Decline in body condition in the Antarctic minke whale (Balaenoptera bonaerensis) in the Southern Ocean during the 1990s

Abstract

Changes in the body condition of Antarctic minke whales (Balaenoptera bonaerensis) have been investigated in a number of studies, but remain contested. Here we provide a new analysis of body condition measurements, with particularly careful attention to the statistical model building and to model selection issues. We analyse body condition data for a large number (4704) of minke whales caught between 1987 and 2005. The data consist of five different variables related to body condition (fat weight, blubber thickness and girth) and a number of temporal, spatial and biological covariates. The body condition variables are analysed using linear mixed-effects models, for which we provide sound biological motivation. Further, we conduct model selection with the focused information criterion (FIC), reflecting the fact that we have a clearly specified research question, which leads us to a clear focus parameter of particular interest. We find that there has been a substantial decline in body condition over the study period (the net declines are estimated to 10% for fat weight, 7% for blubber thickness and 3% for the girth). Interestingly, there seems to be some differences in body condition trends between males and females and in different regions of the Antarctic. The decline in body condition could indicate major changes in the Antarctic ecosystem, in particular, increased competition from some larger krill-eating whale species.

Report of the Scientific Committee

“…The Committee encourages submission of papers at SC69B. Cunen et al (2021) examined changes in the body condition of Antarctic minke whales sampled during the Japanese whaling research programme in the Antarctic (JARPA I from 1987/88 to 2004/05). In 2018, the Committee agreed that all approaches result in point estimates reflecting a decline when fitted to a linear trend in time.…”

“…Furthermore, the Committee encouraged publication in peer-reviewed journals of the results which formed the basis for this agreement. Cunen et al (2021) fulfils this publication request, detailing their analyses which had been based on 'focused information criteria' models, which indicated a substantial decline in all body condition measurements over the study period: 10% for fat weight, 7% for blubber thickness and 3% for girth. The Committee thanks Cunen et al (2021) for responding to its request.…”

Evolution of the recombination regulator PRDM9 in minke whales

“…Antarctic minke whale s inhabit the waters of the Antarctic ocean in the Southern Hemisphere during feeding season but seasonally migrate to the temperate waters near the Equator during the breeding season [ 12 ]. Antarctic minke whale body condition has declined, particularly during the 1990s [ 13 ], and anthropogenic pressures such as commercial whaling and future climate change are expected to exacerbate the decline of baleen whales [ 14 ].…”