Influence of pinniped-caused injuries on the survival of adult

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Influence of pinniped-caused injuries on the
survival of adult Chinook salmon (Oncorhynchus
tshawytscha) and steelhead trout (Oncorhynchus
mykiss) in the Columbia River basin
George P. Naughton, Matthew L. Keefer, Tami S. Clabough, Michael A. Jepson,
Steven R. Lee, Christopher A. Peery, and Christopher C. Caudill
Abstract: Increasing pinniped abundance in the Pacific Northwest has coincided with population declines of Pacific salmon
(Oncorhynchus spp.) and steelhead trout (Oncorhynchus mykiss), and concentrated predation may affect the recovery of
some threatened and endangered salmonid stocks. We used radiotelemetry to evaluate pinniped-caused injury effects on migration survival of 17 007 adult Columbia River Chinook salmon (Oncorhynchus tshawytscha) and steelhead trout. Injuries
from pinnipeds were common (mean injury rate across 29 run-years = 36.5%) and were most common for spring Chinook
salmon and steelhead trout. Injury was not consistently associated with adult survival to spawning tributaries, but some negative survival effects were detected. Pinniped-caused injury rates decreased as annual run sizes increased, indicating densitydependent or saturation effects. Within a run, large fish generally had a higher injury incidence than small fish, suggesting
pinnipeds targeted large fish or more efficiently captured small fish. Seasonal, size-dependent, and density-dependent results
imply that pinniped effects likely differ widely among salmonid populations within the Columbia River basin. A better
understanding of these effects is needed to guide management and conservation strategies.
Résumé : L’augmentation d’abondance des pinnipèdes dans le Nord-Ouest Pacifique coïncide avec les déclins démographiques des saumons du Pacifique (Oncorhynchus spp.) et de la truite arc-en-ciel anadrome (Oncorhynchus mykiss) et la
concentration de la prédation peut affecter le rétablissement de quelques stocks de salmonidés menacés et en péril. La
radiotélémétrie nous a servi à évaluer les effets des blessures causées par les pinnipèdes sur la survie durant la migration de
17 007 saumons chinook (Oncorhynchus tshawytscha) et truites arc-en-ciel anadromes adultes dans le fleuve Columbia. Les
blessures dues aux pinnipèdes sont communes (taux moyen de blessures dans 29 montaisons-années = 36,5 %) et sont plus
abondantes chez les saumons chinook et truites arc-en-ciel anadromes de printemps. Il n’y a pas d'association constante entre les blessures et la survie des adultes jusqu’aux tributaires de fraie, mais on peut déceler des effets négatifs sur la survie.
Les taux de blessures dues aux pinnipèdes diminuent à mesure que la taille des montaisons annuelles augmente, ce qui indique des effets de densité dépendance ou de saturation. Dans une montaison, les poissons plus grands ont généralement
une incidence plus élevée de blessures que les poissons plus petits, ce qui laisse croire que les pinnipèdes ciblent les poissons plus grands ou alors capturent plus efficacement les plus petits. Ces résultats saisonniers et dépendants de la taille et
de la densité amènent à croire que les effets des pinnipèdes diffèrent vraisemblablement beaucoup d’une population de salmonidés à une autre au sein du bassin versant du Columbia. Une meilleure compréhension de ces effets est requise pour
orienter les stratégies de gestion et de conservation.
[Traduit par la Rédaction]
Introduction
Members of the Order Pinnipedia evolved >20 million
years ago, and their distributions have likely overlapped those
of Pacific anadromous salmonids (Oncorhynchus spp.) for
much of their existence. Many pinnipeds (seals and sea lions)
were hunted until only small fractions of their former populations remained in the late 19th and early 20th centuries for
both the fur trade and to reduce fishery interactions (Beddington et al. 1985). However, since passage of the Marine
Mammal Protection Act in 1972, many pinniped populations
in the Pacific Northwest (e.g., California sea lion (Zalophus
californicus), Steller sea lion (Eumetopias jubatus), and
Pacific harbor seal (Phoca vitulina)) have steadily increased
(e.g., Barlow et al. 1995; Baraff and Loughlin 2000) and
may be reaching historically high levels (Jeffries et al. 2003;
Received 1 June 2010. Accepted 11 April 2011. Published at www.nrcresearchpress.com/cjfas on xx August 2011.
J21849
Paper handled by Associate Editor Michael Bradford.
G.P. Naughton, M.L. Keefer, T.S. Clabough, M.A. Jepson, S.R. Lee, C.A. Peery,* and C.C. Caudill. Department of Fish and Wildlife
Resources, University of Idaho, Moscow, ID 83844-3141, USA.
Corresponding author: G.P. Naughton (e-mail: [email protected]).
*Present address: USFWS, Idaho Fishery Resource Office, 4147 Ahsahka Road, Ahsahka, ID 82520, USA.
Can. J. Fish. Aquat. Sci. 68: 1615–1624 (2011)
doi:10.1139/F2011-064
Published by NRC Research Press