María Alejandra Romero

Spatial patterns of the Argentine hake Merluccius hubbsi and oceanographic processes in a semi-enclosed Patagonian ecosystem

Abstract Time-series of fishing position, landings, satellite-derived sea-surface temperature and chlorophyll a concentrations were used to relate the spatial–temporal distribution of the Argentine hake Merluccius hubbsi with seasonal oceanographic processes in San Matías Gulf. Also, the seasonal effect of fishing on the hake population structure was analysed. During summer the fleet was concentrated over the area of the frontal system, obtaining the best catch-per-unit-effort (CPUE) of hake in relatively deep waters. In autumn, the dispersion of the fleet due to a reduction in CPUE coincided with the dissipation of the front, suggesting that the distribution and shoaling of the Argentine hake is associated with seasonal thermal structures. In spring, the thermal structure of the waters and the chlorophyll a blooms seem to modulate the timing of spawning of hake, which occurs mainly in October–November. In addition, the fleet captured a higher proportion of females in the gonadal recovery stage during warm months (November–April). While winter catches (May–October) consisted mainly of males, the intense summer fishing may result in a high impact on the female population. This information is relevant to design of spatial management tools intended to provide biological sustainability to the hake fishery.

Feeding strategy and cannibalism of the Argentine hake Merluccius hubbsi

The diet composition and feeding strategy of the Argentine hake Merluccius hubbsi in the San Matías Gulf were analysed in order to use this information for the sustainable management of the fishery. Merluccius hubbsi behaved as an opportunistic predator. Small M. hubbsi consumed planktonic crustaceans, whereas medium and large fish ate numerous prey taxa with low frequency of occurrence and variable specific abundance. Intra- and intercohort cannibalism were detected in all size groups and were particularly significant in large M. hubbsi. Medium-sized M. hubbsi consumed small conspecifics and large-sized M. hubbsi consumed both small and medium M. hubbsi. These results indicate that the removal of large M. hubbsi by fishing may increase the risk of overfishing by two combined effects: a direct effect of recruitment-overfishing and an indirect effect of growth-overfishing through an enhanced cannibalism of medium M. hubbsi on small M. hubbsi. Intra- and intercohort cannibalism and other trophic relationships in the M. hubbsi should therefore be considered explicitly in stock assessment models.

Solapamiento trófico entre el lobo marino de un pelo Otaria flavescens y la pesquería de arrastre demersal del golfo San Matías, Patagonia, Argentina

As world fisheries began to decline and massive collapses were observed, the competition between marine mammals and fisheries became an issue of growing concern. San Matias Gulf (Patagonia, Argentina) is considered to be a fishery ecosystem independent of the Argentine Continental Shelf waters, with particular oceanographic and biological properties. As a semi-enclosed ecosystem, this gulf may generate particular scenarios for interactions between the demersal trawl fishery fleet and the population of South American sea lions Otaria flavescens. In this paper, the diet of the top predator and the composition of fishery catches were characterized in order to assess the trophic overlap between these two components. This analysis and a comparison of the sizes of prey consumed revealed a low probability of competition for similar resources between the fishing fleet and the marine mammals in the San Matias Gulf ecosystem.

Gastrointestinal parasites of bottlenose dolphins Tursiops truncatus from the extreme Southwestern Atlantic, with notes on diet composition.

We surveyed the gastrointestinal tracts of 6 bottlenose dolphins Tursiops truncatus from Patagonia to check for helminth parasites and characterize dolphin diet. All dolphins harbored parasites (6477 helminths). We recorded 7 species, including nematodes Anisakis simplex s.l., Pseudoterranova decipiens, acanthocephalans Corynosoma cetaceum, C. australe, and digeneans Braunina cordiformis, Pholeter gastrophilus and Synthesium tursionis. Among the gastric helminths, the most prevalent species were C. cetaceum and A. simplex while C. australe and S. tursionis inhabited the intestine at low prevalence. This is the first report of C. australe and P. decipiens in bottlenose dolphins. Regarding diet, 5 stomachs contained food remains (consisting of 103 prey items). The most important prey species were Geotria australis and Stromateus brasiliensis, but their role in parasite transmission is unclear. At the community level, the gastrointestinal parasite community of T. truncatus was depauperate and strongly overlapped the community described for pelagic dolphins inhabiting Patagonia, suggesting a strong local influence in shaping helminth communities. Nevertheless, these observations are at odds with the notion that oceanic cetaceans have comparatively poorer helminth fauna than neritic species such as bottlenose dolphins, due to the lower likelihood of parasite exchange.

