Oceanographic processes driving the feeding ecology of franciscana dolphin off Southern Brazilian coast

Abstract

The franciscana (Pontoporia blainvillei) is a coastal dolphin endemic to the south-western Atlantic Ocean. Incidental captures in fishing gillnets are the greatest conservation concern for this species. The present study examines the biophysical interactions between the franciscana prey composition and the marine environment. The feeding regime of franciscana was investigated from stomach contents of incidentally caught animals along the southern Brazilian coast. The characteristics of the franciscana habitat may reveal potential factors affecting the distribution and abundance of marine species, thus the franciscana prey (species number and size) was treated as a function of the oceanographic variables (sea surface temperature and chlorophyll-a), and the spatial (latitude and water depth), and temporal (season) parameters, through Linear and Generalized Linear Models (LM and GLM). Season and latitude were important predictors of the franciscana diet, followed by water temperature and depth. Chla parameter only influenced one fish species and therefore was not useful as an explanatory variable for our study. The influence of the predictors and prey distribution of the franciscana diet are similar to that found in the habitat by research cruise data. Some structures analysed (e.g. squid beaks) may remain longer in the stomachs. Therefore, the findings not only suggest a fairly opportunistic behaviour but it is likely that franciscana may occupy, and possibly for long periods, small spatial ranges. This behaviour might be a strategy for minimizing energetic costs by restricting movements to short distance areas, which can be an important factor for conservation planning along the southern Brazilian coast.