Brook Trout and Fish Community Use of Spring Ponds Within the Plover River System, Wisconsin

File(s)
Date
2025-01Author
Lins, Jason
Publisher
College of Natural Resources, University of Wisconsin-Stevens Point
Advisor(s)
Raabe, Joshua
Metadata
Show full item recordAbstract
Protecting refugia that provide suitable thermal habitat could be crucial for the persistence of sensitive fish species amid variable and warming climates and anthropogenic habitat alterations. For instance, Wisconsin has thousands of miles of thermally suitable habitat for brook trout Salvelinus fontinalis and other coldwater species that is threatened by changing climate and habitat. Spring ponds may serve as refugia during droughts and periods of extreme weather events because of consistent groundwater input and depth that maintain cold water. However, there is limited knowledge of how brook trout and other fishes use the spring ponds and what pond characteristics support connectivity, demographics, and community compositions. Additionally, spring ponds may meet the definition of small natural features (SNFs), that is, habitats with ecological importance disproportionate to their size. Spring ponds, however, continually fill in with sediment and organic matter as they transition to a wetland, and for example, alteration of riparian habitats and groundwater levels could negatively influence their habitats. This study focused on spring ponds in the Plover River system and spanned from fall 2022 to summer 2024. The Plover River system in central Wisconsin and its spring ponds support a naturally reproducing brook trout population in middle and upstream reaches and high species richness. The objectives of this study were to: 1) determine if brook trout population demographics varied with season, spring pond characteristics, and river reaches and spring ponds, 2) if brook trout use of spring ponds varied by season and water temperature, and if connectivity existed among spring ponds and river reaches, and 3) evaluate community assemblages in spring ponds and whether they are influenced by season, river reach, or pond characteristics. Electrofishing occurred in three focal spring ponds in fall 2022, and spring, summer, fall 2023, and in seven other spring ponds and river sites in summer 2023. Brook trout were tagged with passive integrated transponder (PIT) tags and community data were recorded by counting individuals of other species. Brook trout movement was monitored at the three focal ponds with PIT arrays. Brook trout moved between the Plover River and focal ponds, and on a few occasions between ponds, and brook trout demographics varied seasonally but no clear trend was found. Movement into ponds increased in late spring, electrofishing mean catch per hour (CPE) of brook trout was highest in summer (20.2 / h), and brook trout were larger in focal ponds (mean = 185 mm, SD = 66.1) than in adjacent river reaches (mean = 104 mm, SD = 61.1). Spring pond median depth (P = 0.0081, r2 = 0.60) and mean depth (P = 0.0154, r2 = 0.53) were negatively related to summer CPE, and surface area (negatively) and max depth (positively) were related (P = 0.0038, r2 = 0.79) to proportional size distribution (PSD) of brook trout. In addition to electrofishing, environmental DNA (eDNA) was used to assess community compositions of the ten spring ponds in spring, summer, and fall 2023. Sixteen species were detected in spring ponds using eDNA, prominently brook stickleback Culaea inconstans (71.5%) and white sucker Catostomus commersonii (11.5%), while electrofishing detected 22 species, prominently white sucker (38.3%) and brook trout (14.1%). Depth standard deviation, maximum depth, mean depth, median depth, outlet length, wood density, river reach, volume, surface area, and dredging were related to significant differences in presence/absence and relative abundance (sequencing reads and catch per hour). Community composition was significantly related to waterbody but not season. This study provides information on spring pond fish communities and indicates eDNA is likely to be useful for sampling spring ponds after refinement and that spring ponds fit the SNF definition. Additionally, brook trout appear to use spring ponds as a summer thermal refuge and some individuals throughout the year. Ensuring spring pond habitat quality and connectivity to streams may help coldwater species persist in a warmer environment.
Subject
brook trout
eDNA
fish communities
movement
spring ponds
thermal refuge
Permanent Link
http://digital.library.wisc.edu/1793/94429Type
Thesis