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Malcolm P. Francis - One of the best experts on this subject based on the ideXlab platform.
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life in the open ocean seasonal migration and diel diving behaviour of southern hemisphere porbeagle sharks Lamna nasus
Marine Biology, 2015Co-Authors: Malcolm P. Francis, John C Holdsworth, Barbara A BlockAbstract:A wide range of pelagic predators survive in the open ocean, yet little is known about how they use that environment. Much of the current information on these species comes from studies in shelf waters, and it is not clear how representative the results are of their oceanic lifestyle. We used pop-up satellite tags to explore the horizontal and vertical use of the open ocean by porbeagle sharks (Lamna nasus) in the south-west Pacific Ocean and to identify possible mitigation measures to reduce their bycatch in tuna longline fisheries. Ten porbeagle sharks were tracked in waters around New Zealand for 72–300 days (median 221 days). Sharks made horizontal movements of hundreds to thousands of kilometres, with a maximum estimated track length of almost 10,000 km. Mature females made seasonal latitudinal migrations from ~46–48°S in summer to ~35–38°S during winter–spring, where they are hypothesised to give birth to pups. Porbeagle sharks exhibited diel vertical migration, diving deeper during the day than at night. Dives generally began at dawn and finished at dusk and lasted 11–15 h depending on day length. Porbeagles feed mainly on mesopelagic fish and squid and appear to forage in the vertically migrating deep scattering layer. All sharks dived to at least 600 m with a maximum recorded depth of 1024 m. During the day, most of their time was spent at depths of 200–600 m in the open ocean. Porbeagle shark bycatch could be substantially reduced by limiting longline fishing to daylight hours when they are too deep to be caught. However, longliners currently set mainly at night to avoid seabird bycatch, which would increase unless other mitigation measures were implemented to protect them. A review of factors affecting the bycatch of various species, and the impact of mitigation measures on catches of target species, is required to identify an appropriate suite of management measures.
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Ontogenetic development of teeth in Lamna nasus (Bonnaterre, 1758) (Chondrichthyes: Lamnidae) and its implications for the study of fossil shark teeth
Journal of Vertebrate Paleontology, 2007Co-Authors: Robert W. Purdy, Malcolm P. FrancisAbstract:Abstract Tooth development is traced in dentitions from 169 embryonic Lamna nasus (96–670 mm fork length [FL]), and 8 juvenile to adult L. nasus (67–300 cm FL). The teeth of these dentitions vary significantly in the attitudes and shapes of their crowns, and the forms of their roots. At some stages of their ontogeny they bear characters of carcharhiniform and alopiid shark teeth, and they may also bear ornamentation on their crowns. In early embryos, the teeth are conical with funnel-shaped roots and resemble skate dermal thorns, Raja spp. Tooth shape changes abruptly at about 350 mm FL to a late embryonic dentition, with very elongate lower anterior teeth, as in Pseudocarcharias. Adult teeth also exhibit significant morphological variation, and exhibit some characters that occur also in primitive neoselachians, such as Synechodus and Paraorthacodus. The importance of these tooth ontogenetic and morphological variations for the study of fossil shark teeth is presented, and a generic diagnosis is offered f...
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Age under-estimation in New Zealand porbeagle sharks (Lamna nasus): is there an upper limit to ages that can be determined from shark vertebrae?
Marine and Freshwater Research, 2007Co-Authors: Malcolm P. Francis, Steven E. Campana, Cynthia M. JonesAbstract:Annual deposition of growth bands in vertebrae has been validated for many shark species, and is now widely regarded as the norm. However, vertebrae are part of the shark's axial skeleton, and band deposition may stop in old sharks when somatic growth ceases. We aged vertebral sections from New Zealand porbeagle sharks (Lamna nasus) under reflected white light and using X-radiographs. Bomb radiocarbon assays supported vertebral age estimates up to ∼20 years, but not at older ages. The results suggest that older porbeagles were under-aged by as much as 50% from vertebral band counts, presumably because band width declined to a point where it became unresolvable. This has important implications for growth studies on other long-lived sharks. Estimated ages at sexual maturity were 8-11 years for males and 15-18 years for females, and longevity may be ∼65 years. New Zealand and North Atlantic porbeagles differ in these parameters, and in length at maturity and maximum length, suggesting genetic isolation of the two populations.
