No evidence of malnutrition in dead southern right whale calves off Argentina as inferred from blubber thickness measurements and lipid content analyses
Carina F. Maron, Matias Di Martino, Andrea Chirife, Lucas Beltramino, Lucía Alzugaray, Frederick R. Adler, Jon Seger, Mariano Sironi, Victoria J. Rowntree, Maria Carla Labaque, Marcela Uhart
International Whaling Commission
Marine mammals rely on their subcutaneous fat layer or blubber to store energy, insulate their bodies and provide buoyancy and streamlining. Right whale calves are born with a thin blubber layer and need maternal milk to increase lipid reserves and grow. From 2003 to 2017, at least 706 southern right whale (Eubalaena australis) calves died at Península Valdés (Argentina) calving ground. Malnutrition has been considered as possible contributor to these deaths because it may negatively affect body condition of calves. However, anatomical signs of starvation were not evident during necropsies of calf carcasses. We measured blubber thickness in nine body locations of 345 dead calves to determine whether their blubber was thinner in years with high calf mortality (2003, 2005, 2007-2013) compared to low mortality years (2004, 2006, 2014-2017). Additionally, we asked whether blubber thickness changed with calf length, sex, state of decay and stranding location along the dorsal, lateral and ventral planes of the body. We also analyzed whether the lipid content of the external blubber layer varies among living (n=16) and dead (n=67) calves of similar lengths. Contrary to what we expected, when controlled for calf length and state of decay, our data suggest that blubber was not significantly thinner in high mortality years compared to low mortality years and its lipid content did not vary significantly among living and dead calves. The only variable we found to affect blubber thickness was calf length as it increased as calves grew at all body locations. These findings do not suggest a decline in the blubber condition of calves over the period examined. Moreover, they do not support the hypothesis of reduced transfer of maternal fat reserves to calves in high mortality years. However, this hypothesis should not be discarded, and additional studies should be conducted to further assess the overall health and body condition of right whale calves at Península Valdés.