Feeding ecology of southern right whales (Eubalaena australis) on the South African west coast

Abstract

South African southern right whales (Eubalaena australis, right whales) migrate between their low latitude calving grounds and their high latitude feeding grounds every year. In addition to these high latitude feeding grounds, right whales also feed on the South African west coast, specifically within a vigorously productive upwelling system (the Southern Benguela Upwelling System, SBUS). However, the feeding ecology of right whales here remain unknown, leading to the aims of the current study which, firstly, determined the sex and age class of individuals present on the west coast. Results indicated the presence of mostly female adults with an associated calf, which alluded to the west coast as a potential opportunity to build up energy reserves prior to migration. Secondly, prey hauls were conducted near presumed feeding right whales, as well as in a line of stations to determine targeted prey. Results indicated that right whales targeted mainly Calanoides, a large calanoid copepod that dominates copepod communities within the SBUS. Thirdly, both qualitative and quantitative behavioural data were used to assess right whale feeding behaviour. Qualitative data were available from behavioural observations done in 2003 – 2009, as well as in the current study. Results indicated that right whales were diving to feed at depth in the current study, compared to more frequent surface feeding observed previously, which could suggest a shift in the distribution of dense prey patches from shallower to deeper waters. However, a small sample size limited any firm conclusions. For the first time, quantitative behavioural data were collected by using animal-borne biologging tags, which measured the depth, pitch, roll, speed and heading of right whales during feeding. Results showed that right whales had comparable feeding bout duration and speed to other baleen whales in their feeding grounds. Also, right whales seem to maximize prey uptake by increasing foraging time at depth; well as in shallower waters by increasing foraging speed. This study represents the first steps into quantitatively investigating right whale feeding behaviour in a low latitude feeding ground.