Murphy and Chittenden: Reproduction, age and growth, and movements of Pepnlus burti 



107 



abundant groups of fish 30-60 mm originated 

 then, and the smallest fish caught then usually 

 reflected the more slowly growing Winter- 

 spawned individuals. The few fish 50-60 mm, 

 about 2.5-3 months of age on average, caught 

 September to mid-November, and the one Gravid 

 fish captured in July, probably indicate some sum- 

 mer spawning (Fig. 5). 



Peprilus burti spawn primarily during discrete 

 Winter (late January-mid-May) and Fall (early 

 September-late October) periods. Length com- 

 positions were consistently bimodal off Texas, 

 and modal groups originated from Winter and 

 Fall spawning periods (Fig. 4). Winter-spawned 

 fish first appeared mid-April to early July at 

 lengths of 30-75 mm at an average age of 1.5-4.5 

 months, which indicates spawning from about late 

 January to mid-May. Fall-spawned fish first ap- 

 peared mid-November to early December at 

 lengths of 30-75 mm and an average age of 1.5- 

 4.5 months, which indicates spawning from about 

 early September to late October. Modes for 

 Winter cohorts are readily followed in the periods: 

 (1) mid-April 1978-late February 1979, (2) mid- 

 May 1979-mid-June 1980, and (3) late May-late 

 July 1980. Modes for Fall cohorts can be followed 

 in the periods: (1) early December 1977-mid-July 

 1978, (2) December 1978-mid-October 1979, and 

 (3) mid-November 1979-late July 1980. Calcu- 

 lated mean hatching dates occurred during late 

 January to March for Winter groups and during 

 September for Fall groups (Table 2). 



In contrast to length frequencies, gonad weight 

 and maturity data indicate P. burti spawns dur- 

 ing much of the fall and winter. Gonad weight 

 regressions had maximum slopes and elevations 

 and usually were significant September through 

 February (Fig. 3). Regressions had lower slopes 

 and elevations and usually were not significant 

 March through August (Murphy 1981, Table 2). Most 

 Gravid and/or Ripe fish were captured November 

 through February (Fig. 5). 



The end of the Fall spawning period is not clear, but 

 length frequencies suggest low-level spawning, or 

 spawning success, during late fall and early winter. The 

 consistently bimodal length frequencies must reflect 

 some temporal separation in spawning that originates 

 then. Fall 7 y fish recruited in abundance by mid- Janu- 

 ary to mid-February 1980 when they were 60-105 mm 

 long and 3-7 months of age (Fig. 4). Fall 78 fish re- 

 cruited in abundance by mid-March 1979 when they 

 were 90-110mm and 5.5-7.5 months of age. These data 

 suggest peak fall spawning ends by about late October. 

 No abundant, distinct groups of fish 30-60 mm and 

 1.5-3 months of age originated during any late-fall or 



30 



20- 



OCT 78 

 n=21 



MAY 79 

 n=11 



■'•., 



150 



100 

 50 



OCT 79 

 n=204 



u*. 



DEC 78 

 n=76 



-i^nF ]. 



o 



FEB 79 

 n=93 



40 1 

 20 J 



. 



MAR 79 

 n = 346 



AUG 79 

 n=171 



>L F* 



APR 79 

 n=271 



JU 



JAN 80 

 n = 252 



W, 9 



l linnnn 



L 



120-1 



80 

 40 



SEP 79 

 n=203 



2 3 4 5 6 7 



' 7B 



I ' 1 I 79 



200- 

 100 



FEB 80 

 n=304 



1 2 3 4 5 6 7 8 

 MATURITY STAGE 



1 2 3 4 5 6 7 



Figure 5 



Monthly maturity stages (Table 1) of immature and female Peprilus 

 burti. Bars indicate Fall (F, dark) and Winter (W, light) cohorts and 

 mixtures of two cohorts (diagonals) in which cohort identity is not 

 clear for individual fish. 



early- winter period studied (Fig. 4), although 30-75 mm 

 fish— which we labeled Fall-spawned fish— persisted 

 January through May in 1979 and 1980 and probably 

 reflect some winter spawning. 



Cohort spawning and recruitment periodicity vary 

 within and between years. Winter 78 fish appeared as 

 an abundant, distinct group in mid- April, but few 

 recruited thereafter (Fig. 4). In contrast, Winter 79 

 and 80 fish did not form abundant, distinct groups 

 until June, although a few fish appeared in May. Fall 

 groups first appeared mid-November to early Decem- 

 ber. However, the bimodal size frequencies of the 

 Fall 79 cohort in the period mid-February to early June 

 1980 suggest intragroup variation in spawning or 

 recruitment success and periodicity similar to that for 

 winter cohorts. We have interpreted the lower mode 



