Water Temperatures Matter to Migrating Fraser River Salmon
Editor’s Note: Snowmelt travels from the tops of mountains all the way down to oceans, passing through all walks of life. Our humble river friends, the salmon, perhaps spend more time in the medium than most of us, so they certainly feel any changes to timelines and temperatures.
This piece from Mike Lapointe, David Patterson, Maxine Forrest, Kendra Robinson and Angus Straight explores rising water temperatures in the Fraser River and the correlation to salmon mortality. Does this mean the end of salmon, or will they adapt? Read on!
This article first appeared in the 2019 State of the Mountains Report. We'll continue to publish articles exploring the science on our current state of Canada's alpine on our blog throughout the year. Find them all here.
Spawning Adams River sockeye salmon, 2010. Photo: Ian Guthrie.
Measuring expected migration success
Figure 2 – British Columbia Snow Survey Map denotes snow water index levels for May 1, 2019. Map used with permission from the Government of B.C., Ministry of Forests, Lands, Natural Resource Operations and Rural Development – River Forecast Centre.
High in the Coast Mountains, 1,600 metres above the Fraser Valley, Malcolm Nicol makes one of several visits to the Chilliwack River station to measure the alpine snowpack (Figure 1). Nicol’s station is part of a network of stations visited during the late winter and spring each year that monitor the snowpack, which melts each summer and drains into British Columbia’s many watersheds (Figure 2).¹ While districts and municipalities are often focused on the consequences of snow melt for flood risks during spring freshet, staff at Fisheries and Oceans Canada’s (DFO) Environmental Watch Program (E-Watch) and the Pacific Salmon Commission predict the impact of snowmelt and other factors on summer Fraser River temperatures and flows, and the expected success of sockeye salmon migrating to their natal spawning areas.²
Figure 1 – Malcolm Nicol, snow survey technician with the British Columbia Ministry of Environment performs a manual snow water equivalent verification at Chilliwack River Alpine Snow Water Station. Photo: Ted Litke, BC Ministry of Environment
How warm temps affect migrating salmon
Figure 3 – The relationship between the percent difference between estimates of Fraser River sockeye salmon reaching their natal spawning areas in upstream locales and entering the lower Fraser River, and Fraser River water temperatures (black dots). River temperatures represent 31-day averages centred around each year’s peak of the migration of Fraser River sockeye* in the lower Fraser River. Dashed lines delineate river temperatures greater and less than 18°C and when percentage differences are either greater or less than zero. When Fraser River temperatures exceed 18°C, percentage differences have always been less than zero; indicating that mortality of fish is the major factor contributing to the discrepancy in the estimates between the two sites where abundances are estimated. When river temperatures are less than 18°C, mortality may still occur, but it may be masked by errors in estimates of abundance that occur at both sites.
*Data shown are for the group of Fraser sockeye stocks known as the Summer-run, excluding the Harrison River stock. This group contributes the most to the total Fraser River sockeye return in three out of every four years
Warm temperatures in the Fraser River have been associated with poor migration success (Figure 3). While the discrepancies in Figure 3 result from a variety of factors (in addition to mortality during migration), the physiological effects of warm water temperatures on migrating salmon have been well documented.³ Warm waters contain less oxygen than cool waters, and Fraser River salmon appear to have adapted the capacity to do the most work at river temperatures they have experienced historically.⁴ Prior to the 1990s, average river temperatures in excess of 18°C occurred infrequently – less than fifteen percent of years (Figure 4). Thus, it is not surprising that salmon would experience mortality when temperatures rise above this level. After all, upstream migrating salmon are doing a lot of work, effectively swimming the equivalent of a marathon a day against the river’s current. Spring snowpack levels and seasonal weather forecasts are used to generate expectations for summer river flows and water temperatures, and this information is communicated to fisheries managers to aid in pre-season fishing plans.⁵ These long-range forecasts of river conditions, however, are imprecise due to unpredictable weather events such as heavy rain events.
Figure 4 – Mean Fraser River water temperature during the month of August. Black dots are the annual average temperatures for the month of August plotted for each year, 1950-2018. The dashed line is the best fit regression line. The time trend in Fraser River temperatures is highly statistically significant and the R2 value indicates that nearly one third of the variation in Fraser River temperatures during this nearly 70-year period can be “explained” by a simple linear increasing time trend of 0.3°C per decade. The solid horizontal line delineates river temperatures greater and less than 18°C.
To counteract these sources of uncertainty, managers of Fraser River salmon also use short-term, ten-day forecasts of river temperature and flow, which are produced twice a week each summer by DFO’s E-Watch program. These forecasts rely on weather forecasts provided by Environment Canada and a series of real-time river temperature and flow data loggers located in key locations in the Fraser watershed.⁶ Staff at the Pacific Salmon Commission then use management adjustment models that relate past river conditions (temperature and flow) to historical discrepancies (Figure 3) to predict the expected discrepancy in the current year based on the combination of observed and forecast river conditions.⁷ These predictions inform management decisions; it is common for available harvest levels to be reduced to compensate for expected mortality, providing greater assurance that the target number of fish will reach spawning areas.
