Growth and maturation of winter 

 flounder, Pleuronectes americanus, 

 in Massachusetts 



David B. Witherell 



Massachusetts Division of Marine Fisheries 

 18 Route 6A, Sandwich. MA 02563 



Present address. North Pacific Fishery Management Council 

 605 West 4th Ave.. PO. Box 1 03 1 36. Anchorage. AK 995 1 



Jay Burnett 



Northeast Fisheries Science Center 

 National Marine Fisheries Service, NOAA 

 Woods Hole. Massachusetts. 02540 



Winter flounder, Pleuronectes 

 americanus, is an important com- 

 mercial and recreational species 

 along the Atlantic coast. Previous 

 studies have shown that the winter 

 flounder stock is composed of sev- 

 eral substocks that may consist of 

 estuarine specific populations 

 (Saila, 1961; Poole, 1966a; Pierce 

 and Howe, 1977). Coastal stocks of 

 winter flounder are managed by in- 

 dividual states; area specific growth 

 and maturity information is incor- 

 porated into spawning stock bio- 

 mass-per-recruit models (ASMFC, 

 1992). 



For management purposes, two 

 stocks of winter flounder inhabit 

 Massachusetts waters; one stock 

 north of Cape Cod and the other 

 stock south and east of Cape Cod 

 (Lux et al., 1970; Howe and 

 Coates, 1975; Pierce and Howe, 

 1977). For these stock units, 

 growth parameters and sex ratios 

 were reported from 1964 to 1968 

 coastal tag returns (Howe and 

 Coates, 1975), but no studies us- 

 ing aged scale or otolith samples 

 had been undertaken. Growth 

 rates estimated from tagging may 

 not be equivalent to those based 

 on age-length data (Francis, 1988). 

 The two methods often provide dif- 

 ferent results; faster growth rates 

 are generally estimated from tag 

 returns. 



816 



The primary objective of our 

 study was to determine growth 

 rates of juvenile and adult winter 

 flounder based on aged scale 

 samples. Our second objective was 

 to determine average maturity 

 schedules for the two winter 

 flounder stock units, as maturation 

 is an important life history para- 

 meter for spawning stock biomass- 

 per-recruit analyses. 



Materials and methods 



Winter flounder were sampled dur- 

 ing the 1983-91 Massachusetts Di- 

 vision of Marine Fisheries spring 

 (May) bottom trawl surveys. State 

 waters (0-3 mi) were surveyed with 

 an otter trawl equipped with a fine 

 mesh (13-mm stretch) codend liner 

 that retained small fish. An aver- 

 age of 95 stations per year were sur- 

 veyed in a stratified random man- 

 ner, at a sampling intensity of 1 

 station per 19 square nautical miles. 

 Additional details of trawl survey 

 methodology were provided by 

 Howe (1989). Captured winter 

 flounder were measured to total 

 length (±0.5 cm), sampled for scales 

 and otoliths, and assigned sex and 

 maturity stage based on examina- 

 tion of the gonads, by using estab- 

 lished macroscopic criteria (Burnett 

 et al., 1989). Because samples were 



collected at the end of the winter 

 flounder spawning season, determi- 

 nation of sex and maturity stage 

 was relatively straightforward. 

 Scale samples, taken from the cau- 

 dal peduncle region, were used for 

 age determination. Scales were im- 

 pressed in acetate and aged as de- 

 scribed for Georges Bank winter 

 flounder (Fields, 1988). 



Von Bertalanffy growth curves 

 were fitted to length-at-age data 

 (1983-91 pooled) for males and fe- 

 males of each stock unit, by using 

 mean lengths observed for ages 2-8. 

 Data from age-1 fish were not in- 

 cluded, as preliminary analysis sug- 

 gested that the smaller fish of this 

 age group were either not available 

 or not effectively captured by the 

 sampling gear. Mean lengths at age 

 for older (>8yrs) fish were not used 

 in fitting growth models, because 

 sample sizes were small. Statistical 

 comparison of the results from this 

 study and those of Howe and Coates 

 ( 1975) was not attempted, as growth 

 parameters derived from tagging 

 and age-length information may not 

 be equivalent (Francis, 1988). 



Stock-specific maturity schedules 

 based on aged fish were calculated 

 for both males and females. For 

 each sex within each stock unit, a 

 logistic function was fitted to the 

 proportion of mature winter 

 flounder, ages 2-5, by using non- 

 linear regression. Lengths at 50% 

 maturity (L 60 ) were the inflection 

 point on these curves. Similarly, 

 ages at 50% maturity (A 50 ) were de- 

 termined from logistic curves fitted 

 to observed maturity at age data. 



Results 



A total of 3,035 winter flounder (731 

 males and 986 females south and 

 east of Cape Cod and 509 male and 

 809 female winter flounder north of 



Manuscript accepted 13 May 1993. 

 Fishery Bulletin, U.S. 91:816-820 1 1993). 



