654 



Fishery Bulletin 93(4), 1995 



1980). In addition, citation-size fish have recently 

 declined even though recreational effort has re- 

 mained high. 



The increased abundance of large, presumably 

 older fish apparently reflects increased recruitment 

 or year-class strength in the late 1960's. There is no 

 evidence that fishing mortality decreased. In con- 

 trast, effort increased during this same period ( Wilk, 

 1981), and peak regional landings shifted to North 

 Carolina, where exploitation of smaller weakfish is 

 higher than in more northern regions (Hawkins, 

 1988). The importance offish born in the late 1960's 

 is indicated by the increase offish > 1.8 kg (556 mm 

 TL) in Chesapeake Bay and >1.4 kg (513 mm TL) in 

 Delaware Bay in 1970 and 1971, respectively. Based 

 on current TGW-at-age data (Table 2), the age of 

 these fish would be 4-5 years, and they would have 

 born between 1965 and 1967. By 1976, these fish 

 would be 9-11 years old and >5 kg TGW. The step- 

 wise increase in abundance of fish >5 kg in Chesa- 

 peake Bay and offish >4.6 kg in Delaware Bay from 

 1976 to 1980 indicates that more fish were growing 

 into this size range than were being removed, which 

 would be expected if large numbers of several strong 

 year classes were reaching age 8 or older during this 

 time period. 



Several lines of evidence suggest more than one 

 year class contributed to the increase in abundance 

 of large weakfish in the 1970's and 1980's. First, in 

 Chesapeake Bay the number of citation-size fish >5 

 kg in 1980 was larger than the number of citation- 

 size fish >1.8 kg in 1970. Similarly, in Delaware Bay 

 the number of citation size fish >4.6 kg in 1986 was 

 larger than the number of citation-size fish >1.4 kg 

 in 1971 and 1972. If only one year class was involved, 

 the number offish surviving to older and larger sizes 

 would decrease rather than increase. Second, the 

 pattern in Delaware Bay — of increasing numbers of 

 fish >4.6 kg from 1975 to 1980, with a decrease in 

 1981 and 1982 and then a second increase until 

 1986 — suggests the contribution of more than one 

 year, class. Third, it is unlikely that the more than 

 1,300 fish >5.0 kg recorded in Delaware Bay in 1987 

 were solely from the late 1960's year classes, because 

 they would then be 19-21 years old. 



The factors which produced the large year classes 

 and allowed large numbers of weakfish to survive to 

 older ages are not clear. Joseph (1972) suggested re- 

 productive failure as the cause of the low landings 

 in the 1950's and 1960's, and thus increased repro- 

 ductive output and recruitment in the late 1960's 

 could have caused increased year-class strength. 

 That there was a shift in recruitment appears to be 

 corroborated by the fact that weakfish larvae were 

 rare in Chesapeake Bay in the 1960's (Joseph, 1972); 



yet in 1971-73 Olney (1983) found them to be sec- 

 ond in abundance only to the bay anchovy, Anchoa 

 mitchilli. Such a large shift in recruitment should 

 be reflected in juvenile indices. However, the index of 

 juvenile weakfish abundance, based on trawl surveys 

 of the York River, Virginia, from 1955 to 1982, showed 

 only a small increase in abundance in 1968 — one that 

 did not exceed levels in the 1950's — a larger peak in 

 1970, and an extreme peak in 1980 (Mercer, 1985). 



In addition to variable recruitment, there also may 

 have been changes in adult natural mortality rates. 

 Such fluctuations are not uncommon, although they 

 are difficult to document (Vetter, 1988; Hilborn and 

 Walters, 1992). Factors such as increased food avail- 

 ability, which would increase reproductive output 

 (Houde, 1989), would also be expected to decrease 

 adult natural mortality rates. 



Future research is necessary to understand better 

 fluctuations in year-class strength and interactions 

 between weakfish and other species. Stock-wide 

 mortality rates need to be estimated and weakfish 

 migration needs to be understood better. It is espe- 

 cially important that ages be based on sectioned 

 otoliths — a validated ageing technique — so that fu- 

 ture estimates of growth parameters, mortality, and 

 longevity can be better compared over time and space. 



Acknowledgments 



We would like to thank the Chesapeake Bay com- 

 mercial fishermen, James Owens, and the people 

 working at the Delaware Weakfish Sport Fishing 

 Tournament for helping us obtain the samples. Ri- 

 chard Seagraves provided us with information on the 

 Delaware fishery as well as otolith samples. Rogerio 

 Teixeira and Cindy Cooksey helped with sectioning 

 otoliths. We would like to thank three anonymous 

 reviewers for their helpful suggestions to improve 

 the manuscript. Financial support was provided by 

 the College of William and Mary, Virginia Institute 

 of Marine Science, and by a Wallop/Breaux Program 

 Grant from the U.S. Fish and Wildlife Service 

 through the Virginia Marine Resources Commission 

 For Sport Fish Restoration, Project No. F-88-R3. L. 

 R. Barbieri was partially supported by a scholarship 

 from CNPq, Ministry of Science and Technology, Bra- 

 zil (Process no. 203581/86-OC). 



Literature cited 



Ahrenholz, D. W., W. R. Nelson, and S. P. Epperly. 



1987. Population and fishery characteristics of Atlantic 

 menhaden, Brevoortia tyrannus. Fish. Bull. 85:569-600. 



