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Fishery Bulletin 93(4). 1995 



including weakfish (Lowerre-Barbieri et al., 1994). 

 Thus, ages based on scales may lead to inappropri- 

 ate growth and mortality estimates, which can af- 

 fect yield modeling results and management decisions. 



Weakfish age and growth have been reported to 

 vary geographically, increasing with latitude (Pear- 

 son, 1932; Nesbit, 1954; Shepherd and Grimes, 1983). 

 However, it is unclear whether these differences are 

 due to different population segments (Nesbit, 1954; 

 Perlmutter et al., 1956; Seguin, 1960) or to differen- 

 tial migration (Vaughan et al., 1991). Regardless of 

 the cause, if these differences exist, estimates of 

 growth and longevity throughout the weakfish range 

 will be necessary for proper management. Weakfish 

 age and growth in the Chesapeake Bay region have 

 not been examined since Massmann (1963). A cur- 

 rent study is necessary because changes in landings 

 and maximum size and age suggest that weakfish 

 age structure may have changed. 



This study was undertaken to determine the cur- 

 rent age structure and growth of weakfish in the 

 Chesapeake Bay region, by using a validated ageing 

 method (Lowerre-Barbieri et al., 1994). The hypoth- 

 esis that weakfish in the Chesapeake Bay region 

 reach a lower maximum size and age than weakfish 

 in Delaware Bay (Shepherd and Grimes, 1983) is 

 evaluated, as are historic trends in maximum size 

 and abundance of large fish (>3.6 kg, or =8 lb) in 

 Chesapeake and Delaware Bays. 



Methods 



A total of 4,137 weakfish were collected in 1989-92 

 from pound-net, haul-seine, and gillnet fisheries in 

 the Chesapeake Bay region. On each sampling date 

 either a 22.7 kg (50 lb) box of each available market 

 grade (fish large enough to be sold for human con- 

 sumption, graded as small, medium, or large) or the 

 total catch was purchased and processed for biologi- 

 cal data. Because boxes could not be randomly se- 

 lected, our size and age compositions were not ex- 

 pandable to the overall fishery. However, Chittenden 

 ( 1989a) found little or no variation in fish size (total 

 length) among boxes, within grades. To obtain year- 

 round samples, 344 fish were collected in winter 

 (when weakfish do not occur in Chesapeake Bay: 

 Pearson, 1941; Massmann et al., 1958) from the trawl 

 fishery operating in Virginia and North Carolina 

 shelf waters north of Cape Hatteras. Since age-1 fish 

 are not fully recruited to market grades (see Size and 

 Age Composition heading in Results section), an ad- 

 ditional 200 age-1 and young-of-the-year fish were 

 collected by the Virginia Institute of Marine Science 

 (VIMS) juvenile trawl survey from May to August 



1990-92 in Chesapeake Bay. Details on sampling 

 design and gear of the VIMS survey can be found in 

 Chittenden (1989b) and Geer et al. (1990). 



To increase the number of large fish in this study 

 for comparison of maximum size and age in Chesa- 

 peake and Delaware Bays: 1) 35 fish were collected 

 from the 1992 World Championship Weakfish Tour- 

 nament in Dover, Delaware; 2) 10 fish (>3.6 kg total 

 weight) from Delaware Bay and 5 fish (>3.6 kg total 

 weight) from Chesapeake Bay were collected from 

 commercial catches in 1992 and 1993; and 3) 41 fish 

 (>500 mm total length) taken in Delaware Bay in 

 1985 and 1986 by Villoso ( 1989) were included in the 

 analysis. Fish >3.6 kg (=8 lb) or >500 mm total length 

 (TL) were targeted because these fish were beyond 

 the range common in our regular Chesapeake Bay 

 samples (see Size and Age Composition heading in 

 Results section). To evaluate historic trends in maxi- 

 mum size and abundance of large fish, the annual 

 number of citation-size fish and the total weight (TW) 

 of the largest fish reported were obtained from the 

 Virginia Saltwater Fishing Tournament (1958-92) 

 and from the Delaware State Fishing Tournament 

 (1968-92). Citation-size fish are large and rare 

 enough to be considered trophy fish. Citation size 

 may change if larger fish become more numerable 

 (e.g. weakfish citation size has fluctuated from 1.8 to 

 5.5 kg in the Chesapeake Bay over the past 25 years). 



In general, collections were processed for biologi- 

 cal data as follows: fish were sexed, measured for TL 

 (nearest mm), total gutted weight (TGW, nearest 

 gram), and gonad weight (GW, nearest gram). Gut- 

 ted weights included GW and were used (rather than 

 total weights) because weakfish are piscivorous and 

 can swallow fish a third of their own weight, a char- 

 acteristic that could greatly bias somatic weights 

 (Lowerre-Barbieri, 1994). Somatic weight (SW) was 

 calculated as TGW minus GW. 



Otoliths from 3,290 fish were sectioned and aged 

 by using the validated method described in Lowerre- 

 Barbieri et al. ( 1994). Of 1,191 otoliths read by two 

 separate readers, 99.8% of the assigned ages agreed. 

 In addition, otolith annuli did not show severe crowd- 

 ing at older ages and were easily distinguished (even 

 in a 17-year-old, the oldest fish aged [Fig. 1]). More 

 than 95% of the fish sampled were aged each year 

 except 1990. In 1990, when many small fish were 

 sampled, those to be aged (794 out of 2,098) were 

 selected by systematic subsampling. Ages were as- 

 signed assuming 1 January as an arbitrary birthdate 

 (Jearld, 1983; Shepherd, 1988). This birthdate was 

 selected so that fish of the same year class collected 

 in April and May — before annuli form (Lowerre- 

 Barbieri et al., 1994) — would be assigned the same 

 age as those collected after annuli had formed. 



