Light in lakes and forage habitat

Figure 1.  Capture probabilities for Siscowet Lake Trout at different light intensities

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Recently, we have been investigating how fish habitat changes with daily and seasonal light changes.  With the help of Bryan Matthias, a post-doc at UMD, we have created a light model for Lake Superior that predicts changes in Siscowet Lake Trout foraging habitat on an hourly, daily and seasonal time scale.

Figure 2. A photon of light's path through water

Using Siscowet prey capture data from Keyler et al. (2015), we are able to determine the light intensity associated with 50% prey capture during foraging trials (Fig. 1).  We can then calculate the depth within Superior associated with this light intensity throughout the day and seasons using the model.  

Figure 3.  Changes in solar altitude and angle with seasons

Our model accounts for reflection at the lake's surface, refraction by water, and attenuation within the water (Fig. 2).  Due to the angle and altitude of the sun associated with different seasons (Fig. 3), light penetrates deeper in the summer compared to the winter season. Siscowet forage habitat is therefore greater in the summer, than in the winter (Fig. 4).  

Additionally, we are working on calculating the daily light changes within Lake Superior as well as how light penetration, and respective siscowet forage habitat, will change with climate warming. 

Figure 4.  Solar maximum siscowet habitat depths for cross-section of Lake Superior (right) and associated geographical distribution (left) for spring, summer, fall and winter (from top) within the Western Arm of Lake Superior. 

Publication Link: https://link.springer.com/article/10.1007/s10750-019-3888-9