Franciscana Dolphin (Pontoporia blainvillei)
The franciscana dolphin, Pontoporia blainvillei (figure 1) is an endemic species of the Southwest Atlantic Ocean, inhabiting
coastal waters of Brazil, Uruguay and Argentina (Figure 2).
Although considered by many to be a member of the river dolphins, franciscanas are found mainly in coastal marine waters with occasional occurrences in estuaries. Its distribution, restricted to shallow waters (< 30m depth) makes it particularly vulnerable to many anthropogenic activities, including habitat degradation and interactions with fisheries. Continued incidental mortality in coastal gillnet fisheries is the greatest threat to the species’ survival throughout most of its range distribution. Mortality of franciscana in fishing operations has been observed for almost sixty years. [Figure 1] A Franciscana dolphin incidentally caught in southern Brazil. (Photo: Paulo Ott). Reports on by-catch in shark gillnet fisheries off Uruguay date back to the early 1940s. As early as the late 1960s and early 1970s, annual by-catch estimates reached 1,500 to 2,000 animals. A decade later gillnet fisheries for bottom-dwelling fish also became the major conservation concern for franciscana in both Brazil and Argentina. Nowadays, by-catch have been reported from all the main fishing villages spread out in the coast along most of the species distribution. The existent levels of incidental mortality of the species in some areas seem to be potentially serious and probably unsustainable over the years. In southern Brazil, for instance, recent fishery-mortality studies reported an mortality of 750 dolphins/year, which could represent 4,5% of the estimated population for this area. In view of these high levels of incidental mortality, the franciscana is considered the most threatened small cetacean in the western South Atlantic Ocean. Nevertheless, the real impact of the fisheries on the species is still unknown especially because of the uncertainties about stock structure and abundance estimates. At the present, two distinct populations has been proposed for franciscanas based on morphological and preliminary molecular analyses: one small population restricted to the northern distribution range of the species (between 22°S and 27°S) and a larger population occurring along southern Brazil, Uruguay and Argentina (from 32° to 38°S). [Figure 2] Franciscana dolphin distribution. In collaboration with researchers from Brazil (GEMARS/CECLIMAR & MORG/FURG), the Natural Resource DNA Profiling & Forensic Centre, has been carrying out molecular studies, using mithocondrial and nuclear markers, on franciscana dolphins incidentally caught along most of the species distribution. The principle aim of the project is to better understand the population structure of the species, including levels of subdivision and extent of gene flow among the populations. The delineation of these stock boundaries is urgently needed to define appropriate management units, which are critical for the establishment of effectives conservation plans for the species.