Intra-annual changes in population parameters as indicators of humpback whale (Megaptera novaeangliae) migratory behavior

Many techniques used to study animal migrations rely on observations of specific animals, which provide valuable information about individuals studied but do not capture population variability. By examining changes in population parameters, researchers may gain a better understanding of migratory behaviors. In this study, intra-annual changes in population parameters were used to study migratory behaviors of humpback whales off central California in 2011/2012. Data were compared with a historic dataset from 2004/2005. Parameters measured included sex ratio, pregnancy rate, mitochondrial DNA haplotype frequencies and mean δ13C and δ15N values. Weighted moving averages of the sex ratio were moderately effective at revealing deviations from expected values. Progesterone assays successfully determined pregnancy in humpbacks and revealed a previously undocumented intra-annual decrease in pregnancy rate in 2011. Analyses of mitochondrial DNA haplotype frequencies indicated greater prevalence of haplotypes associated with British Columbia and Washington late in the year; however, the origin of these animals was unclear. Stable isotope ratios proved ineffective for measuring a fasting effect in humpbacks early in the year. The effectiveness of these parameters for investigating migratory behaviors varied, but used in conjunction with traditional methods of study, they may help create a broader understanding of animal migrations