dorsal tips rounded and not white in colour; denticles tricuspidate and rhomboid; 86–90 precaudal and 116–117 total vertebrae). Squalus shiraiisp. nov. is also clearly separated from other Japanese congeners which are herein revisited to include six species, based on the examination of over 150 specimens caught from Japanese waters that were available in ichthyological collections: S. mitsukurii, S. japonicus, S. acutirostris, S. brevirostris and S. suckleyi. Squalus mitsukurii, S. japonicus and S. brevirostris are re-described in detail and the neotype of S. japonicus is herein designated. Squalus acutirostris is treated as a valid species with occurrences in Japan, China and Taiwan and, thus, a provisional diagnosis is given, as well as an updated diagnosis of S. suckleyi. A key to Squalus species from the North-western Pacific Ocean is given and main morphological differences between S. shiraiisp. nov. and the closest related species are discussed.

Ecological risks of demersal fishing on deepwater chondrichthyan populations in the Southern Indian and South Pacific Oceans

AbstractRisks to deepwater chondrichthyans (sharks, rays, and chimaeras) from fishing are poorly understood, particularly in areas beyond national jurisdiction. We adapted productivity–susceptibility analysis (PSA) and sustainability assessment for fishing effects (SAFE) to assess the vulnerability of 173 deepwater chondrichthyans to various demersal fishing gears in the Southern Indian and South Pacific Oceans. Several species were categorized as being at high or extreme vulnerability, including some deepwater shark species in the Southern Indian Ocean that are reported to be commercially targeted. There was good concurrence between PSA and SAFE results for species categorized as being at high or extreme vulnerability by the SAFE, but as expected there was an overall greater number assessed to be as higher vulnerability using PSA due to its precautionary nature. Our results indicate probable misclassifications in the PSA relative vulnerability rankings, highlighting the value of applying more quantitative tools, such as SAFE, when adequate data are available. Our findings indicate that better catch, effort, and biological information are needed to inform the assessment and management of deepwater chondrichthyans. If targeted fishing of deepwater shark species continues in the Southern Indian Ocean, improved assessments and estimates of sustainable yields are urgently required to mitigate the risk of overexploitation.

New records and range extension of the Portuguese dogfish Centroscymnus coelolepis in the south-western Atlantic Ocean, with comments on its morphology.

The Portuguese dogfish Centroscymnus coelolepis is a wide-ranging deep-water shark and a common by-catch component of the catches of several mid- to deep-water fisheries. In the present study, two new records from the south-western Atlantic Ocean are reported based on specimens caught by bottom-longline fishing vessels operating in the Argentinean-Uruguayan Common Fishing Zone. Species identification based on morphology and detailed morphometrics, as well as molecular data are presented for one of the specimens. The distribution of the species over the south-western Atlantic is discussed on the basis of the available bibliography and a thorough revision of museum collections. The records presented here expand the species' previously acknowledged distribution southwards, from around 21° S to at least 38° S, suggesting it occurs continuously along the shelf break of eastern South America. However, given the limited access to specimens of deep-water sharks in the region, the abundance and real extent of C. coelolepis distribution in the south-western Atlantic as well as its interaction with deep-water fisheries remain to be fully assessed.

Diel patterns in swimming behavior of a vertically migrating deepwater shark, the bluntnose sixgill (Hexanchus griseus)

Diel vertical migration is a widespread behavioral phenomenon where organisms migrate through the water column and may modify behavior relative to changing environmental conditions based on physiological tolerances. Here, we combined a novel suite of biologging technologies to examine the thermal physiology (intramuscular temperature), fine-scale swimming behavior and activity (overall dynamic body acceleration as a proxy for energy expenditure) of bluntnose sixgill sharks (Hexanchus griseus) in response to environmental changes (depth, water temperature, dissolved oxygen) experienced during diel vertical migrations. In the subtropical waters off Hawai‘i, sixgill sharks undertook pronounced diel vertical migrations and spent considerable amounts of time in cold (5–7°C), low oxygen conditions (10–25% saturation) during their deeper daytime distribution. Further, sixgill sharks spent the majority of their deeper daytime distribution with intramuscular temperatures warmer than ambient water temperatures, thereby providing them with a significant thermal advantage over non-vertically migrating and smaller-sized prey. Sixgill sharks exhibited relatively high rates of activity during both shallow (night) and deep (day) phases and contrary to our predictions, did not reduce activity levels during their deeper daytime distribution while experiencing low temperature and dissolved oxygen levels. This demonstrates an ability to tolerate the low oxygen conditions occurring within the local oxygen minimum zone. The novel combination of biologging technologies used here enabled innovative in situ deep-sea natural experiments and provided significant insight into the behavioral and physiological ecology of an ecologically important deepwater species.

