Improving methods and assessing the impacts of crayfish and crayfish trapping on unarmoured three-spine stickleback in San Francisquito Creek

This research investigated the impact and management of invasive red swamp crayfish (Procambarus clarkii) on the endangered unarmored threespine stickleback (Gasterosteus aculeatus williamsoni) in San Francisquito Creek, California. Funded by the National Fish and Wildlife Foundation (NFWF), this two-year study (2023-2025) employed a multifaceted approach, integrating crayfish trapping, biodiversity and water quality monitoring, laboratory and field-based experiments, and survivorship modeling. Trapping efforts tested various methods, revealing cage traps as particularly detrimental due to high bycatch, while mesh traps offered a more selective capture. Stream surveys documented population trends of target species, revealing fluctuations in stickleback and mosquitofish abundance, and provided baseline water quality data. Laboratory mesocosm experiments examined the direct and indirect effects of crayfish on stickleback and mosquitofish proxies, revealing species-specific responses to crayfish presence, though significant differences in mass change were not observed. Survival analysis during direct exposure to crayfish highlighted predation risks. Survivorship models (Weibull and Cox Proportional Hazards) aimed to forecast long-term impacts and inform management strategies. Findings are still in the preliminary stages of development but suggest a combined approach of targeted season-specific crayfish trapping, habitat management through restoration and protection. This research provides crucial data for the conservation of the endangered unarmored threespine sticklebacks and various other aquatic species currently threatened by crayfish in California.