DURBIN ET AL: MENHADEN AGE. GROWTH, AND CHEMICAL COMPOSITION 



The relationship between wet weight and fork 

 length in the 1976 fish was determined by 

 regressing logio wet weight on log™ fork length. 

 The functional regressions determined for age 

 groups 2-5 were not significantly different in 

 slope or elevation (P<0.05), and a common rela- 

 tionship for all ages combined was therefore 

 determined; where W = wet weight (g) and L = 

 fork length (mm): 



log™ W=- 5.3055 +3.2441 logic L (2) 



r= 0.9615 

 n = 2,015. 



Back-Calculated Size-at-Age and 

 Growth Rate 



The fork length, at the time a menhaden 

 formed each of its scale annuli, was calculated by 

 direct proportion by: 



L 



S. 



(3) 



where L, = fork length ( mm) at the time scale an- 

 nulus i was formed 

 . Si = width of scale ( mm ) from focus to an- 



nulus i 

 L c — fork length (mm) of the fish at time 



of capture 

 S c = width of scale (mm) from focus to 

 outer margin, at time of capture. 



Mean back-calculated fork lengths of each age 

 group at the time of annulus formation are 

 presented in Table 2. The overall length-weight 

 relationship (Equation (2)) was used to convert 

 the back-calculated fork lengths of each fish to 

 wet weight; mean values for each age group are 

 presented in Table 2. 



These back-calculated lengths and weights 

 were then used to calculate the annual instan- 

 taneous growth rate of each fish during previous 

 years (Table 3), where 



G t (L) = log,, L(i+i, - log, L 



(i) 



(4) 



where G,(L) = instantaneous yearly growth rate 



Table 2.— Mean back-calculated fork length and wet weight of Atlantic menhaden caught in Rhode Island waters 

 during 1976, using the overall length-weight relationship (Equation (2)). 



Table 3.— Mean annual growth in fork length (L) 1 and in wet weight (W) 2 of each age group of Atlantic 

 menhaden during previous years. These individual growth rates were then averaged to provide an estimate of 

 the mean growth of each age group during successive years of its life. 



'Growth was calculated individually for each fish from its back-calculated fork length at the time of annulus formation in 2 succes- 

 sive years, where instantaneous yearly growth rate, G, (L) = log. Li,+n - log. Lw 



2 Growth was calculated individually for each fish from its back-calculated wet weight at the time of annulus formation, where 

 instantaneous yearly growth rate, G, (IV) - log, Wum - log, Wai. 



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