| Data on top predator movement are often measured relative to broad scale oceanographic processes (>100 km), but foraging decisions are made at the scale of an individual predator (<10 km) both in horizontal and vertical dimensions. Using a series of case studies, I examined the distribution of prey relative to predators in a series of ecosystems by combining novel technologies including fisheries acoustics, oceanographic sensors, and digital archival tags. In the Gulf of Mexico, fish distributions at fine scales (both horizontal and vertical) were measured relative to hypoxic bottom waters to understand potential food web effects. Low oxygen bottom waters led to a vertical compaction in biomass that may influence predation risk and access to food. Geostrophic currents structured the distribution and density of the deep scattering layers (DSL) in the central tropical Pacific which I compared to sightings of marine mammals in the area. Scattering layers were denser near the equator correlated to primary productivity and during the night. In the Gulf of Maine, I measured forage fish distribution (sand lance, Ammodytes spp.) relative to physical features and oceanographic processes, concurrent with individual humpback whale (Megaptera novaeangliae) movement. Prey density and school shape increased the likelihood of humpback surface feeding, while physical features that correlated with sand lance abundance also correlated with increased surface feeding likelihood. In all case studies, oceanography influenced distribution and abundance of prey species. Ultimately, ecological analyses of predator distributions are improved by prey and oceanographic data collected at appropriate scales. |
