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The broadnose sevengill shark, Notorynchus cepedianus (Péron, 1807), is a large marine top predator in temperate coastal ecosystems. Some aspects of its life history have been determined, but its growth pattern is yet to be fully understood. The authors used a multi‐modelling approach and a sensitivity test to estimate growth parameters from young‐of‐year (YOY) length data collected off San Antonio Cape (SAC), Argentina, a critical habitat in the Southwest Atlantic Coastal Zone (SACZ). The best selected model, a sex‐combined logistic growth model, estimated an asymptotic length (L∞) of 92.58 cm TL (95% C.I.: 86.48–105.89 cm), a growth coefficient (K) of 0.006818 days −1 (95% C.I.: 0.004948–0.008777) and a size at birth (L0) of 40.73 cm. The predicted annual growth (i.e., L1 –L0) was 43.2 cm TL. Males had smaller L0, higher K and achieved larger sizes after 1 year. The YOY in SAC attained a larger L1 and grew faster than their Australian and South African wild counterparts. The consistent year‐round presence of YOY in the SAC highlights the importance of this area as a pupping ground and potential nursery for N. cepedianus; this has direct implications for the allocation of research and management effort for the conservation of this species in the Southwest Atlantic. [ABSTRACT FROM AUTHOR]

Knowledge 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. [ABSTRACT FROM AUTHOR]

The San Matías Gulf (SMG) is a semi-enclosed ecosystem where the Argentine hake Merluccius hubbsi (AH) has been the main fishery resource since 1971. During the 20th century the South American sea lion Otaria flavescens (SASL) population was severely reduced in this ecosystem due an intense hunting, but in the 1970's conservation was promoted and hunting was banned. As a consequence SASL have been slowly recovering, until the 1990's when rapidly rebuilt their populations. Recent studies indicate that they feed mostly over commercially profitable medium-sized AH. Also, medium-sized and large hake are well-known cannibals that feed heavily over smaller AH. Fishing trawlers affect juvenile and medium-sized AH and artisanal long-liners capture exclusively large AH. The objective of this study was to evaluate the effect of a growing SASL population over the AH in the SMG, considering the changes in the fishing activity as well as the size-structured cannibalism within the AH population. The evaluations were based on time series of hake and SASL biomass using the “Ecopath with Ecosim” dynamic modelling approach. The analyses show that over 4 decades the increase in Sea Lions biomass has not generated a significant increase in the predation mortality over AH. On the other hand, an increase and subsequent variations in the fishing mortality seems to be related with long-term variations in large AH abundance, and a decrease in medium-sized AH abundance, constraining the cannibalism mortality. This led to a positive effect over juvenile AH abundance due to a released cannibalism pressure, even considering that the less abundant larger AH are also the main spawners of the population. In this scenario, where it seems that trawlers and long-liners have replaced several predators over the SMG food web, SLAS population is still growing but they may not reach the pristine abundance levels of the time before hunting. [ABSTRACT FROM AUTHOR]

We document the southern records of three species of tropical bony fishes along the coast of Buenos Aires Province, Argentina (CBAP, 36-38ºS). Rachycentrum canadum, Elops saurus and Caulolatilus chrysops were caught by bottom-trawl commercial vessels. Records presented here significantly extend southward their latitudinal distribution from those previously reported. Using sea surface temperature satellite images we show a southward warm circulation event from Brazil as a putative factor to explain the occurrence of these bony fishes in the CBAP. [ABSTRACT FROM AUTHOR]