Abstract
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/km2) compared to those surrounded by agricultural land or native prairie (0-1/km2). In contrast, cormorant and pelican densities were highest in areas with an undeveloped shoreline (0-22/km2), 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/km2 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.
Highlights
Humans and piscivorous birds are often in conflict over aquatic habitats and fisheries resources worldwide
Our first objective was to document angler perceptions; our survey data show clearly that anglers view birds to be a significant threat to fisheries, and that double-crested cormorants are perceived most negatively in this regard
Western grebes were not perceived as a threat to fisheries despite consistently high densities in all lake sections
Summary
Humans and piscivorous birds are often in conflict over aquatic habitats and fisheries resources worldwide. Current management practices for cormorants include culling of adults, disruption of breeding, and exclusion of birds from potential foraging areas [3, 4]. These programs cost millions of dollars annually, and are part of one of the most widespread wildlife management issues in history [5]. Many aquatic bird species have shown marked declines associated with high levels of human development, which may result in the loss of both nesting and foraging habitat [6, 7]. Disturbance of birds by boating activities may force them into suboptimal habitats, or cause
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