Unexplained recurring high mortality of southern right whale Eubalaena australis calves at Península Valdés, Argentina

A concerning surge in unexplained calf mortality among southern right whales (Eubalaena australis) at Península Valdés, Argentina, between 2003 and 2011, threatens the recovery of a critically depleted subpopulation. During this period, hundreds of calves died, with mortality rates increasing faster than the growth of living calves over the preceding three decades. The pattern of deaths varied seasonally, with some calves reaching at least one meter in length before perishing, suggesting they were healthy prior to death. Large calves (>6 m) also died in early calving seasons (2008-2009), hinting at potential population-wide stressors like nutritional deficiencies. Despite extensive tissue sampling and analysis, no consistent lesions, pathogens, or algal biotoxins have been identified as the cause. This study documents these mortality events, contextualizes them historically, and highlights ongoing efforts to pinpoint their causes, emphasizing the urgent need for conservation action to prevent further decline of this endangered species.

Rowntree, V., Uhart, M., Sironi, M., Chirife, A., Di Martino, M., La Sala, L., Musmeci, L., Mohamed, N., Andrejuk, J., McAloose, D., Sala, J., Carribero, A., Rally, H., Franco, M., Adler, F., Brownell Jr, R., Seger, J., & Rowles, T. (2013). Unexplained recurring high mortality of southern right whale Eubalaena australis calves at Península Valdés, Argentina. Marine Ecology Progress Series, 493, 275–289. https://doi.org/10.3354/meps10506