Project: Resolving Migratory Connectivity of Basking Sharks (Cetorhinus maximus) in the Western Atlantic Ocean: Integrating Novel Geochemical Tracers with Satellite Archival Tags

From NSF abstract:
Animal migrations represent one of nature's most spectacular and yet mysterious phenomena. Movement patterns also have considerable biological significance, determining gene flow among geographically separated populations over ecological time scales and migratory connectivity among populations over ecological time. Unfortunately studies of migration in ocean ecosystems have lagged behind those in terrestrial environments due to the logistic constraints associated with tracking aquatic animals that may travel vast distances in an opaque 3-dimensional environment. Recent research using electronic tags have, however, revealed remarkable basin scale migrations in large pelagic fishes. Nonetheless, limited by size and battery life, artificial tags cannot yet provide lifetime migration histories of long-lived species. The investigators therefore will combine electronic archival tags and natural isotope markers in vertebrae to examine dispersal and migratory connectivity of basking sharks (Cetorhinus maximus) in the western North Atlantic Ocean. The project will build on preliminary archival tag data that has shown basking sharks moving from Cape Cod Bay to waters off the coast of Brazil. The results will provide insights relevant to conservation efforts directed at the world's second largest fish species that is globally distributed but listed on the IUCN Red List of Threatened Species as vulnerable due to overfishing throughout its range.

Stable isotopes have been used successfully to trace migratory connectivity in birds and to examine natal homing in teleost fishes. The investigators hope to transform the field by analyzing carbon and nitrogen isotopes in specific organic compounds isolated from vertebral samples to examine lifetime movement patterns of basking sharks. They will avoid confounding movement and a change in diet by analyzing essential and non-essential amino acids that differ in the degree of trophic fractionation for C and N isotopes. Results from pop-up archival tags will be combined with a meta-analysis of plankton carbon and nitrogen isotopes in the North Atlantic Ocean and used to generate predicted stable isotope profiles that will then be tested against observed patterns in the basking shark vertebrae. Fisheries and conservation biologists have come to the realization that many of the biological and physical processes that underlie population dynamics of marine-capture fish species have important spatial aspects. The investigators will develop and apply tools that will provide unique estimates of dispersal and migratory connectivity in a large pelagic shark. The tools will be readily applicable to other large pelagics that make basin-scale migrations and particularly those that take advantage of high primary and secondary productivity in high latitudes during summer months.

Publications resulting from this research:
Skomal, G.B., Zeeman, S.I., Chisholm, J.H., Summers, E.L., Walsh, H.J., McMahon, K.W., and Thorrold, S.R. 2009. Transequatorial migrations by basking sharks in the western Atlantic Ocean. Current Biology, v.19, p. 1019. doi: 10.1016/j.cub.2009.04.019