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.

The food habits of the beaked skate were studied utilising 274 individuals obtained from the incidental catches of the Argentine hake (Merluccius hubbsi) fishery. The most important prey were the Argentine hake, the southern cod (Patagonotothen ramsayi), the Argentine shortfin squid (Illex argentinus), the isopod (Serolis schythei), the ''raneya'' (Raneya brasiliensis, Pisces: Ophidiidae), and the Argentine anchovy (Engraulis anchoita). A total of 45 prey species was identified. No differences in the diet between sexes, but significant differences among size classes and between immature and mature individuals were found. Two size-related dietary shifts previously reported in this species, at around 35 cm and 85 cm total length were confirmed and related to changes in habitat utilisation. The first shift entails a major change from benthic prey (mostly crustaceans) to demersal-benthic prey (mostly fishes) and the second change from demersal-benthic to demersal-pelagic prey (increased consumption of Argentine hake and decreased consumption of southern cod). The second shift coincides with sexual maturation and may reflect a behavioural response to maturation. International Council for the Exploration of the Sea

No abstract

Dolphin watching is a relatively newly developed tourist activity. Although it is assumed to contribute to the conservation of marine ecosystems, its long-term adverse effects are still unknown. The present work aims to assess the impact of tour vessels on the behavior pattern of dusky dolphins displaying diurnal and cooperative feeding. We evaluated potential bias of commercial vessels to specific activities, short-term responses of dolphins to vessel approach, and longer-term effects of these changes, particularly on the activity budget and the time dolphins need to resume an activity. Several field experiments were carried out in which dolphins were approached by a research vessel or by commercial vessels. Group tracking was also made from a research vessel. Behavioral sequences were modeled by stochastic matrix models. Activity budget and time to return to an activity were obtained from matrix properties. Commercial trips found mostly feeding groups. Feeding showed the highest rate of change at the moment of vessel approach, and commercial vessels had an effect on the direction of change. Over the longer term, feeding and socializing time budgets decreased when commercial vessels were present. The time to return to feeding as well as the time it took for a group of dolphins to feed increased in the presence of commercial vessels. Dusky dolphins in South Atlantic waters feed during the day on patchily distributed prey. Our study demonstrates that boat presence negatively affects the longer-term feeding efficiency of dusky dolphins.

No abstract

This is the first study in Argentine waters on the abundance of the threatened Franciscana dolphin, Pontoporia blainvillei. During 2003–2004 we carried out 17 aerial surveys using line transect sampling methodology. We observed 101 Franciscanas in 71 sightings. In northern areas density was estimated at 0.106 individual/km2. Density was lower in southern areas (0.055/km2) and declined with depth beyond 30‐m isobaths (0.05/km2). A correction factor for submerged dolphins was applied to density and then extrapolated to the strip between the coastline and the 30‐m isobath. Abundance in the northern area was estimated at 8,279 (4,904–13,960) individuals, while in the southern area it was estimated at 5,896 (1,928–17,999) individuals. Considering an annual mortality of about 500–800 individuals, about 3.5%–5.6% of the stock may be removed each year by the fishery and over the 2% recommended by the International Whaling Commission (IWC) and may not be sustainable by the population. Higher densities in coastal areas make Franciscanas more vulnerable to coastal fishing camps, which increased mortality in recent years. A remarkable finding was that while density decreases to the south, values of catch per unit effort (CPUE) increases, indicating different catchability of dolphins between areas.