Mortality of La Plata River Dolphin, Pontoporia blainvillei, in Southern Buenos Aires Province, Argentina (1998): Big changes that change nothing.

CAPPOZZO, H.L; MONZÓN, F.; PEREZ, J. E.; CORCUERA, J.

European Cetacean Society Conference Guide & Abstracts

Universitat de Valencia

Lugar: Valencia; Año: 1999 p. 52 - 52

The La Plata River dolphin or Franciscana, Pontoporia blainvillei, an endemic small cetacean of the Southwest Atlantic coast, is threatened all along its distribution by a sustained high level of incidental mortality in artisanal fisheries. Here we assess the incidental capture levels in Argentinian waters between 1998-2000. We surveyed 15 localities along the coast of the Buenos Aires Province,  between General Lavalle (35° 06´ S, 57° 08´ W) and Bahía Blanca (Ingeniero White harbour: 38° 47´S,  62° 16´ W). We registered data on  incidental mortality, fishing gears and fishing effort for the whole surveyed area. By means of 91 personal interviews with fishermen and on‑board observations during spring and summer 1999-2000. We estimated the annual Mortality (M), the Fishing Effort (FE) and the Catch per Unit of Effort (CPUE) for each locality. We analized data set with the same methology that was used in the past. The mean total mortality estimated in bottom gillnets, purse seine (Mar del Plata harbour only) and bottom trawls was 372 dolphins per year (the upper Poisson confidence limits arise the mortality level of 533 dolphins per year). A comparison with data obtained in 1993 for southern area and in 1998 for northern area of Buenos Aires Province show some significant differences. San Clemente del Tuyú showed high mortality level in both sampled oportunities (M1998= 58,  CI 95 % = 44-75 vs. M2000= 94  CI 95 % = 75.90-115). Cabo San Antonio area (include 6 small localities) mortality is still high too (M1998= 135.95,  CI 95 % = 86.6-207.5 vs. M2000= 111.5 , CI 95 % = 68.20-173.6). Mortality registered at Puerto Quequén is still low (M1993= 4.7,  CI 95 % = 1.40-11.00 vs. M2000= 12.8; CI 95 %= 6.56‑21.60), the FE diminished 63 % and its CPUE2000 was 8 times higher than CPUE1993. Claromecó (M1993= 34,  CI 95 % = 23.50-47.50 vs. M2000= 7.5 , CI 95 % = 3.10-15.10) and Monte Hermoso (M1993 = 91.5,  CI 95 % = 73.70-112.30 vs. M2000= 30, CI 95 % = 20.20-42.80) are fishing camps and mortality levels of Franciscana decreased in both localities. In IngenieroWhite-Puerto Rosales showed similar mortality in both periods surveyed (M1993= 85.50,  CI 95 % = 64.40-112.80 vs. M2000= 83 , CI 95 % = 66.10-102.90), though the vessel fleet has duplicated and the fishing gear that caused mortality in 1993 was the bottom gillnet and changed to shrimp bottom trawl in 2000. Overall, the data show that, although the fishing effort and the fishing gear changed dramatically in southern area of Buenos Aires Province (the main cause of M is now the shrimp gear, not the gillnet, given the collapse of the latter) at the end of this decade, artisanal fishing still proves to be a potential threat to the conservation of this small dolphin. Trends in M need, therefore, to be periodically monitored. An abundance estimation of and identity of stocks of the species is urgent in Argentina.