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... The metabolically sluggish lifestyle typical of deep-sea fishes is therefore advantageous, combining low basal metabolism, low activity, slow growth and, at least in some species, high food conversion efficiency (Koslow, 1996(Koslow, , 1997. Below, we assess the general hypothesis that chondrichthyans are excluded from the oligotrophic abyss because they have distinct metabolic and nutritional demands compared with teleosts (Musick and Cotton, 2015;Priede et al., 2006). ...
... The dual role of liver lipids in buoyancy and energy storage in chondrichthyans may place additional constraints upon abyssal colonization. Musick and Cotton (2015) suggested that mobilization of lipid fuels (TAG, DAGE) to sustain fasts between infrequent meals in the abyss could compromise neutral buoyancy, leading to unsustainable locomotory costs. However, because of associated mobilization of body protein mass, HSI and liver lipid content of sharks are maintained during prolonged starvation (Baldridge, 1972;Kajimura et al., 2008), suggesting unperturbed buoyancy. ...
... Accumulation of relatively inert squalene, and its trade-off against TAG levels (Fig. 3), could limit starvation endurance in deep-sea squaloids (Musick and Cotton, 2015). However, it is unclear whether a starvation (or any other) penalty of squalene accumulation constrains depth limits because squaleneaccumulating squaloid sharks are the deepest chondrichthyans (along with skates, in which squalene presence remains unexplored). ...
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The deep sea is the largest ecosystem on Earth but organisms living there must contend with high pressure, low temperature, darkness and scarce food. Chondrichthyan fishes (sharks and their relatives) are important consumers in most marine ecosystems but are uncommon deeper than 3000 m and exceedingly rare, or quite possibly absent, from the vast abyss (depths >4000 m). By contrast, teleost (bony) fishes are commonly found to depths of ∼8400 m. Why chondrichthyans are scarce at abyssal depths is a major biogeographical puzzle. Here, after outlining the depth-related physiological trends among chondrichthyans, we discuss several existing and new hypotheses that implicate unique physiological and biochemical characteristics of chondrichthyans as potential constraints on their depth distribution. We highlight three major, and not mutually exclusive, working hypotheses: (1) the urea-based osmoregulatory strategy of chondrichthyans might conflict with the interactive effects of low temperature and high pressure on protein and membrane function at great depth; (2) the reliance on lipid accumulation for buoyancy in chondrichthyans has a unique energetic cost, which might increasingly limit growth and reproductive output as food availability decreases with depth; (3) their osmoregulatory strategy may make chondrichthyans unusually nitrogen limited, a potential liability in the food-poor abyss. These hypotheses acting in concert could help to explain the scarcity of chondrichthyans at great depths: the mechanisms of the first hypothesis may place an absolute, pressure-related depth limit on physiological function, while the mechanisms of the second and third hypotheses may limit depth distribution by constraining performance in the oligotrophic abyss, in ways that preclude the establishment of viable populations or lead to competitive exclusion by teleosts.
... While teleosts have successfully colonised the deep sea, chondrichthyans are uncommon 5 . The species who live there rely on their sensory systems to gather information about their environment and to guide their behaviour 30 . ...
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Animals that continually live in deep sea habitats face unique challenges and require adaptive specializations solutions in order to locate and identify food, predators, and conspecifics. The Ampullae of Lorenzini are specialized electroreceptors used by chondrichthyans for important biological functions. Ampullary organs of the ghost shark Chimaera monstrosa, a deep-sea species commonly captured as by-catch in the bottom trawl fishery, are here described for the first time using macroscopic, ultrastructural and histological approaches. The number of ampullary pores in C. monstrosa is about 700, distributed into the whole cephalic section of C. monstrosa, and organized in12 pore clusters and they are arranged into different configurations and form a distinct morphological pattern for this species, showing some anatomical peculiarities never described before in others cartilaginous fishes and may constitute an evolutionary adaptation of this ancient chondrichthyan species to the extreme environmental conditions of its deep sea niche.
... Poulsen, personal observation). However, this must be considered in a context of habitat adaptations, as teleosts and chondrichthyans have evolved differently with regard to deep-sea trophic guilds (Musick and Cotton 2015). ...
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As part of an ongoing effort to monitor the fish diversity in Greenland waters using morphological and molecular taxonomy, and construct pragmatic identification keys, we here update distributions of all known halosaurs (Halosauridae) and notacanthids (Notacanthidae) in the subarctic Atlantic Ocean. New distributions are included for Aldrovandia oleosa, Halosauropsis macrochir, and Notacanthus bonaparte, all caught once in the Denmark Strait off SE Greenland. We also present the first observation of luminous tissues in halosaurs. Photo, illustrative and text identification keys are included for pragmatic identification corroborated by molecular barcoding data, produced as part of the Greenland Fishes Barcoding Project (GLF) introduced in this study. Barcoding data revealed five operational taxonomic units (OTUs) of Notacanthus cf. chemnitzii present, including three distinct haplotypes observed off SE Greenland alone, within this species complex currently described as one circumglobal species.
... The "Biology of Deep-Water Chondrichthyans" symposium included 26 presenters (20 oral and 6 posters) from 9 countries. This special issue of Deep-Sea Research II includes 14 contributed papers from the symposium, covering topics ranging from taxonomy (Straube et al., 2015;Weigmann et al., 2015), biodiversity (Brooks et al., 2015), trophic ecology (Churchill et al., 2015a(Churchill et al., , 2015bMusick 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). ...
... Par ailleurs, le taux de vacuité a été plus important chez les individus matures et de tailles moyennes/grandes (> 31,5 cm). Ceci s'expliquerait par des tailles de proies plus importantes et donc plus rares à trouver (Musick & Cotton, 2014). Effectivement, nous avant montré une corrélation positive entre la taille de Micromesistius poutassou et celle de son prédateur. ...
... This is corroborated by the difference in depth use by animal 150486 compared to the other three tagged individuals. Therefore, although abiotic factors such as temperature, ambient light, and pressure may drive the more extreme limits of vertical habitat use (Musick and Cotton, 2015), further information is required to delineate more pertinent drivers of Cuban dogfish behaviour. Finally, resilience to a broad range of temperatures may also drive the higher rates of postrelease survivorship in this species (see Talwar, 2016), as exposure to high sea surface temperatures have been associated with significant mortality in other less resilient taxa such as gulper sharks (Centrophorus spp.; Talwar, 2016). ...
