Simple dynamics underlie sockeye salmon (<I>Oncorhynchus nerka</I>) cycles

Abstract

A variety of mechanisms have been proposed to explain the renowned British Columbia sockeye salmon (Oncorhynchus nerka) cycles, most of which invoke between-brood interactions (delayed density dependence) or depensatory harvest practices. We examine the dynamics of the Ricker model with realistic parameter values and suggest that the cycles could result from a stable mode excited by stochastic forcing. The previously proposed mechanisms are not required to generate cyclic patterns, although they could play a role in reinforcing cycles. Our results suggest that relaxing harvest rates will increase yields and decrease variability in sockeye abundances.Résumé : On a envisagé toutes sortes de mécanismes pour expliquer les cycles bien connus qu'on observe chez le saumon rouge (Oncorhynchus nerka) de la Colombie-Britannique : dans la plupart des cas, on suppose des interactions entre les pontes annuelles (effet retardé dépendant de la densité) ou des pratiques de pêche anticompensatoires. Nous avons étudié la dynamique du modèle de Ricker en attribuant aux paramètres des valeurs réalistes et nous pensons que les cycles du saumon rouge pourraient refléter un mode stable stimulé par un forçage stochastique. Les mécanismes envisagés antérieurement ne devaient pas nécessairement provoquer un effet cyclique, même s'ils pouvaient avoir un effet de renforcement. D'après les résultats que nous avons obtenus, la diminution de la pêche devrait se traduire par une augmentation des rendements et une baisse de la variabilité des effectifs du saumon rouge.[Traduit par la Rédaction]

Cycles, stochasticity and density dependence in pink salmon population dynamics

“…The high level of environmental stochasticity inherent in salmon survival rates from parents to recruitment of their offspring likely prevents a stable carrying capacity from being reached. Previous theoretical analyses have suggested that stochastic excitation of the stable node in the Ricker model could be responsible for 4-year cycles observed for some sockeye salmon (O. nerka) populations [8]. Others have also suggested that density-dependent mortality between age classes may underlie the 4-year cycles in sockeye salmon [3,26].…”

“…Nonlinear deterministic processes such as overcompensation and delayed density-dependent mortality can produce complicated dynamics [3,4], even without environmental stochasticity. The latter can influence dynamics of natural populations, such as by synchronizing fluctuations [5,6] or by perturbing equilibria [7,8]. Thus, disentangling the deterministic and stochastic components of population dynamics is a central challenge [9,10].…”

Environmental change effects on life history traits and population dynamics of anadromous fishes

“…The effects of environmental change on wild populations, both in abundance (Lane, Kruuk, Charmantier, Murie, & Dobson, 2012;Ozgul et al, 2010) and in dynamics (Cornulier et al, 2013;Nelson & Yamanaka, 2013) explained the occurrence of this dynamics to be caused by tritrophic interactions (Guill, Drossel, Just, & Carmack, 2011), stochastic processes (Myers, Mertz, Bridson, & Bradford, 1998), depensatory predation or genetic effects (Levy & Wood, 1992). Our model successfully predicts the oscillations as a result of the density-dependent feedback between individuals within a cohort through the food density in the breeding habitat that causes the alternation of a fast and a slow-growing cohort (Fig.…”