| dc.description.abstract | The Lake Winnebago System (LWS) in East-Central Wisconsin supports one of the largest lake sturgeon Acipenser fulvescens populations in North America, which provides a popular spear fishery each February. Lake sturgeon in the LWS primarily spawn in the Wolf River and some of its tributaries and the Fox River, but the potential contribution of these different spawning groups to the overall population remains unknown. Larval lake sturgeon were routinely collected in drift net samples between 2018 and 2021 at spawning sites in the Wolf River drainage. However, during this same period no larvae were captured in the Fox River spawning sites of Princeton, indicating that successful hatching may not be occurring in the Fox River. Differences in habitat characteristics may influence spawning success of lake sturgeon spawning in different locations within the LWS. Understanding differences in habitat characteristics and lake sturgeon spawning stock characteristics among rivers is important to devising and implementing management strategies designed to increase lake sturgeon recruitment. Consequently, my research objective was to determine if habitat characteristics differed among spawning sites within the Wolf River and its tributaries where larval sturgeon have been collected and spawning sites in the Fox River where larvae were not collected. Additionally, mark-recapture information obtained by the Wisconsin Department of Natural Resources during spawning stock assessments was assessed to determine if lake sturgeon spawning in the Fox River exhibit site fidelity and to compare sex ratios and length frequency distributions of spawning fish among rivers. Although not linked to a specific objective, I continued to monitor whether hatching occurred at lake sturgeon spawning sites.
During 2022 and 2023, I sampled three lake sturgeon spawning sites in the Wolf River drainage (Shiocton and Highway X in the Wolf River; Pfeifer Park in the Embarrass River) and two spawning sites in the Upper Fox River (Princeton and Riverside Park). Habitat characteristics were assessed at spawning sites for three weeks following spawning during both years. During this time, depth (m) was measured using a depth rod, dominant substrate was assessed using a bathyscope, total dissolved solids (TDS; mg/L), dissolved oxygen (DO; mg/L), and pH were measured using a YSI Multi-Probe System (Yellow Springs, Ohio), and water velocity (m/s) was recorded three times weekly at the substrate/water interface using a Marsh-McBirneyTM Model 2000 portable flow meter (Loveland, Colorado). Additionally, water temperature (°C) was recorded at one-minute intervals for a period of six weeks using OnsetTM HOBO MX2201 Pendant Wireless Temperature Data Loggers (Bourne, Massachusetts) deployed at each location.
Siltation traps created from plastic containers (28 cm x 18.4 cm x 7.6 cm) filled with clean river rock (5-64 mm in diameter) were deployed at spawning sites to assess siltation (g/hr). Periphyton biomass (g/m2) was assessed by scraping fixed-area (0.0046 m2) samples from five randomly-selected cobble-sized rocks (64 - 256mm diameter) at each spawning site each year. Periphyton growth (g/m2) during egg deposition and incubation was assessed by deploying six unglazed ceramic tiles at each site (8.255 x 8.255 cm) for a period of six weeks which were subsequently scraped clean. Macroinvertebrate communities were sampled at spawning sites using Hester-Dendy samplers set for a period of six weeks, as well as a water-pump to dislodge macroinvertebrates from the substrate. Relative egg abundance was assessed by pumping a mixture of eggs and water from the substrate where eggs are deposited and pouring the sample over a fine mesh net (1.2mm) and counting the eggs collected. I compared spawning-site habitat metrics and relative egg abundance among individual spawning sites using analysis of variance (ANOVA). If ANOVA indicated significant differences existed, Tukey’s (HSD) post hoc tests were used for pairwise comparisons.
The Wisconsin Department of Natural Resources conducts annual surveys in the Lake Winnebago tributaries using dip nets to collect spawning lake sturgeon. During this time fish are measured for total length (TL; nearest 0.10 in and converted to mm), sexed, and inserted with a passive integrated transponder (PIT; Biomark., Boise, Idaho). This information was used to assess site fidelity of lake sturgeon to individual rivers (i.e., Wolf or Fox). A chi-squared test of independence was used to assess if there were differences in the proportions of lake sturgeon exhibiting site fidelity among rivers. Additionally, sex ratios (expressed as percent female), and sex-specific mean lengths were assessed to identify differences in groups of lake sturgeon spawning in different rivers. These metrics were compared among rivers using analysis of variance (ANOVA). Tukey’s (HSD) post hoc tests were used for pairwise comparisons.
