Marine growth patterns of southern British Columbia chum salmon explained by interactions between density-dependent competition and changing climate

Abstract

Thirty-nine years of scale growth measurements from Big Qualicum River chum salmon (Oncorhynchus keta) in southern British Columbia demonstrated that competition and climate variation affect marine growth and age-at-maturity. A longitudinal study design that accounted for correlation among individuals revealed growth at all ages was reduced when the biomass of North American chum, sockeye (Oncorhynchus nerka), and pink salmon (Oncorhynchus gorbuscha) was high. When North Pacific Gyre Oscillation (NPGO) was positive, indicating increased primary productivity, predicted growth increased. Climate variation influenced competition effects. For instance, density-dependent competition effects increased when NPGO became more positive and Pacific Decadal Oscillation became more negative (indicating cool conditions), causing the greatest range in predicted scale size. Chum salmon are likely to exhibit continued reduction in growth at age due to increased ocean temperatures driven by climate change and high aggregate salmon biomass that includes hatchery releases. If evidence of biomass and climate effects presented here are common among Pacific salmon populations, reduction of hatchery releases should be considered. Résumé :Des mesures sur 39 ans de la croissance des écailles de saumons kétas (Oncorhynchus keta) de la Grande rivière Qualicum, dans le sud de la Colombie-Britannique, démontrent que la concurrence et les variations climatiques ont une incidence sur la croissance en mer et l'âge à la maturité. Un plan d'étude longitudinale qui tient compte de la corrélation entre individus révèle que la croissance à tous les âges est plus faible quand la biomasse des saumons kétas, sockeyes (Oncorhynchus nerka) et roses (Oncorhynchus gorbuscha) d'Amérique du Nord est élevée. Quand l'oscillation du tourbillon nord-pacifique (OTPN) est positive, indiquant une productivité primaire accrue, la croissance prédite augmente. Les variations du climat ont également une incidence sur ces effets de concurrence. Les effets de la concurrence dépendant de la densité augmentent quand l'OTPN devient plus positive et l'oscillation décennale du Pacifique, plus négative (indiquant des conditions fraîches), ce qui produit la plus grande fourchette de tailles d'écailles prédites. Il est probable que les saumons kétas continueront de présenter une diminution de la croissance selon l'âge en raison de la hausse des températures océaniques causée par les changements climatiques et de la forte biomasse totale de saumons incluant les individus issus d'écloseries. Si les indices d'effets de la biomasse et du climat relevés dans la présente étude s'avéraient répandus dans les populations de saumons du Pacifique, il serait pertinent d'examiner la possibilité de réduire les lâchers de poissons issus d'écloseries. [Traduit par la Rédaction]

Changing salmon: An analysis of body mass, abundance, survival, and productivity trends across 45 years in Puget Sound

“…These include dramatic increases in the number of humans living near the Sound, increased marine mammal predation (Chasco et al, ), changes in hatchery salmon and steelhead production (HSRG, ), increased shoreline armouring (Habitat Strategic Initiative et al, ; Morrison et al, ), changes in the frequency of El Nino events (Wolter & Timlin, ), changes in herring, other forage fish, and jellyfish abundance and distribution (Greene, Kuehne, Rice, Fresh, & Penttila, ; Siple & Francis, ; Siple et al, ) and increased total salmon abundance in the Sound (as reported here). Each of these factors may have influenced growth and feeding conditions and thus body size of Puget Sound salmon and steelhead in a variety of ways, as they have been shown for these species in other areas within and outside the Salish Sea (Debertin et al, ; Jeffrey et al, ).…”

“…Reduced body size of Pacific salmon has been linked to a variety of factors including fisheries-induced evolution (Fukuwaka & Morita, 2008;Kendall, Dieckmann, Heino, Punt, & Quinn, 2014), hatchery practices (Hankin, Fitzgibbons, & Chen, 2009;Swain, Riddell, & Murray, 1991), environmental and climate conditions (Debertin et al, 2017;Jeffrey et al, 2017;Morita & Fukuwaka, 2007), density-dependent effects (Ruggerone & Irvine, 2018) and increased natural mortality (e.g. predation by killer whales; Ohlberger et al, 2018).…”

“…These changes coincided with a significant increase in abundance of hatchery‐produced salmon, which in recent years have represented >40% of the total salmon biomass in the North Pacific (Ruggerone & Irvine, ). While causes of contrasting patterns of salmon body size and abundance are not completely understood, the studies cited above and others discussed possible links to environmental conditions, management practices and density dependence (Claiborne et al, in press; Debertin, Irvine, Holt, Oka, & Trudel, ). Together, these and numerous other studies (Kendall, Marston, & Klungle, ; Kilduff, Botsford, & Teo, ; Ohlberger, Ward, Schindler, & Lewis, ; Zimmerman et al, ) highlight the importance of multidecadal time series documenting basic salmon demographic data across multiple populations for management and conservation purposes.…”

The Economic Impacts of Humpback Whale Depredation on Hatchery‐Released Juvenile Pacific Salmon in Southeast Alaska

“…) due to predator sheltering (i.e., strength in numbers) and (2) a negative relationship in the offshore environment (Debertin et al. ; Yasumiishi et al. ) due to resource competition.…”

“…; Debertin et al. ). The hatchery organizations’ stakeholders are the licensed commercial fishermen that own limited‐entry salmon permits for the region and directly benefit economically from hatchery production by capturing these fish as they return to the hatchery as mature adults.…”