CONICET | Buscador de Institutos y Recursos Humanos

In this paper we summarize the development of high seas fisheries off Patagonia and the effects on marine mammals populations. Incidental mortality affected dusky dolphins, Lagenorhynchus obscurus, Commersons dolphins, Cephalorhynchus commersonii, common dolphins, Delphinus delphis, and South American sea lions, Otaria flavescens. Mid-water trawling is the most harmful fishing type for dolphin species although with a low effort. The dynamic of the fishery makes that the annual mortality may fluctuate through years. Seventy species are prey for top predators and the fishery but only nine of them are important. Nevertheless the trophic overlap of the fishery onto marine mammals is of low importance. We complemented the analysis of direct and indirect effects by modeling marine mammal populations and the dynamic of several high trophic predators. Mortality levels of dusky dolphins are a cause of concern since there is a probability of 0.85 that observed mortality levels exceeded the more conservative critical value. Our multispecific model also indicates a negative trend in this population when the incidental catches are incorporated. South American sea lions population appears to be influenced neither by the fluctuations of the Argentine shortfin squid biomass nor by the decrease of the Argentine hake stock. Moreover, despite of the observed fishing mortality rates, this population is currently increasing. Marine mammals and other top predators must be considered in the fishery management, including monitoring and improving catch rate estimates. Furthermore, the developing of multispecies and alternative models are the key for a comprehensive evaluation of the overall effect of the fisheries onto the dynamics of this marine system.

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