FISHERY BULLETIN: VOL. 81. NO. 1 



in fork length for a fish age i 

 L( () = back-calculated fork length at 

 the time annulus i was formed 

 L ((+ D = back-calculated fork length at 

 the time annulus i + 1 was formed. 



The instantaneous annual growth in wet weight, 

 Gj (W), was similarly calculated from back- 

 calculated wet weight of each fish at the time 

 each annulus was formed (Table 3). 



Growth calculated in this way is the "true 

 growth rate" of the individual fish, as opposed to 

 the "population growth rate" derived from the 

 mean size-at-age of a fish population and which 

 generally underestimates the true rate (Ricker 

 1975a). However, individual growth rates cal- 

 culated according to Equation (4) may still 

 underestimate growth of the average individual 

 in prior years, if the back-calculations of size-at- 

 age are affected by Lea's Phenomenon. Although 

 Lea's Phenomenon has been observed in men- 

 haden (June and Roithmayr 1960; Nicholson 

 1972), we are unable to assess the importance of 

 this potential bias in Tables 2 and 3, because we 

 lack the necessary information on actual mean 

 size and seasonal growth rates of the menhaden 

 population during 1970-75. 



Among age groups 3-6 (1970-73 year classes), 

 the mean back-calculated size-at-age and the 

 annual instantaneous growth rates of fish of 

 equivalent age were not significantly different 

 (P<0.05) (Tables 2, 3). Annual growth rates 

 declined with increasing age of the fish. The 

 mean back-calculated size-at-age of age 2 men- 

 haden (1974 year class) was, however, signifi- 

 cantly larger (P<0.05) than that of fish of earlier 

 year classes (Table 2), indicating that age 2 men- 

 haden had grown significantly more at age and 

 age 1 than fish from the older age groups. 



Further information on total menhaden 

 population movements and on age and size 

 structure during 1976 is needed in order to 

 evaluate the Narragansett Bay data in terms of 

 the population as a whole. However, some pre- 

 liminary conclusions may be drawn, based on 

 comparisons with data from 1955 to 1971. 



The summer distribution of the Atlantic men- 

 haden is discontinuous, with a southern group 

 ranging from Florida to Virginia and a northern 

 group (composing the main body of the popula- 

 tion) ranging from Chesapeake Bay to Maine 

 (June and Reintjes 1959, 1960; June 1961; June 

 and Nicholson 1964; Nicholson and Higham 

 1964a, b, 1965a, b; Nicholson 1971, 1975). During 



summer the northern group is age-stratified 

 along the coast, with younger fish in the more 

 southern part of the range and older fish pre- 

 dominating in the north. Nicholson (1971) con- 

 cluded that age 1 menhaden were most abundant 

 from Chesapeake Bay to New Jersey; age 2 from 

 New Jersey to the south shore of Long Island; age 

 3 from Long Island Sound to Nantucket Sound; 

 and age 4+ from Nantucket Sound to Maine. The 

 average size of individuals within each age 

 group also increased with latitude, especially 

 with age 1 and age 2 fish. This size stratification 

 was much less pronounced for age 3 and older 

 menhaden. 



Since Rhode Island is located within the 

 summer population center of age 3 menhaden, 

 Rhode Island landings should provide a good 

 estimate of the mean size of age 3 menhaden in 

 the population. However, since Rhode Island is 

 near the northern limit of the age 2 fish, we 

 would expect the landings to represent only the 

 larger members of this age group. 



Records from 1955 to 1971 suggest that age 2 

 menhaden caught in Narragansett Bay during 

 1976 were probably the larger members of the 

 1974 year class and were not representative of 

 the year class as a whole. The comparatively 

 large size-at-age and the growth rates back- 

 calculated for the age 2 menhaden at age and 

 age 1 (Tables 2, 3) are consistent with this sug- 

 gestion. 



Menhaden of all ages (including age 2) caught 

 in Narragansett Bay during 1976 were among 

 the smallest fish for their age ever recorded, and 

 resembled the very small menhaden typically 

 caught in Chesapeake Bay in earlier years (June 

 and Reintjes 1959, 1960; June 1961; June and 

 Nicholson 1964; Nicholson and Higham 1964a, b, 

 1965a, b; Nicholson 1971). The back-calculated 

 fork lengths of the 1976 fish demonstrated that 

 they had been small since age 1. Size differences 

 between age groups were also greatly reduced 

 (Tables 1, 2, 3). 



The reason for the small size of menhaden 

 caught in Narragansett Bay during 1975 and 

 1976 is not known. Present results are open to 

 two interpretations: 1) Migratory patterns 

 during 1976, and possibly 1975, did not 

 follow the pattern observed in earlier years, and 

 therefore the size of the menhaden from 

 Narragansett Bay was not representative of any 

 age group in the overall population; or, 2) there 

 has been a significant, overall reduction since 

 1971 in size-at-age within the Atlantic men- 



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