Spatial and temporal variations in parasite communities of an overxploted fish species: the argentine hake, Merluccius hubbsi marini (gadiformes:Merluciidae)

CANTATORE, DELFINA; LANFRANCHI, ANA L.; TIMI, JUAN T.

Melbourne, Australia

Conferencia; ICOPA XII; 2010

The Argentine hake is main target of Argentine fishery, representing the Patagonian stock (south of 41°S) near 85% of the estimated biomass. Its overexplotation had produced a severe decline in population size, spatial changes in spawning aggregations and a more scattered distribution. These changes could affect the structure of parasite populations, especially for monoxenous and specific parasites, which require a minimum threshold of host population size/density to ensure transmission and sustaining viable populations. A decade ago, parasites were successfully used to discriminate between Patagonian and Bonaerense (north of 41ºS) stocks. Although the actual number of stocks in Patagonian waters remains controversial, no comparisons among samples from the former were carried out. Three samples of hake (two Patagonian separated by 1° latitude one Bonaerense) were examined for parasites and compared with previous Patagonian samples. The aims of this study were; 1) to determine if differentiation among Bonaerense and Patagonian stock persists after decade; 2) to search for variations between zones within the Patagonian regions; 3) to asses whether these variations are caused primarily by changes in abundance or composition of parasite communities, and 4) evaluate if temporal changes in parasite populations are linked with the decline of hake populations. Univariate and multivariate analyses of parasite abundance and composition showed that: 1) clear discrimination of both stocks still exists, given mainly by compositional differences; 2) Patagonian samples showed significant differences in parasites abundances at spatial and temporal scales, which were more important over space, but constituted an homogeneous group in relation to Bonaerense hakes; 3) temporal variability was mainly due to an increase in unspecific larval parasites abundance. So, variability at large spatial scale was mainly compositional, while smaller spatial scale and temporal variation were driven by changes in relative abundance, particularly by numerically dominant taxa, instead of specific hake parasites.