FISHERY BULLETIN: VOL. 80, NO. 3 



termination of the major food items consumed. 



As is apparent from Table 1, P. vetulus feeds on 

 a wide variety of benthic animals. Juvenile bi- 

 valves, harpacticoid copepods, Magelona palps, 

 and amphipods are particularly abundant in 

 English sole guts. On most sampling dates, the 

 frequency of occurrence of these four prey in the 

 diet of English sole was high, although typically 

 only one or two items dominated the diet numeri- 

 cally. Occasionally a food item which was usually 

 rare became a major component in the guts of 

 English sole, such as free-living nematodes on 25 

 July 1978 or echinoid tube feet on 30 June 1979. 

 The diet of /. isolepis was very similar to that of 

 P. vetulus, with the exception that butter sole fed 

 to a greater extent on mysids and decapods. Ci- 

 tharichthys stigmaeus fed equally on large epi- 

 benthic crustaceans (amphipods, decapods, 

 cumaceans) and pelagic prey. Polychaetes were 

 totally lacking in the diet. Psettichthys melano- 

 stictus consumed mysids almost exclusively; only 

 on 8 August 1979 were other pelagic prey found 

 in the guts of this species. Average H' diversity of 

 food consumed per sampling date in 1979 was 

 1.38 for English sole, 1.47 for butter sole, 0.81 for 

 speckled sanddabs, and 0.14 for sand sole. The 

 similarity in diets of these four species was com- 

 pared by computing the percent similarity index 

 (PSI; Whittaker 1960) based on the average 1979 

 proportions of prey consumed by each species 

 (Table 2). Two of these paired comparisons, 

 Parophrys vetulus-I. isolepis and C. stigmaeus- 

 Psettichthys melanostictus, indicate similarities 

 exceeding 50%. In the case of the speckled sand- 

 dab and the sand sole, this dietary overlap is 

 based on their common utilization of one food 

 category, mysids. English and butter soles share 

 a wide variety of prey which were consumed in 

 very similar proportions, e.g., 29 May 1979. 



Observations of 20-25 mm Parophrys vetulus 

 feeding in laboratory aquaria revealed two basic 

 types of foraging behavior. In the first, fish re- 

 mained motionless on the bottom and then peri- 

 odically lunged forward 1-2 cm, striking at ob- 

 jects located on the surface of the sediment. In 



Table 2.— Percent similarity of prey consumed by English 

 sole. Parophrys vetulus; butter sole, Isopsetta isolepis; speckled 

 sanddab, Citharichthys stigmaeus; and sand sole, Psettichthys 

 melanostictus, based on the average 1979 diets shown in Table 

 1. 



the second, fish slowly raised their heads above 

 the bottom then rapidly thrust forward, causing 

 the upper few millimeters of sediment to billow 

 into suspension. Parophrys vetulus would then 

 strike in rapid succession at small objects pre- 

 sumably temporarily displaced from the bottom. 

 Neither type of behavior predominated; both 

 were detected in all of the individuals observed. 

 After monitoring these responses for several 

 hours, fish were sacrificed and the guts exam- 

 ined. Harpacticoid copepods dominated the diet 

 of these fish. 



Shifts in prey preference as a function of fish 

 size (age) were observed in English sole. The 

 average diets of all P. vetulus less than and 

 greater than 35 mm SL were computed using the 

 1979 data and then compared (Table 3). The dra- 

 matic difference in prey of these two size classes 

 is apparent. Smaller fish (17-35 mm SL) con- 

 sumed small prey almost exclusively, while 

 larger fish (35-82 mm SL) only occasionally in- 

 gested these small items, choosing instead amphi- 

 pods and cumaceans. Isopsetta isolepis showed a 

 similar shift in the preferred size of prey as stan- 

 dard length increased from 30 to 40 mm. Four- 

 teen butter sole (17-35 mm SL) caught on 29 May 

 1979 fed predominantly on small food items, 

 while the gut contents of four larger fish (49-60 

 mm SL) caught 1 d later were composed of am- 

 phipods, cumaceans, and decapods (Table 1). A 

 similar distinction was found in fish collected on 

 19 July 1979. Neither C. stigmaeus nor Psettich- 

 thys melanostictus altered the taxonomic com- 

 position of their diet within the size ranges of fish 

 we examined, although, as with English and but- 

 ter soles, larger fish ate larger prey. 



The guts of all four species were generally 

 <25% full in the morning before 0900 h. Stomach 

 fullness gradually increased during the late 

 morning and afternoon. The correlation between 



Table 3.— Mean numerical proportions of dominant 

 prey items in the guts of Parophrys vetulus less than 

 and greater than 35 mm SL. 



Species 



P. vetulus 

 I. isolepis 

 C. stigmaeus 



I. isolepis 

 077 



C. stigmaeus 



0.29 

 039 



P. melanostictus 



001 

 0.05 

 0.64 



560 



