The bluntnose sixgill shark,
, is a widely distributed demersal species found in tropical and temperate waters of the Pacific, Atlantic, and Indian Oceans, inhabiting continental shelves and slopes, ...islands, and mid-ocean ridges at depths ranging from 200 to 1100 m. In the Southwestern Atlantic, this species has been recorded from northeastern to southern Brazil, Argentina, and Uruguay. Despite this, the known distribution of this species in the Southwestern Atlantic is very patchy and, in some cases, still mostly ignored in the literature, such as in northeastern Brazil. This study, therefore, aimed to report 23 new records of
in the Tropical Southwestern Atlantic and highlight the presence of this species off the northeastern Brazilian coast. So far,
was officially reported from the Fernando de Noronha Archipelago, Saint Peter and Saint Paul Archipelago, and the state of Ceará along the northeast coast of Brazil. Herein, the known distribution is extended to the continental shelf breaks and upper slopes of other Brazilian states, reinforcing the previously reported occurrence of the species near the Saint Peter and Saint Paul Archipelago.
The activity patterns for most animals are determined through a trade-off among competing processes, such as foraging behaviour, predator or competitor avoidance, and maintaining bioenergetic ...efficiency. We used active and passive acoustic telemetry to examine what processes may contribute to diel and seasonal patterns of vertical movement in 27 sixgill sharks in Puget Sound, WA, U.S.A., from December 2005 to December 2007. We found clear and consistent patterns of diel activity; sixgill sharks were typically shallower and more active at night than during the day. In Elliott Bay, WA, sixgill sharks made direct vertical movements at sunrise and sunset, while vertical movements were more variable in deeper, main channel waters. The greatest rates of ascent and descent in sixgill sharks occurred most often during night-time ebb tides. Seasonally, sixgill sharks occupied deeper habitats during the autumn and winter than during spring and were most active in the autumn. We also found synchronous vertical movements in three of four shark pairs tracked simultaneously, evidence that these sharks were responding to similar stimuli. Clear and consistent patterns of diel activity throughout the year across size and sex of sharks and across multiple spatial scales is most consistent with the hypothesis that foraging behaviour is responsible for the patterns of diel vertical movement of sixgill sharks in Puget Sound.
Identifying feeding patterns of large-bodied predators is necessary for predicting their potential effects on food web dynamics. However, diet information from stomach contents can be impractical to ...obtain because required sample sizes can be prohibitively large. In contrast, diet estimates obtained using Bayesian stable isotope mixing models require less sampling effort and can also reveal both population- and individual-level variation in diet. Here, we used an extensive stable isotope data set to evaluate the trophic role of bluntnose sixgill shark (
Hexanchus griseus
), a globally distributed species and among the largest sharks in the North Pacific. In total, 43 subadult sixgill sharks were sampled from Puget Sound, Washington, USA. Mixing model results indicated that the population feeds primarily on benthic fish and invertebrates (estimated median diet percentages: 33 and 35%, respectively). Further, the model indicated low individual variation in diets and that the feeding behavior of both individuals and the population as a whole tended towards generalism. Specifically, sixgill sharks appear to feed on prey groups approximately in proportion to their average biomass densities in the Puget Sound food web. As generalists, sixgill sharks are less likely to be affected by changes in the abundance of any single prey resource, and our results suggest they are unlikely to be important predators to at least some species of management concern. In addition, stable isotope data obtained opportunistically from an adult sixgill shark supports previously suggested ontogenetic movement patterns, whereby some adults make brief migrations into Puget Sound from outer coastal habitats, likely to birth, and pups feed, grow, and remain resident in Puget Sound for several years. Our findings provide insights into the trophic role of this important but understudied species and demonstrate how stable isotope analyses can further understanding of shark ecology.
Deep-sea chondrichthyans, like many deep-water fishes, are very poorly understood at the most fundamental biological, ecological and taxonomic levels. Our study represents the first ecological ...investigation of deep-water elasmobranch assemblages in The Bahamas, and the first assessment of species-specific resilience to capture for all of the species captured. Standardised deep-water longline surveys (n=69) were conducted September to December 2010 and 2011 between 472m and 1024m deep, resulting in the capture of 144 sharks from 8 different species. These included the Cuban dogfish, Squalus cubensis, the bigeye sixgill shark, Hexanchus nakamurai, the bluntnose sixgill shark, Hexanchus griseus, the smooth dogfish, Mustelus canis insularis, the roughskin dogfish, Centroscymnus owstoni, Springer׳s sawtail catshark, Galeus springeri and the false catshark, Pseudotriakis microdon. Preliminary genetic analysis indicated two or more species of gulper sharks, Centrophorus spp.; however, for the present study they were treated as a single species complex. Water depth and distance from the rocky structure of the Exuma Sound wall were inversely correlated with species richness, whereas seabed temperature was directly correlated with species richness. These variables also had a significant influence on the abundance and distribution of many species. Expanded depth ranges were established for S. cubensis and H. nakamurai, which, in the case of S. cubensis, is thought to be driven by thermal preferences. At-vessel mortality rates increased significantly with depth, and post-release mortality was thought to be high for some species, in part due to high post-release predation. This study highlights the importance of utilising strategic geographic locations that provide easy access to deep water, in combination with traditional expedition-based deep-ocean science, to accelerate the acquisition of fundamental ecological and biological insights into deep-sea elasmobranchs.
