Effects of fishing and climate variability on spatio-temporal dynamics of demersal chondrichthyans in the Río de la Plata, SW Atlantic

The structure of marine communities is affected by both fishing and climate variability. The Argentinean–Uruguayan Common Fishing Zone (AUCFZ) comprising the Río de la Plata and its oceanic front (SW Atlantic, 34° 30’ to 39° 30’ S) has a high environmental variability. Intensive trawling activity results in the bycatch of many chondrichthyan species. Using generalized linear mixed models, we analyzed the effects of commercial fishing effort, sea surface thermal anomalies (SSTA) and depth on the spatio-temporal dynamics of chondrichthyan species richness and total number of individuals in 3 zones of the AUCFZ between 1984 and 2009. Species richness increased with fishing effort in warmer years in the northern zone but displayed the opposite trend in the river and southern zones. While the total number of individuals decreased in the coldest years and at greater depths in the northern zone, these 2 variables had opposite effects in the southern zone. Depth had a stronger effect on both chondrichthyan species richness and the total number of individuals than the other 2 explanatory variables. While SSTA and depth had statistically significant effects on species richness and the total number of individuals, commercial fishing effort was significantly related only with species richness. The spatial variability of both response variables was greater than their temporal variation during the study period. These findings contribute to a greater understanding of the spatio-temporal dynamics of demersal chondrichthyans in the AUCFZ and are of relevance to the long-term sustainable management of chondrichthyans in this area and elsewhere.