Hydrilla Management Impacts on a Largemouth Bass Fishery: A Case for a Balanced Management Approach

Lake Austin, in central Texas, supported a popular trophy largemouth bass (Micropterus salmoides) fishery concomitant with conservative hydrilla (Hydrilla verticillata) management during the period 2002–2011. However, a change from this conservative approach to an aggressive stocking rate of triploid grass carp (Ctenopharyngodon idella) in response to excessive hydrilla growth between 2011–2013 subsequently resulted in the eradication of all submerged aquatic vegetation (SAV). The loss of SAV quickly changed the angling dynamics of the reservoir, resulting in a controversial decline in the quality angling experience. The objectives of this case study were to compare how available population metrics of largemouth bass and important prey fish differed between periods of SAV presence (1997–2013) and absence (2014–2022) to inform which SAV management approach better supports a sustainable trophy fishery goal. These comparisons revealed evidence of declines in largemouth bass relative abundance (CPUE), body condition (Wr ), and growth rates when SAV became absent, but no changes in population length structure. There were no apparent changes observed in selected prey species populations between the two periods. While linking changes in fish population metrics with a single environmental attribute in a reservoir is difficult, SAV has been widely associated with quality largemouth bass fisheries. As such, our results suggest a long-term conservative triploid grass carp stocking management approach to best protect SAV habitat that supports adequate largemouth bass population performance alongside other reservoir functions. Management needs to consider multiple priorities among relevant stakeholders in support of a balanced system for all uses. Further, SAV surveys should explore use of volumetric biomass assessments in response to triploid grass carp herbivory for better supplemental stocking estimates while trying to anticipate how climate driven changes in hydrology and temperature might impact SAV extent.