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Fishery Bulletin 93(4), 1995 



Age compositions of weakfish in Chesapeake Bay 

 commercial catches are affected by migration. The 

 pattern found in this study — of older fish arriving in 

 Chesapeake Bay in April and May and then appar- 

 ently leaving approximately when yearlings arrive — 

 was also reported by Nesbit ( 1954) and Massmann 

 (1963). This pattern indicates that Chesapeake Bay 

 catches at any one time do not accurately represent 

 relative weakfish abundance at age in the Bay. It is 

 not known whether the old fish that occur in Chesa- 

 peake Bay originated there, nor is it known where 

 they go after leaving the Bay. It has been reported 

 that some weakfish that spend their younger years 

 in Chesapeake Bay migrate farther north as they grow 

 older, and that large fish are more abundant farther 

 north (Pearson, 1932; Nesbit, 1954; Perlmutter et al., 

 1956). The location of large fish may also vary from 

 year to year. For example, fish >age 4 made up only 

 4.5% of our 1990 Chesapeake Bay samples but 17.1% 

 and 17.6% of the 1991 and 1992 samples, respectively. 



The occurrence of a 17-year-old fish suggests past 

 estimates of weakfish longevity and natural mortal- 

 ity may need to be reevaluated. The maximum age 

 previously reported was age 12 (Shepherd, 1988 ). How- 

 ever, all former maximum ages were based on scales, 

 which underage weakfish older than age 6 (Lowerre- 

 Barbieri et al., 1994). The 17-year-old was aged as 7 by 

 using scales (Villoso, 1989) — suggesting older fish may 

 have occurred in the late 1970's and early 1980's but 

 were underaged. The occurrence of a 17-year-old seems 

 to indicate weakfish are longer-lived and experience 

 lower natural mortality than previously believed, given 

 the relationship between longevity and natural mor- 

 tality (Hoenig, 1983; Gulland, 1983; Vetter, 1988). 



Growth 



Adult weakfish size at age showed a large range and 

 much overlap. Broad size-at-age distributions have 

 been reported for weakfish and attributed to the long 

 spawning season from May through August (Welsh 

 and Breder, 1923; Massmann et al., 1958; Thomas, 

 1971; Chao and Musick, 1977). An extended spawn- 

 ing season affects size at age in two ways: 1) true 

 age at first annulus deposition varies from 7 to 12 

 months, depending on birthdate; and 2) fish born in 

 different months encounter different environments, 

 e.g. temperature, salinity, and prey availability, 

 which affect larval growth (Goshorn and Epifanio, 

 1991) and mortality rates (Thomas, 1971). In addi- 

 tion, spawning pulses may result in several distinct 

 size groups or modes within juvenile size distribu- 

 tions (Massmann et al., 1958; Thomas, 1971). 



Delaware Bay fish did not demonstrate a greater 

 longevity or maximum size than Chesapeake Bay fish 



in 1992-93. Maximum age was 11 in Delaware Bay 

 and 12 in Chesapeake Bay. Maximum size in both 

 regions was 875 mm TL. This is in contrast to Shep- 

 herd and Grimes' (1983) hypothesis that weakfish 

 show different regional patterns, longevity and 

 growth being lowest in the South Atlantic region, in- 

 termediate in the Chesapeake Bay region, and high- 

 est in Delaware Bay and northward. Shepherd and 

 Grimes (1983) observed a maximum age of 11 (810 

 mm TL) in the northern region and 6 (710 mm TL) 

 in the Chesapeake Bay region. However, they 

 sampled the two regions differently. Samples repre- 

 senting the Chesapeake Bay region came only from 

 a NMFS groundfish trawl survey along the Atlantic 

 coast, whereas sampling in more northern regions 

 included commercial fisheries within Gardiners Bay, 

 New York; Sandy Hook Bay, New Jersey; and Dela- 

 ware Bay. Because large fish are able to avoid trawls 

 (Gunderson, 1993), estimates of maximum age may 

 have been inaccurate owing to their sampling method 

 (Hawkins, 1988). The Virginia Saltwater Fishing 

 Tournament data show that more than 1,000 fish >5 

 kg (771 mm TL) were captured in 1980, indicating 

 that large fish did occur in the area. 



Recent studies have reported similar asymptotic 

 lengths for weakfish throughout their range. Our 

 estimate of L m (919 mm TL) is comparable to recent 

 estimates from different regions: 893 mm TL from 

 Delaware Bay (Villoso, 1989) and 917 mm fork length 

 from North Carolina (Hawkins, 1988). In contrast, 

 Shepherd and Grimes (1983) reported much lower 

 L^ estimates for the Chesapeake Bay region (686 mm 

 TL) and North Carolina (400 mm TL). 



Differential migration by size is an alternative 

 explanation for the reported higher abundance of 

 large, presumably older weakfish in the northern end 

 of the range (Pearson, 1932; Nesbit, 1954; Perlmutter 

 et al., 1956). Because swimming speed is a function 

 of body size (Moyle and Cech, 1988), larger weakfish 

 would be expected to travel faster and farther than 

 smaller fish in a given amount of time. If weakfish 

 constitute a single coastwide stock, as genetic re- 

 search suggests (Crawford et al., 1988; Graves et al., 

 1992), and most fish overwinter off North Carolina 

 (Pearson, 1932; Hawkins, 1988), then larger fish 

 would arrive in northern estuaries before smaller 

 ones in the spring. This is the pattern observed in 

 Chesapeake Bay (Hildebrand and Schroeder, 1928; 

 Massmann, 1963; the present study) and Delaware 

 Bay (Feldheim, 1975; Villoso, 1989). In addition, be- 

 cause larger fish would travel farther north, they would 

 be more abundant at the northern end of the weakfish 

 range, thus causing a size-dependent distributional 

 pattern similar to that reported for Atlantic menha- 

 den, Brevoortia tyrannus (Ahrenholz et al., 1987). 



