Nelson Age; growth, mortality; and distribution of Lagodon ihomboides 



591 



Mortality 



This study is the first to report total instantaneous mortal- 

 ity (Z) rates (0.88-1.08) for pinfish older than young-of-the- 

 year. It is difficult to conclude whether the mortality rate in 

 Tampa Bay is really higher than that in the Gulf The small 

 mesh characteristics of the sampling gear, the restricted spa- 

 tial coverage of sampling from Tampa Bay to the shallows of 

 the estuary where young pinfish dominate (most gears were 

 employed in waters <3 m), or the migration of pinfish from 

 estuaries to offshore waters to spawn may have contributed 

 to the older (>age 1) fish being underrepresented in the 

 sampling of bay waters (Hansen, 1970; Darcy, 1985; Nelson, 

 1998). By assuming that pinfish are fully recruited at age 

 2 (Table 4), I estimated that Z from data for both areas 

 combined is probably more realistic because the numerical 

 proportions of pinfish ages 2 and older in Tampa Bay were 

 nearly identical to the numerical proportions of pinfish age 

 2 and older from the Gulf of Mexico. The estimate of Z from 

 data for both areas combined (0.90/vr) was close to the natu- 

 ral mortality estimate of 0.78/yr, suggesting that the portion 

 of annual mortality attributed to fisher activity, calculated 

 by (Z-M)/Z, is low [13%]. 



Distribution 



Darovec (1995). Franks et al. (1972), and Darcy and 

 Gutherz (1984) reported that pinfish from the Gulf of 

 Mexico occurred in trawls to depths between 73 m and 

 93 m. However, most pinfish captured in Gulf waters 

 off west-central Florida were captured from depths <19 

 m (Darovec, 1995). The results from the baitfish survey 

 were very similar in that most pinfish (95%) were caught 

 in waters <17 m, but the abundance-depth relationship 

 varied between years, and larger pinfish were generally 

 associated with greater depths. The propensity of pinfish 

 to limit their depth distribution and alter their size dis- 

 tribution with depth is probably due to the distribution of 

 their epibenthic prey (Stoner, 1980; Nelson and Bortone, 

 1996), the distribution of their predators, and (because 

 pinfish are visual feeders) reduced light intensity with 

 depth (Kjelson and Johnson, 1976; Luczkovich, 1988). 



In summary, ages determined from whole otoliths 

 ranged from to 7 years, and von Bertalanffy growth 

 model parameters for all aged fish were L^=219.9 mm 

 SL, k =0.33/yr, and <g =-1.10 years. High gonadosomatic 

 indices during October-December indicated that some 

 spawning may occur in Tampa Bay. Estimated lengths at 

 50% maturity were 132 mm SL for males and 131 mm SL 

 for females. Total instantaneous mortality rates from the 

 Chapman-Robson estimator ranged from 0.88 to l.OS/yr, 

 and natural mortality based on Pauly's (1980) equation 

 was 0.78/yr. Catch rates of pinfish were related to depth 

 in the Gulf of Mexico. 



Acknowledgments 



Support for this study was provided in part by the State 

 of Florida Recreational Fishing License and in part by the 



Department of the Interior, U. S. Fish and Wildlife Service, 

 Federal Aid for Sportfish Restoration, project number 

 F-43 to the Florida Fish and Wildlife Conservation Com- 

 mission. I thank the staff of the Fisheries-Independent 

 Monitoring Program at the Florida Marine Research 

 Institute for their dedication to sampling. B. Mahmoudi 

 and D. Pierce provided the baitfish cruise data. M. Murphy 

 was the second age reader E. Robillard and D. Merryman 

 sectioned the otoliths. F. Astaire provided encouragement 

 throughout the study. Comments by L. Barbieri, L. Bull- 

 ock, R. Cody, J. Lieby, J. Quinn, R. Taylor and two anony- 

 mous reviewers improved the quality of the manuscript. 



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