GABRIEL and PEARCY: FEEDING SELECTIVITY OF DOVER SOLE 



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°lll-20 I 21 -26 127-32 133-38139-421 

 FISH LENGTH INTERVAL (cm) 



Figure 2.— Five patterns of change in the frequency of occur- 

 rence of prey for different sizes of Dover sole at SG29. Curve 

 shape I typified by Decamastus gracilis, shape II by Myriochele 

 oculata. shape III by Anaitides groenlandica , and shape IV by 

 Nothria elegans. 



Glycinde picta,Prionospio sp., Tharyx sp., the am- 

 phipod Harpiniopsis excavate, the Aplacophora, 

 unidentifiable Pelecypoda, and Macoma sp. 



At SGIO, 19 out of the 26 principal prey species 

 showed no significant change in frequency of oc- 

 currence over the range offish sampled (24-43 cm). 

 The frequency of occurrence of Melphidippa 

 amorita, an amphipod, increased significantly in 

 fishes 32 cm or longer. Occurrence of two amphipod 

 taxa, Nicipe tumida and Metopa sp., decreased 

 significantly in fish 32-33 cm or larger. In the case 

 of the four remaining taxa, the series of chi-square 

 tests produced intervals across which frequency of 

 occurrence changed gradually, rather than defin- 

 ing a well-marked break in frequency at one par- 

 ticular length. Glycinde picta, a tubeless, subsur- 

 face deposit feeding polychaete, increased in fre- 

 quency in fish 28-29 cm or longer. Odontogena 

 borealis, a small bivalve, increased over the 25-32 

 cm fish size interval. Aplacophorans increased in 



frequency in 26-27 cm fish and longer, and 

 Ophiuroidea increased in the 30-32 cm interval. 



Selectivity 



A chi-square test of 2 x 2contingency tables was 

 used to test the null hypothesis that the relative 

 abundance of a taxon among items consumed is 

 dependent on the relative abundance of the taxon 

 in the environment. Ivlev's (1961) index of electiv- 

 ity 



E =(ri -pi)l(n +pi), 



where r, = percentage of ration composed of a 

 given prey taxon i and p, = percentage of food 

 complex in environment composed of prey taxon i, 

 was used to determine whether selection was posi- 

 tive or negative. Overall trends in selectivity by 

 major taxa for all fish from each station are shown 

 in Table 5. Ophiuroids were the most highly 

 selected food taxon at SG29. The calculations of 

 electivity indices and chi-square values for this 

 taxon were based on number of occurrences rather 

 than number of individuals consumed, and hence 

 underestimated the importance of ophiuroids. 

 Ophiuroids were removed from the data sets for 

 subsequent calculations so that estimations for 

 other taxa were unbiased by this representation. 

 Polychaetes were selected food of fish at both 

 locations. Chi-square values were larger for 

 polychaetes than any other positively selected 

 taxon. Molluscs, especially pelecypods and 



Table 5. — Summary of selectivity considered by major taxa at 

 stations SG29 and SGIO for Dover sole of all sizes. 



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