Article
Acquiring movement data for small-bodied, deep-water chondrichthyans is challenged by extreme effects of capture and handling stress, and post-release predation, however, it is urgently required to examine important fisheries interactions and assess the ecological role of these species within deep-water food webs. Here we suggest a novel release-cage mechanism to deploy pop-up satellite archival tags, as well as present vertical habitat data for a data-deficient, small-bodied, deep-water bycatch species, the Cuban dogfish (Squalus cubensis). Data were gathered from seven of eight High Rate X-Tags deployed on mature Cuban dogfish in the Exuma Sound, The Bahamas. Recovery periods appeared variable between individuals and are likely driven by capture-and-handling stress and tag burden. Application of the cross-correlation function to time-series depth and temperature data indicated three of the seven individuals suffered mortality through predation, which occurred during daytime, and suggests Cuban dogfish may constitute a proportion of deep-water apex predator diet in the Exuma Sound. Two animals were successfully released via a novel release-cage mechanism and displayed either no, or rapid (< 15 mins) vertically stationary recovery periods and were not consumed by predators; data for these individuals were recorded for the entire deployment duration (14 days). Vertical habitat data suggests Cuban dogfish are diel-vertical migrators, similar to other deep-water taxa, and exhibit a relatively broad temperature and depth range, which may be driven by preference for specific bathymetric structures. These techniques provide an important first step into acquiring and presenting vertical habitat data for small-bodied, deep-water chondrichthyans, which can be directly applied to fisheries and ecosystem-based management approaches.
... We also note that chondrichthyans were absent beyond 2000 m in the NE Caribbean; the deepest observation was of an unknown skate (family Rajidae) at a depth of 1715 m. This lends support to the premise that chondrichthyans are uncommon deeper than 2000 m, which may be due to their high energy demands created by near-constant swimming and an oilrich liver for buoyancy (see Musick and Cotton (2015)). ...
Article
Recent investigations of demersal fish communities in deepwater (>50 m) habitats have considerably increased our knowledge of the factors that influence the assemblage structure of fishes across mesophotic to deep-sea depths. While different habitat types influence deepwater fish distribution, whether different types of rugged seafloor features provide functionally equivalent habitat for fishes is poorly understood. In the northeastern Caribbean, different types of rugged features (e.g., seamounts, banks, canyons) punctuate insular margins, and thus create a remarkable setting in which to compare demersal fish communities across various features. Concurrently, several water masses are vertically layered in the water column, creating strong stratification layers corresponding to specific abiotic conditions. In this study, we examined differences among fish assemblages across different features (e.g., seamount, canyon, bank/ridge) and water masses at depths ranging from 98 to 4060 m in the northeastern Caribbean. We conducted 26 remotely operated vehicle dives across 18 sites, identifying 156 species of which 42% of had not been previously recorded from particular depths or localities in the region. While rarefaction curves indicated fewer species at seamounts than at other features in the NE Caribbean, assemblage structure was similar among the different types of features. Thus, similar to seamount studies in other regions, seamounts in the Anegada Passage do not harbor distinct communities from other types of rugged features. Species assemblages, however, differed among depths, with zonation generally corresponding to water mass boundaries in the region. High species turnover occurred at depths <1200 m, and may be driven by changes in water mass characteristics including temperature (4.8–24.4 °C) and dissolved oxygen (2.2–9.5 mg per l). Our study suggests the importance of water masses in influencing community structure of benthic fauna, while considerably adding to the knowledge of mesophotic and deep-sea fish biogeography.
... This depth limitation is not universal among fishes, as several teleost taxa (e.g., ophidiid, liparid, macrourid) may occur to 8145 m (Linley et al., 2016). The following explanations have been proposed for the relative lack of deep-sea penetration by chondrichthyans: 1) their urea-based osmoregulatory system may conflict with the interactive effects of low temperature and high pressure on membrane function (Treberg and Speers-Roesch, 2016), 2) energetic limitations imposed by the use of the liver for dual purposes of lipid storage and buoyancy control (i.e., energetic advantage of a swim bladder in teleosts) (Priede et al., 2006), 3) dietary limitations on the amount of nitrogen available to synthesize trimethylamine N-oxide (TMAO) to stabilize proteins in the presence of high urea concentrations (Laxson et al., 2009), and 4) trophic limitations (i.e., elevated energetic needs as upper trophic level predators, less efficient at using and storing available food, absence of typical chondricthyan trophic guilds) (Musick and Cotton, 2015). Based on the totality of available evidence, there appears to be a temperature/pressure-related depth limit to homeostasis and, ultimately physical function for chondrichthyans. ...
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We report on 18 years of in situ observations of seven skate species (2192 individual observations) in the eastern North Pacific (Vancouver Island, Canada to the Gulf of California, Mexico) between 200 and 3322m depth. Biological (species, sex, maturity, behavior) and abiotic (geographic location, depth, habitat type, temperature, oxygen) data were evaluated for each species. This study extends the depth and geographic ranges of Bathyraja microtrachys and B. trachura. Additional species studied include Amblyraja hyperborea, B. abyssicola, B. kincaidii, B. spinosissima, and Beringraja rhina. Bathyraja trachura was shown to be uniquely tolerant of low oxygen environments and B. spinosissima is distinctive in that it was most frequently found actively swimming over lava fields. Our video recording of a potentially undescribed species at 3321m represents the deepest reported in situ visual observation of a skate to date.
... More than 50% of chimaeras, sharks, and rays (Chondrichthyes) occur in depths greater than 500 m; however, they become extremely rare at depths over 3000 m. The deepest records for a chimaera belong to the chimaerid Hydrolagus affinis (De Brito Capello 1868) at 3000 m, for the sharks, to the dalatiid Isistius brasiliensis (Quoy and Gaimard 1824) and the somniosid Centroscymnus coelolepis Barbosa du Bocage and de Brito Capello, 1864 at 3700 m, and for a skate, to the rajid Rajella bigelowi (Stehmann 1978) at 4156 m (Priede et al. 2006, Musick andCotton 2015). The bony fishes (Actinopterygii) comprise the majority of the biodiversity, and the deepest records belonging to the liparid Pseudoliparis amblystomopsis (Andriashev 1955) at 7703 m, and the ophidiid Abyssobrotula galatheae Nielsen 1977, known as the deepest-living known vertebrate, living at 8370 m (Nielsen 1977;Smith Fujii et al. 2010). ...
