Fish and shrimp migrations in the northern Gulf of Mexico analyzed using stable C, N, and S isotope ratios.
Natural stable isotope tags were used in the northern Gulf of Mexico to interpret migrations of five commercial fish and shrimp species: Leiostomus xanthurus, Microponias undulatus, Penaeus aztecus, P. duorarum, and P. setiferus. Along the south Texas and Florida coasts, isotopic analysis showed that seagrass meadows and possibly other shallow estuarine habitats are important feeding grounds for shrimp that are later caught in offshore fisheries. Thus stable carbon, nitrogen, and sulfur values of juvenile shrimp in grassflats coincided with isotopic values of small shrimp collected offshore. These values were -11 to 14 o/oo for C13, and +6 to +8 o/oo for both N15 and S34. In contrast to these south, during feeding and growth offshore, eventual convergence about offshore isotopic values should result for the migratory species studied. However, striking differences in convergence patterns were evident for the five species, ranging from close convergence at small, subadult sizes (P. aztecus and P. duorarum) to nonconvergence among adults L. xanthurus). These differences point to contrasts in the basic life history patterns of migration (especially the juvenile vs. adult size at which offshore migration occurs), and, for one species, showed that isotopic methods can trace yearly variations in these patterns.