Effect of Beaver on Brook Trout Habitat in North Shore, Lake Superior Streams

Author

Kathryn Renik

Date of Award

8-2019

Document Type

Thesis

Department

Biology

First Advisor

Andrew Hafs

Abstract

In Minnesota, North American Beavers Castor canadensis (hereafter Beaver) are considered to have an overall negative affect on native Brook Trout Salvelinus fontinalis. Brook Trout provide a valued and productive sport fishery to the North Shore streams of Lake Superior and since revival of the Beaver population from past trapping and timber harvest, a reexamination of the complex ecological relationship where the two taxa interact is imperative. Suitable Brook Trout habitat is characterized by cold, spring- fed water with silt-free rocky substrate and abundant cover, all of which Beaver may directly, or indirectly, affect. Data collection occurred on 79 (200 m) stream sections and 21 Beaver ponds spanning the North Shore during summers 2017 and 2018. Habitat suitability index (HSI) were used to determine the average HSI and quantity of suitable Brook Trout habitat (m2/100 m2) in both stream and pond sites. A bioenergetics model was employed to calculate growth availability (m2/100 m2) and mean growth (g/day) for Brook Trout in stream sites. Classification regression trees were used to identify significant thresholds in which Beaver activity, such as distance to nearest Beaver pond and number of dams upstream of sampled sites, influenced the quantity or quality of Brook Trout habitat and growth.

No significant predictor variables were identified in the regression tree as affecting the average HSI, area of suitable Brook Trout habitat, Brook Trout growth availability, or growth rates in stream sites. Alternatively, the quantity and quality of Brook Trout habitat in streams of this region appears to be better described by microhabitat variables (depth, velocity, temperature) that are eminent in individual stream sites. Brook Trout growth in stream sites was strongly influenced by velocity (m/sec) and mean prey concentration (mg dry mass/m3). Results from interpolated habitat maps of Beaver pond sites indicated that 12 of the 21 ponds sampled contained suitable Brook Trout habitat, with dissolved oxygen (mg/L) identified as a threshold for determining if ponds contained suitable Brook Trout habitat. This study recommends focusing on individual stream characteristics and Beaver pond dissolved oxygen concentrations to achieve desired Brook Trout habitat and aid in the development of management strategies pertaining to these two taxa in North Shore, Lake Superior streams.

Recommended Citation

Renik, Kathryn, "Effect of Beaver on Brook Trout Habitat in North Shore, Lake Superior Streams" (2019). Biology Graduate Theses. 9.
https://pines.bemidjistate.edu/thesis-biol/9