Sevengill Shark Notorynchus Cepedianus Research Articles

Morphological characterization of dermal denticles of the Broadnose Sevengill Shark Notorynchus cepedianus (Elasmobranchii: Hexanchidae)

Shark skin is covered by small structures called dermal denticles whose functions are diverse, such as protection, bioluminescence, hydrodynamics, among other functions. These structures have a great variety of shapes and sizes, which can be a useful approach for specimen identification as diagnostic characters between species. The present study aims to describe the dermal denticles morphology of the broadnose seven-gill shark Notorynchus cepedianus, evaluating differences among life-stage (neonate, juvenile and adult), sex and body region (dorsal and ventral). For achieving it, 39 specimens were collected at six landing points along the Peruvian coast. The dermal denticles from two body regions(dorsal and ventral) were photographed, measured (length, width, angle and density), and described using a stereoscope. Dermal denticles measures showed significant morphological differences between body regions as well as stages of development, but not between sexes. The differences are: (1) Crown shape: as the individual grows, it can be seen that the cross shape is losing, (2) Crown cusps: cusps length varied according to the stage of each individual, it was also observed that the lateral cusps are larger in dorsal than ventral region, and (3) Union peduncle - crown: adult specimens and both body regions, the observed union was very dimly and it did not have a defined shape. On the whole, these reported variations in measured traits could be useful as diagnostic characters to identify the stage of development at which the landed and marketed specimens are found.

Observations of coastal aggregations of the broadnose sevengill shark (Notorynchus cepedianus) in Chilean waters.

The presence of four sharks was documented in coastal waters of Antofagasta (Chile) using an unmanned aerial video camera. Fishers took advantage of this aggregation to catch and sold three adult broadnose sevengill sharks Notorynchus cepedianus. Species identity was determined by using the cox1 gene. One additional video was later recorded 3000 km south of Antofagasta, and shows a large female interacting with a salmon farming facility. Shallow water records of N. cepedianus were previously undocumented in Chilean waters, yet historically have provided an opportunistic event to fishers in Chile.

Movements and growth rates of the broadnose sevengill shark Notorynchus cepedianus in southern Africa: results from a long-term cooperative tagging programme

Top predators are important components of healthy ecosystems but are at risk of overexploitation due to insufficient data on life-history characteristics and population dynamics to guide management. We investigated the movements and growth rates of the broadnose sevengill shark Notorynchus cepedianus in southern Africa, using data from the Oceanographic Research Institute’s Cooperative Fish Tagging Project (ORI-CFTP). A total of 3 513 N. cepedianus were tagged between 1984 and 2017, with 195 (5.6%) recaptured. Distribution ranged from Cape Fria, northern Namibia, to the Great Kei River, Eastern Cape, South Africa, representing a range extension of ∼200 km in comparison with that previously reported. Most captures occurred along the west coast of South Africa, and recaptures showed connectivity between the west and south coasts, but not between South Africa and Namibia. Site fidelity was evident, with the majority of recaptures (66.6%, n = 130) occurring <50 km from the release site, and many recaptures (32.8%, n = 64) occurring <1 km from the release site. Few sharks (22.6%, n = 44) were recaptured >100 km from the release site, while only three sharks (1.5%) were recaptured >500 km from the release site. Growth rates for N. cepedianus at reference precaudal lengths of 100 cm and 160 cm were estimated to be 4.7 cm y-1 and 4.0 cm y-1, respectively, which are lower than previous growth estimates. The slow growth rate and site fidelity evident in N. cepedianus, coupled with being captured in several commercial fisheries, necessitate the need for improved management of this species.

