An independent stock of Engraulis anchoita in north Patagonian waters? Parasite tags as evidence

Fish parasites are widely used as biological indicators of stocks and populations of their hosts. In this work we examine the stability of the stock structure of Argentine anchovy, Engraulis anchoita, after a period of three decades using parasite tags. A total of 295 anchovies were examined for parasites. Two samples were collected at Northern stock (Necochea and El Rincón), two from the Southern stock (Rawson and San Jorge Gulf), and two from the intermediate zone between Northern and Southern stocks (San Matías Gulf and boundary between Northern and Southern stock). The structure and composition of both parasite infracommunities and component communities were analysed by uni and multivariate statistics. Our results showed certain compositional homogeneity after three decades as well as the presence of three groupings, with those from San Matias Gulf being part of a “central” stock or population distributed also outside the gulf on the continental shelf. This newly identified stock was probably overlooked in the previous study since all parasites were considered in the multivariate comparisons, whereas the present data were restricted to long-lived, and therefore more suitable biological tags, parasitic species. Further studies based on other kinds of evidence and carried out at broader temporal and spatial scales are necessary to corroborate the occurrence of a population in San Matías Gulf. In such a case, considering the ecosystem relevance of E. anchoita, the establishment of its temporal dynamics will be a first step for the conservation and safeguarding of the entire marine ecosystem at a regional scale.