Lake Use by Three Avian Piscivores and Humans: Implications for Angler Perception and Conservation

Humans and colonial piscivorous birds are often perceived to be in conflict over shared aquatic habitats and fisheries resources in inland lakes. We examined angler perception of birds and the relative abundance of American white pelicans ( Pelecanus erythrorhynchos ), double-crested cormorants ( Phalacrocorax auritus ), western grebes ( Aechmophorus occidentalis ), and boats on two lakes in Saskatchewan, Canada. Anglers perceived cormorants to be the biggest threat to fisheries (60%), compared to pelicans (47%), and western grebes (34%). The density of these birds and boats varied significantly between sections of the two study lakes. Boat density was higher in developed sections with shoreline communities (range 0-7/km 2 ) compared to those surrounded by agricultural land or native prairie (0-1/km 2 ). In contrast, cormorant and pelican densities were highest in areas with an undeveloped shoreline (0-22/km 2 ), and were reduced to near zero in developed sections. Western grebes did not follow the same pattern as the other two species; grebe density was generally more uniform within lakes (0-23/km 2 in all sections). Boat density was a negative predictor of pelican and cormorant density on one lake, but was a positive predictor for grebes on both lakes. Our results indicate that pelicans and cormorants avoid sections of lakes that have higher levels of human development, potentially altering the location of their foraging sites on the scale of kilometres. In contrast, western grebes were abundant in all areas of the two lakes and did not appear to avoid human development or activity. We conclude that angler perceptions are not congruent with levels of habitat use overlap with birds. In addition, western grebe responses to human activities appear counterintuitive, making interpretations difficult in a conservation context; further study is required.