Assessing juvenile native fish demographic responses to a steady flow experiment in a large regulated river

River Research and Applications
By: , and 

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Abstract

The Colorado River below Glen Canyon Dam, Arizona, is part of an adaptive management programme which optimizes dam operations to improve various resources in the downstream ecosystem within Grand Canyon. Understanding how populations of federally endangered humpback chub Gila cypha respond to these dam operations is a high priority. Here, we test hypotheses concerning temporal variation in juvenile humpback chub apparent survival rates and abundance by comparing estimates between hydropeaking and steady discharge regimes over a 3-year period (July 2009–July 2012). The most supported model ignored flow type (steady vs hydropeaking) and estimated a declining trend in daily apparent survival rate across years (99.90%, 99.79% and 99.67% for 2009, 2010 and 2011, respectively). Corresponding abundance of juvenile humpback chub increased temporally; open population model estimates ranged from 615 to 2802 individuals/km, and closed model estimates ranged from 94 to 1515 individuals/km. These changes in apparent survival and abundance may reflect broader trends, or simply represent inter-annual variation. Important findings include (i) juvenile humpback chub are currently surviving and recruiting in the mainstem Colorado River with increasing abundance; (ii) apparent survival does not benefit from steady fall discharges from Glen Canyon Dam; and (iii) direct assessment of demographic parameters for juvenile endangered fish are possible and can rapidly inform management actions in regulated rivers.

Additional publication details

Publication type Article
Publication Subtype Journal Article
Title Assessing juvenile native fish demographic responses to a steady flow experiment in a large regulated river
Series title River Research and Applications
DOI 10.1002/rra.2893
Volume 32
Issue 4
Year Published 2016
Language English
Publisher John Wiley & Sons
Publisher location Chichester, West Sussex, UK
Contributing office(s) Southwest Biological Science Center
Description 13 p.
First page 763
Last page 775
Online Only (Y/N) N
Additional Online Files (Y/N) N