Eating catch of the day: the diet of porbeagle shark Lamna nasus (Bonnaterre 1788) based on stomach content analysis, and the interaction with trawl fisheries in the south‐western Atlantic (52° S–56° S)

Abstract

This work examined the diet of the porbeagle shark Lamna nasus in the south‐west Atlantic Ocean (SWAO, Argentina, 52° S–56° S) by analysing the stomach content information obtained by scientific observers who sampled specimens captured as by‐catch on‐board commercial fishing vessels from 2010 to 2020. A total of 148 fishing sites were analysed, in which the estimated catch was composed mainly of hoki Macruronus magellanicus (56.00%) and southern blue whiting Micromesistius australis (33.13%). From 413 porbeagle sharks sampled (292 females and 121 males) ranging from 71 to 241 cm total length (LT) (mean: 179.76 ± 26.74 cm), 310 (75.06%) contained food in the stomachs. The forage fish were mainly hoki M. magellanicus (23.53%) and southern blue whiting M. australis (19.05%), followed by the Patagonian sprat Sprattus fuegensis (4.48%) and nototheniids (1.4%). Cephalopods and crustaceans accounted for 10% of the diet. The estimated trophic level was 4.35. Generalized linear models revealed that the consumption of hoki M. magellanicus and southern blue whiting M. australis increased with the LT of the porbeagle shark. Moreover, smaller porbeagle sharks preyed upon both small and large teleost fish, whereas larger porbeagle sharks predated exclusively upon large fish. The diet of porbeagle shark involved interactions with fisheries as it fed upon the fish species that constituted the main catch in the analysed fishing sites, as well as the main catches of the austral trawl fisheries. The ecological role of porbeagle shark observed in the SWAO exposed implications for fisheries management from a multispecies perspective.

Determination of Mercury, Methylmercury and Selenium Concentrations in Elasmobranch Meat: Fish Consumption Safety

“…More specifically, blue sharks with epipelagic feeding habits, a diet dominated especially by cephalopods [ 43 ], exhibited lower THg accumulation than other shark species, that because of their relationship with seafloor sediments showed more significant levels (e.g., picked dogfish: 1.25 μg g −1 w.w., smooth hound: 1.03 μg g −1 w.w.). Porbeagle, also an epipelagic shark species but with a strictly carnivore feeding pattern [ 44 ], presented higher values than blue sharks. These findings further support the aforesaid and are in accordance with previous studies on Hg accumulation in fish, confirming the well-known fact that Hg concentration is heavily controlled by feeding habits and habitat [ 45 , 46 ].…”

New insights into the reproduction and migration of the porbeagle shark Lamna nasus (Bonnaterre 1788) in the Southwest Atlantic Ocean

“…In addition to competition for access to food resources, females in the austral Atlantic zone have access to prey with high-fat content, such as hoki M. magellanicus and southern blue whiting M. australis (Massa et al, 2018). Thus, the identification of the austral zone of the Southwest Atlantic Ocean as a critical feeding area (Belleggia et al, 2021) suggests that the costs associated with migrating to colder waters would outweigh the investment in reproduction (ovarian and embryonic development) due to the access to prey with high-energy content and the low cost of searching for optimal foraging areas (without interspecific competition), allowing for the maximization of intake and assimilation necessary to maintain endothermy (Bernal et al, 2012). F I G U R E 6 Monthly variation in the mean fork length (L F , cm) of porbeagle Lamna nasus embryos caught in the austral region of the southwestern Atlantic Ocean.…”

“…More recently, using traditional stomach content analysis of porbeagles caught by trawl fisheries (freezers, factories, and ice-chilled vessels), Belleggia et al (2021) found that these sharks feed on hoki (Macruronus magellanicus) and southern blue whiting (Micromesistius australis) and additionally that the low percentage of empty stomachs would suggest that this region is a critical feeding area. In addition to these puzzle pieces, there is a lack of reproductive knowledge regarding maturity, litter size, and reproductive cycle.…”

First Use of Free-Diving Photo-Identification of Porbeagle Shark (Lamna nasus) off the Brittany Coast, France

“…Porbeagle sharks can reach a large body size and perform long seasonal movements [2,3]. Lamna nasus mainly feeds on small pelagic fishes and cephalopods [4] although its feeding behavior is considered opportunistic because its diet varies among regions [5,6]. Since the 1930s, porbeagle sharks were subject to commercial fisheries that resulted in a severe decrease in their North Atlantic populations [7,8].…”