Movements and migrations of manta rays, pacific bluefin tuna, and white sharks [electronic resource] : observations and insights at the intersection of life history strategy and marine ecosystem structure
Keywords: Biology.

Recent large-scale fisheries declines, trophic cascades, and predictions of ecosystem collapse have caused a shift in focus among managers and scientists from single-species fisheries management to "ecosystem based management." Research on the relationships between large marine predators and their environments informs this recent paradigm shift in conservation strategy and illuminates how future ecosystem change might impact populations of both protected and commercially exploited species. The dissertation research presented here examines possible mechanistic linkages between the movements and migrations of three large predators and a spectrum of complex life histories and marine ecosystem structures. In the equatorial Pacific Ocean, I explore the movements of Manta rays (Manta sp.) to and from Palmyra Atoll as an indication of an important linkage between shallow reefs and ocean depths. Nighttime diving exceeding 100 meters and daytime focused visitation of reefs suggest that filter feeding on deep scattering layer organisms may necessitate mutualism with small fish at "cleaning stations." Although mantas ranged as far as 126 km from the atoll, the dependence on shallow reefs for periodic cleaning may limit their range in the open ocean. In the North Pacific Ocean, the success or failure of oceanic migrations of Pacific bluefin tuna (Thunnus orientalis) are shown to be related to seasonal changes in the availability of a migration corridor based on temperature and phytoplankton biomass, such that successful migrations only occur between the winter and summer solstices. Furthermore, two of every three fish abort migrations without visiting known forage or spawning grounds, evidence that suboptimal habitats may limit spawning behavior or fitness. In the northeast Pacific subtropical gyre, I examine spatial and temporal variability in oceanic habitat suitability in an important pelagic refuge for white sharks (Carcharodon carcharias). Changes in sea surface temperature, oceanic heat content and oxygen limitation at depth describe the spatial dimensions of available habitat but temporal changes in these factors, if present, are not resolved. However, the annual deepening of the mixed layer is coincident with the temporal pattern of habitat utilization in winter and spring, suggesting food web dynamics influence the presence or absence of white sharks. Key intra-annual changes in ecosystem structure as they relate to habitat quality are largely a function of ocean-atmosphere interactions. These seasonal variations are windows into the impacts of future climate change on marine ecosystems and indicate that "ecosystem based management" must account for such environmental dynamism. The research presented shows that ecosystem structure intersects with life history strategy in profound ways for each of the species studied; future scientific, management and conservation efforts should be directed at better understanding these baselines and estimating their potential to change.