Chapter
The Brazilian Continental Margin (BM) hosts one of the most poorly known deep-water fauna in the world, especially those referred to as habitat forming such as scleractinians and octocorallians (Cnidaria: Anthozoa). In waters deeper than 150 m, these anthozoans are the framework builders for coral reefs and coral gardens. Together, these habitats host the highest diversity of metazoans on the external shelf and slope. Although only a few surveys have been dedicated to the study of these organisms in the BM, it is known that Desmophyllum pertusum (former Lophelia pertusa), Solenosmilia variabilis, and Madrepora oculata form extensive reefs especially on the southern and southeastern regions. In the same way, Octocorallia representatives, such as those of the families Priminoidae, Clavulariidae, Plexauridae, Alcyoniidae, Isididae, Coralliidae, and Paragorgidae, also have great ecological importance at the BM and are particularly abundant at the northern and northeastern continental shelves and slope. In order to set a baseline for future research, the present chapter provides a historical review of the studies of these anthozoans from the BM, including a list of all records and their geographical and depth distributions. Based on part of these records, the BM distributional modeling of these organisms is predicted using habitat suitability models, which suggest that carbonate saturation state, temperature, dissolved oxygen, and particulate organic carbon are the main factors structuring habitat suitability along the BM. In addition, a comprehensive review of the studies focusing on reproduction of the main species occurring at the BM, a key process for the maintenance and renewal of coral populations and, therefore, design of marine protected areas, as well as the human-based impacts imposed to the habitats structured by these species, are provided.
Article
Hydrostatic pressure (HP), increasing by 1 atm per 10 m in the ocean, perturbs many cellular processes, for example, by rigidifying membranes and disturbing protein folding and ligand binding. Membranes can be fluidized to work under high HP by increasing unsaturated fatty acids, for example, docosahexaenoic acid. Over generations, some deep-sea proteins have evolved intrinsic resistance to HP, but often incompletely. These may be protected from HP with piezolytes, small organic molecules with pressure-counteracting properties. The key example is the osmolyte trimethylamine N-oxide (TMAO), which marine fishes and crustaceans accumulates linearly with depth. TMAO can effectively counteract many inhibitory effects of HP on numerous proteins. For short-term HP stress, cellular stress (transient) and homeostasis (persistent) responses (CSRs, CHRs) remain poorly characterized, but across different taxa of shallow and terrestrial organisms, they include common CSR/CHR mechanisms known for other stressors-heat shock proteins (HSPs), boosted energy metabolism, antioxidants, cellular repair systems. For vertically migrating marine animals, HP stress responses are even more poorly characterized. Some species (e.g., Anguilla silver eel, king crab Lithodes maja, snubnosed eel Simenchelys parasiticus) cope with HP changes in their habitat range by intrinsic adaptations, lipid desaturase activation, and metabolic adjustments, but perhaps not common CSR mechanisms. Such species may have constitutive stress proteins and/or are able to adjust membrane saturation and/or TMAO rapidly with depth. For permanent deep-sea species, CSR/CHR mechanisms have not been directly tested, but evidence in Mariana Trench amphipods and snailfish suggest that HSP and desaturase genes, and possibly piezolyte synthesis, have undergone habitat-related selection.
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Deep-sea chondrichthyans are cryptic species subject to increasing anthropogenic exploitation. Defining their role in deep-water ecosystems is therefore crucial for predicting the ecosystem-wide effects of their removal. Stable isotope analyses (SIA) of carbon and nitrogen have been increasingly used in chondrichthyan studies as a non-lethal method to investigate aspects of their ecology. In recent years these methods have been applied to deep-sea chondricthyans to investigate their trophic structure, niche width, and describe energy flow in the deep sea. Despite the increasing popularity of SIA in deep-sea chondrichthyan studies, methods rely on a multitude of assumptions, such as the need to determine accurate trophic discrimination and tissue turnover rates, which are currently lacking for most species. These uncertainties may preclude the reliability of isotope-based approaches, and as a result inferences from isotopic data must be viewed with relative caution. Due to the growing use of isotopic-based approaches in deep-sea chondrichthyans, we review the literature in the context of current methodological challenges and ecological inferences. We provide recommendations and novel approaches that may help develop and refine a rapidly growing field of study.
Chapter
The deep sea is the largest and one of the most extreme environments on Earth. It is estimated that 10–15% of all fish species are dwelling in the deep sea, most of which have unique morphological and physiological adaptations. Biological expeditions to sample the deep ocean off Brazil started with the British HMS Challenger Expedition (1872–1876), followed by a few fishery stations made by the German RV Ernst Haeckel (1966) and the North-American MIV Oregon II (1957–1975), the cruises of the French RVs Marion Dufresne (1987) and Thalassa (1999, 2000), the Brazilian RV Atlântico Sul (1996–1999), the FV Diadorim and FV Soloncy Moura (1996–2002), OSB Astro Garoupa (2003), and, more recently, the American RV Luke Thomas and Seward Johnson (2009, 2011), the French RV Antea (2015, 2017), and the Brazilian RV Alpha Crucis. A total of 712 species of deep-sea fishes were recorded, including five species of Myxini, six species of Holocephali, 81 species of Elasmobrachii, and 620 species of Actinopteri. As in other parts of the world, the Brazilian deep-sea ichthyofauna struggles under severe anthropogenic impacts caused by the commercial fishing, and the extraction of oil and gas. The deep ocean is a delicate environment and its recovery is considerably slower than an equivalent in shallow water habitat. Therefore, increasing the research efforts is needed to avoid that part of its diversity disappear without our accurate knowledge.
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We reviewed literature on the diet of the Galeus melastomus Rafinesque, 1810, from the Mediterranean Sea. Specific keywords (“Galeus melastomus diet”, “feeding habits”, “trophic position”, “biology”, “deep environment adaptation”) in the principal data sources, such as Web of Science, PubMed, and Google Scholar were used. Seventeen studies conducted on the diet and trophic position of G. melastomus have been considered for Mediterranean Sea regions. The feeding habits have been analyzed in many areas of the western basin; instead, for the Tyrrhenian, Adriatic, and central Mediterranean Seas, information is outdated and fragmentary. In all investigated sub areas, the data showed that G. melastomus is an opportunistic demersal supra benthic predator, benthic feeder, and scavenger, that adapts its diet to the seasonal and geographical fluctuations of the prey availability. It occupies a generalist niche showing individual specialization. In all reviewed Mediterranean sub areas, the most important prey groups were crustaceans, cephalopods, and teleost fishes. Taxa percentage in its diet composition can vary depending on different habitats with ontogenetic development of individuals, depth (that is correlated with the ontogenetic development), seasonal availability, and distribution of different prey groups. Widening knowledge of G. melastomus feeding habits is a fundamental tool for better understand meso and bathy-pelagic ecosystems.
Chapter
There is a curious, intuitive fascination about buoyancy at great depths in the ocean. It was reported of ancient mariners that they feared burial at sea because they thought that the weighted body would only sink so far and no further. In some confused way, they thought the depths prevented the body sinking further, so it would drift with the currents. Not a proper burial. We are now clearer about Archimedes Principle, probably the most widely known law of physics.
