DURBIN KT AL: MENHADEN AGE. GROWTH. AND CHEMICAL COMPOSITION 



The mean dates on which growth was initiated 

 during 1976 were calculated as 10 April and 21 

 April for age 2 and age 3 menhaden, respectively 

 (Equations (5) and (6) in Table 4). These esti- 

 mates fell within the time period (March-early 

 May) during which growth is believed to resume 

 and the annular ring is formed (June and 

 Roithmayr 1960). 



Seasonal Growth Rate 



In addition to these short-term estimates of 

 daily growth rate described above, the total 

 seasonal growth increment was determined for 

 individual fish from the amount of growth of the 

 scale and from back-calculations of growth in 

 fork length and wet weight, since the 1976 

 annulus was formed. By early June, age 2 and 

 age 3 menhaden had already grown considerably 

 since their 1976 annulus was formed (Table 5). 

 Age 2 menhaden had grown more in length and 

 weight, and showed a greater exponential incre- 

 ment in size, than age 3 menhaden. These results 

 mean that during the spring of 1976, either the 



Table 5. — Seasonal growth of age 2 and age 3 Atlantic men- 

 haden caught in Narragansett Bay during 1976. Absolute 

 growth (in mm fork length and g wet weight), and the instan- 

 taneous growth increment since the formation of the 197(i 

 annulus are shown. 



'Using the length-weight relationship for age 2 menhaden, where 

 log, o fork length = -5 4799 + 3 3166 log,o wet weight, 



r = 0.963, and 



n =633. 

 2 Using the length-weight relationship for age 3 menhaden, where 

 log,o fork length = -5 2138 + 3 2062 log,o wet weight, 



r= 0.956, and 



n =1,224 

 3 Average size on this date (Table 4, Equation (9)). 

 'Average size on this date (Table 4. Equation (10)). 

 5 Based on data from all fish (Table 2) 

 6 Average size on this date (Table 4, Equation (13)). 

 'Average size on this date (Table 4, Equation (14)). 



age 2 fish had a higher instantaneous daily 

 growth rate than age 3 menhaden, or they 

 resumed growth in the spring earlier than the 

 age 3 fish, or both. 



By 8 September the mean growth of age 

 groups 2 and 3 during 1976 was considerably 

 greater than the average yearly growth rates of 

 age 2 and age 3 menhaden in other years, as 

 estimated from the back-calculations of size-at- 

 age (Tables 2, 3). For example, during 1976 the 

 scale annuli of age 3 menhaden indicated that 

 when these fish were age 2, their total exponen- 

 tial increments in fork length and wet weight 

 (i.e., their instantaneous yearly growth rates) 

 were 0.2406 and 0.7805, respectively. In com- 

 parison, by 8 September the mean exponential 

 increments in fork length and wet weight of age 

 2 menhaden during 1976 were 0.3256 and 1.0644. 

 Similarly, age 4 menhaden caught during 1976 

 increased in fork length by 0.1608 and in wet 

 weight by 0.5218 as age 3 fish during 1975. 

 During 1976, the increments in fork length and 

 wet weight of age 3 menhaden were 0.2700 and 

 0.8440 by 8 September. Some additional growth 

 may have taken place after 8 September; June 

 and Roithmayr (1960) found that growth of the 

 scale margin in Atlantic menhaden continued 

 until September or October. 



Results indicate that significant differences in 

 the growth rate of menhaden occur, probably 

 because menhaden, found over an extensive geo- 

 graphic area during the summer, experience a 

 wide range of temperature and food conditions" 

 that could affect growth. Further investigation 

 into regional and annual differences in the 

 instantaneous growth rates may provide a basis 

 for determining which geographic regions can 

 potentially contribute most to menhaden pro- 

 ductivity and could provide considerable insight 

 into ways of maximizing the yield from this 

 fishery. 



Chemical Composition 



The mean carbon, nitrogen, caloric, and ash 

 contents and dry weight of menhaden from 

 Narragansett Bay are summarized in Table 6. 

 The ratio of dry weightwet weight remained 

 fairly constant in all samples; otherwise, there 

 was a consistent trend in those fish with a high 

 caloric content toward high carbon content and 

 low nitrogren and ash content as a percent of dry 

 weight (Fig. 4). 



Ash, caloric, and moisture contents of the men- 



139 



