Comparison of two techniques for estimating tilefish, yellowedge grouper, and other deepwater fish populations.
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Tilefish Lophopatilus chamaeleonticeps and yellowedge grouper Epinephelus flavolimbatus are deepwater fishes and targets of a relatively recent bottom longline fishery in th Gulf of Mexico. They are long-lived, slow growing, have very limited movements and distribution, and are susceptible to longlines. However, population size and life-history parameter estimates are generally unknown for Gulf fish. This study compared two methods for estimating population sizes to determine the most cost-effective one for use on long-term fishery-independent stock assessments. Bottom longlines were used to deplete fish from a small area, and a regression of catch per effort on cumulative catch was used to estimate the area's population prior to fishing. The population was also estimated by counting fish burrows from a submersible and expanding the mean number per unit area by the study site's area after correcting for the number of occupied burrows. Longlines and submersibles provided significantly different estimates of tilefish populations, the only species for which estimates could be compared. Longline estimates were probably more accurate because errors in area estimation and double counting were evident in submersible data. Longlines were less expensive to operate ($5000 vs. $8000 per day) and they afforded collection of size, age, and sex data on each fish caught. These data were not available from the submersible. Longlines could be used more cost-effectively than submersibles in determining long-term population changes. However, direct observation of fish behavior was not available from longlines, but was from the submersible. Submersibles also provide data on habitat and gear assessment, including deployment, efficiency, bait predation, and potential catch loss during retrieval.