Chondrichthyans as an umbrella species-complex for conserving South African biodiversity

Conservation surrogates, such as umbrella and flagship species, could help focus South Africa’s limited resources for research and management and enhance the conservation gains from marine protected areas (MPAs). Sharks, rays and chimaeras (Chondrichthyes), which are charismatic and ecologically diverse, are potential umbrella candidates, but tests of the ecological suitability of putative marine umbrella species are lacking. Using baited remote underwater video in and around two MPAs in the Western Cape Province, we assessed the potential of chondrichthyans as an umbrella species-complex by quantifying the relationships and co-occurrence patterns between chondrichthyan abundance and diversity and those of other taxa (primarily teleosts and crustaceans). Sites with abundant chondrichthyans, with catsharks or large sharks (>1 m total length), all had significantly greater abundance and diversity of these other taxa, and associations with species of commercial and conservation interest (e.g. roman Chrysoblephus laticeps). Endemic scyliorhinids (notably dark catshark Haploblepharus pictus) and the broadnose sevengill shark Notorynchus cepedianus also had many strong positive co-occurrences (28% and 21% of interactions, respectively). The puffadder catshark H. edwardsii had the highest centrality of any species, denoting its high connectedness to other taxa. Overall, chondrichthyans, especially the dark and puffadder catsharks and the broadnose sevengill shark, show strong potential as an umbrella species-complex in South Africa.

Habitat use, seasonality and demography of the broadnose sevengill shark Notorynchus cepedianus in central Patagonia: Another piece of the puzzle

AbstractThe habitat use, seasonality and demography of the broadnose sevengill shark Notorynchus cepedianus were investigated in central Patagonia, where a data gap exists for the species. Catch and effort and video‐derived indices indicated high relative abundance of sharks during warm months. Video stations revealed differences in the spatial use by sharks, being more frequently observed in the inner section of the bay. Complementary tagging efforts evidenced both a seasonal residence pattern and site fidelity between consecutive warm seasons. Juveniles outnumbered adults, which suggests that they may use the study area as a secondary nursing ground. Evidence from spontaneous regurgitation further suggests that prey abundance may be driving the seasonal occurrence of sharks in the region. This study allows for a more comprehensive understanding of the population structure and dynamics of sevengill sharks in the Southwest Atlantic.Abstract in Spanish is available with online material.

Trophic ecology of young‐of‐the‐year elasmobranchs in a critical habitat within the Río de la Plata outer estuarine waters

AbstractKnowledge on the trophic ecology of elasmobranch species in all their size classes is important to determine complex trophic roles and relationships between members of the community, which ultimately promotes the development of more effective conservation measures. This study investigates the diet of young‐of‐the‐year from two shark and one skate species that are common within the Southwest Atlantic Ocean. Identification and analysis of stomach contents indicated that the broadnose sevengill shark Notorynchus cepedianus fed mostly on fishes (96.08%IRI), whereas the angular angel shark Squatina guggenheim, and the smallnose fanskate Sympterygia bonapartii preyed mainly on crustaceans (68.73–99.96%IRI). In particular, Artemesia longinaris, a widely distributed small shrimp, was an important prey item for the two crustacean feeders. The high proportion of stomachs with food and the trophic levels suggest that the three species are active predators at a very young age. A high frequency of neonates was also observed for all species, suggesting that parturition events are probably occurring nearby. Overall, this study suggest that the nearshore waters of northern Argentina are functioning as an important feeding ground for co‐occurring elasmobranch species within an important estuarine habitat.

Habitat use, seasonality and demography of an apex predator: sevengill shark Notorynchus cepedianus in northern Patagonia

