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¹ University of New Mexico, Albuquerque, Nuevo Mexico,Biology Department,
² Centro de Investigacion Cientifica y Educacion Superior de Ensenada, Unidad La Paz, La Paz, Laboratorio de Macroecologia Marina
³ Instituto Politécnico Nacional, Centro Interdisciplinario de Ciencias Marinas, Instituto Politecnico Nacional, Centro Interdisciplinario de Ciencias Marinas, La Paz
⁴ 5VE Enterprises, Arcata, California
⁵ Museo de la Ballena y Ciencias Marinas, La Paz,
⁶ 7Marine Mammal Program, Prescott College Kino Bay Center for Cultural and Ecological Studies, Bah´ia de Kino,
⁷ Universidad de Colima, Manzanillo, Facultad de Ciencias Marinas
⁸ Centro de Investigacion Cientifica y de Educacion Superior de Ensenada, Ensenada, Mexico
⁹ Universidad Autonoma de Baja California Sur, La Paz,Departamento Academico de Ciencias Marinas y Costeras

Migration is a complex behavior that has evolved in multiple taxonomic groupsas a means of accessing productive foraging grounds and environmentallystable areas suitable for reproduction. For migratory whales that foragethroughout the year because of their high energetic demands, changes in theabundance of prey in different areas along their migratory route(s) can haveserious implications for individual fitness and population viability. Thus,identifying the regions these species use to forage and breed while evaluatingtheir migratory plasticity at the individual level can provide key information fortheir management and conservation. Serial stable isotope analysis of whalebaleen, a continuously growing but metabolically inert tissue, has proven usefulin generating individual migratory and foraging records over several years priorto death. We measured carbon (d13C) and nitrogen (d15N) isotope values alongthe length of baleen plates collected from thirteen blue whales of different sexand age classes, representing the largest collection analyzed to date in thenortheast Pacific Ocean. Adult females exhibited relatively stable seasonalmovements between temperate latitude foraging grounds and subtropicalbreeding grounds, although two skipped migration one year andsubsequently moved to the same subtropical breeding ground near the CostaRica Dome, potentially to give birth. Adult males exhibited two movementstrategies with most remaining at temperate latitudes for 3-4 years beforedeath, while two migrated to subtropical breeding grounds. In contrast,movement patterns in juveniles were erratic. These results are potentiallydriven by the energetic requirements during pregnancy and nursing in adultfemales, intra-specific competition among adult males, and inexperience inlocating prey in juveniles. We also describe baleen d15N patterns in recentlyweaned whales (<16.5m) that reflect switching from the consumption of milk tosolid food (krill). In addition, baleen d13C data suggest that weaned whalescontinue to use stored nutrients (blubber) acquired during the nursing periodlong after they are weaned. These results broaden our understanding of habitatselection in this species, highlight the importance of nursing for the criticalperiod after weaning, and indicate that the Costa Rica Dome is an importantcalving region for this endangered population.

Palabras clave: blue whales, migratory strategies, feeding ecology, stable isotopes, baleen plates,; intraspecific competition, nutrient transfer, northeast Pacific ocean

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