RATE OF INCREASE DECLINING AND MORTALITY RATES INCREASING AS INDICATORS OF DENSITY-DEPENDENCE IN SOUTHERN RIGHT WHALE, EUBALAENA AUSTRALIS, IN PATAGONIA.

PEDRAZA, SUSANA; PEDRAZA JUAN CARLOS; CRESPO, ENRIQUE; COSCARELLA, MARIANO A.

Congreso; XII CONGRESO DE LA SOCIEDAD LATINOAMERICANA DE ESPECIALISTAS EN MAMÍFEROS ACUÁTICOS.; 2018

This paper reports on aerial surveys conducted to estimate the relative abundance, trend in growth and mortality ratesof the southern right whale (Eubalaena australis) population from Península Valdés using GLM procedures basedon data of number of individuals obtained in aerial surveys carried out from 1999 to 2017 in Peninsula Valdes (PV).We modelled the total number of whales, the number of Calves, the number of Solitary Individuals and the numberof individuals in Breeding Groups using as predictive variables the Year, Julian day and Julian day2. The numberof whales counted tripled from 1999 to 2016. The rate of increase decreased from near 7% in 2007 to a 0.06% and2.30% for total number of whales and number of calves, respectively for 2016. Trends in the rates of increase fortotal number of whales and number of calves were negative (-0.732% and -0.376%, respectively). The habitat use ofthe whales changed along the years, with mothers and calves using more heavily the near-shore strip, resulting in adecreasing trend for solitary individuals and breeding groups in near-shore waters. We conclude that whales are stillincreasing their abundance, while the rate of increase is decreasing. Differences in the rates of increase of the grouptypes and changes in habitat use are thought to be consequence of a density dependence process. Data of live anddead calves were obtained for the period 1971-1973, 1981-1982 and 2003-2014 from published records. The numberof estimated calves born each year was obtained by means of a cumulative function developed from the GLM. It isclear that mortality is variable among years. Maximum rates were observed in 2007, 2008 and 2009, being the highestrate in 2008 reaching almost 30% while minimum rates were as low as those observed in 2004 and 2014. The ratesobserved in the former years show the same pattern of variability with ranging 2-10%. The analysis of the MR since theearly 70´s shows an increase. All these facts together are coherent with a density-dependence response.