Stable isotope ratios as tracers of migration during the early life stages of marine fishes

In previous work, we showed the delta(13)C and delta(15)N of red drum (Sciaenops ocellatus) larvae changed following recruitment from planktonic, coastal habitat to seagrass meadows in an estuary. Stable isotope ratio (SIR) measurements therefore served as endogenous tracers of estuarine recruitment. We developed and validated an empirical model based on SIR to back-calculate the time between recruitment and capture for individual larvae (T(rec)) and the standard length at which estuarine immigration occurred (L(rec)) for an entire recruitment season. T(rec) estimates were used to reconstruct the daily pattern of estuarine recruitment. L(rec) values were used to identify the size-class specific abundance of larvae that immigrated successfully to the estuary. We propose that SIR's may be used to study recruitment to a variety of marine systems. We outline the groundwork necessary for using the empirical model. Lastly, published growth rates are used to estimate the window of opportunity in which recent recruits can be identified based on their SIR and within which the model can be applied.