RELATIONSHIP BETWEEN SEDIMENT CHARACTER AND 

 SEX SEGREGATION IN ENGLISH SOLE, PAROPHRYS VETULUS' 



D. Scott Becker^ 



ABSTRACT 



English sole, Parophrys vetulus, were collected by otter trawl in the nearshore zone of Puget Sound, 

 Washington, during two surveys conducted in 1981-82 and 1984. Stations in both surveys were distributed 

 across a broad range of sedimentary environments. Sex segregation by English sole was strongly 

 associated with the grain-size characteristics of bottom sediments. This association was persistent across 

 a variety of sampling conditions, including different years, seasons, embayments, and depths. Fish age 

 did not appear to influence the observed association. Results of this study provide the first documenta- 

 tion of the influence of sediment character on sex segregation by a pleuronectid, and suggest that this 

 relationship should be considered in future studies of English sole and, perhaps, other pleuronectids as well. 



Sex segregation by fishes of the family Pleuronec- 

 tidae (i.e., righteye flounders) has been documented 

 for numerous species from the United States (Alver- 

 son and Chatwin 1957; Fadeev 1970; Alton 1972), 

 Europe (Rae 1965), and Asia (Moiseev 1953; 

 Kovtsova 1982). These patterns have been related 

 to such factors as geographic location, depth, 

 season, and age of fish. However, because most of 

 these observations have been made while fishes 

 were being collected for other purposes, the under- 

 lying reasons for the observed patterns are poorly 

 understood. 



Several studies have documented sex segregation 

 in English sole, Parophrys vetulus, a pleuronectid 

 found in nearshore areas along the west coasts of 

 the United States and Canada (Hart 1973). In de- 

 scribing the catch of the English sole fishery in 

 Hecate Strait, British Columbia, Ketchen (1956) 

 noted that considerable sex segregation takes place, 

 particularly during the summer months. In a study 

 of the population characteristics of this species in 

 Puget Sound, Holland (1969) found a difference of 

 18% between the percentages of males in the pop- 

 ulations from two locations. Because both of these 

 accounts were largely anecdotal, no evaluations of 

 the observed patterns were made. 



One factor that has yet to be evaluated with 

 respect to sex segregation by pleuronectids is the 

 character of bottom sediments. Because pleuronec- 

 tids live in close association with the sea floor, it 



'Contribution No. 759, School of Fisheries, University of Wash- 

 ington, Seattle, WA 98195. 



^School of Fisheries, University of Washington, Seattle, WA 

 98195; present address: PTI Environmental Services, 3625 132nd 

 Ave. S.E., Bellevue, WA 98006. 



might be surmised that the characteristics of that 

 environment exert a differential influence on the 

 distributions of the two sexes. Additional support 

 for this hypothesis comes from the fact that the 

 influence of sediment character on the overall 

 distribution (i.e., both sexes pooled) of several 

 pleuronectids has been well documented (Ketchen 

 1956; Alverson et al. 1964; Feder et al. 1974; Pearcy 

 1978; Scott 1982; Becker 1984). 



In this paper, I evaluate patterns of sex segrega- 

 tion by English sole in relation to the character of 

 bottom sediments in nearshore areas of Puget 

 Sound, WA. This study provides the first determina- 

 tion of how sediment character influences sex segre- 

 gation in a pleuronectid. In relating sediment 

 character to sex segregation in English sole, I also 

 evaluate the potential influences of depth, season, 

 and fish age on the observed relationships. 



METHODS 



English sole were sampled during two independ- 

 ent surveys conducted in several embayments of 

 Puget Sound in 1981-82 and 1984. The relationship 

 between sex segregation and sediment character 

 was evaluated separately for each survey. Although 

 the two surveys differed with respect to such vari- 

 ables as station locations, sampling times, and sam- 

 ple sizes, the basic collection and analytical methods 

 used in both surveys were similar. 



In both surveys, the sex ratio of the English sole 

 captured at each station was represented by the pro- 

 portion of the sample comprised of males (i.e., male 

 proportion). Sediment character at each station was 

 represented by the percentage (by weight) of the 



Manuscript accepted April 1988. 



FISHERY BULLETIN: VOL. 86, NO. 3, 1988. 



517 