Feeding habits of Bigeye Houndshark, Iago omanensis (Elasmobranchii; Triakidae); a typical deep water shark from the Gulf of Oman

In this study, the feeding habits of Bigeye Houndshark, Iago omanensis , a typical deep water shark, were examined in the Gulf of Oman by analyzing of stomach contents. In addition, the effects of sex and seasons (spring and summer) on its feeding habits were evaluated. Bigeye Houndshark diet consists of mostly teleost fishes, and to a lower extent on crustaneans, molluscs and sea snakes. The great importance of teleost in the diet of Bigeye Houndshark may be due to the fact that teleosts are the dominant in terms of biomass and abundance in the area where Bigeye Houndshark exist, allowing them to exploit food resources available in the environment. No significant differences were found between sexes and seasons. This species occupy high trophic position within the food webs. These results present new data that will allow us to understand the role of Bigeye Houndshark in the deep water of Gulf of Oman to effect of fishing activity on its population dynamics in the future.

Assemblages of deepwater shark species along the north east Atlantic continental slope

Significant variation in deepwater shark assemblages between those found in the 500 m depth band, and those of deeper waters is identified in the analysis of data from the northeast Atlantic continental slope and the northern slope of the Porcupine Bank. Deepwater shark data from four research surveys carried out between 2006 and 2009 yielded twenty-one deepwater shark species from five depth strata across three areas. It is suggested that a new grouping of sharks, “slope”, be considered to reflect those species that are not easily categorised as either Shelf or Deepwater. This may have implications for assessment and management. Depth was identified as having a major influence on the variability of shark catch per unit effort (CPUE), whilst less variability was detected across the area or between years, indicating that depth based management rather than local or regional management measures may be more appropriate.

Ecological features and swimming capabilities of deep-sea sharks from New Zealand

Currently the ecology of deep-water sharks is poorly documented, especially in situ information for these elusive species are lacking. In this study, stereo-Baited Remote Underwater Videos (stereo-BRUVs) were deployed to collect ecological data from New Zealand deep-sea sharks. The results showed differences in abundance between species, with Etmopterus granulosus (Etmopteridae) found in greatest numbers. Moreover, the known depth range increased for Scymnodon macracanthus (Centrophiridae). Deep-sea shark species were generally found to swim at slower cruise speeds (0.36 ± 0.04 m s−1) than their shallow-water counterparts (0.63 ± 0.05 m s−1). However, the swimming speed of deep-sea sharks was clearly not uniform, with some species displaying higher cruise swimming speeds than others. The fastest sharks (Centrophorus harrissoni, Etmopterus granulosus and Etmopterus molleri) had swimming abilities comparable to benthic shallow water sharks (0.48 ± 0.02 m s−1). The higher cruise swimming speed in the family Etmopteridae could be an advantage for these luminous sharks if they follow isolumes to match their ventral light intensity with the down-welling light of their environment. This study revealed that alternative non-destructive methods can be effective for ecological studies of deep-sea marine fauna.

A New Species of Neoalbionella (Copepoda: Siphonostomatoida: Lernaeopodidae) from Skin of the Gulper Shark, Centrophorus Granulosus (Squaliformes: Centrophoridae) in the Northern Gulf of Mexico

Using light and scanning electron microscopy of male and female copepods, we herein describe a new species of Neoalbionella Özdikmen, 2008 (Copepoda: Lernaeopodidae), Neoalbionella benzipirata n. sp., infecting the skin of the gulper shark, Centrophorus granulosus (Bloch and Schneider, 1801), in the northern Gulf of Mexico. Females of the new species were assigned to Neoalbionella by having 3 setae on the maxillule lateral palp (vs. 2 setae in Lernaeopoda Nordmann, 1832) and a single accessory denticle on the maxilliped subchela claw (vs. ≥2 denticles in Lernaeopoda). Females of the new species resemble those of Neoalbionella longicaudata ( Hansen, 1923 ) Özdikmen, 2008 but can be differentiated from them and those of all congeners by having a unique configuration of 16 dorsocephalic sensilla; an antennule terminal segment having 6 apical setae comprising tubercles 1 and 3, digitiform seta 4, 2 subequal setae of complex 5, and flagelliform seta 6; an antenna exopod with a thickened dorsal ridge, smooth (convex) outer surface with 2 short papillae, and rugose (concave) inner surface plus a terminal endopodal segment having a large dorsal hook, medial spine, bifid distal tubercle, and spinulose ventral process; a mandible having the formula P1, S1, P1, S1, P1, S1, B5; and a single pair of anterolateral spines on the mouth cone labium. Males attached to the posteroventral surface of the females' genital trunk were assigned to Neoalbionella by having tapered (not inflated) caudal rami directed posteroventrally. They were differentiated from previously reported congeneric males by having an antennule with the same number and configuration of apical setae as the female; an antenna with a spatulate exopod having minute spinules along its apex plus a terminal endopodal segment with components the same as the female; a mandible with formula P2, S1, P1, S1, B5; a labium with 1 pair of anterolateral spines like the female; and a conspicuous mediative process with bifid tip. Detail of the dorsocephalic shield (in females) and mouth cone labium (in both sexes) previously had not been used to diagnose Neoalbionella spp. We also dissected voucher specimens of " Neoalbionella longicaudata" (collected from gulper sharks in the western Pacific Ocean off Japan by Shiino in 1956), which we morphologically diagnosed as an innominate species, Neoalbionella sp. This is the first report of a species of Neoalbionella from the Gulf of Mexico and the second species of Neoalbionella reported from C. granulosus, a deepwater shark seldom encountered and surveyed for parasitology.

