HOGUE and CAREY: FEEDING ECOLOGY OF 0-AGE FLATFISHES 



the time of capture (ranging between 0830 and 

 1800 h) and average gut fullness for English sole 

 was significant; r = 0.49, P = 0.05. On 22 March 

 1979 two otter trawl hauls were made, one at 

 1000 and another at 1800 h. Guts of 10 English 

 sole ranging in size between 19 and 35 mm SL 

 were examined from both trawls. The diets of 

 both groups of fish were the same, but the fish 

 collected at 1800 h had an order of magnitude 

 more food items in their guts than the earlier 

 collection: 90% full, 198±56 SD items, vs. 10% 

 full, 18±17 SD items. Isopsetta isolepis, C. stig- 

 maeus, and P. melanostictus showed similar 

 daily trends. 



Sufficient numbers of English sole of the same 

 size were collected on 23 January and 29 May 

 1979 to compare the similarity of diets within 

 and between replicate trawls. The PSI was used 

 to quantify the proportion of food items found in 

 common for each possible pair of fish collected on 

 a sampling date. Mean similarity values were 

 then obtained by averaging the PSI values for 

 the fish within the same trawl and for fish col- 

 lected in different trawls. Comparing replicate 

 samples obtained at the same depth (Table 4), the 

 average PSI for fish guts within the same trawl 

 in both January and May, as well as the mean 

 PSI between fish in different trawls in January, 

 were approximately the same, 50%. The simi- 

 larity between two trawls at the same depth in 

 May, though, is very low (3%). Table 4 (bottom) 

 also shows a comparison of within-trawl and 

 between-trawl similarity, where trawls were 

 collected at different depths (20 m and 30 m). 

 Again the within-trawl affinities are high in 

 both January and May, as is the between-tow 

 similarity in January. The average PSI in May 

 for fish from different depths is low. The in- 

 creased between-trawl variability in food habits 

 noted on 29 May was a general feature observed 

 in all late spring and early summer replicate col- 

 lections of Parophrys vetulus. For example, on 13 



Table 4.— Average percent similarity of index of Parophrys 

 vetulus diets within and between replicate trawls on 23 Janu- 

 ary and 29 May 1979. 



July 1978, trawls were made at 15 m and 20 m. 

 Magelona palps numerically comprised 72% of 

 the English sole diet at 15 m butonly 19% at 20 m, 

 while juvenile bivalves and harpacticoid cope- 

 pods combined to form 19% of the prey consumed 

 at 15 m and 63% at 20 m. 



The diet of recently settled English sole 

 changed continually among sampling months. 

 Comparing similar-sized fish (17-35 mm SL) 

 caught in 1979 (Fig. 3) reveals that dominant 

 food items on a numerical basis varied from 

 Magelona palps (November 1978, January 1979), 

 juvenile bivalves (March 1979), bivalve siphons 

 (April and May 1979), to juvenile bivalves and 

 harpacticoid copepods (July 1979). Examination 

 of samples collected in 1977 and 1978 showed 

 that the sequence of changes noted in 1979 does 

 not repeat each year. Magelona palps, which in 

 1979 were never a dominant item in the diet of P. 

 vetulus after January, were numerically the 

 most abundant food on two sampling dates in the 

 summer of 1978. Other between-year differences 

 exist, e.g., 5 September 1978 and 24 September 

 1979, but it is impossible to determine whether 

 these differences are real or a result of spatial 

 variability in diet combined with insufficient 

 sampling. 



The apparent increased equitability of prey 

 items shown in Figure 3 for April and May rela- 

 tive to January and March does not indicate that 

 spring and summer diets of individual fish are 

 more diverse than in winter. Instead, the differ- 

 ence is an artifact of the spatial variability pre- 

 viously noted, being generated by averaging the 

 data for all fish caught in different tows. The 

 average dietary diversity {FT ) of an individual 

 fish on 23 January 1979 (0.43±0.35 SD, n = 24) 

 was not significantly different from that on 29 

 May 1979 (0.37 ±0.41 SD, n = 32). 



The only seasonal data currently available on 

 the abundance of benthic organisms at Moolach 

 Beach are for nematodes and harpacticoid cope- 

 pods. Nematodes are very abundant {x = 1,050 • 

 10 cm" 2 ), but quantitatively, with the exception of 

 one sampling date, are not significant in the diet 

 of the fish species we studied. Harpacticoids are 

 important in the diets of English and butter 

 soles, yet are not abundant at the study site. 

 Their average density for the eight sampling 

 dates between July 1978 and September 1979 

 was 12.2±4.0 SE • 10 cm" 2 . Only the larger spe- 

 cies found in the 0-1 cm depth increment were 

 present in fish guts. Halectinosoma spp. com- 

 prised more than 80% of all harpacticoid prey. 



561 



