BIOLOGY OF THE REX SOLE, 

 GLYPTOCEPHALUS ZACHIRUS, IN WATERS OFF OREGON 



Michael J. Hosie 1 and Howard F. Horton 2 



ABSTRACT 



Data are presented on the life history and population dynamics of rex sole, Glyptocephalus zaehirus 

 Lockington, collected from Oregon waters between September 1969 and October 1973. Length-weight 

 relationships vary little between sexes or with time of year. Otolith annuli form primarily from 

 January through May and were used for age determination. Age and length are highly correlated 

 (r = 0.9945 for males and 0.9864 for females), with females growing faster and living longer than 

 males. Estimates of total instantaneous mortality rate (Z) appear less variable when calculated by the 

 catch-curve method (mean Z of 0.64 for males and 0.51 for females), than by the Jackson method. Age at 

 50% maturity occurs at 1 6 cm ( about 3 yr ) for males and at 24 cm (about 5 yr ) for females. Spawning off 

 northern Oregon occurs from January through June, with a peak in March-April. Fecundity is 

 correlated (r = 0.9620) with length offish. There were 15 recaptures (0.59% ) from 2,537 fish tagged off 

 northern Oregon during March and June 1970. Maximum movement of recaptured fish was only 53.9 

 km, but the low recovery precludes definite conclusions. Twenty loci were detected by starch-gel 

 electrophoretic analysis using rex sole muscle tissue. Of these, three loci were polymorphic, but showed 

 no discernible variation between collections from northern, central, and southern Oregon in April 

 1973. 



Investigation into the life history of rex sole, 

 Glyptocephalus zaehirus Lockington, by the Ore- 

 gon Department of Fish and Wildlife provided new 

 information on this species. The broad objective 

 was to develop knowledge of the biology and 

 population dynamics of rex sole found off the 

 Oregon coast which would enhance management 

 of this species. 



Specific objectives were to: 1) determine the 

 length-weight and age-length relationships; 2) 

 estimate the total instantaneous mortality rate by 

 two independent methods; 3) determine rela- 

 tionships of maturity and fecundity with length 

 and age, and with the spawning season; and 4) 

 determine if rex sole off Oregon are composed of 

 separate stocks 3 which undergo predictable 

 movements. 



The rex sole is a slender, thin flatfish belonging 

 to the family Pleuronectidae (Starks 1918; Nor- 

 man 1934), the right-eyed flounders. Of the three 

 species of Glyptocephalus , rex sole is the only one 

 reported in the eastern Pacific Ocean (Pertseva- 

 Ostroumova 1961). Geographically distributed 



'Oregon Department of Fish and Wildlife, Marine Field 

 Laboratory, P.O. Box 5430, Charleston, OR 97420. 



2 Department of Fisheries and Wildlife, Oregon State Uni- 

 versity, Corvallis, OR 97331. 



3 The rex sole spawning in a particular marine location (or 

 portion of it) at a particular season, and which do not interbreed 

 to a substantial degree with any group spawning in a different 

 place, or in the same place at a different season (modified from 

 Ricker 1972). 



from southern California to the Bering Sea (Miller 

 and Lea 1972), it is found bathymetrically to 730 

 m (Alverson et al. 1964). Rex sole is important in 

 the commercial trawl fishery from California 

 northward through British Columbia. In 1972, rex 

 sole was the fifth most important flatfish in weight 

 (1.54 million kg [3.4 million pounds]) in the 

 domestic northeastern Pacific trawl food fishery. 

 Glyptocephalus zaehirus is also important in the 

 domestic trawl fishery for animal food (Best 1961; 

 Niska 1969), although this fishery has declined in 

 recent years. On the continental shelf off the 

 northern three-fourths of the Oregon coast, rex 

 sole was third in biomass 4 and first in numbers of 

 all flatfish caught with an 89-mm (3.5-inch) mesh 

 trawl. 



There is little published information on the 

 biology of rex sole. Villadolid (1927) and Frey 

 (1971) reported briefly on the time of spawning, 

 size and age at maturity, and food habits for 

 specimens captured off California. Hart (1973) 

 summarized the life history of rex sole off Canada 

 and suggested that the lack of information re- 

 sulted in doubtful deductions. An aging study was 

 conducted on rex sole by Villadolid (1927) who 

 used scales. Domenowske (1966) used otoliths, 



Manuscript accepted August 1976. 

 FISHERY BULLETIN: VOL. 75. NO. 1. 1977. 



4 Demory, R. L., and J. G. Robinson. 1973. Resource surveys on 

 the continental shelf of Oregon. Fish Comm. Oreg. t Commer. 

 Fish. Res. Dev. Act Prog. Rep., July 1, 1972 to June 30, 1973, 19 

 p. (Unpubl. manuscr.). 



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