Boldt et al Factors influencing cannibalism and abundance of Theragra chalcogramma on the eastern Bering Sea shelf 
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Figure 3 
General additive model results showing the additive effect of two smoothed covariates on walleye pollock 
(Theragra chalcogramma) catch per unit of effort (CPUE) from the National Marine Fisheries Service 
bottom trawl survey on the eastern Bering Sea shelf, during 1982-2006 (excluding 1983 and 1984). 
The two smoothed covariates are location (North latitude and West longitude; left column) and habitat 
(bottom depth [ml and bottom temperature [°C1; right column). Shown are the additive effect of these 
two smoothed covariates on ln + 1 transformed large (>200 mm standard length I SL] ) pollock CPUE 
( LgPollock ; top row), ln + 1 transformed small (60-200 mm SL) pollock CPLTE ( SmallPollock\ middle 
row), and the co-occurrence of the two ( Overlap ; bottom row). 
Bottom temperature (°C) 
vided an opportunity to improve our understanding 
of factors affecting cannibalism. As found in previous 
studies (Dwyer et al., 1987; Lang and Livingston, 1996), 
the diet of pollock comprised mainly euphausiids and 
copepods, and cannibalism was prevalent in many sam- 
ples. The occurrence and amount of cannibalism in the 
EBS decreased during 1982-2006 and were affected by 
environmental factors. As expected, the area of overlap 
between predator and prey pollock was the area where 
the occurrence of cannibalism was most frequently 
observed, on the northwest middle and outer domains. 
The greatest amount of cannibalism occurred in the 
offshore portion of the middle domain and the outer 
domain and increased with temperatures (between 1°C 
and 5°C) and bottom depths. Moreover, the amount of 
cannibalism increased with higher prey pollock abun- 
dances and increasing predator sizes. 
We found that, in the summer, the occurrence of can- 
nibalism was related to location with its associated 
bottom depth and temperature, the presence of the 
cold pool, and the overlap between adult and age-1 
pollock. The less frequent occurrence of cannibalism 
in the cold pool reflected the tendency of large pollock 
to avoid these areas. Where cannibalism did occur, the 