Description of a new deep-water dogfish shark from Hawaii, with comments on the Squalusmitsukurii species complex in the West Pacific.

Dogfish sharks of the genus Squalus are small, deep-water sharks with a slow rate of molecular evolution that has led to their designation as a series of species complexes, with low between-species diversity relative to other taxa. The largest of these complexes is named for the Shortspine spurdog (Squalusmitsukurii Jordan & Snyder), a medium-sized dogfish shark common to warm upper slope and seamount habitats, with a putative circumglobal distribution that has come under investigation recently due to geographic variation in morphology and genetic diversity. The Hawaiian population of Squalusmitsukurii was examined using both morphological and molecular analyses, putting this group in an evolutionary context with animals from the type population in Japan and closely-related congeners. External morphology differs significantly between the Hawaiian and Japanese S.mitsukurii, especially in dorsal fin size and relative interdorsal length, and molecular analysis of 1,311 base pairs of the mitochondrial genes ND2 and COI show significant, species-level divergence on par with other taxonomic studies of this genus. The dogfish shark in Hawaii represents a new species in the genus, and the name Squalushawaiiensis, the Hawaiian spurdog, is designated after the type location.

Squalus clarkae sp. nov., a new dogfish shark from the Northwest Atlantic and Gulf of Mexico, with comments on the Squalus mitsukurii species complex.

Sharks of the genus Squalus have slow reproductive rates coupled with low genetic diversity, as is typical of deep-water sharks, making this group slow to rebound from depletion due to overfishing. The number of species within Squalus has been expanding recently due to increased attention on taxonomic revision, and a growing research focus on little-known deep-water sharks in general. Here we use genetics and morphology to describe a new species of dogfish shark, Squalus clarkae sp. nov. from the Gulf of Mexico (GoM) which replaces Squalus mitsukurii in this region, and place it in the context of congeners from the Atlantic and elsewhere. Previously, S. clarkae sp. nov. was considered a part of the Squalus mitsukurii species complex, a group of closely related but distinct species. We sequenced the mitochondrial cytochrome oxidase I and the NADH Dehydrogenase II gene of S. mitsukurii from the type location in Japan, S. clarkae sp. nov. from the GoM, as well as three closely related species (S. cubensis, S. blainville, and S. megalops) and S. cf. mitsukurii from Brazil. Squalus clarkae sp. nov. is genetically distinct from other species with significant statistical support (>98.6% bootstrap support/posterior probability), and 2.8% divergent from S. mitsukurii in the type location of Japan. Morphological estimates also revealed differences between S. clarkae sp. nov., S. mitsukurii, and other Atlantic Squalus species, with S. clarkae sp. nov. exhibiting a longer body, smaller interorbital space, shorter caudal fin, and a differently-proportioned first dorsal fin. In general, dogfish sharks in the Atlantic and GoM are characterized by similar but distinct morphology, significant genetic variation, and small species ranges.

<b>On the taxonomy of the first record of rare deep-water rough shark species of Oxynotidae (Chondrichthyes: Squaliformes) in the western Indian Ocean</b>

An immature female specimen of rough shark was collected south of Reunion Island in the Madagascar Basin in 2009 aboard R/V Dr. Fridtjof Nansen, representing the first official record of the family Oxynotidae in the western Indian Ocean. The specimen is herein identified as Oxynotus sp. due to morphological differences with its closely similar congeners O. centrina and O. bruniensis regarding morphometrics, shape of dorsal, pectoral and caudal fins, shape of the head and colouration, refuting the hypothesis of occurrence of these two species in the region. These results indicate that Oxynotus sp. is possibly an undescribed species. A general description of the external morphology, external morphometrics and photographs of Oxynotus sp. are provided. The specimen has a hepatosomatic index of 36.33% which reveals that it was possibly approaching maturation, suggesting that a viable population of Oxynotus sp. exists in the western Indian Ocean. Intraspecific variations in O. centrina from the Mediterranean Sea and eastern Atlantic Ocean are also noticed, requiring further taxonomic scrutiny.

