Conservation and management measures for large mobile sharks are more effective when information on migratory patterns and environmental cues are known. In the absence of long-term monitoring data or tracking programs, available information is based on occasional catch/sighting records from a variety of sources, usually constrained in space and time. This study demonstrates the utility of developing temporally explicit habitat suitability (HS) models to infer the migratory pattern of large mobile sharks. Bimonthly presence-only HS models (MaxEnt algorithm) were developed for the broadnose sevengill shark Notorynchus cepedianus in the South-west Atlantic based on an exhaustive collection of data records, and ecologically relevant predictors. The six final models showed good predictive power, and were evaluated with independent data. A migratory pattern characterised by two main displacements was inferred from the models. We show that HS models can be applied as a no-cost desk-based alternative to infer broad-scale movements of large mobile sharks. This methodology is relevant as an important first step toward informing management plans in data-poor and financially limited regions, or under urgent conservation need.

The first case of dicephalia in tope Galeorhinus galeus analysed in developing foetuses removed from a pregnant female caught off the Mar del Plata coastal waters, Argentine Sea, is reported here.

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The aim of this study was to assess the influence of environmental factors on the fish distribution and abundance in Mar Chiquita coastal lagoon. Seasonal fish sampling stations were distributed along the lagoon and grouped in three zones from a mixo-oligohaline waters zone with high contribution of freshwater to a mixo-eurihaline waters zone with high marine water influence. A mixo-mesohaline waters zone characterized the middle part of the lagoon. The results showed that the fish composition was dominated by marine estuarine dependent (ED) species in all three zones and in all seasons: Odontesthes argentinensis, Brevoortia aurea, Mugil liza and Micropogonias furnieri were the most representative species. The following important ecological category was freshwater fishes (FW), with Platanichthys platana and Jenynsia multidentata being the most representative species. According to the best model selected, by fitting generalized linear models, abundance of ED increased as water temperature increased during summer and autumn in all three zones. The highest abundance was recorded in the mixo-eurihaline waters zone. On the other hand, FW abundance increased with high rainfall and also when easterly winds blew. In conclusion, a differential habitat use by the species that occur in the Mar Chiquita coastal lagoon was observed. A few ED species dominated the fish composition but FW species also made use of the lagoon during periods of heavy rainfall.

The aim of this study was to evaluate the effects of sex, maturity stage, and body size on the diet of the Magellan skate, Bathyraja magellanica, in the Southwest Atlantic off Argentina, by examining stomach contents using a multiple hypothesis modeling approach. Relationships between the number of prey and sex, maturity stage, and total length (TL) were assessed by built generalized linear models (GLM). Furthermore, we tested whether there was a threshold size at which B. magellanica started or quit consuming a given prey. The overall diet of B. magellanica was mainly consisted of teleosts, followed by amphipods, isopods, and decapods. Ontogenetic diet shifts were independent of sex and maturity stage. However, discrete shifts in diet with TL were found, with individuals larger than 554 and 623 mm TL ceasing to consume amphipods and isopods, respectively. The consumption of teleosts progressively increased with increasing predator size. Likewise, ontogenetic shifts in foraging behavior were also observed with smaller individuals showing specialization on amphipods with larger specimens consuming teleosts. These results confirm that ontogenetic shifts in diet of B. magellanica are more a function of predator size rather than any other life-history traits. We propose that these food shifts are probably related to morphological limitations and abilities associated with feeding habits of skate, so when specimens of B. magellanica reach an optimum body size, they may have access to higher quality trophic resources. Our results suggest that evaluating the importance of life-history stages on the feeding habits of a species is essential for understanding how that species exploits food resources, which, in turn, is an important factor in developing a suitable plan of marine ecosystem conservation.

Biogeographic regionalization identifies natural species assemblages of a given region. In this study, the geographic distribution of chondrichthyan species richness and species assemblages for the Southwest Atlantic were identified. The geographic distribution of 103 chondrichthyans was estimated through modelling. Based on the obtained binary maps, the distribution of chondrichthyan richness was obtained at four taxonomic levels: class Chondrichthyes (chondrichthyans), subclass Holocephali (chimaeras), division Selachii (sharks), and division Batomorphi (batoids). The continental shelf off Uruguay and southern Brazil presented the highest levels of chondrichthyan richness, and a smaller peak was found in El Rincón (northern Argentina). Shark richness concentrated mainly off Lagoa dos Patos (southern Brazil). Batoid richness was maximal off Uruguay and northern Argentina, including modes in El Rincón, San Jorge Gulf, and slope of the Argentinean shelf. Classification analyses revealed the presence of a hierarchical regionalization, with three main and six minor assemblages. Main assemblages are hierarchically identifiable as provinces and minor ones as ecoregions or districts. Two of the main assemblages correspond with the Argentinean and Magellanic Provinces; the third one is identified here for the first time, the Patagonian Slope Province. This regionalization provides the basis for the design of protected area networks for conservation or management purposes.

The feeding habits of the Rio skate, Rioraja agassizi, from off Uruguay and north Argentina were evaluated using a multiple-hypothesis modelling approach. Relationships between number of preys and sex, maturity stage, body size, season and region were assessed by building generalized linear models. Rioraja agassizi fed mainly upon crustaceans (shrimps, crabs and amphipods) and teleosts, but also upon isopods, cumaceans, lancelets and polychaetes. Ontogenetic diet shifts were found: small R. agassizi consumed amphipods, cumaceans and isopods and large individuals on shrimps, crabs and teleosts. The consumption of crustaceans (amphipods, shrimps, crabs, isopods and cumaceans) was higher in the northern (34°–38°S) than in the southern area (38°–41°S). Rioraja agassizi consumed more teleosts in the cold season and preyed more on lancelets in the warm season. Prey size increased with increasing body size of R. agassizi, but large individuals also consumed small prey. Ontogenetic shifts may be related to body size rather than other life-history traits. Rioraja agassizi adapts its feeding habits in response to regional and seasonal changes.

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