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 603:147-160 (2018) - DOI: https://doi.org/10.3354/meps12715 Habitat use, seasonality and demography of an apex predator: sevengill shark Notorynchus cepedianus in northern Patagonia Alejo J. Irigoyen1,*, Agustín M. De Wysiecki1, Gastón Trobbiani1, Nelson Bovcon2, Cynthia A. Awruch1,3, Federico Argemi4, Andrés J. Jaureguizar5,6 1Centro para el Estudio de Sistemas Marinos (CESIMAR), Consejo Nacional de Investigaciones Científicas y Técnicas (CCT CENPAT-CONICET), Puerto Madryn U9120ACD, Argentina 2Departamento de Pesca Deportiva, Secretaría de Pesca de la Provincia del Chubut 9020, Argentina 3School of Natural Sciences, University of Tasmania, Hobart, Tasmania 7001, Australia 4Aquarium Fundación Temaiken, Buenos Aires 1625, Argentina 5Comisión de Investigaciones Científicas de la Provincia de Buenos Aires (CIC), La Plata 1900, Argentina 6Instituto Nacional de Investigación y Desarrollo Pesquero (INIDEP), Mar del Plata B7600EEP, Argentina *Corresponding author: alejo@cenpat-conicet.gob.ar ABSTRACT: Gaining insight on how species relate to their environment and other members of the trophic community is critical for their management. We investigated habitat use, seasonal patterns of abundance and population structure of the broadnose sevengill shark Notorynchus cepedianus in the marine temperate environment of a northern Patagonian bay (Argentina). We expected N. cepedianus to exhibit strong seasonality in the bay driven by the seasonal occurrence of important marine mammal prey. However, an alternative or complementary hypothesis arose from the possibility that N. cepedianus uses the area seasonally as mating grounds. To explore these hypotheses, a suite of baited remote underwater video stations and catch per unit effort data indices were used to estimate the seasonal relative abundance of the species inside the bay. Reproductive hormone levels were measured to determine reproductive status and maturity stages of the population. Results indicated that N. cepedianus uses the bay year-round, showing a peak abundance during spring when individuals aggregate, likely for feeding and mating purposes. Male and female total lengths at maturity were 170 and 190 cm, respectively. Contrary to other studies in the Southwest Atlantic, population composition remained similar throughout the seasons, with adults dominating over juveniles, and adult females prevailing in the population at all times. Considering the historical abundance decline recently reported for the species, protection and enforcement within protected areas across the Southwest Atlantic must remain of high priority in government initiatives. KEY WORDS: Baited remote underwater video station · BRUVS · Catch per unit effort · CPUE · Reproductive hormones · Seasonal occurrence · Caleta Valdés · Southwest Atlantic Full text in pdf format PreviousNextCite this article as: Irigoyen AJ, De Wysiecki AM, Trobbiani G, Bovcon N, Awruch CA, Argemi F, Jaureguizar AJ (2018) Habitat use, seasonality and demography of an apex predator: sevengill shark Notorynchus cepedianus in northern Patagonia. Mar Ecol Prog Ser 603:147-160. https://doi.org/10.3354/meps12715 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 603. Online publication date: September 17, 2018 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2018 Inter-Research.

Highest catch of the vulnerable broadnose sevengill shark Notorynchus cepedianus in the south-west Atlantic.

An exceptional catch of 97 broadnose sevengill sharks Notorynchus cepedianus in Samborombón Bay, Argentina, in 2013 is described from a single overnight gillnet fishing operation. Sixty-five female and 32 male N. cepedianus, ranging in size between 105-201 and 112-190 cm LT , respectively, were recorded in this catch. Fishers' observations and published information suggest that this species aggregates in the area seasonally for feeding.

The utility of bioenergetics modelling in quantifying predation rates of marine apex predators: Ecological and fisheries implications

Predators play a crucial role in the structure and function of ecosystems. However, the magnitude of this role is often unclear, particularly for large marine predators, as predation rates are difficult to measure directly. If relevant biotic and abiotic parameters can be obtained, then bioenergetics modelling offers an alternative approach to estimating predation rates, and can provide new insights into ecological processes. We integrate demographic and ecological data for a marine apex predator, the broadnose sevengill shark Notorynchus cepedianus, with energetics data from the literature, to construct a bioenergetics model to quantify predation rates on key fisheries species in Norfolk Bay, Australia. We account for the uncertainty in model parameters by incorporating parameter confidence through Monte Carlo simulations and running alternative variants of the model. Model and parameter variants provide alternative estimates of predation rates. Our simplest model estimates that ca. 1130 ± 137 N. cepedianus individuals consume 11,379 (95% CI: 11,111–11,648) gummy sharks Mustelus antarcticus (~21 tonnes) over a 36-week period in Norfolk Bay, which represents a considerable contribution to total predation mortality on this key fishery species. This study demonstrates how the integration of ecology and fisheries science can provide information for ecosystem and fisheries management.

