Abstract

The red drum (Sciaeoops ocellatus) is an estuarine-dependent species that supports recreational fisheries in the Gulf of Mexico and western Atlantic Ocean. In the mid-1980s, concerns about overfishing of red drum resulted in recreational catch limits and a han on commercial fishing in Florida. Recent studies offshore of Tampa Bay, Florida, suggest that at least in this area the species is recovering. However, it is not known if this recovery is occurring throughout the entire Gulf of Mexico. Genetic studies have shown that there are weakly differentiated sub-populations in the Gulf. This could mean that a local recovery would not affect the entire region. We examined otolith chemistry as an independent measure of stock discreteness or connectivity. Otolith chemistry is a useful natural tag for examining the stock structure of fishes because it can refleet the elemental composition of the water in which the fish resides. Juvenile red drum otoliths from Texas, South Carolina, and Georgia and from three sites in Florida- Tampa Bay, Cedar Key, and Indian River- were analyzed using solution-based inductively coupled plasma-mass spectrometry (ICP-MS). Five elements (Mg, Mn, Zn, Sr, and Ba) were routinely detected above background levels. A MANOVA (multiple analysis of variance) indicated significant differences in the otolith chemistry of the red drum colleeted at different sites (Wilk's Lambda = 15.80, P = 0.0001). Using a cross-validation procedure, we were able to correctly classify otoliths from the Florida sites with an accuracy rate of up to 95%. This research demonstrates that otolith chemistry may be useful in delineating the stock structure of red drum throughout their range. We plan to use this method to examine sources of recruitment to the Tampa Bay area and thereby examine the conneetivity of Gulf stocks in general.

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