Since 1989, interactions between marine mammals and fisheries have been monitored along the Atlantic Patagonian coast. The Argentinian national fishing fleet in the area is composed of approximately 208 vessels (75% trawlers; 16% jiggins; 9% longliners). The fleet operates the year-round from eight harbours between Escondida Island and San Jorge Gulf (80 000 naut. miles 2). The important target species are: hake (Merluccius hubbsi), shortfin squid (IIlex argentinus) and shrimp (Pleoticus muelleri), while several tons of other fish are discarded. The dusky dolphin (Lagenorhynchus obscurus), the Commerson's dolphin (Cephalorhynchus commersonii) and the southern sea lion (Otaria flavescens) are incidentally caught. The dolphins become entangled mainly in mid-water trawls at night, while the sea lions become entangled in any kind of trawl. Annual mortality rates obtained are 170-480 sea lions (mostly males; figure estimated to be 1-2% of the population size in the area), 70-200 dusky dolphins (70% females) and 25-170 Commerson's dolphins. Feeding habits of top predators, fish catch and bycatch of the fishery were also studied. Dusky dolphins in the area prey mainly on anchovy and squid, while hake was the most important food item for Commerson's dolphins and male southern sea lions. Squid is also important prey for sea lions and overlaps in size with the fish taken by the commercial fishery. Fishing areas for squid taken by jigging vessels overlap in part with those of foraging sea lions. Even though the commercial size for hake is 30 cm or larger, smaller hakes are largely discarded by the fishery. A combination of operational and specific interactions have been detected. At present, mortality rates seem to be low and there is insufficient evidence of competition for prey species. However, there is concern about the large amounts of fish (particularly hake) discarded by the fishery.

The size of and trend in the South American sea lion (Otaria flavescens) population located in northern Patagonia were estimated and changes in the distribution, size, and structure of individual sites were analyzed during the period 1983-2002. Total counts were made during the reproductive season. Regression models were used to analyze the trend. Pups represented around 40% of the animals counted. The annual rates of change for pups and nonpups were not significantly different (p > 0.05, n = 7), although some rookeries showed higher rates of change for pups than for nonpups. Pup numbers have been increasing at the rate of 3.4% per year at the oldest rookeries, but the rate of increase was higher at new rookeries. Using Bayes' methods, the precision of the estimates and the contribution to the abundance of each rookery produced an alternative estimate of the trend in pup numbers in 5.7%. The key in the recovery of this population includes higher survival rates of juveniles combined with increased available habitat for newly reproducing individuals. This process led to the occupancy of new areas for hauling out and breeding. This hypothesis could explain the higher rates of increase in pups in peripheral areas while reproductive rates remain unchanged.Résumé : Nous avons estimé la taille et la tendance de la population du lion de mer d'Amérique du Sud (Otaria flavescens) du nord de la Patagonie et nous avons analysé les changements dans la répartition, la taille et la structure des sites individuels de 1983 à 2002. Nous avons fait des dénombrements complets durant la saison de reproduction. Des modèles de régression ont permis d'analyser la tendance. Les petits représentent environ 40 % des animaux dénombrés. Les taux annuels de changement pour les petits et les autres lions de mer ne diffèrent pas significativement (p > 0,05, n = 7), bien que dans certaines échouries les taux de changements sont plus élevés pour les petits que pour les autres. Le nombre de petits augmente au taux de 3,4 % par année dans les échouries les plus anciennes et le taux est encore plus élevé dans les nouvelles échoueries. Au moyen de méthodes bayésiennes, la précision des estimations et la contribution de chaque échouerie à l'abondance ont généré une nouvelle estimation de la tendance dans le nombre de petits de l'ordre de 5,7 %. Le facteur essentiel de la récupération de cette population est un taux de survie plus élevé des jeunes combiné à la disponibilité d'habitats pour les individus qui débutent leur reproduction. Ce processus a eu comme conséquence l'occupation de nouveaux sites pour l'échouage et la reproduction. Cette hypothèse pourrait expliquer les taux plus élevés d'accroissement des petits dans les zones périphériques, alors que les taux de reproduction demeurent inchangés.[Traduit par la Rédaction] Dans et al. 1690

This paper reports on aerial surveys conducted to estimate the relative abundance and trend in growth of the southern right whale (Eubalaena australis) population from Península Valdés. The number of whales counted tripled from 1999 to 2016. We modeled the number of whales, the number of calves, the number of solitary individuals and the number of individuals in breeding groups using as predictive variables the year, Julian day, and Julian day2 by means of generalized linear models. The rate of increase decreased from near 7% in 2007 to 0.06% and 2.30% for total number of whales and number of calves, respectively for 2016. Trends in the rates of increase for total number of whales and number of calves were negative (−0.732% and −0.376%, respectively). The habitat use of the whales changed along the years, with mothers and calves using more heavily the near‐shore strip, resulting in a decreasing trend for solitary individuals and breeding groups in near‐shore waters. We conclude that whales are still increasing their abundance, while the rate of increase is decreasing. Differences in the rates of increase of the group types and changes in habitat use are thought to be the consequence of a density‐dependence process.

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