Depletion of trophy large-sized sharks populations of the Argentinean coast, south-western Atlantic: insights from fishers' knowledge

Abstract Globally, sharks are impacted by a wide range of human activities, resulting in many populations being depleted. Trophy large-sized sharks of the Argentinean coast, the sand-tiger Carcharias taurus , the copper Carcharhinus brachyurus and the sevengill shark Notorynchus cepedianus are under intense sport and artisanal fishing since the 50's decade. However, the current and historical information for the assessment of its populations status is scarce. The aim of this work was to analyze the status of conservation of these species through the gathering of expert fishermen knowledge (FK) on semi-structured interviews. Abundance variation perception between the beginning and the end of fishermen careers revealed a critical status for the species study (means variation between -77 and -90 %). Furthermore, a best day's catch analysis reinforce this result in the case of the sand tiger shark. The school shark Galeorhinus galeus was included on this work with the objective of contrast FK with formal information available of catch-per-unit-effort (CPUE) time series. Both sources of information, despite are not comparable, shows declines ~ - 80%. The critical conservation situation of study species needs urgent management action, particularly for the san tiger shark which could became regionally extinct before the reaction of stakeholders occurs.

Estimating Finite Rate of Population Increase for Sharks Based on Vital Parameters.

The vital parameter data for 62 stocks, covering 38 species, collected from the literature, including parameters of age, growth, and reproduction, were log-transformed and analyzed using multivariate analyses. Three groups were identified and empirical equations were developed for each to describe the relationships between the predicted finite rates of population increase (λ’) and the vital parameters, maximum age (Tmax), age at maturity (Tm), annual fecundity (f/Rc)), size at birth (Lb), size at maturity (Lm), and asymptotic length (L∞). Group (1) included species with slow growth rates (0.034 yr-1 < k < 0.103 yr-1) and extended longevity (26 yr < Tmax < 81 yr), e.g., shortfin mako Isurus oxyrinchus, dusky shark Carcharhinus obscurus, etc.; Group (2) included species with fast growth rates (0.103 yr-1 < k < 0.358 yr-1) and short longevity (9 yr < Tmax < 26 yr), e.g., starspotted smoothhound Mustelus manazo, gray smoothhound M. californicus, etc.; Group (3) included late maturing species (Lm/L∞ ≧ 0.75) with moderate longevity (Tmax < 29 yr), e.g., pelagic thresher Alopias pelagicus, sevengill shark Notorynchus cepedianus. The empirical equation for all data pooled was also developed. The λ’ values estimated by these empirical equations showed good agreement with those calculated using conventional demographic analysis. The predictability was further validated by an independent data set of three species. The empirical equations developed in this study not only reduce the uncertainties in estimation but also account for the difference in life history among groups. This method therefore provides an efficient and effective approach to the implementation of precautionary shark management measures.

