Pink shrimp (Farfantepenaeus duorarum, formerly Penaeus duorarum) have an estuarine-dependent life cycle on the southwestern Florida shelf. Juveniles are found inshore 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 1997, 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 13C-enriched values of −9 to −15‰ that were distinct from −18 to −29‰ values of animals from twelve mangrove-lined bays. On average, 75% of the shrimp
at each station had similar isotope distributions (i.e., within a ± 1‰ range for C and N isotopes), suggesting that these shrimp were residents with similar diets. However, the remaining 25% of the shrimp 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 animals. About 60% of the smaller, <20 g shrimp had similar values similar to the large, long-term residents.
The remaining 40% of the smaller shrimp were classified as recent immigrants, and usually had −9 to −14‰ δ13C values consistent with an origin from seagrass meadows, with only a few animals showing −17 to −20‰ 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.
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