Natural stable isotopic signatures are found in a variety of animals and plants. Differences in the composition of these isotopes are derived from the environment and diet. Stable isotopes have proven to be powerful markers for ecological studies. Environmental and foodweb isotopic signatures can vary spatially based on a variety of biogeochemical processes. Organisms moving between isotopically distinct foodwebs or regions may incorporate these distinguishable signatures into their tissues. Trophic level, temperature, depth, and latitude are some factors known to influence the enrichment or depletion of atomically ‘heavier’ isotopes (fractionation) in tissues. Organisms moving between isotopically distinct foodwebs or regions may incorporate these distinguishable signatures into their tissues. The feasibility of stable isotope analysis is being tested to track size- and age-specific movement patterns of the blue shark (Prionace glauca). Blue sharks have been found to sexually segregate during the year and have been shown to exhibit large migrations. Analysis of stable composition deposited within vertebrae will be used to identify changes in environmental regimes and will be related to geographic areas inhabited during movement. Analyses will be performed on stable carbon, nitrogen, and oxygen isotopes using the mass spectrometer at the Earth Sciences Laboratory, University of California at Santa Cruz. Currently, vertebral and muscle tissue samples are being collected from specimens throughout the Pacific Ocean.