Exploring effectiveness of two common trap designs for capturing fish diversity in small freshwater bodies

The biodiversity crisis in freshwater habitats is intensifying due to human-induced changes, leading to significant biodiversity loss. Freshwater fish, in particular, are experiencing alarming population declines. Effective monitoring by direct capture is critical to track and mitigate these losses, but small water bodies often present challenges for active monitoring methods. In such cases, passive sampling techniques, like traps, offer a practical alternative for conservation agencies, though their effectiveness in monitoring fish biodiversity for conservation purposes is not yet fully understood. This study evaluates the effectiveness of two passive sampling techniques fyke nets and umbrella-shaped traps (umbrella traps) for capturing fish diversity in small freshwater habitats. Sampling was conducted overnight in 39 water bodies, and fish density was quantified using catch per unit effort (CPUE). A beta regression model was applied to analyze species capture rate and the influence of habitat parameters on catch success. The CPUE revealed a 6.82-fold higher mean individual capture rate and a 2.05-fold higher species richness per deployment for umbrella traps compared to fyke nets indicating significantly higher sampling efficiency under comparable conditions. Rarefaction curves and non-metric multidimensional scaling analyses demonstrated that umbrella traps more effectively characterized littoral fish diversity and captured higher species richness than fyke nets in small freshwater bodies. The study underscores the utility of umbrella traps as a reliable tool for assessing fish diversity through direct capture, particularly for monitoring elusive or invasive non-native species. These findings aim to enhance conservation oriented species capture and inform conservation planning in often-overlooked small freshwater ecosystems, which play a crucial role in the long-term conservation of fish species.