Warlen: Spawning time and recruitment of Brevoortia tyrannus 



425 



the end of the recruitment year (Fig. 5). Larvae re- 

 cruited to the estuary were always >20 mm SL, ex- 

 cept early in the recruitment year (November-De- 

 cember) when the mean size could be as low as 15 

 mm (Fig. 5). The overall recruitment year mean SL 

 of larvae varied between 23.2 and 25.4 mm for the seven 

 years and the mean SL over all years was 24.6 mm. 



Spawning time 



The menhaden spawning season in North Carolina 

 was estimated from the birthdate distributions of 

 larvae that survived to recruit to the estuary. The 

 percentage distribution of spawning by week (Fig. 

 6) was based on the relative abundance of larvae col- 

 lected at Pivers Island throughout the recruitment 

 year. The spawning season was protracted, lasting 

 four to six months (Fig. 6). Estimated spawning was 

 variable among birthweeks. In every spawning sea- 

 son, there was a dominant birthweek mode that con- 

 tributed from 25 to 43% of the total estuarine re- 

 cruits. Except for 1987-88 (20 December 1987), these 

 modes occurred very close to the new moon phase of 

 the lunar cycle ( 10 January 1986, 3 1 December 1986, 

 9 December 1988, 28 December 1989, 15 January 

 1991, and 6 December 1991). Median spawning and 

 modal spawning peaks were always in December or 

 January as were the second and third quartile inter- 

 vals of the distributions, except in 1989-90 when the 



second quartile interval extended into November 

 (Fig. 6). Over all seven years, an average of more 

 than 76% of all spawning occurred in December- 

 January (Table 3). Earlier season spawning (Octo- 

 ber-November) contributed an average of 16%> of the 

 total, although November spawning alone could 

 sometimes account for about 26% (Table 3). Little 

 spawning occurred in February ( . 7%) and in only 

 two years did the March contribution exceed 1%. 



The data suggest that within-season spawning fre- 

 quency may be multimodal. There was an indication 

 in 1985-86, 1986-87, 1989-90, 1990-91, and 1991- 

 92 that a small, early mode may have occurred in 

 October or November (Fig. 6). If there was an early 

 mode in 1988— 89, it may have blended with the mode 

 for later spawned fish. A small, late season mode 

 ( February or March ) may also have been present and 

 was most evident in the 1986-87, 1988-89, 1989- 

 90, and 1991-92 spawning seasons. 



Recruitment of birthweek cohorts 



Individual birthweek cohorts were recruited to the 

 estuary over periods from one week to several months 

 (Fig. 7). Those birthweek cohorts that recruited over 

 the shortest time periods were generally spawned 

 either early (October) or late (February-March) in 

 the season. Birthweek cohorts spawned from mid- 

 November through January usually recruited over 