Markov models and network analysis reveal sex‐specific differences in the space‐use of a coastal apex predator

Understanding the links between external variables such as habitat and interactions with conspecifics and animal space‐use is fundamental to developing effective management measures. In the marine realm, automated acoustic tracking has become a widely used method for monitoring the movement of free‐ranging animals, yet researchers generally lack robust methods for analysing the resulting spatial‐usage data.In this study, acoustic tracking data from male and female broadnose sevengill sharks Notorynchus cepedianus, collected in a system of coastal embayments in southeast Tasmania were analyzed to examine sex‐specific differences in the sharks’ coastal space‐use and test novel methods for the analysis of acoustic telemetry data.Sex‐specific space‐use of the broadnose sevengill shark from acoustic telemetry data was analysed in two ways: The recently proposed spatial network analysis of between‐receiver movements was employed to identify sex‐specific space‐use patterns. To include the full breadth of temporal information held in the data, movements between receivers were furthermore considered as transitions between states of a Markov chain, with the resulting transition probability matrix allowing the ranking of the relative importance of different parts of the study area.Both spatial network and Markov chain analysis revealed sex‐specific preferences of different sites within the study area. The identification of priority areas differed for the methods, due to the fact that in contrast to network analysis, our Markov chain approach preserves the chronological sequence of detections and accounts for both residency periods and movements.In addition to adding to our knowledge of the ecology of a globally distributed apex predator, this study presents a promising new step towards condensing the vast amounts of information collected with acoustic tracking technology into straightforward results which are directly applicable to the management and conservation of any species that meet the assumptions of our model.

Intraspecific differences in movement, dive behavior and vertical habitat preferences of a key marine apex predator

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 495:249-262 (2014) - DOI: https://doi.org/10.3354/meps10563 Intraspecific differences in movement, dive behavior and vertical habitat preferences of a key marine apex predator Kilian M. Stehfest1,2,*, Toby A. Patterson2, Adam Barnett1,3, Jayson M. Semmens1 1Fisheries, Aquaculture and Coasts Centre, Institute for Marine and Antarctic Studies (IMAS), University of Tasmania, Hobart, Tasmania 7001, Australia 2CSIRO Wealth from Oceans National Research Flagship, Hobart, Tasmania 7000, Australia 3School of Life and Environmental Sciences, Deakin University, Burwood, Victoria 3125, Australia *Corresponding author: kilian.stehfest@utas.edu.au ABSTRACT: Understanding the patterns of large-scale movements of highly mobile marine predators is essential to understanding the impacts of anthropogenic pressures on the animals and the ecosystems they frequent. The broadnose sevengill shark Notorynchus cepedianus is one of the most important apex predators in temperate coastal areas around the world, yet little is known of its seasonal large-scale movements. Five male and five female sevengill sharks were equipped with pop-up satellite archival tags (PSATs) in a coastal embayment in southern Tasmania, that collected depth and temperature data during winter, when the animals leave the coastal embayment, resulting in a dataset covering a total of 818 d. Animal tracks indicated that males moved northwards into warmer waters, whereas females remained in southern waters. Three of the females stayed in the Tasmanian coastal areas while the other two left, with one of them moving into deeper waters of up to 360 m depth at the southern edge of the Tasmanian shelf before returning to the Tasmanian coast. These sex-specific differences in large-scale movement could potentially lead to the differential exploitation of the sexes when the sharks leave the protected areas where they were tagged. Both males and females switched between diel vertical migration and reverse diel vertical migration over the course of their tracks and displayed oscillatory vertical movements, probably linked to foraging. These vertical movements persisted throughout the tracks, suggesting that sevengill sharks foraged continuously during their migration rather than switching between transiting and foraging modes. KEY WORDS: Broadnose sevengill shark · Notorynchus cepedianus · Pop-up satellite archival tag · Biotelemetry · Wavelet analysis · Sex-specific · Hexanchiformes Full text in pdf format PreviousNextCite this article as: Stehfest KM, Patterson TA, Barnett A, Semmens JM (2014) Intraspecific differences in movement, dive behavior and vertical habitat preferences of a key marine apex predator. Mar Ecol Prog Ser 495:249-262. https://doi.org/10.3354/meps10563 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 495. Online publication date: January 09, 2014 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2014 Inter-Research.

