Myxozoans have been successfully used as tags for fish stock identification around the world. However, few studies using myxozoan tags have been carried out in the Southern Atlantic, a region with complex oceanography that constitutes a potentially suitable scenario for testing the utility of myxozoans as indicators. Its usefulness was tested using six samples of Merluccius hubbsi in two different regions of the Argentine Sea. Generalized linear models were performed to assess the effects of fish size and sex, and year and region of capture and selected using the Information Theoretic approach. Three myxozoan species were recorded: Kudoa rosenbuschi, Myxoproteus meridionalis and Fabespora sp. Results of modelling species individually showed differential capabilities for detecting geographical population structure at different spatial scales, with K. rosenbuschi and Fabespora sp. allowing the discrimination of northern and southern stocks, but Fabespora sp. also as a promissory indicator of intrapopulation sub-structure due to different migratory routes during non-reproductive periods. This work confirms that myxozoans offer a set of suitable markers at different spatial scales, which can be selected individually or in any combination, depending on the geographical extent of the study, constituting tools adaptable to the objectives of further research on fish population structure.

Many marine fisheries in South American Atlantic coasts (SAAC) are threatened by overfishing and under serious risk of collapsing. The SAAC comprises a diversity of environments, possesses a complex oceanography and harbours a vast biodiversity that provide an enormous potential for using parasites as biological tags for fish stock delineation, a prerequisite for the implementation of control and management plans. Here, their use in the SAAC is reviewed. Main evidence is derived from northern Argentine waters, where fish parasite assemblages are dominated by larval helminth species that share a low specificity, long persistence and trophic transmission, parasitizing almost indiscriminately all available fish species. The advantages and constraints of such a combination of characteristics are analysed and recommendations are given for future research. Shifting the focus from fish/parasite populations to communities allows expanding the concept of biological tags from local to regional scales, providing essential information to delineate ecosystem boundaries for host communities. This new concept arose as a powerful tool to help the implementation of ecosystem-based approaches to fisheries management, the new paradigm for fisheries science. Holistic approaches, including parasites as biological tags for stock delineation will render valuable information to help insure fisheries and marine ecosystems against further depletion and collapse.

Bycatch in longline fisheries is considered one of the main threats for the conservationof albatrosses and petrels worldwide. However, the relative impact of fisheries on all theaffected populations or species still remains poorly understood. This paper applied aProductivity and Susceptibility Analysis (PSA) and the concept of “Potential BiologicalRemoval Level” (PBR) to assess the relative impact caused by the Uruguayan pelagiclongline fishery on several populations. This two-step approach allowed us to obtain anobjective view of the relative impact of the Uruguayan pelagic longline fleet on most ofthe populations or species of albatrosses and petrels with high association with thisfishery. Of fifteen species considered, fourteen were finally assessed and a ranking ofrisk derived. The concept of PBR was applied to the nine most at-risk species. The impactof fishing on populations could not be straightforwardly inferred from their bycatchrates. Results indicate that large albatrosses (Diomedea spp.) andThalassarche chlororhynchos are more affected than some of the mainspecies caught by the fishery (i.e. Thalassarche melanophrys andProcellaria aequinoctialis). Diomedea exulans fromSouth Georgia is likely to be the population most affected by the Uruguayan fleet. Thiswork should be seen as a case study of the fisheries operating in the southwesternAtlantic. The Uruguayan fleet within its operation area was responsible for only the 4.3%to 12.5% of the total annual effort deployed by the different fleets during 2004–2008. Thecombined impact of these fleets could be sufficiently high to account for many of theobserved declines in the populations of D. exulans, D. dabbenenaand T. chlororhynchos. However, the seabird bycatch numbers formost of the pelagic longline fleets that operate in the southwest Atlantic remain unknown.Applying mitigation measures to reduce the impact of pelagic longline fleets operating inthis region should be considered a high priority.

The use of parasites as biological tags allowed the identification of 3 stocks of Argentinean sandperch, Pseudopercis semifasciata (Cuvier), in the Argentine Sea. A total of 100 specimens caught in 3 zones: Villa Gesell (37°15′S, 57°23′W; n=20), Miramar (38°03′S, 57°30′W–38°44′S, 58°44′W; n=30) and Península Valdes (42°00′–42°45′S; n=50), were examined and 28 parasite species were found, 15 of them being new host records. Both univariate and multivariate analyses identified discrete stocks in each zone. The observed differences were not related to the host size or sex. Each locality was characterized by its own indicator species. Villa Gesell was typified by unidentified cestode plerocercoids, Corynosoma cetaceum and Hysterothylacium sp., Miramar by Heterosentis sp. and Pseudoterranova sp. and Península Valdes by A. simplex s.l. Fishes from both northern localities shared gnathiid pranizae, Corynosoma australe and Grillotia sp. as indicators, whereas Miramar and Península Valdes shared only Trifur tortuosus. The most distant localities showed no indicator species in common. Discriminant analyses of parasite assemblages agreed with populational comparisons in identifying the same set of biological tags, whereas some differences in the identity of indicator species were obtained by similarity analysis. However, the 3 approaches were congruent in identifying Grillotia sp., C. australe and C. cetaceum as indicators of northern localities, and A. simplex s.l. as related to Patagonian waters. Differences among zones could be enhanced by the sedentary habits, limited dispersal and high site fidelity of P. semifasciata, and their spawning in rocky outcrops, which are isolated environments.