Seasonal changes in abundance of southern right whales Eubalaena australis around Peninsula Valdés

CRESPO, ENRIQUE ALBERTO; ARIAS, ALEJANDRO; DANS, SILVANA LAURA; COSCARELLA, MARIANO ALBERTO; PEDRAZA, SUSANA NOEMÍ

Cork

Congreso; 14th Annual Conference of the European Cetacean Society; 2000

European Cetacean Society

Payne and colleagues have carried out long term studies in Southern right whales since the early 70´s. Estimation of population size and other parameters were derived from sighting data based on individual pattern of callosities and the rate of increase was estimated to be close to 8%. The objective of this work was to develop a method for monitoring the population which could lead to study seasonal changes within and through years. Individuals were classified as: a) mother and calf pairs (MC), b) solitary individuals (SI) and c) breeding groups (BG) considering one female and n-1 males. Aerial surveys were carried out from May to December 1999, flying parallel to the coast at a distance of 500m and an altitude of 600 feet, between the mouth of Chubut River (42°30´) and Puerto Lobos (42°). In this way most of the whales could be censused because they use to stay in the 5-10 meters isobath. The first flight was done in May 19, and the period between fligths ranged among 46 and 39 days. These periods are beyond the average permanence of whales in the area, so ideally during each census new individuals were being censused. Only 5 SI were counted in May, then the number increased reaching a maximum of 204 individuals in August. BG also showed a maximum of 98 individuals involved in breeding activities in August, declining to only 6 individuals in early November. The number of newborn calves increased from July to September when a peak of 179 was reached and then declined. Sexual activity seems to occur earlier in the season than births, which occur mainly from the middle of the breeding season to the end.