AHRENHOLZ ET AL.: ATLANTIC MENHADEN POPULATION AND FISHERY 



mortality apparently again increased, as the age 

 structure became markedly constricted by 1965, 

 and drastically truncated by 1967. Recruitment 

 began to improve by 1971, culminating with rela- 

 tively large year classes in 1975 and 1979. Mor- 

 tality rates for some ages began to decline during 

 the late 1970's, and the older age groups began to 

 strengthen, consistent with the decline of the 

 catchability coefficient with increased population 

 size. 



With respect to yield per recruit, there appears 

 to be no recorded period of Atlantic menhaden 

 fishing when an ideal harvesting regime existed 

 in the purse seine fishery. Age-0 fish have been 

 harvested since at least 1955 (Figs. 8, 9). Except 

 for influences of the exceptionally large 1951 and 

 1958 year classes, most of the catches sampled for 

 age have been dominated by age 2 relative to 

 biomass, and ages 1 and 2 relative to numbers. 

 Major numerical but minor biomass contribu- 

 tions have been evident for age-0 fish. Inferences 

 of the fishery's high dependency on younger age 

 groups can be traced back to 1940. Given that the 

 population distributes itself by age and size along 

 the Atlantic coast, the quantity of landings and 



degree of effort expended in areas where younger 

 and smaller fish predominate suggests a similar 

 age composition for total catches during the pre- 

 sampling period (Figs. 3, 5). 



Landings in the middle Atlantic area domi- 

 nated the fishery in earlier years, but a shift had 

 occurred by 1964, at which time Chesapeake Bay 

 landings began to dominate (Fig. 4). Responding 

 to a reduced population of larger and older fish, 

 the industry increased the proportion of fishing 

 effort exerted in areas closer to the large nursery 

 areas of Chesapeake Bay and the south Atlantic 

 area. Further, the fishery shifted from one that 

 harvested the larger age I's and 2's, and older 

 fish, to one that harvests the smaller and younger 

 fish. The larger, older fish were and still are vul- 

 nerable to the fishery during their fall migra- 

 tions, but effort on these fish appears to be re- 

 duced within the north Atlantic and middle 

 Atlantic areas. 



A comparison of age-specific estimates of ex- 

 ploitation rates supports the earlier discussion on 

 age dependency, population sizes, and age struc- 

 ture (Fig. 26). In the mid-1950's, the exploitation 

 rates, although varying, were lower than those 



g 



I- 

 < 



0. 

 X 



m 



< 



IT 



1.00- 

 .90 

 .80 

 .70 

 .60 

 .50 

 .40 

 .30- 

 .20 

 .10 

 

 .80- 

 .70 

 .60 

 .50 

 .40 

 .30 

 .20 

 .10 



Age 5 



Age 4 





/ 



Age 2 



V / \° ' / • ?^ —  o 



-Age 3 



/\ 



Age 1 



\. 



j^l^i. 





/, 



^— Age 



_L 



1956 60 64 68 72 76 80 



YEAR OF FISHING 



Figure 26. — Estimates of annual rates of exploitation of Atlantic men- 

 haden, ages through 5. 



597 



