Role of Nest Raiding and Egg Predation in Regulating Population Density of Threespine Sticklebacks (Gasterosteus aculeatus) in a Coastal British Columbia Lake

The consequences of nest raiding and egg predation for population regulation of sticklebacks (Gasterosteus aculeatus) were studied in a British Columbia coastal lake. Stickleback eggs were present in the stomachs of 23 and 11% of all sticklebacks sampled from the field in 1982 and 1985 respectively. On average, males consumed more eggs than did females. Seasonal egg consumption increased with increases in stickleback density in breeding colonies. In experimental enclosure studies, nest densities varied between 0 and 3∙m−2 as stickleback numbers were manipulated from 1.5 to 12∙m−2. Peak nest densities occurred at 5.8 fish∙m−2. Stickleback density explained 70–86% of the variation in nest numbers in an application of a Ricker stock–recruit model and weekly rates of nest survival exhibited strong density dependence. Our evidence indicates that both nest raiding and egg cannibalism are important in limiting the production of stickleback fry as population density increases in scattered, lakeshore, breeding colonies of Kennedy Lake.