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Length at maturity in three pelagic sharks (Lamna nasus, Isurus oxyrinchus and Prionace glauca) from New Zealand
2004Co-Authors: Malcolm P. Francis, Clinton DuffyAbstract:Reproductive data collected from porbeagle, shortfin mako, and blue sharks caught around New Zealand were used to estimate the median length at maturity. Data on clasper development, presence or absence of spermatophores or spermatozeugmata, uterus width, and pregnancy were collected by observers aboard tuna longline vessels. Direct maturity estimates were made for smaller numbers of sharks sampled at recreational fishing competitions. Some data sets were sparse, particularly over the vital maturation length range, but the availability of multiple indicators of maturity made it possible to develop estimates for both sexes of all three species. Porbeagle shark males matured at 140–150 cm fork length and females at about 170–180 cm. New Zealand porbeagles therefore mature at shorter lengths than they do in the North Atlantic Ocean. Shortfin mako males matured at 180–185 cm and females at 275 –285 cm. Blue shark males matured at about 190 –195 cm and females at 170–190 cm; however these estimates were hampered by small sample sizes, difficulty obtaining representative samples from a population segregated by sex and maturity stage, and maturation that occurred over a wide length range. It is not yet clear whether regional differences in median maturity exist for shortfin mako and
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Re-identification of a lamnid shark embryo
2002Co-Authors: Henry F. Mollet, Antonio D. Testi, Via A. Solari, Leonard J. V. Compagno, Malcolm P. FrancisAbstract:nant female lamnid shark was caught that the morphometric arguments in the Strait of Messina, Mediterra- used by Sanzo (1912) did not rule out nean Sea. She was reported to contain the shortfin mako (Isurus oxyrinchus 25–30 embryos, one of which was Rafinesque, 1810) but that the high saved and taken to the local Marine fecundity of 25–30 was more consis-Institute, where it was subsequently tent with C. carcharias than with I. examined by Sanzo (1912). The male oxyrinchus or a Lamna species. A lack embryo measured 36.1 cm total length of information on lamnid reproduction (TL), weighed 800 g, and had a greatly and the misidentification of a likely distended abdomen, as is typical of Galeorhinus galeus (Stevens2) with a embryos of oophagous lamnoid sharks litter of 30 as Lamna by Neill (1811), (Gilmore, 1993). The mother and the may have led Sanzo (1912) to consider remaining embryos were not saved. the porbeagle Lamna nasus (Bon-Because Sanzo was not able to exam- naterre, 1788) instead of the shortfin ine the adult female from which the mako as the most likely alternativ
Steven E. Campana - One of the best experts on this subject based on the ideXlab platform.
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Transboundary movements, unmonitored fishing mortality, and ineffective international fisheries management pose risks for pelagic sharks in the Northwest Atlantic
Canadian Journal of Fisheries and Aquatic Sciences, 2016Co-Authors: Steven E. CampanaAbstract:The shortfin mako (Isurus oxyrinchus), porbeagle (Lamna nasus), and blue shark (Prionace glauca) are three frequently caught shark species in the northwestern Atlantic Ocean. Satellite tagging studies show that all three species range widely across many national boundaries but spend up to 92% of their time on the high seas, where they are largely unregulated and unmonitored. All are caught in large numbers by swordfish and tuna fishing fleets from a large number of nations, usually unintentionally, and all are unproductive by fish standards, which makes them particularly sensitive to fishing pressure. Landing statistics that grossly underrepresent actual catches, unreported discards that often exceed landings, and high discard mortality rates are threats to the populations and roadblocks to useful population monitoring. The influence of these threats is greatly magnified by inattention and ineffective management from the responsible management agency, the International Commission for the Conservation of A...