Sequential movement into coastal habitats and high spatial overlap of predator and prey suggest high predation pressure in protected areas

In theory, predators should attempt to match the distribution of their prey, and prey to avoid areas of high predation risk. However, there is a scarcity of empirical knowledge on predator and prey spatial use when both are moving freely in their natural environment. In the current study, we use information collated on a predators’ diet, its population structure, as well as predator and prey relative abundance, and track the movements of predator and prey simultaneously to compare habitat use and evaluate predation pressure. The study was conducted in elasmobranch protected areas of coastal Tasmania, Australia. The species considered were the broadnose sevengill shark Notorynchus cepedianus, the apex predator in the area, and five chondrichthyan prey species. Notorynchus cepedianus and its prey show similar seasonality in the use of these coastal areas: more abundant in warmer months and absent in winter. Predator and prey also showed high spatial overlap and similar habitat use patterns. These similar movement patterns of predator and prey combined with the additional ecological information (diet, population structure of predator, relative abundance of predator and prey) suggests that N. cepedianus move into coastal areas to exploit seasonally abundant prey. Also, while in protected areas, chondrichthyans are subjected to high predation pressure. Overall, results illustrate the value of simultaneously recording and integrating multiple types of information to explore predator–prey relationships and predation pressure.

Scale and pattern of broadnose sevengill shark Notorynchus cepedianus movement in estuarine embayments

The detailed movements of 32 acoustically tagged broadnose sevengill shark Notorynchus cepedianus were documented in and around north-east Pacific Ocean estuarine embayments from 2005 to 2007. Arrangements of passive acoustic receivers allowed analysis of movement at several spatial scales, with sex and size examined as possible factors influencing the pattern and timing of these movements. Notorynchus cepedianus exhibited a distinctly seasonal pattern of estuary use over three consecutive years, entering Willapa Bay in the spring, residing therein for extended periods of time during the summer and dispersing into nearshore coastal habitats and over the continental shelf during the autumn. Notorynchus cepedianus within Willapa Bay showed spatio-temporal patterns of segregation by size and sex, with males and small females using peripheral southern estuary channels early in the season before joining large females, who remained concentrated in central estuary channels for the entire season. Individuals displayed a high degree of fidelity not only to Willapa Bay (63% were documented returning over three consecutive seasons), but also to specific areas within the estuary, showing consistent patterns of site use from year to year. Cross-estuary movement was common during the summer, with most fish also moving into an adjacent estuarine embayment for some extent of time. Most winter and autumn coastal detections of N. cepedianus were made over the continental shelf near Oregon and Washington, U.S.A., but there were also examples of individuals moving into nearshore coastal habitats further south into California, suggesting the feasibility of broad-scale coastal movements to known birthing and nursery grounds for the species. These findings contribute to a better understanding of N. cepedianus movement ecology, which can be used to improve the holistic management of this highly mobile apex predator in regional ecosystems.

Intrapopulation variations in diet and habitat use in a marine apex predator, the broadnose sevengill shark Notorynchus cepedianus

Intrapopulation differences in diet and/or movement are important for understanding the role mobile predators play in different systems. However, ecological studies traditionally overlook individual differences. δ13C and δ15N were used in conjunction with diet and movement information to identify intrapopulation differences in diet and movement patterns of the apex predator broadnose sevengill shark Notorynchus cepedianus in southeast Tasmania. Sevengill samples from 3 inshore and 3 offshore sites were collected, and δ13C and δ15N compared between sites, sizes and sexes. Individuals captured offshore had lower δ15N than those captured inshore, indicating some degree of spatial segregation. Sevengills also had variable δ13C and δ15N within coastal habitats, suggesting intrapopulation differences in diet or migration schedules. In comparison to their main prey, most individuals had δ15N lower than expected for a top predator, also suggesting that they do not reside permanently in these areas, as their tissue was not in isotopic equilibrium with their known prey. This is in agreement with tracking data that showed seasonal use of coastal areas, with most animals leaving for the colder months but returning the following year. There was also a group of females with relatively high δ13C that suggests greater association to coastal habitats, again in agreement with tracking data, as some tagged females remained in the coastal areas over winter. Overall, together with diet and tracking information, results indicate that there are differences in movement and possibly diet in this sevengill population. This multimethods approach allowed a better understanding of sevengill ecology than the use of any one of the techniques alone.

