NOTE Yang: Diet changes of Gadus macrocephalus associated with climate changes in Pavlof Bay 



403 



D Pacific cod 

 G Walleye pollock 

  Arrowtooth flounder 



Main prey items 



Figure 3 



Percentage by weight of the main prey in the diet of Pacific cod (n=129), walleye pollock (n= 

 and arrowtooth flounder <h = 43) collected in Pavlof Bay in 1995. 



216) 



pal prey of Pacific cod collected in Pavlof Bay in 1995. This 

 is a large change in diet composition compared with that 

 observed 15 years earlier (Albers and Anderson, 1985). 

 In Albers and Anderson's (1985) study, pandalid shrimp, 

 capelin. and walleye pollock were the main prey of Pacific 

 cod (Fig. 4). The change in main prey from pelagic prey in 

 the 1980s to benthic prey in 1995 corresponds to changes 

 in species abundance trends in nearshore small-mesh 

 trawl surveys observed by Anderson and Piatt (1999). In 

 that study, they described that the community reorgani- 

 zation in the Gulf of Alaska was triggered by a shift in 

 ocean climate during the late 1970s. They showed that the 

 abundance of species such as pandalid shrimp and capelin 

 declined while the abundance of predators such as Pacific 

 cod, walleye pollock, and flatfish increased between 1972 

 and 1997. 



The mean weight of pandalid shrimp consumed by Pa- 

 cific cod in 1995 was only 0.5 g/cod. In contrast, the mean 

 weights of undigested pink shrimp in Pacific cod stomachs 

 ranged between 4.5 g/cod and 24.4 g/cod during 1980 and 

 1981. This finding corroborates those of Anderson (2000) 

 and show that pandalid shrimp abundance continued to 

 decrease in the late 1990s and Pacific cod abundance con- 

 tinued to increase during that same period. 



The diet of Pacific cod in the present study was also 

 compared with the diet of Pacific cod in the broader Gulf 

 of Alaska shelf area (Fig. 5) (Yang and Nelson, 2000). The 

 values of the percentage by weight of capelin in Pacific cod 

 stomachs in the Gulf of Alaska in 1990, 1993, and 1996 

 were similar (all were less than 3%) to that in Pavlof Bay 

 in 1995. However, pandalid shrimp were an important 



food item of Pacific cod throughout the Gulf of Alaska, 

 comprising from 11% to 15% by weight of the total stom- 

 ach contents of Pacific cod in the Gulf of Alaska in 3 years 

 (1990, 1993, and 1996) (Yang and Nelson, 2000). These 

 values are higher than that in Pavlof Bay (2% by weight). 

 By comparing the depths of the sampling locations of the 

 Pacific cod, high percentages of pandalid shrimp were 

 found in the cod diet in deeper offshore areas of the Gulf 

 of Alaska in 1990, 1993, and 1996, whereas low percent- 

 ages of pandalid shrimp were found in cod diet in much 