Parmaturus nigripalatum n. sp., a new species of deep-sea catshark (Chondrichthyes: Carcharhiniformes: Scyliorhinidae) from Indonesia.

Parmaturus nigripalatum, a new species of catshark of the genus Parmaturus is described from a single specimen collected from a deep-water shark longliner operating in south Sumbawa waters, Indonesia. This new species is distinguished from its closest geographic congener P. lanatus by having prominent enlarged caudal crests, well-developed labial furrows with the uppers and lowers of equal lengths, mouth roof blackish with dark pores, first dorsal fin origin more posteriorly positioned on body trunk, and much lower tooth counts than all other known Parmaturus species. This is the second Parmaturus species recorded from Indonesian waters.

Management of deep-water sharks’ by-catch in the Portuguese anglerfish fishery: from EU regulations to practice

The European Union banned fishing operations with trammel, entangling and gillnets in Portuguese continental waters at depths >200m in consideration of the potential impact of fisheries on deep-sea sharks. Derogation could be considered if Member States demonstrate that by-catch mortality does not adversely affect this group of species. This regulation has had an impact on the trammel net fishery for anglerfish (Lophius piscatorius and Lophius budegassa), one of the most important Portuguese multi-species fisheries. This study evaluates the impact of this fishery on deep-water shark populations by looking at onboard observations of by-catch in the commercial fishery and by analysing survey catch composition. Results suggest that this fishery has a very low impact on deep-water shark populations: by-catch was <5% by weight of the total catch in 98% of the hauls conducted in the depth range allowed for this fishery (<600m). Frequency of occurrence of deep-water sharks was also low. Etmopterus spinax and Etmopterus pusillus were the only species found to overlap with this fishery to any great extent; all the others largely distribute at depths greater than 600m. A higher overlap is expected in hauls catching L. piscatorius, which seems to distribute at greater depths, but more information is needed to clarify the distribution pattern of this species. Scientific data supports the proposed change to the EU regulation. If necessary, future management measures may rely on spatial closures, but would require enhanced knowledge on species’ spatial distributions and also on social and economic aspects of this fishery.

Insights about depth distribution, occurrence and swimming behavior of Hexanchus griseus in the Cantabrian Sea (NE Atlantic)

The bluntnose sixgill shark, Hexanchus griseus, is a relatively common, wide-spread and deepwater shark that occurs along outer continental shelves and upper slopes. However, very little information exists about its distribution patterns, migrations and behavior. Data on occurrence and behavior of sixgill sharks inhabiting waters north of Spain (Galicia and Cantabrian Sea, NE Atlantic) were obtained from yearly oceanographic trawl surveys, commercial fishing boat records, and a pop-up satellite archival tag that was deployed for 75 days on a juvenile specimen. Most of the specimens were caught in Galician waters, and nearly all of those from surveys were juveniles (length range, 60–121 cm). Catch depth from surveys and commercial vessels ranged from 90 to 800 m and 90 to 1750 m respectively. Combining all data, a moderate relationship was observed between catch depth and size of the sharks (r2=0.5001). The sex ratio was 1:1.86 in favor of females. September and February were the months with more catches reported from commercial vessels. Data obtained from one electronic pop-up tag (Mini PAT), provided information about depth and temperature preferences over 75 days. Mean depth obtained during that period was 913 m (depth range 727–1247 m), and the mean temperature was 10.3 °C, (range 8.0–10.8 ° C). Movements up and down in the water column within a single day ranged from 50 to 385 m. No cyclic diel vertical migration was however observed, the shark moved smoothly without a defined pattern. Vertical movements at semidiurnal frequency were intermittently observed. The thereby differences observed in the swimming behavior of H. griseus compared to other areas could be attributed to size, foraging activity or atypical behavior.

NOTES ON THE RECORD OF GOBLIN SHARK (Mitsukurina owstoni Jordan, 1898) FROM INDONESIA

A goblin shark, Mitsukurina owstoni,was captured by deepwater shark longline targeting squaloid sharks off Palabuhanratu, West Java, Indonesia at about 200 m depth. Morphological measurements were taken and compared to other records from Australia, New Zealand and Japan. This new recordfrom Indonesian waters extends the distribution of this species in the Indian Ocean.

First record of blurred smooth lanternshark, Etmopterus bigelowi from Indonesia

The blurred smooth lanternshark, Etmopterus bigelowi Shirai and Tachikawa, 1993 was recorded for the first time from Indonesian waters based on two specimens collected from a deepwater shark fishery operated in the Flores Sea, eastern Indonesia. This is also the second confirmed record of Etmopterus species from this country.