Investigation of pygmy sperm whale (Kogia breviceps ) populations in the southeastern United States using stable isotopes of carbon, nitrogen, and oxygen in teeth

The pygmy sperm whale (Kogia breviceps) is currently the second-most commonly stranded cetacean in the Southeastern United States (SEUS), but information concerning their population structure is severely limited. This study utilized stable isotope analysis to investigate the possible migratory patterns and population structure of K. breviceps among six different regions in the SEUS. Combined growth layers from different regions of the teeth were subsampled via dental drill and analyzed representing four different age classes: calf, juvenile, sub-adult, and adult, as well as four yearlings that had stranded with their mothers. Stable isotope ratios of carbon and nitrogen were measured in the organic component of 46 teeth, and oxygen isotope ratios were measured in the inorganic (hydroxyapatite) component of 21 teeth obtained from stranded individuals. There was a high degree of individual variability in delta13C, delta 15N, and delta18O resulting in no significant differences between the six different regions: South Carolina, Georgia, Northern, Central, and Southern Florida, and the Gulf of Mexico. Differences between the age classes were significant for delta13C and delta 15N. Adults exhibited significantly more negative delta13 C than subadults. These results support a previously hypothesized inshore-offshore migration for Kogia breviceps. Yearlings displayed significantly higher delta15N values than all other age classes due to nursing. A slight increase in delta15N from juvenile to adult supports a possible ontogenetic shift in the trophic level of prey. Results from this study provide the first carbon and nitrogen isotope values from different age classes of pygmy sperm whales as well as the first reported oxygen isotopes values for this species.