Recent rapid increases in the right whale (Eubalaena australis) population off southern Brazil

Abstract

Right whales (Eubalaena australis) that gather on a wintering ground off southern Brazil have been aerial surveyed and photographically identified since 1987. As of 2003 the Brazilian Right Whale Catalogue has 315 different individual whales of which 31 were resighted in other years (23 females, 3 yearlings and 5 whales of unknown age/sex). No resightings occurred prior to 1994 and 71% (n=24) were recorded in 2003. The modal observed interval between calving events is 3 years, consistent with successful reproduction. From 1997 to 2003 the number of reproductive females in the Central Survey Area off Brazil increased at a rate of 29.8% per year (95% CL 15.7, 44.0), and at 14% per year (95% CL 7.1, 20.9) from 1987 to 2003. These rates are significantly different from zero (t=4.133, p<0.009 and t=4.06, p<0.004, respectively). The increase from 1997 to 2003 is higher than the rates observed for right whales in other wintering grounds in the South Atlantic. The right whales on the Brazilian wintering ground are not just transients. Ten percent of the whales have been resighted. If the number of whales continues to increase they will probably expand their distribution throughout their historical 2,400 km range and come into increasing conflict with human activities.