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Southern right whale mortalities at Península Valdes, Argentina: updated information for 2016-2017

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Mariano Sironi, Victoria J. Rowntree, Matias Di Martino, Lucia Alzugaray, Virgina Rago, Carina F. Maron and Marcela Uhart

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International Whaling Commission


Southern right whales (Eubalaena australis) have experienced high mortality rates at Península Valdés, Argentina in recent years (Rowntree et al., 2013). In 2003, the Southern Right Whale Health Monitoring Program was established by a consortium of NGOs to monitor the health status of this population by post-mortem examinations. Previous reports to the IWC included information on the mortalities through 2015. Here we update information for the 2016-2017 seasons. A total of 774 dead whales were recorded on the Península Valdés calving ground (Chubut Province) since 2003. The number of dead whales was 15 in 2016 and 28 in 2017. As in previous years, most of the dead whales were newborn calves (93% of strandings in 2016 and 96% in 2017; 94.5% for both years combined). More dead whales were recorded in Golfo Nuevo (87% in 2016 and 72% in 2017) than in Golfo San José (13% in 2016 and 28% in 2017). Most whales died in July - August (8 individuals, 56%) in 2016, and in September – October (19 individuals, 68%) in 2017. One juvenile whale stranded alive in Caleta de Los Loros, Río Negro Province on 24 June, 2016 and died seven days later. The remaining whales were dead when reported or found, and post-mortem examinations were performed when and to the extent that carcass condition allowed. Biotoxins, infectious diseases, malnutrition, the physiological and behavioral effects of Kelp Gull (Larus dominicanus) attacks on newborn calves and density-dependent processes have been proposed as hypotheses to explain the high calf mortalities in this calving ground (IWC 2011, 2015). Results on biotoxins (Wilson et al., 2015), Kelp Gull lesions (Marón et al., 2015a) and histological findings suggestive of infectious and non-infectious processes (McAloose et al., 2016) were published by Southern Right Whale Health Monitoring Program researchers and collaborators and reported to the IWC Scientific Committee. New lines of research are being developed at present to test the hypothesis that stress from injuries in southern right whales (predominantly due to Kelp Gull attacks) negatively affects their physiological homeostasis and could be a contributing factor to calf deaths in this population.

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