The future of Pacific salmon and changing conditions?
Unfortunately, as other researchers have documented the rapid recession of mountain glaciers, Fraser River temperatures are increasing. The timing of peak snowmelt and spring freshet is shifting to occur earlier in the season, which leaves less cool water to buffer the river from warm summer air temperatures. In the forty-year period prior to 1990, there were only five years when the average Fraser River water temperature exceeded 18°C (less than 15 per cent of years). In the twenty-eight years since 1991, the average Fraser water temperatures exceeded 18°C in fifteen of those years (greater than 53 per cent), including every year since 2012 (Figure 4). Average Fraser River temperatures during August have increased by more than 2°C since 1950 (Figure 4).
Will Pacific salmon adapt to these changing conditions? Experience in hatcheries and evidence from other locations (such as sockeye salmon in the Okanagan basin) suggests that salmon have the evolutionary capacity to adapt, but their response will likely depend on how fast their environments change relative to the speed of their adaptation.⁸
The Adams River, British Columbia.Photo: Ian Guthrie
Mike Lapointe was Chief Biologist with the Pacific Salmon Commission (PSC; he retired in February 2019, after 27 years of service). David Patterson has been lead biologist for Fisheries and Oceans Canada’s Environmental Watch (E-Watch) Program for more than 15 years. In addition to leading PSC’s management adjustment models, Maxine Forrest manages the PSC’s scale lab based in Vancouver, BC. Kendra Robinson, a biologist, and Angus Straight, a graduate student, work with Patterson in the E-Watch program, which is located on the campus of Simon Fraser University in Burnaby, BC.
Acknowledgements
The development of management adjustment models and their implementation is a team effort. In addition to those listed in the references, we thank Keri Benner and her staff for their upstream assessments; Fiona Martens, Cory Lagasse and their teams which generate hydroacoustic estimates of abundance of salmon reaching the lower Fraser River at Mission, BC; Water Survey of Canada and others for their help with data loggers located the throughout Fraser River and its tributaries; and past members of DFO’s E-Watch team who provided forecasts of daily Fraser River temperature and flow values twice each week during the summer salmon migrations. Lastly, decisions regarding the formal adoption of management adjustment factors are the purview of the Fraser River Panel, an advisory body of the Pacific Salmon Commission that is charged with decisions regarding the harvest of Fraser River sockeye and Pink salmon.
Pacific Salmon Commission, 1155 Robson Street, Suite 600, Vancouver, BC, V6E 1B5. www.psc.org
Department of Fisheries and Oceans Canada, School of Resource and Environmental Management, Simon Fraser University, Burnaby, BC, V5A 1S6. www.pac.dfo-mpo.gc.ca/science/habitat/frw-rfo/index-eng.html
Tough going for this Adams River sockeye salmon, 2010. Photo: Ian Guthrie
References
1. Litke, T. A snapshot of BC’s snow survey program. The Avalanche Journal Vol. 114, 10-11 (2017) ( https://issuu.com/theavalanchejournal/docs/vol114 ).
2. Morrison, J., Foreman, M.G.G. Forecasting Fraser River flows and temperatures during upstream salmon migration. Journal of Environmental Engineering and Science 4 (2), 101-111 (2005); Macdonald, J.S., Patterson, D.A., Hague, M.J., Guthrie, I.C. Modeling the influence of environmental factors on spawning migration mortality for sockeye salmon fisheries management in the Fraser River, British Columbia. Transactions of the American Fisheries Society 139, 768–782 (2010); Hague, M.J., Patterson, D.A. Evaluation of statistical river temperature forecast models for fisheries management. North American Journal of Fisheries Management 34 (1), 132-146 (2014).
3. Crossin, G.T. et al. Exposure to high temperature influences the behaviour, physiology, and survival of sockeye salmon during spawning migration. Canadian Journal of Zoology 86 (2), 27-140 (2008); Martins, E.G., et al. Effects of river temperature and climate warming on stock-specific survival of adult migrating Fraser River sockeye salmon (Oncorhynchus nerka). Global Change Biology 17, 99–114 (2011); Eliason, E.J. et al. Differences in thermal tolerance among sockeye salmon populations. Science 332 (6025), 109-112 (2011).
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5. Patterson, D.A., et al. A perspective on physiological studies supporting the provision of scientific advice for the management of Fraser River sockeye salmon (Oncorhynchus nerka). Conservation Physiology doi:10.1093/conphys/cow026 (2016).
6. Hague, M. J., Patterson, D.A., Macdonald, J.S. Exploratory correlation analysis of multi-site summer temperature and flow data in the Fraser River basin. Canadian Technical Report of Fisheries and Aquatic Sciences 2797, 1-60 (2008).
7. Macdonald et al. (2010); Hague and Patterson (2014).
8. Hague, M.J., et al. Modelling the future hydroclimatology of the lower Fraser River and its impacts on the spawning migration survival of sockeye salmon. Global Change Biology 17 (1), 87-98 (2011).