Blue whales in the eastern Pacific Ocean (EPO) migrate between habitats that exhibit contrasting baseline nitrogen (δ15N) and carbon (δ13C) isotope values. We hypothesized that blue whale tissues record these biogeochemical changes occurring at the base of the food webs, and thus provide insights into its foraging ecology and movement patterns. To test this we analyzed the δ15N and δ13C of blue whale skin biopsies (n=405) and baleen plates (n=4) collected in different regions across the EPO from 1980 to 2011. Skin δ15N exhibited regional gradients: Alaska-California Current (13.6±0.7ppt), Gulf of California (15±0.6ppt), Costa Rica Dome (11±0.9ppt) and Galapagos-Peru (7.5±1.2ppt). There was an overlap of δ15N among the first three regions due to the isotopic turnover of the skin, which we indirectly estimated to be ~3 months, by using the monthly increment in the Gulf of California and decrement in the California Current of this isotopic signal. The δ15N range (5 to 9ppt) of whale skin in Galapagos-Peru did not overlap with the other regions, which indicates that these blue whales generally did not forage further north. Within-individual variation in δ15N along sub-sampled baleen plates suggests individual migratory strategies. During a period of ~4 years, two females migrated seasonally to the winter-spring grounds in the early 2000s, whereas two males remained within the summer-fall grounds during the 1980s. The patterns in males could be related to previously describe multi-decadal changes in resource availability. The δ15N variations of migratory whales allowed us to estimate a baleen growth rate of 1 cm/month. The δ13C from all the sampled tissues did not exhibit regional gradients, which suggests that the combined use of nearshore and offshore habitats is consistent in the species regardless of the population. Our results show that stable isotope analysis provide unique ecological and physiological information that cannot be obtained otherwise.
Citation:
Busquets-Vass, GR, S Newsome, J Calambokidis, S Aguiñiga-García, G Serra-Valente, J Jacobsen, D Gendron. 2015. Foraging ecology and movement patterns of blue whales in the eastern Pacific Ocean inferred by stable isotopes. Abstract (Proceedings) 21st Biennial Conference on the Biology of Marine Mammals, San Francisco, California, December 14-18, 2015.