McDonough and Wenner: Growth, recruitment, and abundance of juvenile Mugil cephalus 



355 



October also coincided with seasonal increases in photope- 

 riod and temperature. 



The mean size at one year of age has been found to vary 

 from 140 mm to 222 mm (TL, FL, SL) in striped mullet 

 (Broadhead, 1956; Anderson, 1958; Thomson, 1966; Chubb 

 et al., 1981). This wide range is most likely due to differ- 

 ences in methods of measurement. Previous studies have 

 used length frequencies or ages determined from scales to 

 calculate size at one year of age. These techniques are not 

 as accurate in determining age as methods where otoliths 

 are used (Campana et al., 1995). Our estimates of size at 

 one year of age were 157 ±9.20 mm total length for the 

 rotenone-caught fish and 157 ±19.4 mm for the fish in the 

 juvenile aging study. Again, these sizes (in this case, mean 

 size at one year of age) are consistent between the two 

 studies, despite the different time scales used to calculate 

 the growth curves. The ability to estimate size at age is im- 

 portant in the determination of the first annulus; however, 

 the first annular growth increment for striped mullet in 

 South Carolina was deposited in July at 15 to 23 months 

 of age (McDonough, unpubl. data). Therefore, at 12 months 

 of age the first annular increment would not have been 

 deposited yet. The time lag between 12 months in age and 

 the actual time of annual increment deposition probably 

 also contributed to the wide range in sizes at one year of 

 age in the literature. 



The wide range of size at age of both juveniles and adult 

 striped mullet is probably due to a range of environmen- 

 tal and biological factors that affect their growth. Kuo et 

 al. (1973) found the greatest mortality in striped mullet 

 during the first ten days of life. The end of this period co- 

 incided with the onset of intensive feeding behavior, which 

 was approximately five days after complete yolksac deple- 

 tion. The differences in the size range of these striped mul- 

 let during the 42-day larval period indicated differential 

 growth. In Kuo et al.'s (1973) experiment, food was not a 

 limiting factor and all the fish were hatched at the same 

 time. A similar wide range in size at age was observed in 

 the fish from the juvenile aging study. If food was not a 

 growth-limiting factor for these fish, the only biological 

 processes that could account for the differences would be 

 either differing specific metabolic rates or intraspecific 

 competition among larvae. These fish could have come 

 from a wide range of geographic areas (where spawning 

 occurred) at different times of the spawning season and 

 food resources offshore could have been better for some 

 groups of larvae than for others. Environmental factors 

 that may have affected growth could include temperature 

 and photoperiod, which could vary for larvae spawned at 

 different times of the spawning season. Fish spawned in 

 the mid-part of the spawning season (December to Febru- 

 ary) may have some advantage over fish spawned either 

 earlier or later in the season. Rooker and Holt ( 1997 ) found 

 cohort-specific growth rates to be higher in larval red drum 

 (Sciaenops ocellatus) that were spawned during mid-sea- 

 son versus fish spawned at the beginning and end of the 

 season. Fish that arrived earlier would spend more time in 

 cold water and have slower growth. In addition, resources 

 at spawning locations probably vary and these differences 

 may show up as differential growth in comparably aged 



fish. We have found that variability in size at age is even 

 more apparent in adult fish (McDonough, unpubl. data). 

 The wide range of size at age found in the adults may be 

 due to the same factor that causes differential growth in 

 larval and juvenile striped mullet. This would not be un- 

 common because processes that occur during the larval 

 phases of oceanic spawning fishes have been found to af- 

 fect many characteristics of the adult population, namely 

 recruitment, abundance, and growth (Houde, 1987, 1997; 

 Bradford, 1992; Mertz and Myers, 1995; Comyns, 1998; 

 Levin, 1998). 



In summary, striped mullet in South Carolina deposit 

 daily growth increments on the sagittal otoliths. The 

 spawning season for these fish, as determined through 

 birthdate back-calculation, was from October though 

 April and subsequent recruitment occurred from January 

 through May. However, there was evidence that young-of- 

 the-year striped mullet can recruit as early as November. 

 After recruitment, juvenile striped mullet were found 

 most frequently at mesohaline and polyhaline salinities 

 within the estuaries of South Carolina. Growth during the 

 first year appears to be relatively consistent over time for 

 juvenile striped mullet as indicated by the similarities in 

 growth between fish collected in our study (1998 to 2000) 

 and those collected in the rotenone study (1986 to 1991). 



Acknowledgments 



A great debt of gratitude is owed to all of those who assisted 

 in this study. We thank Ted Smith, Wallace Jenkins, and 

 Charlie Bridgham of the Marine Resources Research 

 Institute (MRRI) for providing the facilities used to con- 

 duct the validation experiment, as well as expert advice 

 and assistance in oxytetracycline marking. We also thank 

 J. Archambault, H. Von Kolnitz, W. Hegler, L. Goss, G. 

 Riekerk, C. Johnson at the MRRI for assistance in collec- 

 tions and sampling, and C. Altman from the S.C. Depart- 

 ment of Health and Environmental Control for additional 

 freshwater samples of juvenile striped mullet. Lastly, we 

 thank B. Roumillat and M. Brouwer, as well as the anony- 

 mous reviewers, for careful and helpful suggestions for 

 this manuscript. This research was made possible through 

 National Marine Fisheries Service MARFIN Grant no. 

 NA77FF0550 and National Marine Fisheries Service 

 Grant no. NA97FL0359. 



Literature cited 



Anderson,W. W. 



1958. Larval development, growth, and spawning of striped 

 mullet (Mugil cephalus) along the south Atlantic coast of 

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Anonymous. 



1959. Symposium on the classification of brackish waters, 

 Venice. Archives for Oceanography and Limonology 2 

 (suppl.l):l-24. 



Arnold, E. L.. and J. R. Thompson. 



1958. Offshore spawning of the striped mullet, Mugil cepha- 

 lus, in the Gulf of Mexico. Copeia 1958:130-132. 



