Re-establishing the three-spined stickleback fish as part of the holistic restoration of an urban lake, California, USA

Summary

The three-spined stickleback (Gasterosteus aculeatus), though not globally threatened, was the only native fish ever recorded at Mountain Lake in San Francisco's Presidio National Park before disappearing by 1928 as the lake's ecosystem degraded. The Presidio Trust made stickleback reintroduction central to a broader holistic lake restoration, since the species would also serve as an essential host fish for a concurrently reintroduced native mussel and help with community-benefiting mosquito control. Because highway construction had permanently severed the lake's connection to source populations, natural recolonization was impossible; the Trust first addressed polluted point-source runoff through bioswale construction and drainage improvements, then, after two years of multi-agency coordination, applied the piscicide rotenone to eradicate an entrenched community of invasive carp, bass and mosquitofish. Six months later, working with the National Park Service, staff and volunteers collected 1,100 stickleback via seine nets and minnow traps from a nearby source population over ten months, holding them briefly to acclimate before release, with local schools and media invited to participate. No stickleback were detected in the first year due to low visibility in the lake's dense vegetation, but young-of-the-year began appearing in traps the second spring, and by the third year the species was breeding widely throughout the shallows; an unexpected bullhead catfish incursion two years post-rotenone triggered ongoing mechanical removal. The project rates itself successful, citing the species' fast reproduction, strong interagency coordination, well-designed methods, and an on-site aquatic-pet amnesty box that has intercepted other potential invasives.