Chapter
In the latter half of the twentieth century a group of North American biochemists embarked on studies of the enzymes of deep-sea fish, using the established methods of enzyme biochemistry mentioned earlier, in Chapter 2. Their objective was to understand the molecular adaptations required of deep-sea animals in general and of fish in particular, to high pressure. They were led by the young but soon to be distinguished Canadian biochemist Peter Hochachka, who organised the highly significant 1971 cruise of the R V Alpha Helix, a ship designed for experimental work at sea, operated by the Scripps Institution of Oceanography, (Somero and Suarez 2005). The Alpha Helix was based in the deep water close to, and sheltered by, the Galapagos Islands. From this and subsequent cruises, Hochachka, together with George Somero and their numerous colleagues from the USA, Canada and elsewhere, developed an understanding of biochemical adaptations to high pressure, (Somero and Suarez 2005). Many other cruises followed and some of the experiments arising from them are described below. Over time the North American biochemical work became a major contribution to deep-sea Biology, supplemented by scientists from Europe and particularly from Japan.
Article
Modes of reproduction and embryonic development vary greatly among the elasmobranchs, and prior studies have suggested that the energetic toll of embryogenesis in lecithotrophic species depletes embryonic organic matter by 20% or more. Matrotrophic species experience a lesser reduction or an increase in organic matter during embryogenesis. To investigate the maternal-embryonic nutritional relationship, we measured changes in organic matter from fertilization to near-parturition in embryos of Centrophorus granulosus and Etmopterus princeps. Embryos of C. granulosus experienced a reduction of 19.5% in organic matter, while E. princeps embryos experienced a reduction of 7.7% in organic matter over the course of embryonic development, suggesting some level of matrotrophy occurs, particularly for the latter species. Uterine villi were present in both species and developed concurrently with the embryos, increasing in length and thickness while becoming progressively vascularized. Embryos of C. granulosus were dissected to track the partitioning of water, organic matter, and inorganic matter to the liver, external yolk sac, internal yolk sac, digestive tract, and evicerated body throughout development. Mating was aseasonal for both species and spatially mediated segregation by sex and maturity stage was observed. Ovarian cycles were concurrent for C. granulosus and consecutive for E. princeps. Size at maturity for C. granulosus was determined to be 111 cm TL for males and 143 cm TL for females, with an average fecundity of 5.3 embryos (range=4–7). Size at maturity for E. princeps was determined to be 56.5 cm TL for males and 61 cm TL for females north of the Azores and 54 cm TL for males and 69 cm TL for females near the Charlie Gibbs Fracture Zone. Average fecundity was 11.2 embryos (range=7–18) for this species. This is the first reporting of reproductive parameters for these two species, and the information provided will be valuable for informing stock assessment models in areas where these species are fished.
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Skates by virtue of their abundance and widespread occurrence appear to play an influential role in the food webs of demersal marine communities. However, few quantitative dietary studies have been conducted on this elasmobranch group. Therefore, to better understand the ecological role of skates, standardized diet compositions and trophic level (TL) values were calculated from quantitative studies, and compared within and among skate and shark taxa. Prey items were grouped into 11 general categories to facilitate standardized diet composition and TL calculations. Trophic level values were calculated for 60 skate species with TL estimates ranging from 3.48 to 4.22 (mean TL = 3.80 ± 0.02 SE). Standardized diet composition results revealed that decapods and fishes were the main prey taxa of most skate species followed by amphipods and polychaetes. Correspondingly, cluster analysis of diet composition data revealed four major trophic guilds, each dominated by one of these prey groups. Fish and decapod guilds were dominant comprising 39 of 48 species analyzed. Analysis of skate families revealed that the Arhynchobatidae and Rajidae had similar TL values of 3.86 and 3.79 (t-test, P = 0.27), respectively. The Anacanthobatidae were represented by a single species, Cruriraja parcomaculata, with a TL of 3.53. Statistical comparison of TL values calculated for five genera (Bathyraja, Leucoraja, Raja, Rajella, Rhinoraja) revealed a significant difference between Bathyraja and Rajella (t-test, P = 0.03). A positive correlation was observed between TL and total length (L T) with larger skates (e.g. >100 cm L T) tending to have a higher calculated TL value (>3.9). Skates were found to occupy TLs similar to those of several co-occurring demersal shark families including the Scyliorhinidae, Squatinidae, and Triakidae. Results from this study support recent assertions that skates utilize similar resources to those of other upper trophic-level marine predators, e.g. seabirds, marine mammals, and sharks. These preliminary findings will hopefully encourage future research into the trophic relationships and ecological impact of these interesting and important demersal predators.
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Chapter
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Introduction Although it is widely recognized that sharks and other elasmobranchs often play a role in the transfer of energy between upper trophic levels within marine ecosystems, our understanding of the dynamics of prey consumption and processing of food in elasmobranchs remains rudimentary. To fully comprehend energy flow through elasmobranchs in marine communities it is necessary not only to know what they eat, but also to characterize the rates at which they ingest, digest, and process energy and nutrients contained in prey that is consumed. As with other areas of elasmobranch biology, investigations on dynamics of feeding and processing food lag behind such studies on other marine fishes and vertebrates. By far the most common elasmobranch feeding studies simply describe stomach contents of a particular species in a particular location. Rate of consumption, feeding patterns, and the fate of food once ingested have been examined for very few species of elasmobranchs.
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Introduction Perhaps the most remarkable thing about the elasmobranch feeding mechanism is its functional diversity despite its morphological simplicity. Compared to the teleost skull, which has approximately 63 bones (excluding the branchiostegal, circumorbital, and branchial bones), the feeding apparatus of a shark is composed of just 10 cartilaginous elements: the chondrocranium, paired palatoquadrate and Meckel’s cartilages, hyomandibulae, ceratohyals, and a basihyal. Furthermore, the elasmobranchs lack pharyngeal jaws and the ability to further process food by this secondary set of decoupled jaws as do bony fishes. Despite this, sharks, skates, and rays display a diversity of feeding mechanisms and behaviors that, although they do not match those of the bony fishes, is truly remarkable, especially considering there are only approximately 1200 species of elasmobranchs compared to about 24,000 species of teleost fishes (Nelson, 1994; Compagno, 2001). The elasmobranchs capture prey by methods as diverse as ram, biting, suction, and filter feeding, and feed on prey ranging from plankton to marine mammals (Moss, 1972; Frazzetta, 1994; Motta and Wilga, 2001). Understanding the elasmobranch feeding mechanism will shed light on how this functional versatility is achieved and whether or not it parallels that of the bony fishes.
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The time required for a meal to be completely eliminated from the digestive tract of the lemon shark Negaprion brevirostris was determined X-radiographically, with barium sulfate as a contrast medium. Two food markers and X-radiography showed that initial voidance of fecal matter began 16–17 h after feeding. Alimentary tracts emptied completely within 68–82 h after food ingestion. Passage of a meal through the digestive tract took substantially longer than in most teleosts. A slow rate of food passage may contribute to the low consumption of food and slow growth that have been observed for the lemon shark.
