318 



Fishery Bulletin 103(2) 



Estimates of M ranged from 0.15 to 0.51 and were 

 comparable to previous studies on gray snapper from 

 the southeastern United States. Johnson et al. (1994) 

 used the Pauly (1980) and Ralston (1987) methods to 

 estimate M to range from 0.12 to 0.32 for the west coast 

 of Florida, including Louisiana. Manooch and Matheson 

 (1981) used the Pauly (1980) relationship to calculate 

 M = 0.22. Burton (2001) used the same four methods 

 as in our study and found M to range from 0.18 to 

 0.43. It is well known that estimates of mortality are 

 highly variable and depend upon the parameters used 

 to calculate them. The purpose of providing various 

 estimates of M was to demonstrate to the reader the 

 variability in this important life history parameter 

 and to demonstrate how little we actually know about 

 it. Adopting our estimate of Z, we feel that the Hoenig 

 (1983) method (M=0.15) produced the most suitable 

 estimate of M for gray snapper in Louisiana waters 

 of the northern Gulf of Mexico. Based on the appar- 

 ent age-size structure of the stock, historical landings 

 data, and personal observation, all indications are that 

 this species is lightly fished in this study area. Hoenig 

 (1983) indicated that M should be roughly equivalent 

 to Z if the population is lightly exploited. Our estimate 

 of Z (0.17) was indeed roughly equivalent to M (0.15), 

 supporting our belief that fisheries mortality (F) is not 

 yet a significant threat to this fishery. 



Gray snapper could become over-exploited if a large, 

 intensive fishery developed in the northern Gulf of 

 Mexico. Landings of gray snapper in Louisiana have 

 increased dramatically over the last few years, part- 

 ly because of the recent restrictions imposed on red 

 snapper in the Gulf of Mexico. Compared to the gray 

 snapper population structure in the South Atlantic, 

 especially off the coast of south Florida (Manooch and 

 Matheson, 1981; Burton, 2001), the Louisiana popula- 

 tion appears to be healthy. Long-term heavy fishing 

 pressure has probably affected the south Florida gray 

 snapper population (Burton, 2001). As a result, the 

 population structure of south Florida is dramatically 

 different from that of Louisiana. Our estimates of Z are 

 extremely low and indicate that fishing mortality (F) is 

 currently not a significant factor for the gray snapper 

 population in Louisiana waters. A low-intensity gray 

 snapper fishery could take most of the resource without 

 endangering future production. 



Acknowledgments 



Funding and assistance with sampling was provided by 

 the Louisiana Department of Wildlife and Fisheries. We 

 would also like to thank Josh Maier, Brett Blackmon, 

 and Candace Aiken for sampling efforts and otolith 

 processing as well as Brain Milan for providing juvenile 

 gray snapper samples. We thank Steve Tomeny, the boat 

 captains, and deck hands of Captain Steve Tomeny's 

 charters in Port Fourchon, LA, as well as all the recre- 

 ational fishermen that allowed us to sample their catch. 

 We wish to thank Ann P. McNichol of National Ocean 



Sciences (Accelerator Mass Spectrometry facility at 

 the Woods Hole Oceanographic Institution) for otolith 

 radiocarbon analyses. 



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