Effects of river temperature and climate warming on stock-specific survival of adult migrating Fraser River sockeye salmon (Oncorhynchus nerka)

Abstract

Mean summer water temperatures in the Fraser River (British Columbia, Canada) have increased by $1.5 1C since the 1950s. In recent years, record high river temperatures during spawning migrations of Fraser River sockeye salmon (Oncorhynchus nerka) have been associated with high mortality events, raising concerns about long-term viability of the numerous natal stocks faced with climate warming. In this study, the effect of freshwater thermal experience on spawning migration survival was estimated by fitting capture-recapture models to telemetry data collected for 1474 adults (captured in either the ocean or river between 2002 and 2007) from four Fraser River sockeye salmon stockaggregates (Chilko, Quesnel, Stellako-Late Stuart and Adams). Survival of Adams sockeye salmon was the most impacted by warm temperatures encountered in the lower river, followed by that of Stellako-Late Stuart and Quesnel. In contrast, survival of Chilko fish was insensitive to the encountered river temperature. In all stocks, in-river survival of ocean-captured sockeye salmon was higher than that of river-captured fish and, generally, the difference was more pronounced under warm temperatures. The survival-temperature relationships for ocean-captured fish were used to predict historic and future (2010-2099) survival under simulated lower river thermal experiences for the Quesnel, Stellako-Late Stuart and Adams stocks. A decrease of 9-16% in survival of all these stocks was predicted by the end of the century if the Fraser River continues to warm as expected. However, the decrease in future survival of Adams sockeye salmon would occur only if fish continue to enter the river abnormally early, towards warmer periods of the summer, as they have done since 1995. The survival estimates and predictions presented here are likely optimistic and emphasize the need to consider stock-specific responses to temperature and climate warming into fisheries management and conservation strategies.

Getting past the blame game: Convergence and divergence in perceived threats to salmon resources among anglers and indigenous fishers in Canada’s lower Fraser River

“…During the same period, careless environmental practices in agriculture, forestry, mining, and construction impacted water quality and salmon habitat in parts of the Fraser River watershed (Evenden 2004). While the Fraser River remains one of the most productive salmon rivers in the world, old problems are being exacerbated by new threats from climate change, as warming river waters place increased physiological stress on migrating salmon and enhance vulnerability to infection and disease (Farrell et al 2008;Martins et al 2011).…”

Nocturnal river water temperatures: Spatial and temporal variations

“…Extreme Tw can stress or ultimately prove lethal to biota (e.g. Dallas & Rivers-Moore 2012; Martins et al 2011) although some fauna can deploy avoidance strategies and/or acclimate to high temperatures (Breau et al 2011;Cox & Rutherford, 2000;Geist et al 2011). Nonetheless, sub-lethal Tw can still impact on spawning and breeding, hatching, growth, behaviour, distribution and phenology, thereby altering population structure and dynamics (Durance and Ormerod, 2007;Thackeray et al 2010;Ward & Stanford 1982).…”

Exceptional aerobic scope and cardiovascular performance of pink salmon (Oncorhynchus gorbuscha) may underlie resilience in a warming climate

“…With a further increase of 2-4°C estimated for the Fraser River by the end of this century (Morrison et al, 2002;Hague et al, 2011;Martins et al, 2011), many Pacific salmonids may begin to encounter brief periods of summer water temperatures exceeding 24°C during their upriver migration to spawning grounds. While most other Fraser River salmon species will likely have to modify migration timing to avoid peak summer temperatures, adapt to the warmer conditions, or perish, the present data indicate that both sexes of Harrison River pink salmon will retain >92% of maximal aerobic scope and >83% of maximal cardiac scope at 24°C and therefore may hold an advantage over other salmonids with future river warming.…”

“…This burden is becoming progressively worse, as the peak summer temperature of the Fraser River has warmed by around 2°C over the last 60 years and it is now more common for summer-migrating species to encounter temperatures exceeding 20°C (Patterson et al, 2007;Farrell et al, 2008). Probably as a result, high river temperatures have been associated with extreme (>70%) en route mortality in species such as sockeye salmon that have summer-migrating populations Farrell et al, 2008;Mathes et al, 2010;Martins et al, 2011). While many species are of increasing conservation concern, pink salmon have maintained steady populations despite their migration period including summer months, and there is little evidence of significant en route mortality in this species (PSC, 2009) (M. Lapointe, Pacific Salmon Commission, personal communication).…”