Spring flow lost: a historical and contemporary perspective of an urban fish community

Movement and mortality of invasive suckermouth armored catfish during a spearfishing control experiment

Control of non-native, invasive species in groundwater-dependent ecosystems that are also inhabited by regionally endemic or at-risk species represents a key challenge in aquatic invasive species management. Non-native suckermouth armored catfish (SAC; family Loricariidae) have invaded freshwater ecosystems on a global scale, including the groundwater-dependent upper San Marcos River in Texas, USA. We used passive integrated transponder tags to follow the movements and fates of 65 fish in a 1.6 km spring-fed reach of the upper San Macros River to assess the efficacy of a community-based spearfishing bounty hunt for controlling SAC. We found the weekly probability of SAC survival was negatively correlated with the number of fish removed as a part of the bounty hunt each week (P = 0.003, R² = 0.86), while the probability of SAC being speared and reported was positively correlated with the number of fish removed (P = 0.011, R² = 0.53). The majority of SAC used < 25 m² of river over a nine-week tracking period, but the area of river fish used correlated positively with the number of relocations (P < 0.001, R² = 0.36) as might be expected for a population that disperses through diffusive spread. These findings collectively suggest local-scale suppression of the SAC population is possible through community engagement in spearfishing, but over longer time periods immigration might offset some of the removal success. This conclusion provides an explanation for the pattern in which long-term spearfishing tournaments have reduced biomass but ultimately not resulted in eradication of the population.