Fine-Scale Movements of the Broadnose Sevengill Shark and Its Main Prey, the Gummy Shark

Information on the fine-scale movement of predators and their prey is important to interpret foraging behaviours and activity patterns. An understanding of these behaviours will help determine predator-prey relationships and their effects on community dynamics. For instance understanding a predator's movement behaviour may alter pre determined expectations of prey behaviour, as almost any aspect of the prey's decisions from foraging to mating can be influenced by the risk of predation. Acoustic telemetry was used to study the fine-scale movement patterns of the Broadnose Sevengill shark Notorynchus cepedianus and its main prey, the Gummy shark Mustelus antarcticus, in a coastal bay of southeast Tasmania. Notorynchus cepedianus displayed distinct diel differences in activity patterns. During the day they stayed close to the substrate (sea floor) and were frequently inactive. At night, however, their swimming behaviour continually oscillated through the water column from the substrate to near surface. In contrast, M. antarcticus remained close to the substrate for the entire diel cycle, and showed similar movement patterns for day and night. For both species, the possibility that movement is related to foraging behaviour is discussed. For M. antarcticus, movement may possibly be linked to a diet of predominantly slow benthic prey. On several occasions, N. cepedianus carried out a sequence of burst speed events (increased rates of movement) that could be related to chasing prey. All burst speed events during the day were across the substrate, while at night these occurred in the water column. Overall, diel differences in water column use, along with the presence of oscillatory behaviour and burst speed events suggest that N. cepedianus are nocturnal foragers, but may opportunistically attack prey they happen to encounter during the day.

Seasonal occurrence and population structure of the broadnose sevengill shark Notorynchus cepedianus in coastal habitats of south‐east Tasmania

Research longline sampling was conducted seasonally from December 2006 to February 2009 to investigate the occurrence and population structure of the broadnose sevengill shark Notorynchus cepedianus in coastal areas of south-east Tasmania. Notorynchus cepedianus showed a consistent temporal trend in seasonal occurrence in Norfolk Bay characterized by high abundances in summer to near absence in winter. This pattern was less pronounced in the Derwent Estuary, where fish were still caught during winter. The absence of smaller total length (L(T) ) classes (<80 cm) from the catches suggests that N. cepedianus are not using these coastal habitats as nursery areas. Of the 457 individuals tagged, 68 (15%) were recaptured. Time at liberty ranged from 6 days to almost 4 years and all but one of the recaptures were caught in its original tagging location, suggesting site fidelity. The large number of N. cepedianus in these coastal systems over summer indicates that these areas are important habitats for this species and that N. cepedianus may have a significant influence on community dynamics through both direct and indirect predator-prey interactions.

Predator–prey relationships and foraging ecology of a marine apex predator with a wide temperate distribution

The diet of the broadnose sevengill shark Notorynchus cepedianus was investigated over 3 years from 2 coastal locations in south-east Tasmania: the Derwent Estuary and Norfolk Bay. In general, individuals from both locations consumed the same broad dietary categories (sharks, batoids, teleosts and mammals). However, within these categories, species composition differed. Variations in chondrichthyan prey consumed matched estimations of prey abundance: Mustelus antarcticus was the primary prey in Norfolk Bay, where it was also the most abundant prey species; similarly, Squalus acanthias was an important prey and the most abundant in the Derwent Estuary. A decline in the catch rates of N. cepedianus and elasmobranch prey, in particular M. antarcticus over 3 years coincided with declines in dietary occurrence of M. antarcticus. Also, N. cepedianus and M. antarcticus abundances were both higher in Norfolk Bay than the Derwent Estuary. The correla- tion with diet and estimations of predator and prey relative abundance suggests N. cepedianus may move into coastal areas to exploit regular seasonal abundant resources, but they can also be versatile opportunistic predators that exploit a temporarily abundant resource.

