FISHERY BULLETIN: VOL. 81. NO. 1 



Sexual and Maturity Stage Influences 



Of 1,021 fish examined for stomach content 

 analysis, 376 were males, 466 females, and 179 

 were not sexed. Females were slightly larger 

 than males, mean length of 34.4+6.3 vs. 31.8+5.1 

 cm, respectively, and contained a larger mean 

 quantity of prey in their stomachs, 0.57+1.37 g 

 (0.15% body weight) vs. 0.32+0.76 g (0.11% body 

 weight). Females also had a lower percentage of 

 empty stomachs, 29% vs. 36%, than males. The 

 179 fish that were not sexed were small and 

 presumably immature with a mean length of 

 11.7+8.9 cm and mean weight of stomach con- 

 tents of 0.203+0.83 g. 



When the sex of a fish was determined, the ma- 

 turity stage of the gonads was evaluated subjec- 

 tively. A percentage of the fish examined were 

 not classified as to their state of sexual maturity 

 and another group, those <15 cm, was routinely 

 classified as immature. The remainder of the 

 fish were classified as either resting, developing, 

 ripe and/or spawning, or spent. Although the 

 average size of individuals in these last four cate- 

 gories was quite similar, there was a substantial 

 difference in the mean weight per stomach. 

 Spawning fish had the least amount of prey in 

 their stomachs, mean = 0.21 g (0.06% body 

 weight), while developing-stage fish contained 

 the most, mean = 0.58 g (0.16% body weight) 

 although on a percentage body-weight basis rest- 

 ing-stage fish contained a larger quantity of prey 

 in their stomachs than developing-stage fish 

 (0.24% vs. 0.16%). The percentage of empty stom- 

 achs and the actual composition of the diet 

 showed no pattern to the fluctuation in values 

 which was related to the maturity stage of the 

 gonads. 



Physical Factors 



Temperature, over the 12°C range in which 

 yellowtail flounders were caught, had no appar- 

 ent effect on diet composition. In contrast, al- 

 though the data are variable, the stomach con- 

 tent weights appeared to vary with temperature. 

 The weight was higher at the lower tempera- 

 tures, with one exception. In the range from 3° to 

 8°C the stomach content weight ranged from 

 0.13 to 0.26% body weight. Between 9° and 15°C 

 the range was greater, 0.05 to 0.65%. However, 

 exclusion of the 13°C value of 0.65% reduced the 

 high point of the range to 0.14%. The percentage 

 of empty stomachs was also related to tempera- 



ture. Between 3° and 8°C the percentage of 

 empty stomachs averaged 23%, while between 9° 

 and 15°C it averaged 37%. The ranges for these 

 averages were 14-27% and 19-79%, respectively. 

 The value of 79% occurred at the 15°C point, and 

 this may be the result of temperature inhibition 

 of feeding even though 24 fish were collected at 

 this water temperature. Perhaps a more typical 

 range estimate is 19 to 55% with the 55% empty 

 stomachs being recorded at 12°C from a sample 

 size of 118 fish. 



To evaluate the relationship between tempera- 

 ture and fish size, the yellowtail flounder data 

 were divided into two size groups, fish between 1 

 and 15 cm and 21 through 49 cm. For the small 

 size class, fish were collected at temperatures be- 

 tween 4° and 15°C. More fish were collected in 

 the 4° through 7°C temperature range (no sam- 

 ples from 8°C) than the 9° through 15°C range, 

 80 vs. 51, respectively. Fish from this lower range 

 were also, on the average, larger (9.3 cm vs. 5.3 

 cm TL) and had a greater quantity of prey in their 

 stomachs, 0.51% vs. 0.35% body weight. Fish in 

 the 21-49 cm size group were also collected in 

 slightly larger numbers, 426 vs. 373, in the lower 

 temperature range. They were slightly larger 

 fish, mean length of 33.6 cm vs. 32.5 cm and the 

 mean weight of stomach contents was greater, 

 0.15% vs. 0.08% body weight, respectively. 



Yellowtail flounder were caught in depths 

 ranging from shallow water to 220 m. To eval- 

 uate the influence of depth on the stomach con- 

 tent data the data were divided into 37 m depth 

 intervals. The majority of fish (68%) was taken 

 from waters 38 to 73 m deep with an additional 

 23% of the fish taken from the next depth cate- 

 gory, 74-110 m. The average size of fish and the 

 percentage of empty stomachs fluctuated hap- 

 hazardly over the depth class groupings. The re- 

 lation between fish size and depth was further 

 investigated by dividing the data into two size 

 class groupings, 1-15 cm and 21-49 cm. A total of 

 147 fish fell into the smaller size range and, 

 as with the grouped data, most fish (92%) were 

 caught between 38 and 110 m although the maxi- 

 mum depth from which the smaller fish were 

 taken was only 146 m. There was no obvious rela- 

 tionship between depth and size for these small 

 fish or even for depth and the percentage of 

 empty stomachs. The stomach content weight 

 did, however, increase with depth from 0.28% at 

 38-73 m, to 1.29% body weight at 111-146 m. For 

 fish in the 21-49 cm group, the major difference 

 from the smaller fish is that the percentage of 



20 



