FISHERY BULLETIN: VOL 85, NO. 3 



the maximum that the population could support, 

 and thus the rather rapid growth of the fishery in 

 the early to mid-1950's was a response to a sub- 

 stantial increase in abundance of Atlantic men- 

 haden and not simply increased effort applied to 

 an underexploited stock. 



Changes in stock abundance due to fluctuations 

 in spawning success were prevalent in the 1940's. 

 This conclusion is drawn from the statement of 

 purpose for study given by June and Reintjes 

 (1959). They noted changes in abundance among 

 geographic areas and seasons and some poor 

 catches. This condition is expected when recruit- 

 ment fluctuates in a fishery that has a stock 

 which is differentially distributed by age and size. 



Data from early years indicated a limited re- 

 source. Catch closely paralleled effort for the 

 1941-47 seasons, but catches during 1948 and 

 1949 (about 350,000 t) were less than expected 

 given the effort expended (Fig. 1). Apparently the 

 stock subsequently underwent a marked increase 

 in abundance, noticeable first about 1952, but 

 even more pronounced in 1953 and 1954. The 

 fishery responded, as effort again began to rise, 

 but lagged for the next two or three seasons. In 

 1959 catches were dominated by the 1958 year 

 class, which continued to provide significant 

 biomass to the fishery through 1962. 



It appears that the 1950's marked a period with 

 above average recruitment, and this was accentu- 

 ated with the apparently very large 1951 year 

 class, followed by the three relatively large year 

 classes of 1953, 1955, and 1956, and finally the 

 largest documented year class of 1958. Recruit- 

 ment did not return to the level of the 1955 year 

 class (the lesser of the three documented large 

 year classes) until 1975. To obtain some idea of 

 relative sizes, a reconstruction of these earlier 

 year classes was made using arbitrary, but con- 

 servative values for F (F = 0.25 for age 1 and 0.50 



for age 2 + ) (Table 12). Given the (older) larger 

 sized fish which were taken during the peak land- 

 ing years, these speculative year class estimates 

 are less than or nearly equal to a size necessary to 

 support the large catches of the mid-1950's (see 

 Figure 14 and Table 7). 



The age structure of the Atlantic menhaden 

 population has undergone at least two periods of 

 expansion and contraction since about 1950, and 

 has shown signs of expanding again by 1980 

 (Fig. 6). Inferences on early age composition were 

 derived primarily from the early 1952-54 sam- 

 pling of the fishery in the middle Atlantic area 

 (June and Reintjes 1959, their appendix table 2). 

 Age-5 and older fish were 1.0%, 0.8%, and 1.1% by 

 number in the samples from that area for 1952, 

 1953, and 1954 as compared to 1.8% and 2.9% for 

 1955 and 1956. The 1951 year class dominated 

 the catch during this period, comprising 84.59% 

 of the samples as age 1, 98.05% as age 2, and 

 59.02% as age 3 in the middle Atlantic area and 

 87.1 1%> as age 3 in the newly sampled north At- 

 lantic area. Hence, as noted earlier, the stock 

 probably had its strongest age structure in 1955 

 and 1956, which were coincidentally the first 

 years for which port sampling covered the full 

 geographic range of the fishery. This strength 

 was due to the increased population size, subse- 

 quent decrease in the catchability coefficient, and 

 thus a reduced fishing mortality on most age 

 groups. Higher rates of survival led to more indi- 

 viduals in the older age groups. The landings 

 were sustained above 500,000 t in the mid-1950's 

 by contributions of the 1955 and 1956 year 

 classes, but these year classes were too small to 

 prevent an increase in mortality because of in- 

 creased effort and the number of older fish were 

 reduced by 1959. The large 1958 year class aided 

 the replenishment of the older age groups, by 

 about 1960. Without another large year class, 



Table 12. — Estimates from virtual population analyses (mixed time interval, see text) of number at age in tfiousands on 1 March for the 

 1950-59 year classes of Atlantic menhaden. Bracketed values represent estimates obtained from back calculations using arbitrary values 

 of F(0.25 for age 1 and 0.50 for ages 2 + ) 



'This age group may contain a small number of age 9 or 10 individuals, see text 



596 



