North Pacific Anadromous Fish Commission

Technical Report 15

Table of Contents

Changing Productivity, Variability, and Synchrony within Stock Aggregates can Limit Management Effectiveness

Authors:
Cameron Freshwater, Sean C. Anderson, Kendra R. Holt, Ann-Marie Huang, and Carrie A. Holt

Abstract Excerpt:
Asynchrony among component populations can increase the temporal stability of ecological aggregates, a process commonly referred to as the portfolio effect (Doak et al. 1998; Tilman 1999). Within salmon species, population diversity reduces aggregate variability in spawner returns and catches, as well as the probability of fishery closures (Schindler et al. 2010) and can increase long-term resilience given environmental uncertainty (Anderson et al. 2015). Aggregate variability is linked to two metrics—the weighted mean coefficient of variation among components (component variability) and an index of synchrony (Loreau and de Mazancourt 2008; Thibaut and Connolly 2013). Component variability and synchrony may increase due to anthropogenic disturbance (Griffiths et al. 2014) or large-scale environmental processes (Kilduff et al. 2015), resulting in less predictable returns, boom-and-bust fisheries, and increased risk of overharvest. Greater aggregate variability may also be exacerbated by declines in population productivity associated with reduced survival or fecundity (Peterman and Dorner 2012; Minto et al. 2014; Britten et al. 2016). Although changes in component variability, synchrony, and productivity may independently constrain fisheries management, it is not necessarily clear how these processes will interact. We paired a retrospective analysis of observed trends in the dynamics of Fraser River sockeye salmon (O. nerka) with a closed-loop simulation model to evaluate the impact of greater aggregate variability under various productivity regimes (Freshwater et al. in press). The closed-loop simulation is analogous to the quantitative component of a management strategy evaluation (MSE; Punt et al. 2016) and includes a biological model, as well as a model of the mixed-stock fishery that harvests these populations.

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DOI:
https://doi.org/10.23849/npafctr15/4.6.

Citation

Freshwater, C., S.C. Anderson, K.R. Holt, A. Huang, and C.A. Holt.  2019.  Changing productivity, variability, and synchrony within stock aggregates can limit management effectiveness.  N. Pac. Anadr. Fish Comm. Tech. Rep. 15: 4–6.  https://doi.org/10.23849/npafctr15/4.6.