This methodology was applied to the 1980 Pacific 

 whiting stomach data. There was a total of 204 Pacific 

 whiting in this sample, ranging in length from 116 to 

 645 mm, with w, of 862 g. These Pacific whiting con- 

 sumed a total of 8,940 food items [E(EN,)1 with 

 individual u) ranging from 0.002 g for amphipods to 83 

 g for a medusafish, Icicthys lockingtoni. 



The solid lines in Figures 5-7 represent the shape of 

 the predator-prey size curves resulting from the 

 analysis of 1980 data when separated into three pred- 

 ator size groups. However, these curves do not 

 necessarily represent the prey-size preference of 

 Pacific whiting. Lawlor (1980) stated that the propor- 

 tion of a food item in the diet of a predator is a function 

 not only of the predator's choice for that item but also 

 of the item's availability. Only when abundances of all 

 prey items are equal, do the observed proportions of 

 prey items in a predator's stomach reflect the 

 predator preference. 



To determine the prey-size preference of Pacific 

 whiting, we may examine a theoretical situation in 

 which equal numbers of each prey size are offered to 

 the Pacific whiting. Assuming the numbers of each 

 prey type in the environment to be inversely propor- 

 tional to the prey type's weight (Ursin 1973), this situa- 

 tion can be created by multiplying total EN ; by w r To 

 adjust for predator size, this quantity is divided by w t . 

 The dashed lines in Figures 5-7 depict the theoretical 



results of offering equal numbers of each prey size to 

 the whiting. 



Pacific whiting <200 mm, whose diet consisted 

 mainly of euphausiids, have a very narrow prey-size 

 selection curve (Fig. 5) which reflects their choice of a 

 narrow size range of food. The dashed line of the pre- 



2000 



1750 



1500 



1250 - 



1000 - 



750 - 



500 



250 



5 



FlGl'RE 6. — Frequency distribution of predator-prey size scores for 

 Pacific whiting, Merluccius productus, predators 350-549 mm long 

 with an average weight (Si,) of 876.2 g, under natural (— ) and 

 simulated (---) conditions. 



80 r 



70 



60 



50 



40 



30 



20 



10 



6 I 



In (w,/w, 



10 



12 



08 



0.7 



0.6 



0.5 



0.4 



0.3 



0.2 



0.1 



400 r 



-l 0.4 



14 



300 



200 - 



100 



Figure 5. — Frequency distribution of predator-prey size scores for 

 Pacific whiting, Merluccius productus, predators < 200 mm long with 

 an average weight ((?,) of 13.2 g, under natural (—) and simulated)---) 

 conditions. 



Figure 7.— Frequency distribution of predator-prey size scores for 

 Pacific whiting, Merluccius productus, predators 550+ mm long with 

 an average weight (u\) of 1,441.3 g, under natural! — ) and simulated 

 (---) conditions. 



633 



