Warlen: Spawning time and recruitment of Brevoortia tyrannus 



431 



served a similar difference (13-fold) in relative abun- 

 dances of Atlantic menhaden larvae at Pivers Island 

 between 1966-67 and 1967-68. Their low year (1967- 

 68) estimate was about one half that of the low year 

 (1990-91) estimate in this study. Although relative 

 abundances give estimates of larval recruitment 

 among years, it is not known how representative the 

 estimates are of coastwide year-class strength of the 

 species. Virtual population analyses (VPA) indicate 

 that recruitment to the commercial fishery to age-1 

 from the 1987-88 year class was about double that 

 of the previous two years, 1985-86 and 1986-87 

 ( Vaughan, 1993). In comparison, the estimate of lar- 

 val recruitment for 1987-88 was about 3-5 times 

 larger than the 1985-86 and 1986-87 estimates. 



An increase in SL of Atlantic menhaden larvae 

 recruited through each of seven seasons has also been 

 observed in earlier studies. Higham and Nicholson 

 (1964) noted that in plankton collections taken in 

 the vicinity of Beaufort, North Carolina, Atlantic 

 menhaden larvae were smallest in December and 

 largest in April. Lewis and Mann ( 1971) found that 

 the condition factor (weight/length 3 ) of larval Atlan- 

 tic menhaden also increased throughout the season. 

 Checkley et al. (1988) showed that the mean SL of 

 Atlantic menhaden larvae about 10 km offshore in- 

 creased over the period from January 15 to early 

 March. The mean SL of Atlantic menhaden collected 

 by Hettler and Chester (1990) increased from 16.0 

 mm in November to 27.6 mm in March then de- 

 creased to 24.0 mm in April. Similar trends in in- 

 creasing size of larvae collected throughout the recruit- 

 ment season have been observed for spot (Allen and 

 Barker, 1990; Flores-Coto and Warlen, 1993), Atlantic 

 croaker, Micropogonias undulatus (Allen and Barker, 

 1990; Warlen and Burke, 1990) and pinfish, Lagodon 

 rhomboides (Warlen and Burke, 1990), all species that 

 recruit to the estuary with Atlantic menhaden. 



The total time required for transport of larvae from 

 the area of hatching offshore to the estuary can be 

 estimated from the ages of larvae caught at Pivers 

 Island. The observed similarities in patterns of ages 

 over each of the seven recruitment years suggest that 

 similar transport mechanisms operate from year to 

 year. Youngest larvae, which are only recruited at 

 the beginning or end of each season, must be re- 

 cruited most efficiently to the estuary, while at other 

 times in the season transport becomes less efficient 

 as larvae require longer to get to the estuary. Also, 

 as the season progresses it is likely that spawning 

 may occur further offshore (Warlen, 1992) as suit- 

 able spawning temperature water is found farther 

 offshore and, consequently, larvae must be trans- 

 ported a greater distance to estuaries. The extended 

 period of transport allows for mixing of birthweek 



cohorts offshore as evidenced by the greater mix of 

 birthweek cohorts during the late season recruitment 

 peaks. Mixing could also occur if there is "pooling" of 

 larvae outside the inlet. Warlen ( 1992) suggested that 

 larval Atlantic menhaden transported from offshore 

 in North Carolina to the estuary was rapid in No- 

 vember-December. However, in the January-March 

 period transport was only rapid to about the mid- 

 shelf frontal zone, after which the overall transport 

 rate was much slower. It is this latter spawned group 

 that apparently makes up the largest fraction of es- 

 tuarine immigrating larvae each recruitment season. 

 In summary, during an extended period (fall/win- 

 ter/early spring) Atlantic menhaden spawn and their 

 larvae are recruited to estuaries in the northern por- 

 tion of the South Atlantic Bight. Although there is 

 variation, consistent temporal patterns of spawning, 

 recruitment density, and age and size trends are ob- 

 served from year to year. Back-calculated modes in 

 spawning suggest the importance of short periods 

 within the total spawning season and peaks in es- 

 tuarine recruitment suggest the importance of lar- 

 val across-continental-shelf transport and near-shore 

 concentrating mechanisms. 



Acknowledgments 



I gratefully acknowledge the work of Mary Boyd, 

 William Rugen, and Elisabeth Laban who prepared 

 and read otoliths. David Colby gave valuable assis- 

 tance with statistical problems and data manage- 

 ment. Peter Hanson helped with the use of a statis- 

 tical graphics program and Elisabeth Laban worked 

 on data summaries. Lynn Barker, Douglas Vaughan, 

 and David Peters provided helpful, critical reviews 

 of an earlier draft of the manuscript. This research 

 could not have been completed without the able as- 

 sistance of many persons who helped make the lar- 

 val fish collections, especially on many cold winter's 

 nights; I sincerely appreciate their help. Support for 

 portions of this study was received from the South 

 Atlantic Bight Recruitment Experiment (SABRE) 

 program of the National Oceanic and Atmospheric 

 Administration's Coastal Fisheries Ecosystem/Coastal 

 Ocean Program. 



Literature cited 



Ahrenholz, D. W., W. R. Nelson, and S. P. Epperly. 



1987. Population and fishery characteristics of At- 

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 85:569-600. 

 Ahrenholz, D. W., J. F. Guthrie, and C. W. Krouse. 



1989. Results of abundance surveys of juvenile At- 

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