Examining sociological differences and the influence of prey distribution and environmental variability in the distribution of a top marine predator, the bottlenose dolphin (Tursiops truncatus)

Abstract

The purpose of this dissertation was to examine the influence of environmental variability on the distribution of prey, and the influence of prey spatial structure and habitat variability may have on the distributions of bottlenose dolphins (Tursiops truncatus). Additionally I examined how sociological differences (behavior type and the changes in a foraging behavior specific to Cedar Key Florida) influences the relative roles of bottlenose dolphins within the population.

The Gowans et al. scheme assumes that small groups form small communities and that foraging groups are small and rare as there are few foraging benefits to promote grouping. Using network analysis, I found that foraging occurs in small groups or alone, but there were preferential associations between individuals in Overall, Socialize, and Travel networks.

I examined driver-barrier foraging behavior over several field seasons to assess the prediction that there are few foraging benefits to promote grouping. The driver dolphin does have greater catch success than the barrier dolphins regardless of group size. There is also evidence that barrier dolphins may have a role in increasing foraging efficiency by decreasing the number of incomplete bouts. Both the driver and barrier dolphins do better in larger groups when incomplete bouts are factored in. Therefore there are some foraging benefits that can promote grouping.

In bottlenose dolphin foraging research, it is often assumed that habitat use is related to prey availability, though this is rarely directly tested. From my collaborative work using a database collected by the Florida Fish and Wildlife Commission’s Fisheries-Independent Monitoring (FIM) program, I evaluated the abundance of potential prey and their relationship to habitat and other biological and physical variables. I used MULTISPATI, which uses principal components analysis to partition and display patterns of spatial variation. The results show that there are correlations between fish-site scores and environmental variables. Spatial analysis of fish produced clear results, however neither PCA nor MULTISPATI could explain dolphin distribution. This is likely because the spatial scales are not the same grain for the comparisons; dolphins are highly mobile large marine predators (the scale is fine grained), and their prey are significantly smaller and habitat-specific (the scale is coarser).