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Subtropical pupping ground for a cold-water shark
Canadian Journal of Fisheries and Aquatic Sciences, 2010Co-Authors: Steven E. Campana, Warren Joyce, Mark FowlerAbstract:Porbeagle sharks (Lamna nasus) are large pelagic sharks apparently restricted to the cold temperate waters of the northern and southern hemispheres. Despite considerable knowledge of their biology, their pupping (birthing) grounds have never been identified. Pop-up archival transmission tags applied to 21 sharks off eastern Canada indicated that males and immature sharks of both sexes remained primarily on the continental shelf for periods of up to 348 days after tagging. However, mature female porbeagles migrated up to 2356 km through the winter, at depths down to 1360 m beneath the Gulf Stream, to a subtropical pupping ground in the Sargasso Sea. In addition to this pupping ground being well south of their documented range, the placement of such a key life history stage in international, largely unregulated waters poses problems for the conservation and management of a species that is largely fished in Canadian waters.
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POPULATION DYNAMICS OF PORBEAGLE IN THE NORTHWEST ATLANTIC, WITH AN ASSESSMENT OF STATUS TO 2009 AND PROJECTIONS FOR RECOVERY
2010Co-Authors: Steven E. Campana, Mark Fowler, A. Jamie, F. Gibson, Anna Dorey, Warren JoyceAbstract:SUMMARY A forward projecting, age- and sex-structured life history model, fit to catch-at-length and catch per unit effort data to the end of 2008, was used to evaluate porbeagle (Lamna nasus) population dynamics in the northwest Atlantic. Four variants of the population model were evaluated, all of which differ in their assumed productivity. The total population size is currently estimated to be about 22% to 27% of its size in 1961 and about 95% to 103% its size in 2001. The estimated number of mature females in 2009 is in the range of 11,000 to 14,000 individuals, or 12% to 16% of its 1961 level and 83% to 103% of its 2001 value. All population models predict recovery to SSN20% before 2014 if the human-induced mortality rate is kept at or below 4% of the vulnerable biomass. Under the low productivity model, recovery to SSNMSY is predicted to take over 100 years at exploitation rates of 4% of the vulnerable biomass. All models except that with the lowest productivity predict that keeping the rate of human-induced mortality to less than 4% of the vulnerable biomass would be precautionary and would keep expected recovery times to SSNMSY on the order of decades. RESUME
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Changes in baseline growth and maturation parameters of Northwest Atlantic porbeagle, Lamna nasus, following heavy exploitation
Canadian Journal of Fisheries and Aquatic Sciences, 2007Co-Authors: Rachel M. Cassoff, Steven E. Campana, Sigmund MyklevollAbstract:We tested for density-dependent changes in growth and maturation of Northwest Atlantic porbeagle (Lamna nasus) after the population declined by 75%-80% from fishing. Vertebrae and reproductive data collected from the virgin (1961-1966) and exploited (1993-2004) populations were analysed to test for differences in growth rate and age and length at maturity between the time periods. We detected significant differences between reparameterized von Bertalanffy growth models for each period, using likelihood ratio tests. Beyond an age of 7 years, mean length at age was greater during 1993-2004 than during 1961-1966. Between 1961-1963 and 1999-2001, length at maturity de- creased in males (from 179 to 174 cm curved fork length (CFL)) and was invariant in females (216 cm CFL), whereas age at maturity declined in both males (from 8 to 7 years) and females (from 19 to 14 years). An analysis of por- beagle temperature associations indicated that sharks occupied comparable temperature conditions during the mid-1960s and 1990s, ruling out the possibility of temperature-induced growth changes. The observed increase in growth rate and decrease in age at maturity following exploitation support the hypothesis of a compensatory density-dependent growth response.
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Age under-estimation in New Zealand porbeagle sharks (Lamna nasus): is there an upper limit to ages that can be determined from shark vertebrae?
