FISHERY BULLETIN: VOL. 86, NO. 1 



(42) 



1979 



D ILA 



(324) 



I — C 



1980 



LU 



< 



Q 



LU 

 CC 



Q. 

 < 

 O 



(191) 



(80 



)l— {JH 



FL 



rn — HLA 



1980 



(338)h 

 (223)1 — 



1981 



LA 



c±i ^L/ 



-Cp ITX 



(88)1 IJHFL 



1982 



DEC I Jan I FEB ' 



SPAWNING DATE 



Figure 8. — Schematic plots of the spawning times of larval gulf menhaden collected in the northern 

 Gulf of Mexico during 6 cruises of the RV Oregon II from December 1979 to February 1982. In each 

 distribution the vertical line is the median value and 50% of the data points fall within the block. Lines 

 beyond the boxes represent the range of data points. The value in parentheses to the left of each 

 distribution is the number of fish. 



mouths and were 4.5 mm SL. However, develop- 

 mental rates are probably temperature depen- 

 dent (Powell and Phonlor 1986), and hence larvae 

 at lower temperatures would be older at first feed- 

 ing. 



The Gompertz growth model appears to ade- 

 quately describe the growth of larval gulf men- 

 haden in most cases. Except where data are some- 

 what limited (Figs. 6b, d; 7b, d) the fit of the 

 model is relatively good and the r'^ is >0.73 for 

 each transect (Table 2). Gompertz gi'owth models 

 have been used (Zweifel and Lasker 1976; Methot 

 and Kramer 1979; Laroche et al. 1982; Warlen 

 and Chester 1985) to describe growth of larval 

 fishes where the length-age plots are nonlinear 

 and upper asymptotes were apparent. 



Average growth rate of larval gulf menhaden to 

 day 60 was 0.30 mm/day throughout its oceanic 



existence. This rate was very similar to that, 0.28 

 mm/day (estimated from figure 2 of Hettler 1984), 

 for larvae reared in the laboratory at 20° ± 2°C 

 for 60 days. However, wild-caught larvae were 

 from wider extremes in water temperature, with 

 mean early season (December) temperatures 

 from 17.4° to 21.2°C and late season (February) 

 12.9° to 16.4°C. The growth rate of larval Atlantic 

 herring, Clupea harengus , up to 50 days old was 

 similar and varied between 0.23 and 0.30 mm/day 

 (Lough et al. 1982). However, gulf menhaden lar- 

 vae grew slower than the fast growing but rela- 

 tively short-lived engraulids — bay anchovy, An- 

 choa mitchilli (Fives et al. 1986) and northern 

 anchovy, Engraulis mordax (Methot and Kramer 

 1979). 



Only a small number of larvae from all the 

 collections were 2^50 days old. Larvae of this age 



86 



