More whales Eubalaena australis and decreasing trend

ENRIQUE A. CRESPO; SUSANA N. PEDRAZA; SILVANA L. DANS; MARIANO A. COSCARELLA; GUILLERMO M. SVENDSEN; DEGRATI MARIANA; JUAN C. PEDRAZA; ADRIAN SCHIAVINI

San Diego

Workshop; Annual meetings of the IWC scientific committee; 2015

The analysis of the information presented in this paper supports that the Southern Right Whale population is increasing in the nursing area around Península Valdés. In spite that the number of whales in the surveyed area is increasing, the rate is steadily decreasing. Density has been also increasing and whales have been expanding their distribution to deeper waters during the last decade (Crespo et al., 2014). The analysis of mortality rates since the early 70´s show an increase. All these facts together are coherent with a density-dependence response. The same effect was also shown by Rowntree et al., (2013) when they compared the increase in calf mortality with the increase of living calves.With regards to the rate of increase, the calves increasing at a higher rate than the Solitary Individuals and the Mating Groups, which almost show no increase. These differences could also be explained by the fact that some adult whales could be moving to other peripheral areas as shown by the number of breeding groups and solitary individuals sighted in Golfo San Matías. This could be due to a non-stable age structure within this population (Caughley, 1977).It should be considered that the analysis of GLM models and the estimation of the total whales and calves born with the cumulative function only considered the coastal strip. However, in section 2 it was demonstrated that many whales are off the coastal zone in deeper waters. Previously we have reported a shift in the proportion of the different groups type recorded from each side of the plane, and the proportion ofmother-calf pairs is higher than expected on the coastal side (Crespo et al., 2014). The estimates of the number of whales in the deeper waters of Golfo Nuevo are a clear indication that the 5m corridor or ?whale road? proposed by R. Payne is no longer the only place where southern right whales are to be found in large numbers (Payne, 1986). One thing we need to clarify is the proportion of whales that can be found in deeper waters. Also, is clear for us that whales are not evenly distributed in deeper waters, with more whales surrounding the areas of high density in the coastal zone. An extensive boat based survey must be undertaken in the next seasons, including both high and low density areas inside the gulfs, for us to be able to make accurate estimates of the population size.The surveyed area for the southern right whale includes most of the population off the coast of Argentina, and could be considered as the optimum habitat for the species on its breeding grounds. Considering that Península Valdés as the optimum habitat, once it becomes saturated, the rate of growth in the area should decrease, and the whales should start to move to other regions, less dense and in which the rate of growth could be higher. There are clues that indicate that this could be the case, as shown by the number of whales occupying deeper waters in Península Valdés, the increasing number of whales spotted in Golfo San Matías, Buenos Aires, Uruguay and Santa Catarina in southern Brazil (Groch, et al 2005, IWC. 2010). The actual population rate of increase would be a combination of the growth in the optimal habitat and the rate of expansion to more peripheral areas.