Parasites as biological tags for stock discrimination of Trachurus lathami in the southwest Atlantic.

BRAICOVICH, PAOLA E.; LUQUE, JOSÉ LUIS; TIMI, JUAN T.

Melbourne

Congreso; XII International Congress for Parasitology.; 2010

Australian Society for Parasitology, World Federation of Parasitologists.

The stock structure of Trachurus lathami along its distributional range (Gulf of Maine-USA to San Matías Gulf-Argentina) is unknown, but two populations have been suggested to inhabit southern Brazilian waters, which migrate to shallow waters in summer. The same behaviour is observed in Argentinean coasts, with adults appearing in coastal waters during spring to reproduce, ignoring their population composition. Here we used parasites as biological tags to test if the horse mackerel, inhabiting  waters of Brazil and Argentina belongs to discrete stocks. A total of 187 specimens were collected: a sample from Rio de Janeiro, Brazil (n=50; October, 2009; 22°56’S, 56°48W); and 3 monthly samples caught in 2008 from Argentina: Miramar (n=49; August; 38°03’S, 57°30W), Villa Gesell (n=42; September; 37°30’S, 56°20W) and a third from commercial fishery with unknown location (n=46; October). Both univariate and multivariate analyses of parasite abundances showed a complete discrimination between Brazilian and Argentinean samples (dissimilarity >90%), and a higher heterogeneity among individuals in Brasil (similarity= 49%) than in any sample from Argentina (similarity= 58-67%). Comparisons among Argentinean samples showed a higher similarity in relation to Brazilian ones (dissimilarities= 40-43%), but significant differences were also observed between those from Villa Gesell and Miramar; with the commercial catch being similar to the later in terms of parasite  abundance, and probably comes from the same region. Analyses of mean abundance at component community level showed the same pattern. Our results confirm that several stocks of T. latami inhabit along South American Atlantic coasts, with at least two occurring in Argentinean waters. The fact that recently arrived fish to Miramar and Villa Gesell display differences in parasite burden and composition, and that it persists after three months (at least in Miramar) implies that fish probably do not move latitudinally along the cost before returning to the wintering areas.