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Nasus syphoner comp3/11/2023 The model with the best predictive capability used for the spatial delineation of hotspots for L. 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 spatio-temporal, operational, environmental and prey availability variables. 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. Using on-board observer data, we have demonstrated that L. The main objectives of this study were quantify and model the spatio-temporal trend of bycatch for porbeagle shark ( Lamna nasus ) in the Argentinean surimi trawl fleet to identify hotspots in the Southwestern Atlantic Ocean. Bycatch monitoring is an important issue for the development of conservation and management plans for these species. Waste products of yolk digestion accumulate steadily in the spiral valve throughout gestation, and the liver reaches its maximum size in near-term embryos as excess energy from yolk digestion is stored for postnatal use.įisheries bycatch can severely affect the population status of species with low resilience such as sharks. The weight of yolk in the stomach peaks at 30-42 cm FL, and accounts for up to 81% of total body weight. Small embryos have fang-like functional teeth that tear open egg capsules to release the contained ova. Embryos are nourished by oophagy, and develop a grossly distended abdomen as their "yolk stomach" fills with ova. The gestation period appears to be about 8-9 months, but there is considerable variability in embryo length at any one time, suggesting an extended mating period. Embryos grow about 7 cm per month, and are born at 58-67 cm FL. This finding contrasts with data for North Atlantic porbeagles which give birth in spring-summer. Litter size is usually four embryos and parturition probably peaks in June-July (winter). Juveniles grow linearly and rapidly (16-20 cm per year), reaching 110-125 cm FL in three years. Most sharks were juveniles less than 150 cm fork length (FL), and length-frequency distributions showed 3-5 modal peaks that we interpret as age classes. Information on reproduction, embryonic development, and size and sex composition was collected by scientific observers from New Zealand and Australian waters, and supplemented with data from other sources. Porbeagle sharks, Lamna nasus, are caught in large numbers as bycatch in tuna longline fisheries in the southwest Pacific Ocean.
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