Why new scientific information is important for native fish conservation: A case study from the humpback chub (Gila cypha) in the Grand Canyon, U.S.A.

Abstract

Abstract Habitat descriptions found in critical habitat designations and recovery plans are important for protecting endangered species. However, in order to protect critical habitat, it is necessary to update descriptions of habitat use when range shifts occur or new studies change the understanding of habitat use. This study examined the habitat use of a threatened desert fish to determine whether current habitat use matched the descriptions in recovery documents. Recovery documents describe humpback chub (Gila cypha) as being dependent on rocky, canyon‐bound habitats during all life stages, but recent surveys found humpback chub in open, silt‐laden habitats, suggesting this species may be able to occupy a wider range of habitats. Hoop net catch data from a long‐term monitoring project in the Colorado River were used to compare catches of two size classes: juvenile/subadult (<200 mm total length [TL]) and adult humpback chub (≥200 mm TL). Catch information was analysed on an individual net scale and on a geological segment scale using generalized linear mixed models. There was no difference in juvenile/subadult humpback chub catch between hoop nets set in rocky habitat compared with habitat with only fine sediment. Humpback chub catch for all life stages in a river segment characterized by silt banks exceeded or was not significantly different from catch in rocky segments. This case study demonstrates the importance of revisiting habitat descriptions, sampling in areas outside known or expected habitat and incorporating new data related to range expansion or habitat changes in recovery strategies to better describe and protect habitats that can support imperilled species.