FISHERY BULLETIN: VOL. 75, NO. 1 



scales, and interopercles for aging rex sole; by 

 comparing the age-length relationships, he 

 concluded otoliths were the most readable 

 structure. Vanderploeg (1973) conducted food 

 habit studies on rex sole collected off Oregon. 

 Porter (1964) described the larvae of rex sole, and 

 Waldron (1972) and Richardson (1973) reported on 

 distribution and abundance of rex sole larvae. 

 Tsuyuki et al. (1965) conducted a general starch- 

 gel electrophoresis study on the muscle proteins 

 and hemoglobin of 50 species of North Pacific fish 

 and found that rex sole differed from 10 other 

 pleuronectids tested. Benthic distribution of rex 

 sole was investigated by numerous workers 4 

 (Alverson et al. 1964; Day and Pearcy 1968; 

 Demory 1971; Alton 1972). Limited tagging 

 studies (Manzer 1952; Harry 1956) were con- 

 ducted to determine movements of rex sole, but no 

 tagged fish were recaptured. 



METHODS 



Rex sole were collected by otter trawl off Oregon 

 from the Columbia River south to Cape Blanco at 

 depths of 18-200 m during September 1969-73. 

 Most data were obtained from rex sole captured 

 incidentally to a study of pink shrimp, Pandalus 

 jordani, distribution during 1969-70. 5 Rex sole 

 were also obtained from commercial trawl land- 

 ings at Astoria, Oreg., in 1970 and 1973; at 

 Charleston and Brookings, Oreg., in 1973; and 

 from research vessel catches during the 1971-73 

 Fish Commission of Oregon (FCO) groundfish 

 surveys. 4 6 All specimens were frozen until time of 

 examination. 



Rex sole were sexed by examination of gonads, 

 measured for total length (TL) to the nearest 

 centimeter, and weighed to the nearest gram. The 

 left otolith was removed for aging studies, stored 

 in a 50:50 solution of glycerin and water, and read 

 using reflected light on a dark background ( Powles 

 and Kennedy 1967). 



The length-weight relationship, by calendar 

 quarters, of rex sole collected off central and 

 northern Oregon in 1969-72 was determined by 

 the least squares method using the logarithmic 



5 Lukas, G., and M. J. Hosie. 1973. Investigation of the 

 abundance and benthic distribution of pink shrimp, Pandalus 

 jordani, off the northern Oregon coast. Fish Comm. Oreg., 

 Commer. Fish. Res. Dev. Act, Final Rep., July 1, 1969 to June 30, 

 1970, 45 p. (Unpubl. manuscr.). 



6 Demory, R.L. 1974. Resource surveys on the continental shelf 

 of Oregon. Fish Comm. Oreg., Commer. Fish. Res. Dev. Act Prog. 

 Rep., July 1, 1973 to June 30, 1974, 6 p. (Unpubl. manuscr). 



form of the equation W =aL b , where W is weight in 

 grams, L is length in centimeters, and a and b are 

 constants. 



Estimates of the lineal growth of rex sole were 

 obtained from the age-length relationship of fish 

 collected off northern Oregon in September- 

 October 1969 and September 1971. A mean total 

 length (TL) at each age was determined from these 

 data and expressed mathematically in terms of the 

 von Bertalanffy growth equation (Ricker 1958; 

 Ketchen and Forrester 1966). 



To obtain the calculated growth parameters, we 

 used ages 1.5-10.5 yr for males and 1.5-12.5 yr for 

 females. 



Estimates of the instantaneous total mortality 

 rate (Z) were made using age group data obtained 

 from FCO groundfish cruises off northern Oregon 

 in 1971 and 1973 and off central Oregon in 1972. 

 Two methods, a catch curve (Ricker 1958) and the 

 Jackson technique (Jackson 1939), were used for 

 the analyses. 



To determine maturity stages, gonads were 

 examined according to the procedures described 

 by Hagerman (1952), Scott (1954), and Powles 

 (1965). Definitions used for maturity stages are 

 listed in Table 1. 



Fecundity was determined from 13 fish collected 

 in February 1970 and measured to the nearest 

 millimeter (TL). Both ovaries were removed from 



TABLE 1. — Description of reproductive phases of rex sole gonads 

 used in this study. 



Sex 



Maturity 

 stage 



Description 



Females Immature (A): Ovaries very small (<40 mm TL), whitish in color, 

 semitransparent, and gelatinous. No eggs dis- 

 cernible to the naked eye. 

 Mature (B): Ripening. Ovaries enlarging, becoming reddish- 

 orange colored and granular in consistency, full of 

 developing eggs that can be recognized by direct 

 observation. 



(C): Ripe. Ovaries full of mostly reddish-orange colored 

 granular eggs, although a few transparent ova are 

 present. Ova can be extruded from the fish by using 

 considerable pressure. 



(D): Spawning Ovaries full of entirely translucent eggs 

 which will run with slight pressure. 



(E): Spent. Ovaries flaccid, usually empty although 

 occasionally a few eggs will remain. Ovarian 

 membrane very transparent and saclike. 



(F): Recovering. Ovaries filling with fluid, and reddish- 

 orange in color. No ova detectable to the naked 

 eye. 

 Males Immature (A): Testes very small (<3 mm TL), translucent in color 

 and not extending into the abdominal cavity. 

 Mature (B): Ripening Testes enlarged, extending posteriorly 

 into abdominal cavity, light brown to cream colored, 

 but retain sperm under pressure. 



(C): Ripe and/or spawning. Testes full and cream 

 colored. Sperm will run under no or only slight 

 pressure. 



(D): Spent-recovering. Testes shrunken and trans- 

 parent or dark brown in color. 



52 



