ANTHROPOGENIC INFLUENCES ON THE DECLINE, RESTORATION, AND ECO-EVOLUTIONARY DYNAMICS OF LAKE SUPERIOR’S COASTER BROOK TROUT
Date of Award
Open Access Master's Thesis
Master of Science in Biological Sciences (MS)
Administrative Home Department
Department of Biological Sciences
Committee Member 1
Committee Member 2
The coaster brook trout is a life history variant of the brook trout (Salvelinus fontinalis) that is characterized by either lake residency or migration between stream and lake habitats. Coaster brook trout were once widespread throughout Lake Superior and its tributaries, but populations declined sharply in the late 19th and early 20th centuries. Historically, brook trout were a popular target of recreational and subsistence fishing in the Lake Superior basin, and it has been hypothesized that angling pressure combined with multiple forms of industrial development are what drove the coaster brook trout’s decline. In the mid to late 19th century, the logging, lumbering, and mining industries proliferated rapidly, along with the network of railroads, which provided connectivity for industry and access to once remote fishing locations. However, it is unknown to what degree each of the proposed factors influenced the coaster’s decline.
In Chapter 1, we collected and analyzed historical data (Pre 1880-1950) on the distribution & abundance of brook trout in Lake Superior tributaries, along with historical data on the development and expansion of industries around Lake Superior to examine potential associations between specific anthropogenic impacts and coaster brook trout declines. The data were separated into four temporal categories (Pre 1880-1880, 1881-1900, 1901-1920, 1921-1950) to examine reports of brook trout catches during critical time periods in industrial developments around Lake Superior. We performed a geospatial analysis using ArcGIS Pro that demonstrated a decrease in both putative coaster brook trout abundance and range over time. Brook trout decreased notably between the ‘1881-1900’ time period and the ‘1901-1920’ time period, following large increases in both lumber mills and kilometers of railroad. We performed a principal component analysis to reveal potential associations between variation in industrial variables and brook trout abundances in watersheds between the first and final time periods (Pre 1880-1880 & 1921-1950, respectively). Our analysis showed that the majority of watersheds analyzed experienced a decrease in brook trout abundance and suggested that the industrial development variables we examined all are associated with and thus may have all influenced brook trout decline, though to varying degrees, as some developments were highly localized. Angling appears to be an important factor in the decline of brook trout populations around Lake Superior, as active angling (noted removals of brook trout) occurred in every watershed for which we found data. Furthermore, brook trout populations declined almost universally, even in watersheds for which we recorded little to no industrial footprint.
In Chapter 2, I examine historical and modern brook trout management initiatives, use an eco-evolutionary perspective to inform potential management & restoration strategies, and identify potential restoration watersheds using the historical GIS data from Chapter 1. I used these data to create a table of prioritized restoration sites by compiling watersheds that had both a high likelihood of historical migratory brook trout populations and also experienced little industrialization. With this information, we identified several locations in Wisconsin, Michigan, and northern Minnesota that may be optimal coaster restoration watersheds.
Johnson, Austin, "ANTHROPOGENIC INFLUENCES ON THE DECLINE, RESTORATION, AND ECO-EVOLUTIONARY DYNAMICS OF LAKE SUPERIOR’S COASTER BROOK TROUT", Open Access Master's Thesis, Michigan Technological University, 2022.