Colonial Waterbird Predation on Lost River and Shortnose Suckers in the Upper Klamath Basin

Abstract

We evaluated predation on Lost River Suckers Deltistes luxatus and Shortnose Suckers Chasmistes brevirostris by American white pelicans Pelecanus erythrorhynchos and double‐crested cormorants Phalacrocorax auritus nesting at mixed‐species colonies in the Upper Klamath Basin of Oregon and California during 2009–2014. Predation was evaluated by recovering (detecting) PIT tags from tagged fish on bird colonies and calculating minimum predation rates, as the percentage of available suckers consumed, adjusted for PIT tag detection probabilities but not deposition probabilities (i.e., probability an egested tag was deposited on‐ or off‐colony). Results indicate that impacts of avian predation varied by sucker species, age‐class (adult, juvenile), bird colony location, and year, demonstrating dynamic predator–prey interactions. Tagged suckers ranging in size from 72 to 730 mm were susceptible to cormorant or pelican predation; all but the largest Lost River Suckers were susceptible to bird predation. Minimum predation rate estimates ranged annually from <0.1% to 4.6% of the available PIT‐tagged Lost River Suckers and from <0.1% to 4.2% of the available Shortnose Suckers, and predation rates were consistently higher on suckers in Clear Lake Reservoir, California, than on suckers in Upper Klamath Lake, Oregon. There was evidence that bird predation on juvenile suckers (species unknown) in Upper Klamath Lake was higher than on adult suckers in Upper Klamath Lake, where minimum predation rates ranged annually from 5.7% to 8.4% of available juveniles. Results suggest that avian predation is a factor limiting the recovery of populations of Lost River and Shortnose suckers, particularly juvenile suckers in Upper Klamath Lake and adult suckers in Clear Lake Reservoir. Additional research is needed to measure predator‐specific PIT tag deposition probabilities (which, based on other published studies, could increase predation rates presented herein by a factor of roughly 2.0) and to better understand biotic and abiotic factors that regulate sucker susceptibility to bird predation. Received January 19, 2016; accepted June 25, 2016 Published online October 7, 2016

Colonial Waterbird Predation and Angler Catch of Hatchery Rainbow Trout Stocked in Southern Idaho Fisheries

“…Year Although we observed a slight trend of smaller catchable's being consumed more often than larger fish, this trend was not significant after accounting for variation in waterbody size and stocking numbers. Previous studies provide equivocal evidence on size selectivity for various species of predatory colonial waterbirds, with some studies demonstrating selection of smaller-sized fish (Evans et al 2016), larger-sized fish (Radhakrishnan et al 2010), or no size selectivity Scoppettone et al 2014;Teuscher et al 2015). Double-crested cormorants can consume fish that are up to 430 mm in length (Dorr et al 2014), which is larger than any of the fish that were used in our study.…”

“…Previous studies provide equivocal evidence on size selectivity for various species of predatory colonial waterbirds, with some studies demonstrating selection of smaller‐sized fish (Evans et al. ), larger‐sized fish (Radhakrishnan et al. ), or no size selectivity (Hostetter et al.…”

“…In lakes of the upper Klamath River basin, pelicans and cormorants prey upon endangered Lost River Sucker Deltistes luxatus and Shortnose Sucker Chamistes brevirostris (Evans et al. ). In Lake Huron, cormorant predation on Yellow Perch Perca flavescens has negatively affected fisheries by reducing angler catch rates (Fielder ; Seefelt and Gillingham ; Hundt et al.…”

“…Shortnose Sucker Chamistes brevirostris (Evans et al 2016). In Lake Huron, cormorant predation on Yellow Perch Perca flavescens has negatively affected fisheries by reducing angler catch rates (Fielder 2008;Seefelt and Gillingham 2008;Hundt et al 2013).…”

Histopathology and external examination of heavily parasitized Lost River Sucker Deltistes luxatus (Cope 1879) and Shortnose Sucker Chasmistes brevirostris (Cope 1879) from Upper Klamath Lake, Oregon

“…Most mortality in the Upper Klamath Lake is believed to occur within the first year of life (Simon, Terwilliger, & Markle, ). A number of factors have been cited as contributing to the low numbers of fish in the lake including poor underyearling survival, poor water quality, loss of habitat, overfishing, interactions with exotic species, predation, and pathogens and disease (including parasites) (Burdick, ; Cooke et al., ; Crandall, Bach, Rudd, Stern, & Barry, ; Evans et al., ; Markle & Dunsmoor, ; NMFS & USFW S ).…”