Invasive Fishes in Puerto Rico’s Streams: Evaluations of a Removal Method and Extent of Invasions

Aquatic nuisance species (ANS) is a threat to native freshwater species and freshwater streams in Puerto Rico. This thesis evaluates the efficacy of a removal method for and distribution of two introduced taxa, Midas cichlids (Amphilophus spp.) and sailfin catfish (Pterygoplichthys spp.), through a two-part study. Chapter II tests the efficacy of a multi-method removal approach, primarily using triple-pass backpack electrofishing and supplemental techniques, to reduce ANS abundance in the Río Piedras. While short-term reductions in Midas cichlid density were achieved, no significant long-term effects on biomass or density were observed, and recolonization occurred rapidly. Results indicated that sailfin catfish were present at low densities and were more effectively targeted. Chapter III expands the scope to an island-wide assessment of ANS presence across 32 wadeable stream sites, revealing range expansions for Midas cichlids since previous surveys and minimal presence of sailfin catfish. No significant relationship was found between ANS presence and proximity to dams or stream type, suggesting human-mediated spread as the primary driver. Overall, the findings highlight the effectiveness of triple-pass backpack electrofishing as a control method and the widespread distribution of target aquatic nuisance species across Puerto Rico's freshwater systems.