Southern Right Whales Eubalaena australis still growing but at a decelerated speed

CRESPO, ENRIQUE ALBERTO; DANS, SILVANA LAURA; PEDRAZA, SUSANA NOEMÍ; DEGRATI, MARIANA; COSCARELLA, MARIANO ALBERTO; SVENDSEN, GUILLERMO M.

Bled

Workshop; 67th Meeting of the International Whaling Commission Scientific Committee; 2017

International Whaling Commision

This paper reports on aerial surveys conducted to estimate the relative abundance and increasing rate trend of southern right whales from Península Valdés. The number of counted whales tripled from 1999 to 2016. We modelled the number of whales, the number of calves, the number of solitary individuals and the number of individuals in breeding groups using as predictive variables the year, the Julian day and Julian day^2 by means of generalized linear models. The rate of increase decreased from near 7% in 2007 to a 0.06% and 2.30% for total number of whales and number of calves, respectively for 2016. Trends in the rates of increase for total number of whales and number of calves were negative (-0.732% and -0.376%, respectively). The habitat use of the whales changed along the years with mother and calves using more heavily the near-shore strip, resulting in a decreasing trend for solitary individuals and breeding groups in near-shore waters. We conclude that whales are still increasing their abundance, while the rate of increase is decreasing. Differences in the rates of increase of the group types and changes in habitat use are proposed to be consequence of a density dependence process.