STABLE ISOTOPE STUDIES OF PINK SHRIMP (FAREANTEPENAEUS DUORARUM BURKENROAD) MIGRATIONS ON THE SOUTHWESTERN FLORIDA SHELF

摘要

Pink shrimp (Farfantepenaeus duorarum, formerly Penaeus duorarum) have an es- tuarine-dependent life cycle on the southwestern Florida shelf. Juveniles are found in- shore in shallow seagrass meadows and mangrove-lined bays, while adults are caught offshore in the Tortugas and Sanibel fisheries. To trace shrimp movements between inshore and offshore habitats, we collected more than 300 individual pink shrimp in the spring and summer of l997, and analyzed them for carbon and nitrogen stable isotopic compositions. The isotope distributions function as naturally occurring tags or tracers of shrimp diets and movements. Shrimp from seven seagrass meadows had C-enriched values of --9 to --l5/1000 that were distinct from --l8 to --29/1000 values of animals from twelve mangrove-lined bays. On average, 75/100 of the shrimp at each station had similar isotope distributions (i.e., within a ± l/1000 range for C and N isotopes), suggesting that these shrimp were residents with similar diets. However, the remaining 25/100 of the strimp fell outside this central isotope distribution, and were likely transient migrants moving through the site at the time of collection. Offshore, we used analyses of large shrimp, >20 g wet weight, to define isotope distributions characteristic of resident ani- mals. About 60/100 of the smaller, <20 g shrimp had similar values similar to the large, long-term residents. The remaining 40/100 of the smaller shrimp were classified as recent immigrants, and usually had-9 to --l4/1000 δ C values consistent with an origin from seagrass meadows, with only a few animals showing-l7 to-20/1000 values consistent with an origin from mangrove-lined bays. Overall, the chemical tracer studies support the conclusion that the major spring peak of pink shrimp recruits into south Florida offshore fisheries largely consists of migrants from seagrass meadows.