Do No Harm: Using Non-Lethal Techniques to Track Movement and Dietary Shifts Using Isotopic Records in Fin Rays

We examined the δ¹⁵N isotopic records in fin rays collected from the critically-endangered Goliath Grouper, Epinephelus itajara, and related changes of isotopic ratios over time to previously-documented life history characteristics. Fin-ray analysis was used as a non-lethal technique to sample individuals from the west and east coasts of Florida.  The δ¹⁵N data were acquired by mechanically separating the annuli of each fin ray and then analyzing the material in an Irradiance Elemental Analyzer Mass Spectrometer. The δ¹⁵N values were consistent among individuals within populations from each coast, and mirrored the expected changes in food sources during the lives of the fish. Overall, differences were found between δ¹⁵N values at juvenile life history phases versus adult phases, but the patterns associated with these shifts were unique to each population. These differences may have been due in part to the distinct ecosystem dynamics associated with the two coastal shelves of Florida. We demonstrated, for the first time, that δ¹⁵N signatures from fin rays can be used to assess the life histories of Goliath Grouper. Similar non-lethal strategies may be used to acquire information essential to the management of species of concern, such as those that are threatened or endangered.