FISHERY BULLETIN; VOL. 76. NO. 3 



The largest difference between seasons was for 

 coelenterates. Anemones and the feeding polyps of 

 sea pens were unimportant constituents of the 

 food during the summer (<29^ of diet by weight) 

 but were sometimes a major food >30'^ by weight) 

 during the winter. Anemones and sea pens are 

 probably available as prey during both seasons 

 but for some reason only consumed in significant 

 quantities during the winter. 



Seasonal differences in the intensity of feeding 

 were also indicated by the higher frequency of 

 empty stomachs in winter than in summer (Table 

 7). The number of principal prey occurring in the 

 diet of Dover sole was consistently larger during 

 summer than winter regardless of fish size. Al- 

 though the smaller number of stomachs with con- 

 tents during the winter reduces sample size, and 

 hence the number of taxa found, the frequency of 

 occurrence of many of the individual taxa of 

 polychaetes, crustaceans, and mollusks (taxa 

 listed in Table 5) was higher in summer than 

 winter. Bertrand (1971) found no evidence for sea- 

 sonal variations in the numbers or biomass of 

 infauna sampled with grabs at these stations. 

 Therefore a more diverse assemblage of prey was 

 probably available to Dover sole during the sum- 

 mer or fish were usually less selective during the 

 summer than during the winter. The summer is 

 the season of most active growth of Dover sole 

 (Demory 1972) when intraspecific and possibly in- 

 terspecific competition for food may be most in- 

 tense. Decreased prey selectivity is known to occur 

 under conditions of low food abundance or avail- 

 ability (Ivlev 1961; Schoener 1971). 



The number of principal prey taxa generally 

 increased with size of Dover sole (Table 7). This 

 trend may be related to sample size (number of 

 stomachs with food) and to the ability of large fish 

 to consume a larger range of prey sizes than small 

 fish. The less diverse diet of small fish resulted 

 from ingestion of only a few species of polychaetes. 



Table 7. — Frequency of empty stomachs (no. empty stomachs/ 

 no. fish) and the number of principal taxa (occurring in 5% or 

 more of at least 10 observations) of prey for different sizes of 

 Dover sole collected during summer and winter seasons. 



Those prey types eaten by a broad size range (50- 

 400 mm SL) of Dover sole include: Myrochele heeri, 

 Typosyllis hyalina, Lumhrlneris sp., Glyceridae, 

 gammarid amphipods, pelecypods, Megacrenella 

 Columbiana, ophiuroids, unidentified polychaetes, 

 and unidentified crustaceans. 



Annelids and crustaceans were the major food 

 items for rex sole (Figure 3). (Most of the rex sole 

 represented here are juveniles.) Annelids in- 

 creased in importance with an increase in the sizes 

 of rex sole, up to 150-250 mm. This increase was 

 associated with a decrease in the proportion by 

 weight of crustaceans, the dominant food item for 

 small rex sole during both seasons. Euphausiids, 

 decapod crab larvae, copepods, and ostracods were 

 only found as principal prey of rex sole of <200 

 mm. Mollusks formed only a minor portion of the 

 diet. Differences in the FO of principal prey were 

 not pronounced. Some polychaetes (Sternaspis fos- 

 sor, Myriochele heerie ,Nothria geophiliformis , and 

 Chuelia pinnata) were found more frequently in 

 large (220-300 mm SL) rex sole. 



Some seasonal differences in the diet of rex sole 

 were evident. Euphausiids were principal prey 

 only during the summer. Cumaceans and Oiko- 

 pleura were more common during the winter. 

 Principal prey that were commonly ingested by all 

 or most size groups during both seasons were: 

 Sternaspis fossor, Goniada brunnea, unidentified 

 polychaetes, gammarid amphipods, and uniden- 



100 



NUMBER OF FISH 

 f/9J (90) (33 J (41) (2) (6) (48) (63) (50) (82) (13) 



1 I \ \ 



(SUMMER) 



I no 



200 300 100 200 



STANDARD LENGTH (mm) 



300 



Figure 3. — The percent by wet weight of the major food taxa for 

 different length groups of rex sole for summer and winter. 1 = 

 crustaceans, 2 = annelids, 3 = other taxa, and 4 = mollusks. 



646 