Marine and Freshwater Research, 2007Co-Authors: Malcolm P. Francis, Steven E. Campana, Cynthia M. JonesAbstract:Annual deposition of growth bands in vertebrae has been validated for many shark species, and is now widely regarded as the norm. However, vertebrae are part of the shark's axial skeleton, and band deposition may stop in old sharks when somatic growth ceases. We aged vertebral sections from New Zealand porbeagle sharks (Lamna nasus) under reflected white light and using X-radiographs. Bomb radiocarbon assays supported vertebral age estimates up to ∼20 years, but not at older ages. The results suggest that older porbeagles were under-aged by as much as 50% from vertebral band counts, presumably because band width declined to a point where it became unresolvable. This has important implications for growth studies on other long-lived sharks. Estimated ages at sexual maturity were 8-11 years for males and 15-18 years for females, and longevity may be ∼65 years. New Zealand and North Atlantic porbeagles differ in these parameters, and in length at maturity and maximum length, suggesting genetic isolation of the two populations.
Juan A. Waessle - One of the best experts on this subject based on the ideXlab platform.
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hotspots for porbeagle shark Lamna nasus bycatch in the southwestern atlantic 51 s 57 s
Canadian Journal of Fisheries and Aquatic Sciences, 2017Co-Authors: Federico Cortés, Juan A. WaessleAbstract:Fisheries bycatch can severely affect the population status of species with low resilience such as sharks. Bycatch monitoring is an important issue for the development of conservation and management plans for these species. The main objectives of this study were to quantify and model the spatiotemporal trend of bycatch for porbeagle shark (Lamna nasus) in the Argentinean surimi trawl fleet to identify hotspots in the southwestern Atlantic Ocean. Using onboard observer data, we have demonstrated that L. nasus was usually caught as bycatch by the surimi trawl fleet operating in the southern limits of the southwestern Atlantic (51°S–57°S), representing an important part of the reported catch for the Atlantic Ocean. Delta and Tweedie models indicated that bycatch had a relatively stable trend, was concentrated in a limited region of the study area, and was associated with spatiotemporal, operational, environmental, and prey availability variables. The model with the best predictive capability used for the spa...
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Hotspots for porbeagle shark (Lamna nasus) bycatch in the southwestern Atlantic (51°S–57°S)
Canadian Journal of Fisheries and Aquatic Sciences, 2017Co-Authors: Federico Cortés, Juan A. WaessleAbstract:Fisheries bycatch can severely affect the population status of species with low resilience such as sharks. Bycatch monitoring is an important issue for the development of conservation and management plans for these species. The main objectives of this study were to quantify and model the spatiotemporal trend of bycatch for porbeagle shark (Lamna nasus) in the Argentinean surimi trawl fleet to identify hotspots in the southwestern Atlantic Ocean. Using onboard observer data, we have demonstrated that L. nasus was usually caught as bycatch by the surimi trawl fleet operating in the southern limits of the southwestern Atlantic (51°S–57°S), representing an important part of the reported catch for the Atlantic Ocean. Delta and Tweedie models indicated that bycatch had a relatively stable trend, was concentrated in a limited region of the study area, and was associated with spatiotemporal, operational, environmental, and prey availability variables. The model with the best predictive capability used for the spa...
Lisa J. Natanson - One of the best experts on this subject based on the ideXlab platform.
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Age and growth of sharks: do vertebral band pairs record age?
Marine and Freshwater Research, 2018Co-Authors: Lisa J. Natanson, Gregory B. Skomal, Sarah L. Hoffmann, Marianne E. Porter, Kenneth J. Goldman, David SerraAbstract:Inaccurate age estimates can have severe consequences in the management of elasmobranchs. Numerous studies in shark age validation have demonstrated a disconnect between band pair counts and age, resulting in age underestimation, particularly in older individuals. To investigate the relationship between band pairs, vertebral shape and growth, we quantified intracolumn differences in centrum morphology (size and structure) and band pair counts in seven shark species: Squatina dumeril, Carcharodon carcharias, Lamna nasus, Isurus oxyrinchus, Alopias vulpinus, Prionace glauca and Carcharhinus obscurus. In all species examined, band pair deposition was closely related to body girth and the structural properties of the cartilaginous skeleton, relative to maximum size, and body type. These results have strong implications for accurately assessing age for fisheries management of these species.
