FISHERY BULLETIN; VOL. 83, NO. 4 



Table 1.— Number of larval spot per 100 m^ caught off North Carolina during the seasons 

 of 1978-79 and 1979-80. N.S. = No sample taken. 



1978-79 

 cruise 



Station number 



^Same as station 19. 



ing the winter periods of 1967-70 showed major im- 

 migration peaks in February and March (unpublished 

 data from R. M. Lewis, Beaufort Laboratory; Thayer 

 et al. 1974). The duration of estuarine immigration 

 generally reflected the duration of the spawning 

 season (Fig. 2). 



Statistically significant monthly variations 

 (ANOVA, P < 0.05) in both age and length of larvae 

 entering the New^port River estuary were observed 

 from December to April (Fig. 5). Mean age at entry 

 increased linearly from December to March and then 

 decreased in April. Thus, larvae spawned at the 

 beginning or end of the season spent relatively less 

 time in the offshore environment than did larvae 

 spawned in the middle of the season. Length follow- 

 ed a similar trend, except during January and early 

 February when it remained about constant, in- 

 dicating a declining rate of growth. As determined 

 from seven samples collected at Pivers Island (Fig. 

 5) and one at Beaufort Inlet (19 March 1980), spot 

 entering the estuary averaged 59 d-old (range 40-80). 



In general, larvae entering the estuary together 

 had similar spawning dates. As a rule, 50% of the 

 fish in any Pivers Island sample had been spawned 

 within a period of 5 d and all had been spawned 

 within a period of 14 d (Fig. 2). The one exception 

 was the last sample from Pivers Island in which 

 several larvae were more than a month older than 

 the majority of fish. We infer from the generally 

 small variation in age of fish within a sample that 

 a continuum of cohorts moved past Pivers Island 

 enroute to the upstream parts of the estuary and 

 that early juveniles entered the lower estuary 

 segregated by age. 



Growth Estimates 



Average growth of larvae was described by the 

 Laird version (Laird et al. 1965) of the Gompertz 

 growth equation (Zweifel and Lasker 1976) fitted to 

 estimated age and size at time of capture data for 

 1978-79 and 1979-80 (Fig. 6). Variance about the 

 estimated growth curve was assumed to represent 

 genetic differences in growth potential and the ef- 

 fects of differing environmental conditions over the 

 year (Pennington 1979). To stabilize the variance of 

 length over the observed age interval, we used the 

 log-transformed version of the Gompertz growth 

 equation: 



In [L.J = In [L,.,] + 



'(0) 



'W 



(0)J 



a 



[1 - e-"'] 



(2) 



where L,„ = length at time t, 

 length at i = 0, 

 specific growth rate at ^ = 0, 

 rate of exponential decay of the 

 specific growth rata 



'(0 

 ^(0) = 



The time origin {t = 0) was selected as hatching time 

 (day 0) and values for L q,, A,q,, and a were obtain- 

 ed by nonlinear regression. Age accounted for 96% 

 of the variation in length for one year class (1978-79) 

 and 91% of the variance in length for the other 

 (1979-80) in the log-transformed models. We 

 estimated that spot grew from about 1.6 mm SL at 

 hatching to 17-19 mm at 90 d. The predicted size at 

 hatching agrees well with laboratory observations 

 of Powell and Gordy (1980). Population growth 



590 



