Spring cannibalism on 1 year walleye pollock in the Doto area, northern Japan: is it density dependent?

• Published in: Journal of fish biology Vol. 59; no. 3; pp. 645 - 656
• Main Authors: Yamamura, O., Yabuki, K., Shida, O., Watanabe, K., Honda, S.
• Format: Journal Article
• Language: English
• Published: Oxford, UK Blackwell Publishing Ltd 01.09.2001; Blackwell
• Subjects: Agnatha. Pisces; Animal and plant ecology; Animal, plant and microbial ecology; Animals; Autoecology; Biological and medical sciences; cannibalism; density-dependence; Fundamental and applied biological sciences. Psychology; Gadidae; predator-prey size relationship; Vertebrata; Pacific Ocean; Asia; Japan; North Pacific; Predator prey relation; Theragra chalcogramma; Cannibalism; Feeding; Interannual variation; Marine environment; Prey; Vertebrata; Diet; Seasonal variation; Pisces; Body size; Density dependence; Predator; Population density
• ISSN: 0022-1112; 1095-8649
• DOI: 10.1111/j.1095-8649.2001.tb02368.x

Cannibalism in walleye pollock off the eastern coast of the Hokkaido Island, Japan was important only during spring (April to June), and its importance increased from 0% in dry mass for <200 mm LS fish to 48·9% for >400 mm LS fish. Most of the prey was represented by age 1 year fish, showing a unimodal body size distribution with a mode at 121–130 mm. Although cannibal body size was larger in deeper (>150 m) water, there was no difference in prey size by depth, suggesting impingement of the predators inhabiting deeper water into the shallow areas to cannibalize 1 year fish. The minimum ratio cannibal: prey size was 1·74. There was a positive but non‐significant correlation between the contribution of cannibalism to a potential predator's (>300 mm) diet and an estimate of the previous year's recruitment. This was due to an extremely high contribution of cannibalism during 1992, when a distinctly larger size of predators seemed to bias the contribution. When the 1992 data were removed from the analysis, a significant correlation was obtained (r2=0·77, P<0·01), showing that Pollock cannibalism is rather density dependent. Based on the results, it is hypothesized that the‘overflow’ of 1 year fish from the shelf waters due to their high abundance and the weak stratification in the spring water column results in increased co‐occurrence with adult fish and consequent cannibalism.