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SUMMARY
2015Co-Authors: Nancy E. Kohler, Lisa J. Natanson, Patricia A Turner, John J Hoey, Ruth BriggsAbstract:oxyrinchus), and porbeagle (Lamna nasus). The extent of the tagging effort, areas of release and recapture, sources of tags and recaptures, capture methods, and movements of tagged sharks are reported by species. Summary information includes number of males and females tagged and recaptured, overall recapture rate, maximum observed speed, distance traveled, and time at liberty. In order to examine regional trends in size and maturation categories, the North Atlantic Ocean is divided into geographical areas. General migration patterns and stock identity by species are summarized and discussed. RÉSUM
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Application of bomb radiocarbon chronologies to shortfin mako (Isurus oxyrinchus) age validation
Environmental Biology of Fishes, 2006Co-Authors: Daniele Ardizzone, Lisa J. Natanson, Gregor M. Cailliet, Allen H. Andrews, Lisa A. Kerr, Thomas A. BrownAbstract:Age estimation is an issue for the shortfin mako, Isurus oxyrinchus , because of disagreement on vertebral band-pair deposition periodicity. In the 1950s–1960s, thermonuclear testing released large amounts of radiocarbon into the atmosphere, which diffused into the ocean through gas exchange. This influx created a time-specific marker that can be used in age validation. Annual band-pair deposition in the porbeagle, Lamna nasus , was validated in a previous study and indicated preliminary annual deposition in the shortfin mako, using four samples from one vertebra. In the present study, age estimates from 54 shortfin mako vertebrae collected in 1950–1984 ranged 1–31 years. Ageing error between readers was consistent, with 76% of the estimates ranging within 2 years. Twenty-one Δ^14C values from eight shortfin mako vertebrae (collected in the western North Atlantic in 1963–1984) ranged −154.8‰ to 86.8‰. The resulting conformity with the Δ^14C timeline for the porbeagle supported annual band-pair deposition in vertebrae of the shortfin mako.
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Bomb dating and age determination of large pelagic sharks
Canadian Journal of Fisheries and Aquatic Sciences, 2002Co-Authors: Steven E. Campana, Lisa J. Natanson, Sigmund MyklevollAbstract:Despite their notoriety and role as apex predators, the longevity of large pelagic sharks such as the por - beagle (Lamna nasus) and shortfin mako (Isurus oxyrinchus) is unknown. Vertebral growth bands provide an accurate indicator of age in young porbeagle, but age validation has never been reported for any large shark species past the age of sexual maturity. Here, we report the first application of bomb radiocarbon as an age validation method for long- lived sharks based on date-specific incorporation of radiocarbon into vertebral growth bands. Our results indicate that porbeagle vertebrae recorded and preserved a bomb radiocarbon pulse in growth bands formed during the 1960s. Through comparison of radiocarbon assays in young, known-age porbeagle collected in the 1960s with the correspond- ing growth bands in old porbeagle collected later, we confirm the validity of porbeagle vertebral growth band counts as accurate annual age indicators to an age of at least 26 years. The radiocarbon signatures of porbeagle vertebral growth bands appear to be temporally and metabolically stable and derived mainly from the radiocarbon content of their prey. Preliminary radiocarbon assays of shortfin mako vertebrae suggest that current methods for determining shortfin mako age are incorrect. Resume : Malgre leur notoriete et leur role de predateurs superieurs, les grands requins pelagiques, tels que les requins taupes communs (Lamna nasus) et les requins taupes bleus (Isurus oxyrinchus), ont une duree de vie encore inconnue. Les bandes de croissance des vertebres sont des indicateurs precis de l'âge chez de jeunes requins taupes communs, mais aucune validation de l'âge n'a ete faite chez les grands requins au dela de l'âge de la maturite sexuelle. On trou- vera ici une premiere utilisation du carbone radioactif produit par les essais nucleaires pour valider l'âge des requins a grande longevite, par l'analyse de l'incorporation du carbone radioactif dans les bandes de croissance de leurs vertebres a des dates precises. Les vertebres des requins taupes communs ont enregistre et conserve une signature de carbone ra- dioactif provenant des essais nucleaires faits dans les annees 1960. La comparaison des analyses de carbone radioactif faites chez de jeunes requins taupes communs d'âge connu et recoltes dans les annees 1960 avec celles des bandes de croissance chez de vieux requins captures plus tard confirme la validite de l'utilisation des bandes de croissance des vertebres pour determiner avec precision l'âge au moins jusqu'a 26 ans. Les signatures de carbone radioactif dans les bandes de croissance des vertebres des requins taupes communs semblent etre stables dans le temps et peu affectees par le metabolisme; elles sont derivees en majeure partie du contenu en carbone radioactif de leurs proies. Les analyses preliminaires de carbone radioactif dans les vertebres des requins taupes bleus semblent indiquer que les methodes cou - rantes de determination de l'âge chez ce poisson sont erronees.
