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Detecting and determining changes in the occurrence and abundance of species is a priority for effective management of resources and for conservation of biodiversity. In the absence of long-term monitoring data, potential population declines may be very difficult to establish. Therefore, alternative information on occurrence of species to infer population trends is highly valued. Records of sharks (i.e., Notorynchus cepedianus, Carcharias taurus, Galeorhinusgaleus, and Carcharhinus brachyurus) off northern Argentina from a recreational fishing magazine (Weekend), between 1973 and 2008, were reviewed with the aim of evaluating population trends with opportunistic data sources. For each shark species, the number of occurrences per year in the magazine was registered. Our analyses were based on a nonprobabilistic method (McPherson and Myers' approach) designed to determine population trends with opportunistic sighting records. In this approach we included the number of classified ads offering fishing guide services published per year in the magazine as a measure of observation effort. For each species, we fitted generalized linear models with a Poisson error structure and a log link, where the response variable was the number of occurrences per year, the explanatory variable was the year, and the logarithm of the number of fishing guide ads was specified as an offset in each model. For both approaches, the models estimated that populations of the four shark species have suffered declines. Estimates produced by these models will help to determine the magnitude of population changes where a paucity of data prevents more precise analysis. La detection et la determination des variations de la presence et de l'abondance des especes sont des composantes prioritaires d'une gestion efficace des ressources et de la conservation de la biodiversite. En l'absence de donnees de surveillance a long terme, il peut etre tres difficile de deceler d'eventuelles diminutions des populations. D'autres types de donnees sur la presence d'especes permettant d'inferer les tendances de populations revetent donc une grande valeur. Les signalements de requins (c.-a-d. Notorynchus cepedianus, Carcharias taurus, Galeorhinus galeus et Carcharhinus brachyurus) au large de l'Argentine dans un magazine de peche sportive (Weekend), de 1973 a 2008, ont ete examines dans le but d'evaluer les tendances des populations a l'aide de sources de donnees opportunistes. Pour chaque espece de requin, le nombre de mentions par annee dans le magazine a ete note. Nos analyses reposaient sur une methode non probabiliste (l'approche de McPherson et Myers) concue pour determiner les tendances de population a partir de registres de signalements opportunistes. Nous avons inclus dans cette approche le nombre d'annonces classees offrant des services de guide de peche publiees annuellement dans le magazine comme mesure de l'effort d'observation. Pour chaque espece, nous avons cale les donnees sur des modeles lineaires generalises supposant une structure d'erreur de Poisson et un lien logarithmique, ou la variable dependante etait le nombre de mentions par annee, la variable independante etait l'annee et le logarithme du nombre d'annonces de guide de peche etait inclus comme ecart dans chaque modele. Pour les deux approches, les modeles ont estime que les populations des quatre especes de requin ont connu des diminutions. Les estimations produites par ces modeles aideront a determiner l'ampleur des variations de populations dans les cas ou la rarete des donnees ne permet pas une analyse plus precise. [Traduit par la Redaction], Introduction Sharks face multiple threats from fisheries, habitat degradation, and pollution (Ferretti et al. 2010; Dulvy et al. 2014). Detecting population changes that may result from these threats is essential [...]

Here, we highlight the geological processes that resulted in the current conformation of the southern Southwest Atlantic Ocean, and explore the heterogeneous composition of the marine ichthyofauna found between 33° and 56° from a paleobiological perspective. During the early Cretaceous (140 Mya), the South Atlantic was still not formed, and Gondwana was probably a set of united plates with shallow continental waters. In the middle Cretaceous (112 Mya), the major Gondwanan plates started diverging from each other, allowing shallow marine intrusions and the diversification of an endemic fish fauna. By the end of the Mesozoic (66 Mya), the proto‐South Atlantic connected with the North Atlantic, which was still part of the Tethys Sea, allowing its ichthyofauna to colonize the south and reach the Antarctic region. The opening of the Drake Passage in the Oligocene (33 Mya) enabled the cold waters of the Pacific Ocean to reach the South Atlantic, causing drastic effects on the thermophilic fauna and favoring the dispersion of cold‐water species. Successive glaciations during the Quaternary (2 Myr to 10,000 years ago) resulted in the prevalence of Antarctic climatic conditions in the southern Southwest Atlantic. The long history of changing scenarios in the constitution of the southern Southwest Atlantic is reflected in the heterogeneous composition of the marine ichthyofauna between 33° and 56°S, which is characterized by a mixture of cosmopolitan, Tethyan, Pacific, Gondwanan, Antarctic, and endemic origins. [ABSTRACT FROM AUTHOR]

The study of the feeding habits of elasmobranch populations should help to elucidate the ecological role of these fishes in the marine ecosystem. Feeding habits of the apron ray, Discopyge tschudii from San Jorge Gulf were investigated. An evaluation of whether the diet of D. tschudii changes with body size, seasons, maturity stage and sex was performed using a multiple-hypothesis modelling approach. Discopyge tschudii preyed mainly on polychaetes. The consumption of polychaetes was higher in males. Also, amphipods and siphons of clams were preyed more heavily in the cold season and Munida gregaria in the warm season. Stomatopods were consumed more with increasing body size. All prey categories were independent of maturity stage. We concluded that D. tschudii is a benthic feeder. [ABSTRACT FROM PUBLISHER]

The diet and the trophic level of the Argentine hake Merluccius hubbsi was investigated in the south-west Atlantic Ocean. Stomachs from 3405 specimens, ranging from 10 to 94 cm total length, collected on three research cruises carried out during winter 2011 and summer 2012, were examined at the laboratory. Dietary shifts related to sex, maturity stage, size, age, season, region and hour were examined using generalized linear models. The Argentine hake M. hubbsi fed mainly on zooplankton crustaceans (Themisto gaudichaudii, Euphausia lucens and Munida spp.), followed by fish and cephalopods. During summer, cephalopods (mainly Illex argentinus) were the main prey of M. hubbsi, indicating spatio-temporal changes in the diet. This work also revealed ontogenetic dietary changes associated with size, from zooplankton crustaceans during early life stages (E. lucens, T. gaudichaudii and Munida spp.) to fish and cephalopods. The trophic level of M. hubbsi ranged from 3.43 to 4.51 according to season and region. Cannibalism increased with predator length and contributed a maximum of 8.14% to the diet of M. hubbsi during winter on the inner Patagonian continental shelf. [ABSTRACT FROM PUBLISHER]

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The feeding habits of the apron ray, Discopyge tschudii, were investigated, off Uruguay and northern Argentina, and we tested the hypothesis that the diet changes with increasing body size, between sexes and seasons using a multiple-hypothesis modelling approach. Discopyge tschudii preys mainly on polychaetes (88.77% index of relative importance (IRI)) followed by siphons of the clam Amiantis purpurata (8.13% IRI) and amphipods (3.08% IRI). Ontogenetic, sexual and seasonal changes were found. Larger individuals of D. tschudii consumed buried polychaetes more often. The consumption of errant polychaetes was higher in males and in the cold season. Also, amphipods were preyed on more heavily by females and the number of siphons of A. purpurata consumed was higher in the cold season. [ABSTRACT FROM PUBLISHER]