Impacts of Endothall Applications on Largemouth Bass Spawning Behavior and Reproductive Success

Aquatic herbicides are commonly used to control excessive and nuisance levels of submersed aquatic vegetation (SAV). At times, these applications tend to be more effective at the onset of fish spawning in spring; however, they can cause conflicts between anglers and lake management personnel assigned to control excessive SAV. We evaluated the direct application of an aquatic herbicide (Aquathol K [dipotassium salt of endothall]) on the nest behavior and fidelity of largemouth bass Micropterus salmoides and measured the subsequent reproductive success of these fish. Endothall was applied to achieve a shoreline concentration of 5 mg/L of water volume in 0.1‐ha ponds (3 mg/L whole‐pond concentration). It was applied directly on nests in three ponds in March 2005, 2006, and 2007 when largemouth bass initiated spawning; spawning activity was monitored over 14–15 d. Using similar techniques, we applied water to another three ponds where largemouth bass were nesting. For all 3 years, endothall did not affect nest guarding by largemouth bass, and nest fidelity was similar to that for ponds treated with water. Endothall concentrations declined about sevenfold over 21 d but persisted in the water during spawning. Electrofishing of young largemouth bass 2–3 months after spawning showed that their relative abundance and size were similar among the ponds treated with endothall and the control ponds. Similarly, the density and biomass of age‐0 largemouth bass did not vary between treatments for fish killed with rotenone in late August each year. Managers can use these results to address angler concerns about endothall application during largemouth bass spawning and thereby lessen conflicts over efforts to control excessive SAV.