Ontogenetic variation of δ13C and δ15N in male sperm whale teeth – inferences on sperm whale dietary and migratory history in the North Atlantic
Sperm whales, Physeter macrocephalus, are deep diving toothed whales distributed in all oceans and, although they are among the best studied cetaceans, some fundamental questions remain unanswered. In particular, these concern the spatio-temporal patterns of males’ movements once they leave their natal groups and start segregating to higher latitudes.
Isotope ratios (d13C and d15N) of the food are permanently recorded in incremental structures such as tooth dentine and provide a high resolution record of physiological events, habitat use and dietary patterns throughout life. We hope to be able to investigate large-scale movements and dietary history of male sperm whales in the North Atlantic as inferred through determination of carbon and nitrogen isotopic ratios in tooth growth layers.
Teeth from male sperm whales stranded in Scotland and one tooth from a female stranded in Galicia will be analysed. Dentine samples will be cut running parallel to the growth layers, from the pulp cavity edge to the apex.
We expect that large-scale movements of juvenile males to higher latitudes will be reflected in the d13C profiles, showing a gradual depletion concurrent with the negative correlation of d13C with latitude found in tissues of several marine predators. Since females are not thought to undertake large-scale migrations, no such change should be apparent in female teeth. We also predict that for older males the frequency of migrations to and from the breeding areas in low latitudes will be apparent in the tooth profiles, which will therefore show an oscillation in values for d13C. Life-history events such as weaning and an increase in trophic level as the animal grows are expected to be apparent in the d15N profiles which should start to become 15N-rich after an early stage of depletion as the animal weans. We will also be able to investigate if there is geographical or ecological niche segregation of males with age at high latitudes by comparing the profiles of different individuals.
For more details contact:
School of Biological Sciences (Zoology),
University of Aberdeen,
AB24 2TZ, UK