Environmental Niche Overlap between Common and Dusky Dolphins in North Patagonia, Argentina

Research on the ecology of sympatric dolphins has increased worldwide in recent decades. However, many dolphin associations such as that between common dolphins (Delphinus delphis) and dusky dolphins (Lagenorhynchus obscurus) are poorly understood. The present study was conducted in the San Matías Gulf (SMG) ecosystem (North Patagonia, Argentina) where a high diet overlap among both species was found. The main objective of the present work was to explore the niche overlap of common and dusky dolphins in the habitat and temporal dimensions. The specific aims were (a) to evaluate the habitat use strategies of both species through a comparison of their group attributes (social composition, size and activity), and (b) to evaluate their habitat preferences and habitat overlap through Environmental Niche modeling considering two oceanographic seasons. To accomplish these aims, we used a historic database of opportunistic and systematic records collected from 1983 to 2011. Common and dusky dolphins exhibited similar patterns of group size (from less than 10 to more than 100 individuals), activity (both species use the area to feed, nurse, and copulate), and composition (adults, juveniles, and mothers with calves were observed for both species). Also, both species were observed travelling and feeding in mixed-species groups. Specific overlap indices were higher for common dolphins than for dusky dolphins, but all indices were low, suggesting that they are mainly segregated in the habitat dimension. In the case of common dolphins, the best habitats were located in the northwest of the gulf far from the coast. In the warm season they prefer areas with temperate sea surface and in the cold season they prefer areas with relatively high variability of sea surface temperature. Meanwhile, dusky dolphins prefer areas with steep slopes close to the coast in the southwestern sector of the gulf in both seasons.

A stranding of Balaenoptera borealis (Lesson 1828) from Patagonia, Argentina, with notes on parasite infestation and diet

Strandings of baleen whales are uncommon in Patagonia, Argentina. We report on a stranding of an individual sei whale Balaenoptera borealis on the east coast of San Antonio (40°43.5′ S, 64°55.8′ W), Río Negro province, Argentina. It was the eighth reported stranding of this species along the Argentinean coastline. The stomach content of the whale was dominated by crustaceans. Three parasite species were also recovered, namely Ogmogaster antarcticus (Trematoda), Anisakis simplex (Nematoda) and Tetrabothrius affinis (Cestoda). This was the first record of a host carrying the latter two species in the South-West Atlantic Ocean.

Analysing the natural population growth of a large marine mammal after a depletive harvest.

An understanding of the underlying processes and comprehensive history of population growth after a harvest-driven depletion is necessary when assessing the long-term effectiveness of management and conservation strategies. The South American sea lion (SASL), Otaria flavescens, is the most conspicuous marine mammal along the South American coasts, where it has been heavily exploited. As a consequence of this exploitation, many of its populations were decimated during the early 20th century but currently show a clear recovery. The aim of this study was to assess SASL population recovery by applying a Bayesian state-space modelling framework. We were particularly interested in understanding how the population responds at low densities, how human-induced mortality interplays with natural mechanisms, and how density-dependence may regulate population growth. The observed population trajectory of SASL shows a non-linear relationship with density, recovering with a maximum increase rate of 0.055. However, 50 years after hunting cessation, the population still represents only 40% of its pre-exploitation abundance. Considering that the SASL population in this region represents approximately 72% of the species abundance within the Atlantic Ocean, the present analysis provides insights into the potential mechanisms regulating the dynamics of SASL populations across the global distributional range of the species.

Occurrence of South American fur seals Arctocephalus australis in San Matías Gulf, Patagonia, Argentina

Fil: Svendsen, Guillermo. Universidad Nacional del Comahue. Instituto de Biologia Marina y Pesquera Alte.storni;