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The deep benthic fish genus Bathypterois (Pisces: Myctophiformes) is revised on a worldwide basis. A descriptive synopsis of each of the 18 species is provided. A key to these species is presented. Two new species, B. perceptor and B. oddi, are de- scribed. Based on comparative osteology relationships among recent benthic myctophiform genera are re- vised. These genera are placed in three families: Aulopidae (Aulopus), Synodontidae (Synodus, Sau- rida, Trachinocephalus, Harpadon, Bathysaurus), and Chlorophthalmidae (Chlorophthlmus, Parmudis, Bathysauropsis, Ipnops, Bathypterois, Bathytyph- lops, Bathymicrops). The biology of Bathypterois is discussed. The lat- itudinal limits of the genus are found to coincide with the poleward limits of central oceanic water. Bottom temperatures and interspecific competitive exclusion appear to determine the distributions of individual species. Among dominant fish groups of deep Baha- mian basins, the ipnopine genera Ipnops and Bathy- pterois rank third in numerical abundance. In this same region at least two species pertaining to these genera exhibit seasonally synchronized reproduc- tive cycles. Histological examination of the special- ized pectoral fin rays reveals innervation by en- larged spinal nerves and suggests a sensory function for these rays. The stiff elongate pelvic and caudal fin rays are found to be poorly innervated. They appear to function like stilts to raise the fish into the water column. The food of Bathypterois is found to consist primarily of very small planktonic crus- taceans.
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Abyssal fishes of the Caribbean Sea are known from the work of six research vessels, yet only one of these collections has been reported. The most recent collection, that of the USNS Bartlett in 1981, contains 13 new records of rare fish to the Caribbean, including two undescribed species. Twelve species accounts are given, documenting the new finds, along with some taxonomic changes from previous reports. Zoogeographical analysis revealed that the abyssal fish fauna of the Caribbean basins reflects a depauperate, tropical, western Atlantic subunit of a broader, circumglobal pattern of the world's abyssal fish fauna.
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We present the first global-scale analy- sis of standing stock (abundance and biomass) for 4 major size classes of deep-sea biota: bacteria, meta- zoan meiofauna, macrofauna and megafauna. The community standing stock decreases with depth; this is a universal phenomenon that involves a com- plex transition in the relative importance of the different size groups. Bacterial abundance and biomass show no decline with depth. All 3 animal size groups experience significant exponential de- creases in both abundance and biomass. The abun- dance of larger animals is significantly lower and decreases more rapidly than for smaller groups. The resulting drop in average body size with depth con- firms Thiel's size-structure hypothesis on very large spatial scales. In terms of their proportion of total community biomass, smaller size classes replace larger size classes. The upper continental slope is dominated by macrofaunal biomass, and the abyss by bacterial and meiofaunal biomass. The dramatic decrease in total community standing stock and the ascendancy of smaller organisms with depth has important implications for deep-sea biodiversity. The bathyal zone (200 to 4000 m) affords more eco- logical and evolutionary opportunity in the form of energy availability for larger organisms, and conse- quently supports higher macrofaunal and mega- faunal species diversity than the abyss (> 4000 m).
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Data from 105 benthic trawls made in an area south of New England, USA between 40 and 5000 m show the fauna to be zoned with depth, areas of rapid faunal change separating regions of relative faunal homogeneity. Distinct faunal assemblages with characteristic catch rates, diversity, and dominant species are found on the shelf (40 to 264 m), upper continental slope (283 to 650 m), middle continental slope (653 to 1290 m), lower continental slope (1380 to 1947 m), the transitional region from slope to rise (2116 to 2481 m), the upper continental (2504 to 3113 m), the middle continental rise (3244 to 3470 m), and lower continental rise to abyssal plain (3879 to 4986 m). Catch rates and diversity are greatest on the lower continental slope and transition to the upper rise, and are lowest at the greatest depths. Dominance, particularly by echinoderms, is an important aspect of community structure. The 3 major taxa represented (decapod crustaccean, echinoderms, and fishes) do not always display the same patterns within and between assemblages. Generalities derived from study of a single group need not apply to all segments of the deep-ocean community. Overall patterns in the megafauna are similar to those described in other groups and areas, but species assemblages are not the same everywhere and perhaps too much has been made of the horizontal extent of zones. Trophic level is related to degree of zonation, but where predators are generalists their ranges may be wide rather than restricted. Diversity patterns can be understood in terms of the interrelationships of predation, competition, environmental heterogeneity, and trophic level. Faunal zones are of importance as the geographical units within which evolution, community development, and diversification take place.
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Skates by virtue of their abundance and widespread occurrence appear to play an influential role in the food webs of demersal marine communities. However, few quantitative dietary studies have been conducted on this elasmobranch group. Therefore, to better understand the ecological role of skates, standardized diet compositions and trophic level (TL) values were calculated from quantitative studies, and compared within and among skate and shark taxa. Prey items were grouped into 11 general categories to facilitate standardized diet composition and TL calculations. Trophic level values were calculated for 60 skate species with TL estimates ranging from 3.48 to 4.22 (mean TL = 3.80 ± 0.02 SE). Standardized diet composition results revealed that decapods and fishes were the main prey taxa of most skate species followed by amphipods and polychaetes. Correspondingly, cluster analysis of diet composition data revealed four major trophic guilds, each dominated by one of these prey groups. Fish and decapod guilds were dominant comprising 39 of 48 species analyzed. Analysis of skate families revealed that the Arhynchobatidae and Rajidae had similar TL values of 3.86 and 3.79 (t-test, P = 0.27), respectively. The Anacanthobatidae were represented by a single species, Cruriraja parcomaculata, with a TL of 3.53. Statistical comparison of TL values calculated for five genera (Bathyraja, Leucoraja, Raja, Rajella, Rhinoraja) revealed a significant difference between Bathyraja and Rajella (t-test, P = 0.03). A positive correlation was observed between TL and total length (L T) with larger skates (e.g. >100 cm L T) tending to have a higher calculated TL value (>3.9). Skates were found to occupy TLs similar to those of several co-occurring demersal shark families including the Scyliorhinidae, Squatinidae, and Triakidae. Results from this study support recent assertions that skates utilize similar resources to those of other upper trophic-level marine predators, e.g. seabirds, marine mammals, and sharks. These preliminary findings will hopefully encourage future research into the trophic relationships and ecological impact of these interesting and important demersal predators.
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A marked faunal change in abyssal demersal fish assemblages was identified around 34-41oN in the E North Atlantic. Striking contrasts in morphology, ultimate size, feeding pattern, and fecundity were found between the species dominating each assemblage. The zone of faunal change coincides with the location of the boundary region in the near surface waters where deep winter mixing to the N generates a marked seasonality in primary production and a permanent stratification to the S induces a less variable production cycle. The change in relative strength of the seasonal pulse in production, is thought to be the primary cause of the far-reaching effect of this hydrographic feature. -from Author
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Setting the stage. Diversity and distribution of deep demersal fish. Morphological and life history adaptations. Aspects of fish production: general considerations and feeding. Aspects of fish production: growth and reproduction. Adding a trophic link: exploitation beyond the shelf. The ecology of fisheries. Pandora's box: reflections on the future.
