An Individual‐Based Model for Population Viability Analysis of Humpback Chub in Grand Canyon

Abstract

We developed an individual‐based population viability analysis model (females only) for evaluating risk to populations from catastrophic events or conservation and research actions. This model tracks attributes (size, weight, viability, etc.) for individual fish through time and then compiles this information to assess the extinction risk of the population across large numbers of simulation trials. Using a case history for the Little Colorado River population of Humpback Chub Gila cypha in Grand Canyon, Arizona, we assessed extinction risk and resiliency to a catastrophic event for this population and then assessed a series of conservation actions related to removing specific numbers of Humpback Chub at different sizes for conservation purposes, such as translocating individuals to establish other spawning populations or hatchery refuge development. Our results suggested that the Little Colorado River population is generally resilient to a single catastrophic event and also to removals of larvae and juveniles for conservation purposes, including translocations to establish new populations. Our results also suggested that translocation success is dependent on similar survival rates in receiving and donor streams and low emigration rates from recipient streams. In addition, translocating either large numbers of larvae or small numbers of large juveniles has generally an equal likelihood of successful population establishment at similar extinction risk levels to the Little Colorado River donor population. Our model created a transparent platform to consider extinction risk to populations from catastrophe or conservation actions and should prove useful to managers assessing these risks for endangered species such as Humpback Chub. Received August 28, 2012; accepted March 13, 2013

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

“…Due to concerns that are related to the potential effect of the translocations on the donor population, we relied on the results of the population‐viability analyses to assess the effect of the collections of a range of numbers of fish at different life stages on the abundance and extinction risk to the LCR population (Pine et al. ). Until 2014, we targeted juvenile or subadult fish that measured up to 135 mm with baited mini‐hoop nets or seines during July or October, as is described in Spurgeon et al.…”

“…Comparable results to those that were found for the donor population, which is assumed to be self‐sustaining (USFWS 2018a), would signal the likelihood of the long‐term sustainability of a translocated population (Pine et al. ).…”

“…However, these smaller tributaries, some of which are isolated from the Colorado River by barriers to fish movement, may not support large populations of Humpback Chub, potentially leading to a low probability of establishment (Pine et al. ). These isolated refuges may contain habitat that is only marginally suitable to support all life stages, or carrying capacity may be insufficient to maintain genetically diverse and sustainable populations, resulting in failed efforts to restore or maintain isolated populations (Fausch et al.…”

“…2015b) or competition with nonnative fishes may have limited the persistence and establishment of new populations (Pine et al. ; Spurgeon et al. 2015a).…”

Evaluating Population Recovery Characteristics and Potential Recovery Actions for a Long‐Lived Protected Species: A Case History of Gulf Sturgeon in the Apalachicola River

“…() was updated to represent multistanza recruitment (also referred to as “unpacking recruitment”; Hilborn and Walters ; Lorenzen ; Pine et al. ). Multistanza recruitment refers to splitting a single recruitment process into two or more sequential processes, and it is useful for representing mid‐recruitment changes such as altered fish density from stock enhancement.…”