Number of southern right whales Eubalaena australis and population trend in the neighbourhood of Península Valdés during the period 1999-2013 by means of aerial and boat surveys.

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

Bled

Congreso; SCIENTIFIC COMMITTEE OF THE INTERNATIONAL WHALING COMMISSION; 2014

During the last 15 years we developed a method for monitoring the population based on the assumption that around 95% of the whales will be found within the coastal strip. Fig. 1: A monitoring area was defined from the mouth of Chubut River (42°30´) to Puerto Lobos (42°) totalling a coastal strip of 350 nm (620km) (Fig. 1) flying the coastal zone parallel to the coastline at an altitude of 500 feet (Crespo et al., 2011). Aerial surveys were selected to be better to count whales in the monitoring area and the period between flights ranged from 45-50 days, Beaufort Sea State was between 0 and 3. Distance to the coast (on the left side of the plane) was held fairly constant at 500 m, and was controlled several times during the flight. From measures carried out with a clinometer, the effectively covered strip to the right side of the plane (deeper waters) was about 1000m. A total of 55 flights were carried out between May 1999 and December 2000 and June 2005 and November 2013. Not every year had the same number of flights, and hence effort differs yearly. a) Mother-calf pairs (MC) which are one adult female and a calf, b) Solitary individuals (SI) which can be either adult males or females or subadult individuals, c) Breeding groups (BG) which is usually formed by one adult female and n-1 males. Rate of increase estimated from linear regression and trends in abundance Data collected in 1999, 2000, and from 2005 to 2013. It was estimated from the slope of the linear regression of the log-number of whales through time (Caughley, 1977). Two response variables were used: a) the total number of whales in the peak of the season, and b) the number of calves in the peak of the season. For each year we also graphed the curve of counted whales. The number of whales throughout time was obtained for 1999, 2000, and 2005 to 2013 from 55 aerial surveys. Two analyses were carried out: a) considering all surveys carried out on the peak of the season excluding years 2008 to 2010 which were done in suboptimal weather conditions, and b) considering all surveys without exclusions.