BIOLOGY OF THE SUMMER FLOUNDER, 

 PARALICHTHYS DENTATUS, IN DELAWARE BAY' 



Ronal W. Smith and Franklin C. Daiber 2 



ABSTRACT 



Data on the age, growth, food habits, and racial characters of summer flounder, Paralichthys dentatus , 

 from Delaware Bay were examined. Fish were present year-round, although 95% were taken from May 

 through September, and no mature fish were caught during the winter. Fish were aged from annuli on 

 the largest left otolith. The growth rate for males was described by L t +1 = 141.91 + 0.767(L,), and 

 for females L t + j = 136.72 + 0.843(L ( ). The Delaware Bay commercial fishery in 1966 was primarily 

 supported by age-groups 2 through 5. The total length-weight relationship was described by, log weight 

 (grams) = log 0.404 x 10~ 5 + 3.151 log [total length (millimeters)], and the total length-standard 

 length relationship by, total length (millimeters) = 16.695 + 1.55[standard length (millimeters)]. Age 

 and sex made no significant difference in meristic character evaluation. The reported range of varia- 

 tion for some characters was extended: dorsal rays, 89-98; anal rays, 63-78; pectoral rays, 10-13; 

 vertebrae, 40-43; standard length/head length, 3.64-4.30; and head length/upper jaw length, 1 .54-2.26. 



One objective of this study was to investigate the 

 age, growth, and food habits of summer flounder, 

 Paralichthys dentatus (Linnaeus), caught in Del- 

 aware Bay. Previous research on age and growth, 

 Eldridge (1962) and Poole (1961), disagreed and 

 additional study was needed. 



A second objective was to determine the mag- 

 nitude of variation in meristic characters of sum- 

 mer flounder from Delaware Bay for comparison 

 with other geographic areas. Ginsburg (1952) re- 

 ported that summer flounder from Chesapeake 

 Bay and from Beaufort, N.C., might belong to two 

 distinct racial stocks on the basis of gill raker 

 frequency distributions. According to Poole 

 (1966), unpublished studies found no real differ- 

 ences between these populations, but he added 

 that analysis of racial data from Maryland, Vir- 

 ginia, and North Carolina areas suggested the 

 need for additional research. 



Summer flounder are common from Cape Cod to 

 North Carolina and they have been reported from 

 Maine to Texas (Bigelow and Schroeder 1953; 

 Poole 1962). They normally inhabit coastal and 

 estuarine waters during the warmer months of the 

 year and move off on the continental shelf in 20 to 

 100 fm of water during the fall and winter 



'Contribution No. 91, College of Marine Studies, University of 

 Delaware. Based on a thesis by Ronal W. Smith submitted to the 

 University of Delaware as part of the requirements for the M.S. 

 degree in Biological Sciences. 



2 College of Marine Studies, University of Delaware, Newark, 

 DE 19711. 



Manuscript accepted March 1977. 



FISHERY BULLETIN: VOL. 75, NO. 4. 1977. 



(Bigelow and Schroeder 1953). Spawning occurs 

 during the fall and winter while the fish are mov- 

 ing offshore or at their wintering location, and 

 larvae and postlarvae drift and migrate inshore to 

 coastal and estuarine nursery areas (Smith 1973). 



COLLECTION OF MATERIAL 



Most fish examined were caught by a 9-m (30-ft) 

 otter trawl, 7.6-cm (3-in) stretch mesh in the body 

 and 5.1 cm (2 in) in the cod end, during monthly 

 fish survey trips in Delaware Bay. A total of 13 

 sectors were sampled during the period August 

 1966 through November 1971 (Figure 1), with a 

 minimum of 3 and a maximum of 12 sampled in 

 any 1-mo interval. Sectors sampled were selected 

 to cover a range of salinities and depths in Dela- 

 ware Bay. During the summer of 1968, three sec- 

 tors were sampled during the day and again that 

 night. Sampling at each station consisted of mak- 

 ing a Nansen cast within 2 m of the bottom for 

 temperature and a water sample, and trawling for 

 30 min. The mean tow length was 1.2 n.mi. Aver- 

 age water depth for each tow was determined by 

 eye from a recording fathometer trace. Some fish 

 were taken by beach seining, while others were 

 caught during miscellaneous trawling operations 

 through February 1973. 



Stomachs for gut analysis were removed im- 

 mediately on fish capture and placed in 95% iso- 

 propyl alcohol. 



The commercial summer flounder catch from 



823 



