FISHERY BULLETIN; VOL. 83, NO. 4 



Table 3,— The 10 most frequently occurring food items are categorized by 10 cm length (FL) groups of Pacific cod 

 from 30 to 69 cm. Data is presented by percent frequency of occurrence (F), percent by number (A/), and percent 

 by volume (V). 



All sizes of cod examined were feeding on both 

 small and large pink shrimp. Pink shrimp length (CL) 

 distributions measured from cod stomachs and from 

 trawl samples began to overlap at about 12 mm (Fig. 

 3). Piesults from the Kolmogorov-Smirnov test com- 

 paring pink shrimp length distributions >16.5 mm 

 CL from cod stomachs and trawl samples showed 

 no significant difference {P > 0.10) in August 1980 

 and May 1981. There was a significant difference {P 

 = 0.009) in the September 1981 sample. No signifi- 

 cant difference between length distributions in- 

 dicates that cod were not feeding on selective sizes 

 of pink shrimp. A significant difference indicates 

 that cod consumed a greater proportion of smaller 

 shrimp than was captured by the trawl. 



stomach were 24.4 g for May and 11.2 g for 

 September 1981 (Tkble 1). Per day, the average 

 amount of pink shrimp consumed by one cod was 8.1 

 g and 3.7 g for May and September, respectively. 

 The estimated weight of an average length cod 

 was 1,689.5 g for the May survey and 1,720.1 g for 

 the September survey (W = 0.00000593L3168. 

 Owen and Blackburn 1983). Cod biomass estimates 

 were 1,621 t for May and 591 t September, 

 respectively. 



Based on the above parameters, estimates of pink 

 shrimp biomass consumed were calculated using the 

 May and September data (Ikble 5). With May data. 

 Pacific cod consumed an estimated 875 t of pink 

 shrimp over the 112-d period, whereas the 



Table 4.- 



-Size range and mean size of prey and trawl caught animals. Size data were not collected for snow 

 crab in the trawl. CL = carapace length; FL = fork length; CW = carapace width. 



Estimate of Pink Shrimp 

 Biomass Consumed 



The extent of the Pacific cod predation on pink 

 shrimp in Pavlof Bay was examined by estimating 

 total biomass consumed during a 112-d period from 

 late May through mid-September 1981. Analysis 

 using Jones' (1974) equation indicated that for both 

 1981 surveys the average amount of food found in 

 a cod stomach was digested in about 3 d. The average 

 weights of undigested pink shrimp found in a cod 



Table 5. — Calculation of the total pink shrimp biomass consumed 

 by Pacific cod during a 112-d period from late May through mid- 

 September 1981. Two estimates are presented using the May and 

 September data. 



606 