Canyons play a fundamental role in enhancing the abundance and diversity of marine organisms through the transport of organic matter and food resources, the presence of complex physical habitats and ...the absence of trawl fishing. During four baited lander deployments carried out in the Bari Canyon (Southern Adriatic Sea, Central Mediterranean), at depths of 443–788 m, about 43 h of video records were taken, for a total of 619,200 video frames. A total of 12 benthopelagic fish species (five chondrichthyes and seven osteichthyes) were identified. The blackspot seabream (Pagellus bogaraveo) was the most often observed fish species. The depth of 787 m represents a new depth record for this fish in the Adriatic Sea. Groups of up to 40 individuals of P. bogaraveo were attracted to the bait and were shown in single frames. The individuals were observed both exploring the area and feeding actively on the bait. The European conger (Conger conger) was recorded at each deployment. Clear scavenger behaviour was also observed in this teleost fish and in the shark Etmopterus spinax. The shark species Centrophorus granulosus and Hexanchus griseus, which are considered ‘vulnerable’ on the published IUCN Mediterranean Regional Red List, were also recorded but, although attracted by the bait, they were never seen feeding on it. Other fish species, harvested on fishing grounds, such as Merluccius merluccius, Helicolenus dactylopterus and Polyprion americanus, were also recorded. This study represents the first in situ documentation, at very low impact, of the fish fauna in the Bari Canyon, providing new insights into its small scale distribution and behaviour, the first in situ direct observation of the variable feeding behaviour of P. bogaraveo and its gregarious habits, as well as indicating that this canyon could act as a refuge area for species that are vulnerable to fishing on the open slope.
Hexanchus griseus is a globally distributed deep-water shark species. It inhabits tropical and temperate waters throughout the world, including the Mediterranean Sea where it is by-caught by ...small-scale fisheries in the region. In this study, we analysed the genetic variation of H. griseus specimens collected from different areas within and outside the Mediterranean region, to assess its genetic connectivity. The mitochondrial DNA (mtDNA) sequence analysed in this study ranged from cytochrome b to 16S rRNA genes including the control region, the 12S rRNA gene and the interspersed tRNA genes in the region, covering a total of 3731 to 3914 nucleotides. Results have shown that this species exhibits geographically distinct maternal lineages, indicating population structure along geographical ranges. These findings reveal population subdivisions not only between the Pacific Ocean and the Atlantic Ocean, but also within the oceans and on a smaller scale within the Mediterranean Sea. This highlights the need to consider each population subdivision separately when designing management plans for the conservation of this species.
Cartilaginous fish are commonly recognized as key species in marine ecosystems for their fundamental ecological role as top predators. Nevertheless, effective management plans for cartilaginous fish ...are still missing, due to the lack of knowledge on their abundance, distribution or even life-history. In this regard, this paper aims at providing new information on the life-history traits, such as age, maturity, reproductive period, in addition to diet characteristics of eleven rare cartilaginous fish inhabiting the Central-Western Mediterranean Sea belonging to the orders Chimaeriformes (Chimaera monstrosa), Hexanchiformes (Heptranchias perlo and Hexanchus griseus), Myliobatiformes (Aetomylaeus bovinus and Myliobatis aquila), Rajiformes (Dipturus nidarosiensis and Leucoraja circularis), Squaliformes (Centrophorus uyato, Dalatias licha and Oxynotus centrina) and Torpediniformes (Tetronarce nobiliana), useful for their assessment and for future management actions. Particularly, the present paper provides for the first time the age estimation of D. nidarosienis and L. circularis which were both found capable of becoming older than ten years. In addition, the present study updates the sizes of first maturity of C. uyato and D. licha, which appeared to be capable of reproducing earlier than what was previously hypothesized, representing very valuable information for a better understanding of these rare species populations status and, eventually, their conservation. On the basis of the stomach content analysis, it was possible to identify five different predator groups.
Un raro evento di spiaggiamento che ha coinvolto un capopiatto maschio maturo lungo 297 cm (Hexanchus griseus si e verificato lungo la costa toscana nel mar Tirreno centrale. Ľesemplare spiaggiato ...presentava 6 file di denti che indicavano l'appartenenza alla specie H. griseus e non alla specie Hexanchus nakamurai, che ne ha solo 5. Sono stati raccolti dati biometrici su due denti della regione anteriore sinistra della mascella inferiore. Il corpo dell'esemplare non mostrava segni di cattura, solo un profondo taglio all'altezza dell'arco orbitale che suggeriva una collisione o lo speronamento di una barca.
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