Commercial Fishing Nets and Loon Mortality

One of the causes of deaths of loons has been drowning in commercial trap nets set for whitefish in the Great Lakes. After the nesting season, many loons which have occupied inland lakes visit the Great Lakes to feed on fish that they can find readily in the clear waters. The Department of Natural Resources, in the 1980s, estimated that about 260 loons were drowned annually in commercial fishing nets in Michigan waters, with 86 percent of those in trap nets. (The estimated number of breeding loons in Michigan is only somewhat over 400)  Loons apparently are attracted to fish trapped in the 20x20x20 foot "pot" of the trap net and drown when they attempt to surface and become entangled in the mesh of its roof. Traditionally, the roof of the net consisted of 4x4 inch nylon mesh.

Research conducted in 1990 by NMU graduate student, Corinne Carey, sponsored by MLPA and DNR, using temporarily captive loons, revealed that most loons could pass through a 6 by 6 inch mesh. In the early 1990s, graduate student Joe Christiansen, with the cooperation of commercial fishermen,  monitored trap net lifts. He found that under pressure from the Michigan DNR, most commercial fishermen had converted their nets to the 6 by 6 in. mesh. Following such adoption, the estimated seasonal Loon catch on Lake Superior was reduced from an estimated 263 to 77 loons. Fishermen who have converted the tops of their nets to the larger mesh found no significant reduction in fish catch, as the whitefish instinctively tend to go deeper when in trouble, thereby remaining in the pot to be harvested.

With the recent completion of the revised fishing treaty, there may be an opportunity to impact these losses and to decrease the number of loons lost in trap nets. The MLPA is working with the Michigan DNR and the tribal fisheries to accomplish this. A brochure has been developed and distributed to help educate the fishermen about this problem. 

Netting Brochure (PDF)

Reference:

Christiansen, J.L., and Robinson, W.L.; Modification of Trap Nets to Reduce Capture of Common Loons. 1996. Journal of Lake and Reservoir Management 12:(2) 78-90.