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

Abstract

The Brook Trout Salvelinus fontinalis is a native salmonid that provides a valued and productive sport fishery in northeastern Minnesota. Revival of North American beaver Castor canadensis (hereafter, "beaver") populations since their near extermination and concern over their impacts on Brook Trout habitat prompted a reexamination of the complex ecological relationship where the two taxa interact. 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 stream sections (200 m each) and 21 beaver ponds spanning the North Shore of Lake Superior during the summer in 2017 and 2018. Habitat suitability index (HSI) models determined the average HSI and quantity of suitable Brook Trout habitat (m 2 /100 m 2 ) at stream and beaver pond sites, and a bioenergetics model calculated Brook Trout growth availability (m 2 /100 m 2 ) and mean growth (g/d) at stream sites. Classification regression trees identified significant thresholds at which beaver activity (e.g., number of dams upstream of sampled sites and beaver pond age) influenced the quantity or quality of Brook Trout habitat and growth. No significant variables were identified as affecting Brook Trout habitat or growth rates in stream sites. Alternatively, the quantity and quality of Brook Trout habitat in this region appeared to be influenced by microhabitat variables (depth, velocity, and temperature) that are eminent at individual stream sites. Brook Trout growth was strongly influenced by velocity (m/s) and mean prey concentration (mg dry mass/m 3 ). Results indicated that 12 of the 21 sampled beaver ponds contained suitable Brook Trout habitat, with dissolved oxygen (mg/L) identified as a threshold. 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 Lake Superior's North Shore streams.

Relics of beavers past: time and population density drive scale‐dependent patterns of ecosystem engineering

“…Since 1977, there has been no limit on the individual annual harvest of beavers in our study area (Johnson‐Bice et al 2021a). The Minnesota Department of Natural Resources (MNDNR) has overseen a beaver management program in the Knife River watershed since 1994 (MNDNR 2017, Renik and Hafs 2020). Between 1994 and 2017, 607 beaver and 603 beaver dams were removed in the Knife River watershed (D. Hendrickson, MNDNR, pers.…”

The macroinvertebrate fauna of maintained and abandoned beaver dams

“…Naiman et al, 1984;Nummi, 1989;Hood & Larson, 2014;Bush et al, 2016Bush et al, , 2019Nummi et al, 2021), including studies focusing on fish communities (e.g. Hägglund & Sjöberg, 1999;Bylak & Kukuła, 2018;Renik & Hafs, 2020;Bylak et al, 2014;Fritz & Gangloff, 2022). Thereby, beaver dams are generally not considered as movement barriers for fish species, especially for native species (Lokteff et al, 2013;Cutting et al, 2018;Pollock et al, 2022).…”