Density dependent responses in Southern Right whales Eubalaena australis at Península Valés, Argentina

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

Madeira

Congreso; 30TH ANNUAL CONFERENCE OF THE EUROPEAN CETACEAN SOCIETY; 2016

European Cetacean Society

This paper presents information on rate of increase (RI) and mortality rates (MR) for SouthernRight Whales (SRW). 1) RI was estimated using GLM procedures based on data of number ofindividuals obtained in aerial surveys carried out from 1999 to 2015 in Peninsula Valdes(PV). Predictor variables were Year and Julian Day, using also Julian Day2. Response variableswere: a) total number of whales; b) number of calves; c) number of solitary individuals and c)number of mating groups. The total population is increasing at 3.23% annually and the number ofcalves by 5.54%. RI declined from 6.22% (1999-2007) to 3.23 (1999-2014). Solitary Individual andMating Groups are no longer growing, 2) the trend of MR was analysed trough time. Data of liveand dead calves was obtained for the period 1971-1973, 1981-1982 and 2003-2014. The number ofestimated calves born each year was obtained by means of a cumulative function developed fromthe GLM. It is clear that MR is variable among years. Maximum rates were observed in 2007, 2008and 2009, being the highest rate in 2008 reaching almost 30% while minimum rates were as low asthose observed in 2004 and 2014. The rates observed in the former years show the same pattern ofvariability with ranging 2-10%. Finally, the analysis of the information supports that the SRW southAtlantic stock is increasing in the nursing area around PV. Although the number of whales in thesurveyed area is increasing, RI is steadily decreasing. Density has been also increasing and whalesare expanding their distribution to deeper waters during the last decade. The analysis of the MRsince the early 70´s shows an increase. All these facts together are coherent with a densitydependence response.