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The demersal deep-sea fish fauna of the temperate eutrophic Middle Atlantic Bight (MAB) is compared with that of the tropical oligotrophic Bahamas region between depths of 900 and 5500 m. Of 136 species collected, 52 are shared. A taxonomic dichotomy between the two faunas reveals a fundamental pattern of differentiation among Atlantic deep-sea bottomfishes. Taxa of cold temperate-boreal origin with energetically expensive life histories (Moridae, Macrouridae) predominate beneath eutrophic waters. Taxa of warm temperate-tropical affinities with energetically conservative life histories (Ophidiidae, Chlorophthalmidae, Halosauridae) prevail beneath oligotrophic waters. The dichotomy appears to relate to regional differences in benthic macrofaunal prey availability.Numbers and biomass of fishes decline with depth in both regions. Population densities are higher in the MAB than in the Bahamas at slope depths, but are comparable below 3000 m. Biomass is uniformly higher in the MAB by about an order of magnitude at all depths, paralleling a comparable regional disparity in macrofaunal biomass. Mean fish weight displays a "bigger-deeper" trend only in the MAB. Both large and small species are important at all depths in the Bahamas. Species replacement takes place continuously, but at a variable rate. Bathymetric replacement gives the appearance of zonation with depth, but well-defined discontinuities are not apparent. Faunal richness is very stable across station groups and between regions, suggesting that "diversity" does not decline with depth. Species tend to space themselves randomly in the environment; individuals and units of biomass tend to be mildly aggregated. Such patterns suggest independent foraging and selective feeding among species. On the outer rise and abyss two alternative feeding modes prevail: euryphagy by large mobile species or nektonic microphagy by small sedentary species.Competitive exclusion is suggested by bathymetric complementation both within and between regions. This conclusion is reinforced by the limitation of and stability of faunal richness over depth. The longstanding generalization of demersal deep-sea fishes as non-selective, non-competing trophic generalists is inadequate.
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Deep-sea fishes prey on benthic fauna and scavenge on the carcasses of surface-living animals. Few studies have addressed the relative importance of each trophic pathway. Recent documentation of inter-decadal fluctuations in macrourid densities in the abyssal Pacific, related to changing food supplies, hastens the need for information. We conducted stomach content and stable isotope analyses of two abyssal macrourids, carrion sources, and benthic prey, collected concurrently at 4100 m off California. Squid and fishes were the most frequent prey for Coryphaenoides armatus, with small crustaceans numerous in the diet of small specimens. The diet of Coryphaenoides yaquinae included more benthic prey such as crustaceans, polychaetes, and the holothuroid Protankyra brychia. Carrion was present in both species and it was 69% of the mass of food of large C. armatus. Carrion d15N values were comparable to those in abyssal deposit feeders, but carrion was relatively enriched in 13C, giving it a unique isotopic signature compared to benthic prey sources. The highest d13C and d15N values were observed in benthic shrimps and large polychaetes. The two macrourids had intermediate values, with C. armatus having slightly but significantly lower d15N relative to C. yaquinae. Results of isotope mass balance suggest that carrion was the most important prey resource for both species but to a lesser extent in C. yaquinae. These two species bypass the conventional phytodetritus-based abyssal food web for much of their nutrition. Their population dynamics may be tied more closely to fluctuations in epipelagic nekton populations through fishing effects and direct climatic forcing on top trophic levels.
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This chapter describes the problem of buoyancy faced at deep-sea levels and discusses the swim bladder function of fishes. Fish produce hydrodynamic lift mainly by using their pectoral fins as hydrofoils. The metabolic power needed to propel the hydrofoils through the water can be calculated from drag on the hydrofoils and speed. Another strategy to achieve neutral buoyancy is to build up and maintain a buoyancy device—that is, compensate for the high density of most tissues by including special structures or organs characterized by a very low density. In many species, the swim bladder consists of two chambers, including a thick-walled section in which gas can be deposited and a thin-walled chamber in which gas can be resorbed. In other fishes, the resorbing part of the swim bladder is reduced to a special section of the secretory bladder, called “oval,” which can be closed off by muscular activity. The reduction of the effective gas-carrying capacity of swim bladder blood is brought about by the metabolic and secretory activity of epithelial gas gland cells. The specific gravity of gas increases with gas pressure; hence, the difference between swim bladder gas density and water density decreases with increasing water depth.
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This chapter discusses the feeding habits and deep-sea energetics of deep-sea fishes. Direct evidence concerning the feeding habits of deep-sea fishes comes principally from the analysis of gut contents. Deep-sea fishes feed extensively on demersal prey whose distributions are closely associated with the bottom of the sea; however, many demersal fishes feed principally on vertically migrating mesopelagic organisms, such as myctophids and cephalopods. The presence of pelagic prey in the diets of demersal fishes has been interpreted both as an evidence of the occurrence of mesopelagic prey near the bottom and of off-bottom migrations by some demersal species into the mesopelagic realm to feed. Most demersal deep-sea fish species are microphagous, preying on small benthopelagic and epibenthic invertebrates, especially crustaceans. A special subguild of benthivores is adapted as durophages, capable of crushing thick-shelled mollusks and other armored invertebrates. The chemical composition of demersal fishes is also correlated with buoyancy mechanisms. Benthic and benthopelagic species with swim bladders have lower water contents and higher skeletal ash, nitrogen, carbon, and energy contents than do benthopelagic species without swim bladders.
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Some 17 species of berycomorphid and percomorphid teleost fish occurred in pelagic and demersal samples taken in the Rockall Trough during the period 1973 to 1981. Demersal trawls were deployed at approximately 250 m bathymetric intervals between 400 and 2900 m depth. Pelagic rectangular midwater trawls were fished open to depths of approximately 2500 m. The most common species caught were Hoplostethus atlanticus, a subdominant among the species caught in the 1000 to 1250 m bathymetric zones, and Epigonus telescopus and Aphanopus carbo, subdominants among the species caught in the 500 to 750 m zones. The majority of the other species were rare in the samples. Hoplostethus atlanticus and Epigonus telescopus, whose distributions do not overlap bathymetrically, both exploit the benthopelagic fauna. Aphanopus carbo prey primarily on other fish. The exploiters of the epibenthos are Beryx decadactylus, Lycodes spp., Cataetyx laticeps, and Spectrunculus grandis. The rare Nesiarchus nasutus may exploit benthopelagic prey while the remaining eight species are primarily meso- and bathypelagic. Three of them, however, also exploit benthopelagic prey to varying degrees; they are Scopelogadus beanii, Poromitra crassiceps, and possibly Melanostigma atlanticum.
