Space Use by Piscivorous Birds, Fish, and Humans on a Multi-Use Lake in Southern Saskatchewan

Abstract

On the Great Plains of North America, freshwater lakes are a critical resource in a dry landscape. Recreational development and use of lakes, as well as industrial and agricultural uses, may alter habitat and water quality. Consequently, it is important to understand how economically important fish species (walleye Sander vitreus; northern pike Esox Lucius; and burbot Lota lota) use lakes and identify key areas for protection and management efforts. Conflicts between humans and fish-eating birds over fisheries resources have also emerged and may be exacerbated by the limited availability of freshwater. In this context, the double-crested cormorant (Phalacrocorax auritus) and American white pelican (Pelecanus erythrorhynchos) have been targeted by anglers based on their diet, which is almost exclusively made up of fish. In contrast, the western grebe (Aechmophorus occidentalis) is a fish-eating bird of conservation concern and may be declining primarily due to human development of near-shore habitat. My research examined space use by three different user groups on Buffalo Pound Lake, in southern Saskatchewan, Canada: (1) sport fish; (2) fish-eating birds; and (3) humans (boats). Acoustic telemetry based on 30 fixed receivers showed that individuals of all 3 fish species (burbot, northern pike, walleye) were located in almost all portions of the lake at some point in time. In particular, northern pike occupied nearly the entire lake and also made long-distance movements throughout the study period. However, kernel density analysis identified the northwestern portion of the lake as a “hotspot” for all 3 fish species, with the majority of detections in undeveloped portions of the lake that were seldom used for recreation. These results need to be interpreted with caution, given the poor detection of fish on acoustic receivers for most of the study period. Point counts revealed that double-crested cormorants and American white pelicans had the highest relative densities in areas of Buffalo Pound Lake with undeveloped shorelines. Both of these bird species were often most abundant in the same northwestern portion of the lake used by sport fish, further highlighting this area as a “hotspot” for piscivorous species. In contrast, western grebe relative density was much more evenly spread across the entire lake, including areas with high levels of shoreline development and boating disturbance. The relative density of boats was highest in areas with developed shorelines, and few boats were ever detected in the “hotspot” area for fish and birds described above. My results suggest that the northwest portion of Buffalo Pound Lake needs to be a focal area for long-term habitat protection; more research is needed to determine how western grebes are interacting with humans.