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AUTHORS: Nicholas Kludt, South Dakota State University; Mark Fincel, South Dakota Game, Fish and Parks; Eli Felts, South Dakota State University; Brian Graeb, South Dakota State University
ABSTRACT: Recruitment is influenced by both biotic and abiotic pressures, but questions remain about the relative magnitude of these influences. We examined how Lake Herring Coregonus artedi year class strength was affected by two predators (Walleye Sander vitreus, Chinook Salmon Oncorhynchus tshawytscha) and a competitor (Rainbow Smelt Osmerus mordax). Walleye were assessed using standard gill net survey CPUE, and Lake Herring, Chinook Salmon and Rainbow Smelt were assessed using hydroacoustics. We also evaluated the effects of ice-up, ice-out, temperature, overwinter reservoir drawdown, and annual discharge on Lake Herring year class strength. The a priori AIC multi-model analysis revealed increased Lake Herring year class strength, defined using catch-curve regression residuals, was associated with decreased large Walleye (>510 mm) and Rainbow Smelt abundances, which accounted for 91% of ΣAICc(W). Environmental variables explained only 6% ΣAICc(W), with each individual environmental term contributing less weight than the intercept model. Chinook Salmon abundance was analyzed separately due to differing data range, and did not influence Lake Herring year class strength. Odds ratios from a subsequent post hoc AIC multi-model analysis ranked the large Walleye model as 10.95 more likely to explain Lake Herring year class strength than the Rainbow Smelt model, and 23.63 more likely than the intercept model. Community time series suggest an interaction between Rainbow Smelt abundance and Walleye numbers. In flood years (1997, 2009, 2011), Rainbow Smelt populations declined and >380 mm Walleye abundance decreased within 3 years. The typically low density Lake Herring population produced strong year classes in these periods. The removal and re-establishment of predatory and competitive pressures following reservoir hydrologic cycles may have contributed to the ephemeral nature of Lake Herring year class production. Although not directly impacting year class strength, large flood events may have triggered the release of biotic regulation of recruitment.
