Growth Potential of Walleye in Devils Lake, North Dakota

Devils Lake is North Dakota’s largest natural lake and it supports a large, economically important walleye fishery. Recent flooding in Devils Lake has resulted in increased lake productivity and a gradual increase in walleye abundance over time; however, walleyes greater than 500 mm total length remain rare. This suggests that either walleye growth rates have decreased preventing individual walleyes from attaining large sizes or that angler exploitation has decreased size structure. Our objectives were to: 1.) Determine the dominant prey taxa in walleye diets during the 2011 growing season and 2.) Model food consumption and growth potential of Devils Lake walleye under various diet scenarios using bioenergetics modeling to determine if walleyes in Devils Lake are limited by prey availability. Stomachs were removed and processed from 825 walleyes caught during four different sampling periods (June, July, August, and September) during the 2011 growing season. Otoliths were removed from the same walleye and used to determine age specific growth during the growing season. Macroinvertebrates (e.g., amphipods, chironomids, and leeches) comprised the majority of walleye diets during June and July with fish comprising a very small percentage of walleye diets during these two sampling periods. August and September walleye diets were also dominated by macroinvertbrates but fish and especially yellow perch comprised a greater percentage of walleye diets during these two sampling periods. Walleye growth potential was low on a diet dominated by macroinvertebrates and was maximized when yellow perch comprised the majority of walleye diets throughout the growing season.