Incorporating heterogeneity into growth analyses of wild and captive broadnose sevengill sharks Notorynchus cepedianus

AB Aquatic Biology Contact the journal Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections AB 9:131-138 (2010) - DOI: https://doi.org/10.3354/ab00246 Incorporating heterogeneity into growth analyses of wild and captive broadnose sevengill sharks Notorynchus cepedianus J. Matias Braccini1,2,*, Vladimir S. Troynikov3, Terence I. Walker2,3, Henry F. Mollet4,5, David A. Ebert5,6, Adam Barnett7,8, Nicholas Kirby9 1Fisheries Centre, University of British Columbia, Vancouver, British Columbia V6T1Z4, Canada 2Department of Zoology, University of Melbourne, Parkville, Victoria 3052, Australia 3Marine and Freshwater Fisheries Research Institute, Fisheries Victoria, Department of Primary Industries, PO Box 114, Queenscliff, Victoria 3225, Australia 4Monterey Bay Aquarium, 886 Cannery Row, Monterey, California 93940, USA 5Pacific Shark Research Center, Moss Landing Marine Laboratories, 8272 Moss Landing Road, Moss Landing, California 95039, USA 6South African Institute for Aquatic Biodiversity, Private Bag 1015, Grahamstown 6140, South Africa 7TAFI Marine Research Laboratories, Private Bag 49, Hobart, Tasmania 7001, Australia 8CSIRO Marine and Atmospheric Research, PO Box 1538, Hobart, Tasmania 7001, Australia 9Curatorial Department, Melbourne Aquarium, King St., Melbourne, Victoria 3000, Australia *Email: m.braccini@fisheries.ubc.ca ABSTRACT: Growth estimates for shark species are mostly derived from length-at-age data, where age information is commonly obtained from hard structures such as vertebrae and dorsal-fin spines. Unfortunately, hard structures cannot be used for estimating the age of many shark species, particularly those occurring in deep water or belonging to ancient groups. Alternative methods are therefore required for the estimation of growth for these shark groups. The broadnose sevengill shark Notorynchus cepedianus has very poorly calcified vertebrae that cannot be used for age and growth estimations. Three stochastic versions of the von Bertalanffy-Fabens growth model with random parameter k were fitted to length-increment data of captive and of wild tagged and recaptured N. cepedianus from southeastern Australia, California and southern Africa. The model based on a gamma distributed parameter k provided the best fit to the data. Captive females and wild females showed the highest and lowest values of mathematical expectation E[k], whereas wild males and wild females showed the lowest and highest values of mean maximum length L∞, respectively. For a time interval of 1 yr, captive females had the highest length increment, whereas wild females had the lowest length increment. Our approach allows accounting for the natural heterogeneity of growth in the estimation of the growth parameters of N. cepedianus, which has not been done previously for captive and wild sharks. This the first study to provide a representative set of growth parameters for male and female N. cepedianus, which is crucial information for the modelling of the population dynamics of this top predator. KEY WORDS: Growth heterogeneity · Notorynchus cepedianus · Stochastic model · Phenotypic plasticity Full text in pdf format PreviousNextCite this article as: Braccini JM, Troynikov VS, Walker TI, Mollet HF, Ebert DA, Barnett A, Kirby N (2010) Incorporating heterogeneity into growth analyses of wild and captive broadnose sevengill sharks Notorynchus cepedianus. Aquat Biol 9:131-138. https://doi.org/10.3354/ab00246 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in AB Vol. 9, No. 2. Online publication date: April 27, 2010 Print ISSN: 1864-7782; Online ISSN: 1864-7790 Copyright © 2010 Inter-Research.