Effects of River Discharge, Temperature, and Future Climates on Energetics and Mortality of Adult Migrating Fraser River Sockeye Salmon

Abstract

We evaluated the effects of past and future trends in temperature and discharge in the Fraser River on the migratory performance of the early Stuart population of sockeye salmon Oncorhynchus nerka. Fish of lower condition exhibited disproportionately higher mortality during the spawning run, elucidating a critical link between energetic condition and a fish's ability to reach the spawning grounds. We simulated spawning migrations by accounting for energetic demands for an average individual in the population from the time of entry into the Fraser River estuary to arrival on the spawning grounds (about 1,200 km upstream) and estimated energy expenditures for the average migrant during 1950-2001. The model output indicates relatively high interannual variability in migration energy use and a marked increase in energy demands in recent years related to unusually high discharges (e.g., 1997) and warmer than average water temperature (e.g., 1998). We examined how global climate change might effect discharge, water temperature, and the energy used by sockeye salmon during their spawning migration. Expected future reductions in peak flows during freshets markedly reduced transit time to the spawning ground, representing a substantial energy [Article] savings that compensated for the effect of the increased metabolic rate resulting from exposure to warmer river temperatures. We suggest that such watershed-scale compensatory mechanisms may be critical to the long-term sustainability of Pacific salmon, given expected changes in climate. However, such compensation will probably only be applicable to some stocks and may be limited under extremely high temperatures where nonenergetic factors such as disease and stress may play a more dominant role in defining mortality. Our results further indicate that a long-term decline in the mean mass of adult sockeye salmon completing their marine residency could erode their migratory fitness during the river migration and hence jeopardize the sustainability of sockeye salmon and the fishery that targets them. 656 RAND ET AL.

There and back again: migration in freshwater fishes

“…), Atlantic salmon, and American shad (Alosa sapidissima (Wilson, 1811)), and appears to be similar for cyprinids migrating from lakes to streams in winter (Brodersen et al 2008c). Once in the natal river, returning anadromous salmonids may struggle for weeks against falls and rushing rapids and a substantial part of the initial energy reserves may be depleted (Glebe and Leggett 1981;Brett 1995), potentially contributing to en route and prespawning mortality (Rand and Hinch 1998;Rand et al 2006). This is especially important for migrants with a semelparous life history, such as Pacific salmon, because they die after reproduction and thus achieve their total lifetime fitness via this single reproductive event.…”

On the Changing Contribution of Snow to the Hydrology of the Fraser River Basin, Canada

“…The Fraser is the seventh largest river in North America by annual discharge and is also one of the most prolific salmon rivers in the world, with many First Nations relying on the annual upriver migrations for nourishment (Xie and Hsieh 1989;Beamish et al 1997;Benke and Cushing 2005;Fraser Basin Council 2006. However, Rand et al (2006) demonstrate how extremes in flows can lead to high mortality rates in sockeye salmon migrating up the Fraser River. Thus, there may be significant impacts of climate change on the hydrologic regime of the Fraser River with implications to aquatic species and habitat, local communities, and the economy of western Canada.…”

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.…”