Study of deepwater fishes in Lake Superior reveals their visual capabilities

Predator and prey fish inhabiting deepest waters of Lake Superior use vision to detect each other.

The siscowet lake trout is only found in Lake Superior and is the main predator in the deepwater region of the lake. Photo: Shawn Sitar | Michigan Department of Natural Resources
The siscowet lake trout is only found in Lake Superior and is the main predator in the deepwater region of the lake. Photo: Shawn Sitar | Michigan Department of Natural Resources

Lake Superior as compared to the other Great Lakes consists of a relatively simple food web consisting of few major predators and prey fish. The interactions of the predator and prey community in the deep offshore regions of Lake Superior have been well studied except for the role that vision plays in these fish. To learn more about these predator and prey deepwater interactions the University of Minnesota Duluth Biology Department conducted a study on the Visual Sensitivity of Deepwater Fishes in Lake Superior that was published in PLOS. Funding for this project was provided by Minnesota Sea Grant, U.S. Geological Survey Lake Superior Biological Station and University of Minnesota Duluth Biology Department.

The study focused on three key fish that inhabit the deepwater environment of Lake Superior: the siscowet lake trout, deepwater sculpin, and kiyi. The siscowet lake trout is a form of lake trout found in the deepest waters of Lake Superior and is sometimes regarded as a subspecies to the lean lake trout. The siscowet lake trout is only found in Lake Superior and is the main predator in the deepwater region of the lake. The siscowet lake trout feeds near the bottom of the lake during the day and ventures up into the water column at night in search of food. The deepwater sculpin lives and feeds on the bottom of the lake and is a food source for siscowet lake trout. Both of these fish can be found in waters exceeding one thousand feet in depth in Lake Superior. The kiyi, which is a cousin to the lake whitefish, is limited in distribution to the deeper water region of Lake Superior at depths of three hundred to six hundred feet. The kiyi is also preyed upon by the siscowet lake trout.

It was found in this study that visual interactions are possible at the depths and times when this major predator and two prey fish overlap in the water column indicating that vision may play a far greater role at depth in freshwater lakes, such as Lake Superior, than had been previously documented. All three species had broad spectral sensitivities that correlate with prevailing downwelling light in Lake Superior. The spring and summer water column is clearer and contains less particulate matter than fall, thus allowing greater light transmission to depth. In the fall of the year the greater suspension of particulate matter increases light absorbance and thus the light does not travel as far into the depths.

The deepwater water sculpin proved exceptionally sensitive to light stimuli indicating it may be the most sensitive of the three species studied. The deepwater sculpin shows sufficient visual sensitivity to potentially mediate predator-prey interactions throughout the majority of its range. As the deepwater sculpin is the preferred prey of siscowet, its greater visual sensitivity may allow it to detect the siscowet lake trout at sufficient range to evade predation. Its position living on the bottom of the lake provides an additional advantage as it can discern the predator silhouettes illuminated by the downwelling light while the siscowet lake trout faces the more difficult task of visualizing bottom prey against a dark background. At the deep water sculpin’s average depth insufficient light is available for visual function at night and thus it is less likely to be preyed upon as its main predator, the siscowet lake trout, undergoes migration up into the water column and therefore vision may not be necessary during this time.

The siscowet lake trout and kiyi visual sensitivities are sufficient to allow daytime vision throughout most of these fishes’ depths and full moonlight could provide sufficient irradiance to allow vision from one hundred to two hundred feet in depth. Both species may have sufficient visual sensitivity to use vision to feed or avoid predation at night.

These three fish species that comprise the offshore food web of Lake Superior have evolved spectral sensitivity to match the prevailing downwelling light. Their visual sensitivity appears sufficient to utilize visual cues for predator avoidance and prey capture. While other sensory mechanisms may be important for long range detection, most short range predator-prey interactions are mediated by the lateral line and/or vision.

Michigan Sea Grant helps to foster economic growth and protect Michigan’s coastal, Great Lakes resources through education, research and outreach. A collaborative effort of the University of Michigan and Michigan State University and its MSU Extension, Michigan Sea Grant is part of the NOAA-National Sea Grant network of 33 university-based programs.

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