Modeling the Influence of Environmental Factors on Spawning Migration Mortality for Sockeye Salmon Fisheries Management in the Fraser River, British Columbia

Abstract

The impact of freshwater environmental factors on spawning migration mortality was modeled to provide a predictive tool for fisheries management of four run timing groups of Fraser River sockeye salmon Oncorhynchus nerka: early Stuart (Stuart Lake), early summer, summer, and late. We tested the significance of different measures of water temperature, discharge, fish abundance, and entry timing for forecasting discrepancies between lower-river and upriver escapement estimates using multiple regressions of principal component scores. Descriptive discrepancy models (i.e., ''management adjustment'' models) identified using Akaike's information criterion were consistent with the known biology of each group. For example, temperature and discharge thresholds were selected for early Stuart run discrepancy models, reflecting the extremes in both variables experienced by these early migrants. Predictive discrepancy models were also generated for each run timing group by using the limited number of environmental variables that are available in-season to fisheries managers. Even predictive discrepancy models using simple environmental metrics of average river temperature, flow, and river entry timing provide a valuable tool for forecasting relative indices of spawning migration mortality. This study provides an example of how environmentally based predictive tools can be used to inform fisheries management decisions and improve the probability of achieving spawning escapement targets.

Maintenance of Genetic Diversity in Natural Spawning of Captively-Reared Endangered Sockeye Salmon, Oncorhynchus nerka

“…These rates are towards the lower end of those estimated for Sakinaw sockeye salmon during the 1970s through 1990s, which ranged from 1% to 67% [27]. The control of terminal harvest mortality in recent years has been facilitated by concurrent low abundances and conservation efforts implemented for co-migrating Fraser River sockeye salmon populations [50]. Improved husbandry for captive brood and maintenance of harvest control, facilitated by rapid non-lethal genetic detection of Sakinaw sockeye salmon in pre-fishery sampling, has likely contributed to the recent successful return of fish from captive releases and may also benefit rebuilding of the small natural population.…”

Conservation physiology in practice: how physiological knowledge has improved our ability to sustainably manage Pacific salmon during up-river migration

“…Currently, this knowledge provides a much needed rationale for fisheries managers to restrict fishing effort during periods where river temperatures exceed predefined values, in an effort to reduce the stress on migrating salmon and maximize the number of individuals successfully reaching spawning grounds [57].…”

“…(b) Management perspective on conservation physiology The management structure for Pacific salmon has provisions to adjust harvest to increase the probability of achieving spawning targets without unduly compromising harvest opportunities in an attempt to mitigate against environmental factors known to be associated with in-river mortalities, such as high river temperature, disease and captured fish release [57]. This provides a direct application for the results from the conservation physiology research outlined in this paper to aid Pacific salmon management.…”

Integrated watershed management: evolution, development and emerging trends

“…This type of information has helped communities develop long-term flood management strategies, improve the understanding of the risks of climate change, and update infrastructure such as dikes to deal with potential inundation (BC Ministry of Forests, Lands and Natural Resources Operations 2014; FBC 2015d). Models can also be used to understand how climate change will impact salmon migration and spawning (Rand et al 2006;Macdonald et al 2010). Understanding how the salmon populations will fair under a warmer climate is critical for decisions regarding annual allowable catch and development of strategies to facilitate salmon spawning and survival.…”