Successful fisheries management practices developed for one ecosystem can often be used in similar ecosystems. We developed a flexible lake classification framework in collaboration with ~100 fisheries biologists for improved fisheries conservation management in Wisconsin, USA. In total, 5,950 lakes were classified into 15 lake classes using a two‐tiered approach. In tier‐one, lakes were clustered into “simple” and “complex” sportfish assemblages. In tier‐two, lakes were further clustered using accumulated degree days, water clarity, and special cases. We focus on temperature and clarity because these factors often drive fisheries change over time—thus a lake's class can change over time. Lake class assignments were refined through a vetting process where fisheries biologists with expert knowledge provided feedback. Relative abundance, size‐structure, and growth rates of fishes varied significantly across classes. Biologists are encouraged to utilize class interquartile ranges in fisheries metrics to make improved fisheries assessments. We highlight hard‐won lessons from our effort including: (1) the importance of co‐developing classification frameworks alongside fisheries biologists; and (2) encouraging frameworks where lakes can shift classes and fisheries expectations over time due to factors like climate change and eutrophication.
We quantified production, biomass, and production to biomass (P/B) ratios for cisco (Coregonus artedi) in Trout Lake, Wisconsin, USA (2001–2015). Across all years, annual production, biomass, and P/B were variable ranging 0.6–30.2 kg·ha−1·year−1, 1.2–39.7 kg·ha−1, and 0.4–0.9·year−1, respectively. Cisco production exhibited obvious decline. However, neither biomass nor P/B changed significantly over time. Long-term patterns of environmental conditions remained unchanged during the study and were unrelated to cisco production. However, lake trout (Salvelinus namaycush) relative abundance showed a strong inverse relationship with cisco production and biomass. Intense lake trout stocking has occurred in this lake over time to conserve a genetically unique strain of the species. These management efforts may have had the unintended consequence of amplifying top-down predation on cisco. Since cisco P/B has gone largely unchanged, cisco production would be predicted to rebound quickly to adaptive reductions in lake trout stocking. Further increases in lake trout numbers could place both populations at risk of collapse. This study provides an example of a fisheries production approach for understanding and conserving cold-water fisheries, especially in lakes dominated by ciscoes.
The cisco (Coregonus artedi) requires cold, well-oxygenated water and is threatened by climate warming and lake eutrophication, especially at the southern edge of its range in the Laurentian Great Lakes region. In this paper, a method is described to assess the quality, quantity, and variability of suitable cisco habitat. Two metrics are proposed to characterize existing cisco oxythermal habitat in this region: water temperature in the water column at a dissolved oxygen of 6 mg/L (TDO6) and “cisco layer thickness” (CLT), the vertical extent of the water column within which water temperature is ≤22.8 °C and dissolved oxygen is ≥6 mg/L. It is proposed that values of TDO6 = 22.8 °C and CLT = 1 m be used as benchmarks to identify cisco lakes with potentially stressful oxythermal habitat. Long-term summer data from 14 Wisconsin cisco lakes with a wide range of limnological characteristics indicated that TDO6 varied from 4.2 to 27.5 °C and CLT from −6.2 to 66.7 m. Cisco abundance across lakes was greater at lower values of TDO6 and higher values of CLT, and non-attainments of the proposed benchmarks were most likely in lakes with remnant or extirpated cisco populations. Non-attainment of benchmarks could occur from late June through September, and three or more samples across the entire summer would be required to have a reasonable probability of detecting a non-attainment in TDO6 or CLT within any given year. Across years, to detect a single year of non-attainment with an 80% level of confidence, two years of sampling would be sufficient for CLT and three years for TD06; to detect more than one non-attaining year, three years of sampling for CLT and six years of sampling for TD06 would be required. Despite relatively high temporal variation in some lakes, the proposed metrics and benchmarks appear to have value for assessing cisco oxythermal habitat in the Great Lakes region.
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