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Resource ID
10494
Access
Open
Full Title
Linking climate and ocean productivity to the prevalence of southern right whales (Eubalaena australis) in South African waters
Author
Gideon van den Berg, Els Vermeulen, Cang Hui, Ken Findlay, Sophie von der Heyden and Guy Midgley
Abstract
South African coastline surveys conducted since 1972 reveal fluctuations and a recent reversal in a long-running increasing trend in regional abundance of southern right whales (Eubalaena australis, hereafter SRWs), whose populations have been recovering from historic whaling. Furthermore, the surveys reveal that the typical three
year calving cycle of female SRWs has shifted to four- or five years, implying either additional resting years
between successive calving events or calving failure. This study used wavelet analysis, an effective method of
time series analyses on non-stationary data, to reveal significant synchrony in the cycles of SRW cow-calf pair
annual counts along the South African coast and various climate indices (Oceanic Niño Index, September
Antarctic sea ice extent and the Antarctic Oscillation) as well as ocean colour (January chlorophyll a
concentrations in three postulated SRW feeding grounds). In addition, autoregressive integrated moving
average (ARIMA) models were used to investigate the potential role played by ocean colour and the various
climate indices in the inter-annual fluctuations of cow-calf pair counts, as well as the recent reversal in the
increasing trend of regional abundance. The impacts of climate are thought to be mediated through the
influence of physical oceanography on SRW prey (krill and copepod) availability, while chlorophyll a
concentrations have been found to correlate with densities of SRW prey. These aspects ultimately impact
feeding success and body condition of SRWs, and consequently their reproductive condition and migratory
behaviour. ARIMA models analysing the recent reversal in the increasing trend of abundance in SRW cow-calf
pair counts along the coast of South Africa, reveal significant model performance improvement through the
inclusion of the Oceanic Niño Index, the Antarctic Oscillation and chlorophyll a concentration data from one of
the three postulated SRW feeding grounds. Results of this study indicate that SRW calf abundance in coastal
South Africa appear closely influenced by the species’ life cycle, as well as feeding ground productivity and global
climate indices, similar to findings for other SRW populations.