More whales Eubalaena australis growing at a decelerated speed

CRESPO, ENRIQUE A; PEDRAZA, SUSANA NOEMÍ; DANS, SILVANA LAURA; ALBERTO COSCARELLA, MARIANO; SVENDSEN, G.; DEGRATTI, MARIANA; PEDRAZA, JUAN C; SCHIAVINI, ADRIÁN

San Diego

Workshop; Scientific Commitee of the International Whaling Commission; 2015

International Whaling Commission

The IWC conducted its last major review of the status of southern right whales (Eubalaena australis) in 1998 (IWC 2001) and more recently in 2010 (IWC 2010) and 2011 (IWC 2011). Following severe historical depletion by commercial whaling, several breeding populations (Argentina/Brazil, South Africa, and Australia) of southern right whales have shown evidence of strong recovery, with a doubling time of 10-12 years (Bannister 2001, Best et al. 2001, Cooke et al. 2001). The other breeding populations are still very small, and data are insufficient to determine whether they are recovering. Estimated total size for the species in the Southern Hemisphere in 1997 was 7,500 animals (of which 1,600 were mature females, including 547 from Argentina and 659 from South Africa), and the three main populations have continued to increase at a similar rate since then. Illegal Soviet catches (mainly in the 1960s) temporarily inhibited recovery, but overall the population appears to have grown strongly since then (Tormosov et al. 1998).Payne and colleagues carried out long term studies in southern right whales around Península Valdés (Argentina) since the early 70´s and estimated population size and other parameters derived from sighting data based on individual pattern of callosities. The rate of increase r was estimated close to 8% (Payne 1986; Payne et al., 1983, 1990; Whitehead et al., 1986). Those estimations were obtained from a mark-recapture model based on individual recognition of whales. Whereas in 1998 the assumed average growth rate for all populations of southern right whales throughout the Southern Hemisphere was 7.5%, during the 2011 meeting it was agreed to use 6% and 7%. However, Cooke suggested that there has been a substantial decline in the long-term rate of increase for this population in recent years, around 5.0% over the last 10 years (Cooke, per. comm. to the Workshop on SRW).However, the process of gathering the information from photo-id data bases is time consuming, and there is a need from the local management officers to have a quick andrelatively cheap methodology to estimate the abundance and population trend. This isthe main reason why we developed a method based on direct counts of whales on the coastal zone from aerial surveys. Nevertheless, some whales are found in deeper waters at least in Golfo Nuevo (Fig 1). This area cannot be surveyed by plane, and hence, estimations using boat based methodology is needed.With regards to the Península Valdés stock, in the last years the population has experienced an enhanced mortality of calves that has raised concern to the scientific community, national and provincial authorities and local people.Therefore, the objectives of this work were: 1) to estimate the relative abundance in the monitoring zone every year and the rate of increase, 2) to estimate density in deeper waters, 3) to estimate the number of whales moving around PV and calves bornthroughout the year, and 4) to analyse the mortality trend of calves through time.