Foraging patterns of gestating southern right whale mothers estimated from stable isotopic signatures in the baleen of their calves that died at Península Valdés, Argentina

VICTORIA J. ROWNTREE; MARCELA UHART; MARIANO SIRONI; LUCIANO LASALA; LUCIANA POZZI; LUCIANA MUSMECI; NADIA MOHAMED; JULIAN ANDREJUK; ANDREA CHIRIFE; MATIAS DI MARTINO; ALEJANDRO CARRIBERO; LAUREN AUSTIN; LUCIANO O. VALENZUELA

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Conferencia; 20 th Biennial Conference on the Biology of Marinne Mammals; 2013

Hundreds of calves have died since 2005 on the right-whale (Eubalaena australis) calving ground at Península Valdés, Argentina, for reasons that remain obscure.Previous demographic analyses showed that calf output declines following years of low Antarctic krill (Euphausia superba) abundance around South Georgia, one of the whales foraging areas.Genetic and stable-isotope analyses have shown that the whales have a broad foraging range and that calves inherit foraging locations from their mothers.These family traditions take some whales to the Patagonian Shelf where they feed primarily on copepods, while others feed on the Patagonian Shelf and then travel south of the Polar Front to feed on krill.Stable carbon isotope ratios of prey on the Patagonian Shelf are significantly higher than those of Antarctic krill south of the Polar Front.To address the question whether low krill abundance might have contributed to the recent high calf mortality events, we measured stable carbon isotope ratios along the lengths of 30 baleen plates collected from calves that died during the high mortality events.Baby baleen starts growing halfway through gestation so the information from the tip of the baleen to the gum line provides a six-month record of the mothers foraging locations before birth.  Eight (27%) of the baleen plates from dead calves indicated that their mothers fed exclusively on the Patagonian Shelf.This is a larger proportion than implied by the distribution of isotopic ratios for 131 mothers sampled randomly at PV in years prior to the high mortalities, but the difference is not significant due to the small number of baby baleen plates analyzed to date. Isotopic analysis of baleen plates (from adults as well as calves) can provide valuable information about the way baleen whales respond to changes in the Southern Ocean ecosystem.