Hello everyone! My name is Kyle Logan, and I’m from La Fayette, Georgia. I am a rising junior at Wittenberg University in Springfield, Ohio, majoring in biology and minoring in marine science and East Asian Studies. This summer I have the privilege to work with Dr. Benjamin Walther and Matthew Seeley here in Port Aransas, Texas, on a project involving a species of fish significantly important to the economy and culture of the Gulf of Mexico, the Atlantic tarpon (Megalops atlanticus). Tarpon are large migratory fish that are popular targets for recreational fishermen. Historically they were abundant in the Gulf, but their populations have decreased to such an extent that they are now labeled “Vulnerable” by the IUCN. However, little is known about which habitats conservation efforts for tarpon should be focused on.
Tarpon can use habitats of varying salinities over their life histories. Concentrations of trace elements such as barium and strontium and stable isotopes of carbon have been shown to correlate with salinity in aquatic environments. Fish scales grow incrementally in concentric rings throughout the life of the fish and incorporate these trace elements and stable isotopes that reflect the water they’re living in and the food they’re consuming. Provided that they are not regenerated, the rings of these scales can provide information on migrations between environments of different salinities over the course of the fish’s life history. My study will involve analyses of stable isotope ratios in tarpon scales to determine how they change over the lifetime of each fish. I will use carbon stable isotopes to identify movements across salinity gradients, and nitrogen stable isotopes to assess changes in trophic level (an organism’s place in the food chain). Carbon isotopes will be compared to previously obtained trace element analysis data on the same scales to see if the patterns match. For nitrogen isotopes, I expect to see a pattern of increasing enrichment from the core to the outside of the scale because tarpon are known to eat prey of increasing trophic level over the course of their lives. Typical methods for analyzing stable isotopes and trace elements in fish use otoliths, or the ear stone of the fish, which requires sacrificing the fish to obtain the otolith. Scales can be obtained non-lethally from the fish, so if our results are what we expect, this method could be used to understand the migration patterns of catch-and-release species like tarpon to help more efficiently focus efforts to aid in their conservation, and perhaps could be applied to a number of other large migratory fish species with endangered or vulnerable populations! I’m very excited to see how this study turns out, and to learn all that I can this summer!