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The diet of slope dwelling macrourid fishes in the eastern North Pacific is poorly known. We collected several hundred stomach samples to investigate the feeding habits of Coryphaenoides acrolepis and Albatrossia pectoralis, the two dominant slope dwelling macrourids off the continental United States. Coryphaenoides acrolepis exhibited a pronounced ontogenetic shift in diet. Specimens 15cm with scavenged food constituting approximately 20% of the weight of total prey and occurring in approximately 20% of fish 21–29cm. Albatrossia pectoralis consumed primarily midwater fish and squid, and we believe that it feeds in the water column. There were significant differences between the diets of A. pectoralis and C. acrolepis suggesting some degree of niche separation between macrourid species on the continental slope of the eastern North Pacific. Both species are at the top of the food web on the upper continental slope and, because of their abundance, may exert significant pressures on their prey populations.
Estimates have been made of the biomass and abundance of macrobenthic invertebrates off the Gulf of Mexico and Atlantic coasts of the United States. Based on these estimates, it is concluded that deep-sea life is more abundant in the Atlantic than in the Gulf. Regressions of the logarithm (base 10) of biomass and animal density against depth indicate that the abundance of life followed an exponential decline with depth, Y = ae−bx, where Y is either density of individuals or biomass, x is depth and a is proportional to average surface-water phytoplankton production. The rate of decline (b) can be related to the rate of decrease in phytoplankton production in an offshore direction and the efficiency of water-column heterotrophs at utilizing sinking organic matter.The regressions also indicate, through comparison with the literature, that both benthos and zooplankton follow similar exponential decays in quantity of life with depth. The constants (a) both appear to be functions of surface productivity and it can be inferred that the sources of food for zooplankton and benthos in the deep sea are the same. The seemingly conservative nature of organic matter over depth ranges where there is an exponential decrease in life can probably be attributed to the increase in the relative abundance of the refractory organic compounds with depth.
Article
Abyssobrotula galatheae n. gen., n. sp., belonging to the oviparous ophidioids, is described based on 11 specimens caught at nine localities from all oceans. It is characterized by a low pectoral fin-ray count (10-11), elongate pectoral fins, a weak opercular spine, and two median and a pair of basibranchial tooth patches. Abyssobrotula seems related to other small-eyed, elongate genera such as Bassogigas and Holcomycteronus. It is the deepest living species of fish known and at the bottom it is restricted to abyssal and hadal depths (c. 3 100-8370 m).
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The responses of the grenadier fish Coryphaenoidcs (Ncmatonurus) armatus to bait deployed on the sea floor at station M in the North Pacific Ocean (34"50'N, 123"OO'W; 4,100 m deep) in February and October were compared. In February 1990 and 1992, the first fish arrived after an avcragc time of 25 min and stayed an average of 150 min. In October 199 1, the respcctivc times were 15 and 98 min. The faster response in October is correlated with a higher mean swimming speed of 0.0692 m s ' compared with 0.0262 m s ' in February. Fish activity was clcvatcd in October following seasonal enrichment to the benthos by downward flux of particulate organic matter from the surface. Grenadier abundance was estimated from arrival times as 325 individuals km l, corresponding to a wet weight biomass of 146 mg m 7 or 10.2 mgC m '.
Article
Chemical composition was determined for 48 species of deep-sea demersal fishes to evaluate trends in compositional parameters with respect to depth and study area. Specimens were collected from depths of 100 m to over 5,000 m off the U.S. east coast between Cape Hatteras and Cape Cod and from similar depths off the Bahama Islands. Water, ash, nitrogen, and carbon contents were determined. Energy content was calculated based on carbon content. Water level and nitrogen content (% ash-free dry weight) of benthopelagic species with swim bladders increased while carbon (% wet weight), nitrogen (% wet weight), and energy content (kcal 100 g−1 wet weight) decreased as a function of depth. Benthopelagic species without swimbladders had higher water contents and lower skeletal ash (% wet weight), nitrogen (% wet weight), carbon (% wet weight), and energy contents than benthopelagic species with swimbladders or benthic species. Species from the U.S. east coast study area and species common to both study areas had higher energy contents than did species occurring only in the Bahamas. Trends in composition with depth appear to reflect reduced food availability at depth. Moreover, differences in chemical composition between study areas are consistent with the hypothesis that reduced food availability in the Bahamas relative to the temperate western North Atlantic is important in determining the species composition of the respective fish assemblages.
Article
MEASUREMENTS of the oxygen consumption of two common benthopelagic fishes, Coryphaenoides acrolepis and Eptatretus deani, made in situ at 1,230 m in the San Diego Trough1 have indicated low respiration rates. The metabolic measurements reported here for the rattail, Coryphaenoides (Nematonurus) armatus (Hector), at 3,650 m support the earlier findings of low respiration rates in deep-sea rattails. They also support the physiological axiom that respiration increases as a fractional power of body weight in animals2–4. Both the metabolic rate and chemical composition of C. armatus suggest an adaptation to a food-limited deep-sea environment.
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The density of 18 species, measured by weighing them in sea water and in air, was found to vary widely. The weights of these fish in sea water ranged from about 7 % to less than 1 % of their air weights.
Article
A series of samples were taken during the period 1975–81 in successively deeper 250 m bathymetric zones between 400 and 2900 m depth in the Rockall Trough. The bathymetric centres of distribution of the gadoid species are at shallower depths than those of the morid species. Micromesistius poutassou and Gadiculus argenteus thori exploit the pelagic and benthopelagic resources at depths shallower than 750 m depth. Molva molva andMolva dypterygia dypterygia are primarily fish eaters, the latter occurring deeper than the former. Phycis blennoidesand the rarerAntonogadus macrophthalmus are epibenthic feeders. Among the morids, the benthopelagic feeding Antimora rostrata lives primarily at depths of 1500–2500 m. Halargyreus johnsonii and the more common Lepidion eques both live at 750–1000 m depth but exploit different resources in the benthopelagic and epibenthic regimes.