Mean TDS was highest in the Fox River spawning sites of Riverside Park (mean = 264 mg/L; SD = 1.3) and Princeton (mean = 255 mg/L; SD = 6.7), as well as Pfeifer Park (mean = 245 mg/L; SD = 10.9) in the Embarrass River. Mean TDS was lowest at Shiocton (mean = 175 mg/L; SD = 12.5) and Highway X (mean = 198 mg/L; SD = 8.7) in the Wolf River proper. Mean TDS was significantly lower in the Wolf River spawning sites compared among spawning sites in the Fox River and Pfeifer Park in the Embarrass River. However, there were no differences of mean TDS between the Embarrass and Fox spawning sites, or differences between spawning sites within the same river. Mean siltation rates were lowest at the Shiocton (mean = 0.07 g/hr; SD = 0.03) and Highway X (mean = 0.09 g/hr; SD = 0.05) spawning sites in the Wolf River proper and were highest at Fox River spawning sites of Princeton (mean = 0.18 g/hr; SD = 0.01) and Riverside Park (mean = 0.28 g/hr; SD = 0.05), as well as Pfeifer Park in the Embarrass River (mean = 0.16 g/hr; SD = 0.05). However, the only significant differences in mean siltation rates were detected for Riverside Park when compared to both Shiocton and Highway X in the Wolf River. Periphyton biomass at the Princeton spawning site (mean = 50.9 g/m2; SD = 2.55) on the Fox River was significantly higher than biomass at sites in the Wolf and Embarrass rivers (range of means = 21.9 -26.9 g/m2) and at Riverside Park on the Fox River (mean = 23.2 g/m2; SD = 2.3). Macroinvertebrate Index of Biotic Integrity scores were lower at spawning sites in the Fox River (mean = 21.3) compared to the Embarrass (mean = 60) and Wolf rivers (mean = 32.5). Relative egg abundance was lower in Fox River spawning sites of Riverside Park (mean = 0.03 eggs/10-pumps; SD = 0.05) and Princeton (mean = 0.2 eggs/10-pumps; SD = 0.13) compared to Shiocton (mean = 39.0 eggs/10-pumps), Highway X (mean = 16.2 eggs/10-pumps; SD = 18.5), and Pfeifer Park (mean = 9.0 eggs/10-pumps; SD = 3.4) in the Wolf River Drainage. However, the only significant differences in relative egg abundance were detected for Shiocton when compared to both Riverside Park and Princeton.
Adult lake sturgeon initially captured in the Fox River during spawning surveys showed relatively low site fidelity (fidelity = 69.0%; 20 loyal out of 29 fish) and frequently strayed into the Wolf River drainage. Wolf River fish showed little evidence of straying (fidelity = 97.7% 3,796 loyal out of 3,886 fish) and Embarrass River fish were loyal to the Wolf River drainage (fidelity = 98.8%; 168 loyal out of 170 fish). Sex ratios and mean total lengths were similar across rivers.
My results suggest that there are significant habitat differences among spawning sites in the Fox River compared to the Embarrass and Wolf rivers that may influence successful hatching of lake sturgeon, notably siltation and periphyton biomass in the Fox River. However, the low number of adult lake sturgeon using the Fox River for spawning, the lack of eggs collected at Fox River spawning sites, as well as the lack of larvae indicate that the Fox River may currently contribute little to overall lake sturgeon recruitment in LWS. Current methods of direct habitat improvement strategies may be more beneficial in the Wolf River drainage where larvae have been collected. However, habitat management strategies such as direct cleaning of substrate or strategic habitat designs to increase water velocity at spawning sites to remove excess siltation and periphyton may be beneficial to improving spawning success in the Fox River. Additionally, changes to land use at the watershed level such as riparian buffer zones may improve habitat characteristics and increase hatching success in the Fox River. Straying rates suggest that fish spawning in the Fox River appear to spawn in the Wolf River drainage during some years and likely do not represent a distinct stock within the LWS. | en_US |
