Number of Southern Right Whales Eubalaena australis and population trend in the neighbourhood of Península Valdés during the period 1999-2012 by means of aerial and boat surveys.

CRESPO, E. A.; PEDRAZA, SUSANA NOEMI; DANS, S. L.; COSCARELLA, M.A.; G. SVENDSEN; M. DEGRATI

Setubal

Congreso; 27th. ANNUAL CONFERENCE OF THE EUROPEAN CETACEAN SOCIETY; 2013

A quick and cheap methodology was developed to estimate relative abundance and population trend of Southern Right Whales based on direct counts on the coastal zone from Chubut River to Puerto Lobos (620km of coastline). Objectives were to estimate relative abundance in the monitoring zone every year, rate of increase (RI), document changes in the distribution of whales through time, to study the seasonal pattern of arriving and departing of whales in the area and to estimate density out of the coastal zone. We surveyed the coastal zone with aircrafts and deeper waters by boat. Around 95% of the whales is found within the coastal strip. We counted a) mother-calf pairs (MC), solitary individuals (SI) and breeding groups (BG) which are usually formed by one adult female and n-1 males. RI was estimated from the slope of the linear regression of the log-number of whales or calves through time in the peak of the season. Whale density (D) in deeper areas was estimated using the standard distance sampling methods applied to individual animals. RI for the period 1999-2011 was estimated from number of whales (r= 7.0, Lower CI 95%= 4.6, Upper CI= 9.3; R2= 0.93, n= 6) and from the newborn calves (r= 6.5, Lower CI 95%= 2.8, Upper CI= 10.1; R2= 0.82, n= 6) in the peak of the season through time. D obtained in offshore areas was 2.61 whales/km2, and the effective strip width was about 73m and corresponds to whales in transit from the mouth of the gulfs to the coastal zone. A rough estimation of the surface covered by nautical surveys can be around 200 km2, therefore another 500 whales can be moving in deeper waters and added to at least another 1300 whales in the coastal zone during the peak of the season.