Characterizing Growth and Condition of Endangered Humpback Chub in the Lower Colorado River

Translocations, defined herein as the human‐assisted movement of individuals from a source population to other waters within their historical range, are prevalent in recovery plans for endangered fishes. Many translocations fail to establish new populations, however, and outcomes are often poorly documented. Endangered Humpback Chub Gila cypha persist as a self‐sustaining population in Grand Canyon, Arizona, despite threats from introduced nonnative competitors and predators and modified flow, thermal, and sediment regimes due to river regulation. In the decades following the completion of Glen Canyon Dam, the Grand Canyon population has been primarily sustained through reproduction in a single Colorado River tributary, the Little Colorado River (LCR). To establish population redundancy and aid in recovery, we annually translocated between 243 and 509 juvenile Humpback Chub from the LCR to Havasu Creek, a smaller Colorado River tributary in Grand Canyon National Park. Juvenile Humpback Chub were collected from the wild and reared in a hatchery for 8–12 months prior to the translocations. Through biannual mark–recapture sampling in Havasu Creek, we estimated annual abundance for all of the translocated cohorts and found that apparent survival and growth rates met or exceeded the demographic rates that are published for the LCR. We observed reproductively mature adults each year in May, beginning in 2012, and untagged juvenile Humpback Chub beginning in the following year and every year thereafter, with results that indicated successful reproduction. Beginning in 2016, we noted recruitment to maturity of fish that were produced in situ and the population's abundance increased through 2018, indicating potential for the establishment of a self‐sustaining population. As an example of the successful translocation of an endangered species that demonstrates the potential importance of tributaries in the recovery of large‐river fishes, our study may help to inform future recovery planning.

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Establishment of a Reproducing Population of Endangered Humpback Chub through Translocations to a Colorado River Tributary in Grand Canyon, Arizona

Healy

Smith

Schelly

et al. 2020

N American J Fish Manag

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Growth of Endangered Humpback Chub in Relation to Temperature and Discharge in the Lower Colorado River

Pine

Limburg

Gerig

et al. 2017

Journal of Fish and Wildlife Management

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Assessments of growth can provide information needed to understand how fish populations respond to changing environmental conditions and management actions, including ecosystem experimentation. We estimated growth rates and parameter uncertainty from otoliths of endangered Humpback Chub Gila cypha from the Colorado River in Grand Canyon, Arizona. We then compared growth of Humpback Chub , age 2 that were 1) occupying the mainstem Colorado River during a period of variable discharge and cooler water temperatures (1980-1998; epoch 1), 2) occupying the Colorado River during a period of moderate discharge variability and warmer water (2001-2011; epoch 2), and 3) occupying the unregulated Little Colorado River. Because growth rates of juvenile Humpback Chub (, age 2) may be more sensitive to changes in environmental conditions than adult fish, we used analysis of covariance and linear models to compare growth of juvenile fish (slopes) between epochs and capture sites (mainstem Colorado River vs. Little Colorado River). Our analysis of covariance results were ambiguous (age 3 epoch 3 site interaction; P ¼ 0.06). on growth and growth variability useful for parameterizing models to assess population viability and 2) provide empirical information on how growth of juvenile and adult Humpback Chub growth may respond to changing environmental conditions.

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Characterizing Growth and Condition of Endangered Humpback Chub in the Lower Colorado River

Cited by 2 publications

References 49 publications

Establishment of a Reproducing Population of Endangered Humpback Chub through Translocations to a Colorado River Tributary in Grand Canyon, Arizona

Establishment of a Reproducing Population of Endangered Humpback Chub through Translocations to a Colorado River Tributary in Grand Canyon, Arizona

Growth of Endangered Humpback Chub in Relation to Temperature and Discharge in the Lower Colorado River

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