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The short‐tail yellownose skate, Zearaja brevicaudata, occurs off southern Brazil and along the Argentine continental shelf, including waters surrounding the Islas Malvinas and the upper slope, and is very frequently caught by trawl fisheries throughout its range. The age, growth, and maturity of Z. brevicaudata were investigated using 204 individuals collected by commercial fishing vessels from northern Argentina, between March 2016 and September 2019. Age was determined on a sample comprising vertebrae from 151 individuals, 60 males, ranging in size from 391 to 956 mm total length (TL), and 91 females, ranging in size from 324 to 1060 mm TL. Maximum ages determined for males and females were 22 and 29 years, respectively. A Bayesian framework was employed with a set of three candidate models to estimate growth parameters (von Bertalanffy, Gompertz, and Logistic). The von Bertalanffy model had the best fit, and the sexes showed undistinguishable growth parameters. For sexes combined, derived growth mean parameters (± S.D.) were L∞ = 1081 mm ± 64.34 mm, k = 0.09 ± 0.01 years−1, and L0 = 248 mm ± 23.52 mm. The age at maturity was estimated at 13.15 and 14.66 years for males and females, respectively. [ABSTRACT FROM AUTHOR]

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 [...]

The spotback skate Atlantoraja castelnaui (Arhynchobatidae) is a large and threatened skate species subjected to fishing pressure, endemic to the Southwest Atlantic that occurs from Rio de Janeiro, Brazil, to San Jorge Gulf, Argentina. The age, growth, age at maturity and the maximum intrinsic rate of population increase rmax of A. castelnaui were studied using 152 specimens collected from off Uruguay and north Argentina (35°–42° S), between June 2013 and February 2020. Vertebrae from 143 individuals were used for ageing (females: n = 83, size range 404–1300 mm total length, TL; males: n = 60, size range 400–1270 mm TL). Maximum ages determined for females and males were 30 and 28 years, respectively. To fit growth models, non‐linear and Bayesian estimation approaches were considered. For the first approach, a set of four candidate growth (size‐at‐age) models were fitted: three‐parameter von Bertalanffy, two‐parameter von Bertalanffy with fixed L0, Gompertz and Logistic. In the second approach, von Bertalanffy, Gompertz and Logistic were fitted. For non‐linear estimation, model selection indicated that the entire set of candidate growth models were supported by the data. The von Bertalanffy was selected as the best model for Bayesian estimation. There were no differences in growth between sexes. For the sexes combined, the von Bertalanffy growth model by Bayesian method was considered the most adequate to describe the growth of A. castelnaui (growth mean parameters ± S.D.: L∞ = 1210.29 ± 40.68 mm; k = 0.12 ± 0.01 years−1; L0 = 179.20 ± 11.62 mm). The age at maturity was estimated at 16.21 and 14.04 years for females and males, respectively. The maximum intrinsic rate of population increase rmax was estimated as 0.252 years−1. Life‐history traits and rmax provided in the present study suggest that this species has a relatively low productivity and may be vulnerable to an intense fishing pressure. [ABSTRACT FROM AUTHOR]

Aim: We assessed the validity of the division of the Magellanic Province into the four provinces as proposed by Briggs & Bowen (J Biogeogr39 12–30, 2012): Southern Chile, Tierra del Fuego, Southern Argentina and Falkland (Malvinas) Islands. We aimed to (a) present an updated list of the fishes from the region known as 'Magellanic Province', (b) analyse the specific richness of fishes in the Atlantic and Pacific sectors and their degree of endemism and (c) evaluate statistically the validity of the three Provinces proposed for the Atlantic sector. Location: Southern tip of the American continent at latitudes higher than 40° S in the Atlantic as well as in the Pacific Oceans. Taxon: 348 South American marine fish species. Methods: The list of fishes was prepared by consulting more than 140 sources, many related to observations resulting from research cruises, although two ichthyological collections and two ichthyological websites were also used. The South American species with distributions extending outside of the area corresponding to the Magellanic Province, and all cosmopolitan species, were excluded of endemism analyses. For analysing fish distributions in the Atlantic sector, the data employed are from eight research cruises carried out from 1978 to 2006 from 37° to 55° south. A total of 523 fishing trawls have been analysed, grouped into cell of 1° × 1° cells. The species composition of each cell was evaluated by multivariate analysis (non‐metric multidimensional scaling, cluster and similarity analyses). Results: The percentage of endemism in each sector (Atlantic 2.87% and Pacific 2.87%) is smaller than the endemism common to both sectors (9.2%). The total of endemic species in the Province is 14.94%, which is bigger than the 10% indicated as the lower limit for defining a biogeographic province suggested by Briggs (Marine Zoogeography, 1974). In addition, multivariate analyses do not show differences in the species composition, neither between Falkland (Malvinas) Islands and 'Southern Argentina' nor between the latter and Tierra del Fuego. Main conclusions: The ichthyological data indicate only one biogeographic province in the region not four as previously posited. [ABSTRACT FROM AUTHOR]

The bignose fanskate, Sympterygia acuta, is a small-to-medium-sized species endemic to shallow coastal waters of the Southwest Atlantic. Sympterygia acuta displays a clear seasonal reproductive cycle, characterized by maximum egg-laying activity in spring and hatching in summer. We hypothesized that diet and feeding activity change with maturity stage and season and that, given its smallish size, the trophic level is low. Using a multiple-hypothesis modeling approach, the diet of S. acuta in relation to sex, body size, maturity stage, region ( i.e. north and south) and season was analysed; and a potential relationship between feeding activity and the seasonal reproductive cycle was assessed. Sympterygia acuta fed on a broad spectrum of prey, but teleosts were more important (47.97% index of relative importance, % IRI), followed by decapods (39.84% IRI), cumaceans (8.31% IRI) and isopods (1.89% IRI). Maturity stage was a strong determinant of the ontogenetic diet shift of S. acuta, and relationships between number of prey consumed with season and region were found.. Feeding activity was higher in the cold season than in the warm season, and was less important in the south region than in the north region. Unexpectedly, the specific trophic level was high (3.87). Sympterygia acuta shifts its diet with maturity stage, possibly by a combination of an improved ability to capture prey and a change in energy demand of mature individuals. Despite being a small-to-medium-sized skate, S. acuta showed a trophic level similar to that of large-bodied marine predators. It reduces its feeding activity seasonally because in the warm season this species may experience an increased predation risk from large sharks. [ABSTRACT FROM AUTHOR]