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Validated age and growth of the porbeagle shark (Lamna nasus
2002Co-Authors: Lisa J. Natanson, Joseph J. Mello, Steven E. CampanaAbstract:Growth parameters were estimated for porbeagle shark (Lamna nasus) in the northwest Atlantic Ocean on the basis of vertebral annuli. A total of 578 vertebrae was analyzed. Annuli were validated up to an age of 11 years by using vertebrae from recaptured oxytetracycline-injected and known age sharks. Males and females grew at similar rates until the size of male sexual maturity, after which the relative growth of the males declined. The growth rate of the females declined in a similar manner at the onset of maturity. Growth curves were consistent with those derived from tag/recapture analyses (GROTAG) of 76 recaptured fish, and with length-frequency methods using measurements from 13,589 individuals. Von Bertalanffy growth curve parameters (combined sexes) were: L ¥ = 289.4 cm fork length, K = 0.07 and t0 =-6.06. Maximum age, based on vertebral band pair counts, was 25 and 24 years for males and females, respectively. Longevity calculations, however, indicated a maximum age of 45 to 46 years in an unfished population. RÉSUM
Federico Cortés - One of the best experts on this subject based on the ideXlab platform.
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hotspots for porbeagle shark Lamna nasus bycatch in the southwestern atlantic 51 s 57 s
Canadian Journal of Fisheries and Aquatic Sciences, 2017Co-Authors: Federico Cortés, Juan A. WaessleAbstract:Fisheries bycatch can severely affect the population status of species with low resilience such as sharks. Bycatch monitoring is an important issue for the development of conservation and management plans for these species. The main objectives of this study were to quantify and model the spatiotemporal trend of bycatch for porbeagle shark (Lamna nasus) in the Argentinean surimi trawl fleet to identify hotspots in the southwestern Atlantic Ocean. Using onboard observer data, we have demonstrated that L. nasus was usually caught as bycatch by the surimi trawl fleet operating in the southern limits of the southwestern Atlantic (51°S–57°S), representing an important part of the reported catch for the Atlantic Ocean. Delta and Tweedie models indicated that bycatch had a relatively stable trend, was concentrated in a limited region of the study area, and was associated with spatiotemporal, operational, environmental, and prey availability variables. The model with the best predictive capability used for the spa...
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Hotspots for porbeagle shark (Lamna nasus) bycatch in the southwestern Atlantic (51°S–57°S)
Canadian Journal of Fisheries and Aquatic Sciences, 2017Co-Authors: Federico Cortés, Juan A. WaessleAbstract:Fisheries bycatch can severely affect the population status of species with low resilience such as sharks. Bycatch monitoring is an important issue for the development of conservation and management plans for these species. The main objectives of this study were to quantify and model the spatiotemporal trend of bycatch for porbeagle shark (Lamna nasus) in the Argentinean surimi trawl fleet to identify hotspots in the southwestern Atlantic Ocean. Using onboard observer data, we have demonstrated that L. nasus was usually caught as bycatch by the surimi trawl fleet operating in the southern limits of the southwestern Atlantic (51°S–57°S), representing an important part of the reported catch for the Atlantic Ocean. Delta and Tweedie models indicated that bycatch had a relatively stable trend, was concentrated in a limited region of the study area, and was associated with spatiotemporal, operational, environmental, and prey availability variables. The model with the best predictive capability used for the spa...