Article
Twenty-four out of 240 fishes caught by bottom lines at 366–3333 m had something in their stomachs. Stomach contents included parts of cephalopods, fish, cetaceans and bottom-living invertebrates, thin rubber sheet and terrestrial mammal bones. The material provides evidence that four species of cephalopod are at least partially demersal and suggests a means by which the tapeworm Phyllobothrium could pass from its secondary to its primary host. During the five biological cruises of R.R.S. ‘Discovery’ between 1967 and 1971 a total of 31 bottom lines with 1483 hooks were fished in depths of water between 366 and 3333 m. The stomachs of the 240 fish caught were examined and 216 (90%) proved to be empty. The high incidence of empty stomachs is thought to be due to frequent loss of food during the ascent from great depths and accounts for our poor knowledge of the feeding habits of demersal fish living at depths exceeding 400 m. The present collection of food from 25 stomachs (24 from ‘Discovery’ collections and one from a fish caught by Mr G. R. Forster from R. V. ‘Sarsia’) of fish belonging to 11 species (Table 1) probably gives little indication of the usual diet of the fish concerned, but its nature prompts some useful speculation and the rarity of such observations justifies placing them on record (Bigelow & Schroeder, 1948; Marshall, 1954). All the fish were caught on lines which lay on the bottom for several hours and it is our firm belief that they were hooked while on or very near the bottom.
Article
The general composition and diversity of the diets of the 43 most commonly caught pelagic and demersal fish of the Rockall Trough, north-eastern Atlantic Ocean, are assessed. The fish are divided into three Groups. The 8 species in Group I consist of both pelagic and demersal species feeding on relatively few prey-classes and having a diet of low diversity and few items per meal. Group II contains 22 pelagic and demersal species with more diverse diets, less restricted dietary composition, but still consuming relatively few items per meal. Group III is the 12 demersal macrourid species with the most diverse diets, a variable dietary composition and the greatest mean number of items per meal. One species, Maurolicus muelleri, had too many unidentified components in its diet to allow classification in terms of Groups I, II or III. All diets contained dominant items, the diversity within diets offish in Groups II and III arising from the inclusion of subdominants and rare items. The diets of species in Groups I and II can be defined in terms of ecological constitution, trophic diversity and prey-species composition. Those of the Group III macrourids differ in that their definition is liable to be a compromise between the situation where ecological constitution and trophic diversity are adequately defined but not species composition.
Article
The eel genus Histiobranchus Gill occurs benthopelagically over the continental rise and abyss of the World Ocean, primarily beneath temperate and subpolar surface waters. Its generic status within the subfamily Synaphobranchinae is confirmed by comparison of the structure and topography of its cephalic sensory system and skeletal features with Synaphobranchus. At least three species of Histiobranchus are recognized: H. bathybius (panoceanic), H. bruuni (Tasman Sea and waters south-east of New Zealand) and H. australis (two geographical forms; South Atlantic and south-western Indian Ocean, and South Indo-West Pacific Oceans). Collections totalling 319 specimens of H. bathybius from the eastern North Atlantic (1790–5440 m depth) yielded a size range of 99–1370 mm total length (LT), with no apparent sexual dimorphism. Length–frequency distributions indicate a mode of juvenile fish at around 100–200 mm LT and a further two around 600–700 and 1300–1400 mm LT among adults. Generally smaller fish occur in shallower regions, although the size range is broad over the whole depth range. No apparent trend occurs in the size distribution with latitude over the range 17–54) N. Females outnumber males (1 male : 1·7 females) and both sexes are largely distinguishable from 300 mm LT. Ripening eggs occur in females from both adult length modes, with running ripe and spent females of very different size indicating iteroparity.
Article
Standing stocks of four size classes of benthic organisms were compared among three sedimentary provinces in the Venezuela Basin. Total biomass was dominated by microbiota and filter-feeding glass sponges that were abundant in both macrofaunal and megafaunal size classes. The remaingng biomass was divided among predominantly deposit-feeding meiofauna, macrofauna and megafauna. The concentration of biomass in smaller sized classes in the Venezuela Basin was in general agreement with the results of other deep-sea investigations. By contrast, biomass in shallow-water benthic assemblages is concentrated in the larger sized classes. We postulate that these differences in the distribution of biomass among benthic size classes results, in part, from differences in the quality and quantity of organic matter available to shallow-water and deep-sea communities. Most of the labile organic matter that reaches the deep-sea bottom in the Venezuela Basin is consumed at or near the sediment-water interface by surface deposit-feeding and filter-feeding benthos. Transformation of refractory organic matter into utilizable substrate by bacteria in the upper 10–20 cm of sediment provides a source of food for subsurface deposit feeders. Biological mixing may also play a role in the transfer of recently deposited organic matter to subsurface deposit feeders.
Article
Sharks are marine consumers believed to occupy top positions in marine food webs. But surprisingly, trophic level estimates for these predators are almost non-existent. With the hope of helping better define the ecological role of sharks in marine communities, this paper presents standardized diet compositions and trophic levels calculated for a suite of species. Dietary composition for each species was derived from published quantitative studies using a weighted average index that takes into account sample size in each study. The trophic level (TL) values of the 11 food types used to characterize the diet (obtained from published accounts) were then used to calculate fractional trophic levels for 149 species representing eight orders and 23 families. Sharks as a group are tertiary consumers (TL>4), and significant differences were found among the six orders compared, which were attributable to differences between orectolobiforms (TL<4) and all other orders, and between hexanchiforms and both carcharhiniforms and squatiniforms. Among four families of carcharhiniform sharks, carcharhinids (TL=4.1, n=39) had a significantly higher TL than triakids (TL=3.8, n=19) and scyliorhinids (TL=3.9, n=21), but not sphyrnids (TL=3.9, n=6). When compared to trophic levels for other top predators of marine communities obtained from the literature, mean TL for sharks was significantly higher than for seabirds (n=28), but not for marine mammals (n=97). Trophic level and body size were positively correlated (r s =0.33), with the fit increasing (r s =0.41) when the three predominantly zooplanktivorous sharks were omitted, and especially when considering only carcharhinid sharks (r s =0.55).
Article
The sharks and chimaeroids are important members of the deep-water associations of fish of the continental slopes, but little is known about their trophic interactions. The diets of these fish were studied through the deployment of demersal trawls at successive 250 m depth intervals, within a total range of depth of 500 to 2 900 m, in the Rockall Trough to the west of Scotland and Ireland during the period 1975 to 1981. The sharks and chimaeroids, however, only occurred between 500 and 2000 m but principally in the 500 to 1 250 m bathymetric zones. These are the zones of maximum biomass of prey species of fish and probably also of prey species of epibenthos. The sharks divide into 3 trophic groups. Apristurus spp., Centroscymnus crepidater, Ttmopterus spinax and E. princeps exploit micronekton in the vicinity of the sea bed. Centroscyllium fabricii, Centroscymnus coelolepis, Deania calceus and Lepidorhinus squamosus are principally fish eaters. A third group may consist of 2 rarer species in the Rockall Trough, Galeus melastomus and G. murinus that exploit the epibenthos but also, to some extent, the micronekton. The 3 species of chimaeroids (Chimaera monstrosa, Hydrolagus mirabilis and Harriotta raleighana) prey on the epibenthos and the last species may also utilize, to some extent, infaunal species.