The distribution, seasonality and trends in abundance of southern right whales Eubalaena australis off De Hoop Nature Reserve, South Africa

Abstract

Between September 1984 and January 1993, monthly counts of southern right whales were made from up to four vantage points in the De Hoop Nature Reserve, South Africa. Evidence from aerial surveys indicates that these vantage points are well situated in relation to the main concentration of right whales off De Hoop. Right whales arrive in June, reach peak abundance in September and depart in December or January. The incidence of calves increases from zero in June to 15–22% between August and October (reflecting the season of births), before increasing again to 33% in November and 42% in December (reflecting the earlier departure of animals without calves). The numbers of right whales seen off De Hoop on aerial surveys from 1971 to 1992 have increased at a rate faster than that of the inshore population as a whole, indicating a degree of net immigration into the area. The rate of this immigration may have slowed down during the past 10 years. Shore counts for adults show a positive correlation with aerial counts in the same year, confirming their utility in monitoring future trends in abundance.