Isotopic evidence for diverse feeding locations of southern right whales (Eubalaena australis) from Argentina and lack of isotopic fractionation between mothers and calves

VALENZUELA, LUCIANO O; SIRONI, MARIANO

Conferencia; 16th Biennial Conference on the Biology of Marine Mammals; 2005

Premio al mejor poster presentado por un alumno del doctorado.  Stable isotopes can provide insights into the feeding ecology of migratory species whose feeding cannot be observed directly. We describe a stable-isotope analysis of southern right whales designed to a) estimate the number and location of feeding areas and b) determine whether calves are at a higher trophic level than their mothers as a result of lactation. Skin biopsy samples taken from free ranging right whales in 2004 at Peninsula Valdes, Argentina were analyzed for stable isotopes of carbon and nitrogen. Forty-two samples from adults clustered in four different groups suggesting that southern right whales could be using four different feeding areas. The locations of those areas are currently unknown, but the range in δ13C (-23 to -17.5) agrees with values previously reported for southern right whales baleen plates and estimated to represent feeding at or north of the Subtropical Convergence. The skin δ15N and δ13C from 20 calves did not differ from the values of their mothers (Δc-m δ15N = 0.152 ± 0.449; Δc-m δ13C = -0.239 ± 0.639). The lack of enrichment in δ13C can be interpreted as a result of consumption of lipid-rich milk that is 13C-depleted. The lack of enrichment in δ15N is more difficult to understand because the nitrogen ratios or greatly influenced by physiological processes. However, it is speculated that during anabolic states, such as during calf growth, the redirection of amino acids from oxidation/excretion to tissue syntheses and an increase in urea salvage could cause low δ15N values. This study is currently under way. More skin samples are being analyzed and collected from right whales in different bays at Peninsula Valdes.