Fish & Stream Temperature

One of the major impacts of future climate change in the Pacific Northwest is the alteration of native fish communities, which include a substantial number of cold water species (Williams et al., 2014). Projected warming trends in the Pacific Northwest create direct physiological challenges for cold water species and indirect challenges through competition with species that are tolerant of warmer water, especially those species that are not native to the region. Currently, in the entire Willamette River Basin there are 69 species of fish—36 native species and 33 non-natives. 

The objectives of the WW2100 fisheries team were to:

  1. Determine the composition and distribution of native and non-native fish communities along the mainstem Willamette River.
  2. Determine the likelihood of occurrence for representative fish species based on the temperatures at which those species occurred in the Willamette River.

During our field sampling in summers of 2011-2013, we captured more than 36,000 fish including 22 native and 19 non-native species. Most fish captured (more than 90%) were native species. Species richness and abundance exhibited strong longitudinal patterns; higher numbers of fish were collected in the upper river, and a higher proportion of the fish captured were native species. We do not have modeled estimates of water temperature for 2100, but we projected the consequence of a potential temperature change on the likelihood of capturing representative fish species in our standard sampling protocol. Our results suggest that the likelihood of occurrence of native cold-water species, such as juvenile Chinook salmon, would decrease substantially if future river temperature increases by 2° C (3.6° F) or more. 

 

Fisheries Methods in Brief

Field Sampling Methods

We divided the mainstem Willamette River into three sections from its mouth, upstream 301 km to the confluence of the Coast and Middle Fork Willamette, based on analysis of river geomorphology. The SLICES framework served as the geomorphic basis of randomized site selection for fish community assessment. Each 1-km slice of the mainstem river or floodplain slough within a river slice represented a single sampling location. In each 1-km slice in 2011-2013, we captured fish with standardized boat and backpack electrofishing.  Sampling locations included 96 mainstem reaches and 71 sloughs. We measured environmental and habitat characteristics at each site.

We developed a Willamette River Fish Database (http://gis.nacse.org/wrfish/) to make spatially explicit data on fish communities in the mainstem Willamette River publicly available. Watershed councils, land trusts, NGOs, and state and federal agencies have full access to the data for designing projects to conserve or restore the aquatic ecosystems and floodplains of the Willamette River. The information also contributes to the collective development of a guiding vision of a future Willamette River and its floodplain for all partners.

Modeling Approach

We related possible temperature increases in the mainstem river to the likelihood of capturing various fish species in a standard sampling effort (e.g., spring Chinook salmon, coastal cutthroat trout, common carp). Specifically, we describe the consequence of a hypothetical increase (2° C or 3.6° F) in stream temperature on the likelihood of capturing representative fish species in our standard sampling protocol, based on the temperatures at which we observed them in 2011-2013. Such an increase in stream temperature is highly likely in the future during normal flow years.

The fisheries analysis is limited to the mainstem Willamette River, downstream of the major reservoirs, and was not coupled to Willamette Envision, the project's integrative water system model.

Select Findings from Fisheries Analysis

Fish Distribution

During our field sampling in summers of 2011-2013, we collected 41 fish species – 22 native and 19 non-native. Of the total of 36,586 individual fish collected, 93% were native species and 7% non-native (Williams, 2014). In mainstem habitat, 97% of the individual fish captured were native and 3% were non-native. A greater proportion of catch in slough habitats was non-native (13%), but native species comprised the majority (87%) of fish captured in the sloughs as well.

Species richness and relative abundance of fish exhibited significant longitudinal patterns (Fig. 1). Higher numbers of fish were collected in the upper river, and higher proportions of those fish were native species. In contrast, non-native species exhibited the opposite pattern, increasing in relative abundance and total number of taxa from the upper river to lower river. The 1-km standard sample reaches in the upper river contained 16-19 native fish species, but similar samples from the lower river contained only 3-10 native fish species.

Number of native fish species captured in BOAT electrofishing samples for the mainstem Willamette River for 2011 - 2013.

Figure 1. Number of native fish species captured in BOAT electrofishing samples for the mainstem Willamette River for 2011-2013.

Temperature Sensitivity

During our three-year monitoring study, we sampled both fish communities, habitat, and water quality throughout the Willamette River mainstem (Fig. 2). The green and red lines and markers in Fig. 2 represent the maximum daily temperature observed at each station in 2012 and 2013, respectively. We do not have modeled estimates of water temperature for 2100, but we projected the consequence of a potential temperature change on the likelihood of capturing representative fish species in our standard sampling protocol. If water temperatures in the Willamette River increase by 2° C (3.6° F, less than the projected air temperature), the longitudinal profile (blue line and markers) would increase to more than 26° C (78.8° F) in the lower river. Such an increase is highly likely in the future during normal flow years. As a frame of reference, the USGS gaging station in Portland recorded temperatures of 26.8° C (80.2° F) in early July 2015, a year that was extremely warm and when flows in the river were much lower than average (Fig. 3).

Longitudinal pattern of river temperature in observed in 2012 and 2013 (green and red, respectively) and longitudinal pattern of river temperature in 2100 if river temperatures increase by 2°C.

Figure 2. Longitudinal pattern of river temperature observed in 2012 and 2013 (green and red, respectively) and longitudinal pattern of river temperature in 2100 assuming an increase in river temperatures of 2° C (3.6° F).

Temperature at the USGS gaging station in Portland in summer 2015.

Figure 3.  Temperature at the USGS gaging station in Portland in summer 2015.

We estimated the likelihood of occurrence of juvenile Chinook salmon in our standard sampling protocol based on the temperatures at which we observed this species in 2011-2013. Projections for the likelihood of occurrence currently decreases from approximately 50% in the upper river to less than 30% in the lower river (Fig. 4). The projected temperature increase by 2100 would lower that likelihood to less than 40% in the upper river and roughly 15% in the lower river. Coastal cutthroat trout are a cold-water salmonid that resides in the Willamette River throughout the year. Cutthroat trout exhibited even greater sensitivity to temperature (based on the locations they were captured). The likelihood of occurrence of cutthroat trout in the lower river would be extremely low under potential future temperatures (Fig. 5). In contrast, the likelihood of occurrence of common carp, a warm-water non-native species, increase longitudinally and would increase to more than 90% in the lower river by 2100 (Fig. 6).

These projections of the likelihood of cold-water fish species occurrence at higher temperatures are likely to be overestimates because the National Marine Fisheries Service (NMFS) does not allow us to sample at temperatures higher than 18° C (64.4° F). We are extrapolating beyond observed temperatures and occurrences.  Based on the incipient lethal levels of these species, it is highly unlikely to observe Chinook salmon, cutthroat trout, or other salmonids in water warmer than 26° C (78.8° F).

Longitudinal pattern of the likelihood of capturing juvenile spring Chinook salmon in our standard sampling protocol based on the river temperatures in observed in 2012 and 2013..

Figure 4.  Longitudinal pattern of the likelihood of capturing juvenile spring Chinook salmon in our standard sampling protocol based on the river temperatures observed in 2012 and 2013 (green and red, respectively) and longitudinal pattern of river temperature in 2100 if river temperatures increase by 2° C (3.6° F).

Longitudinal pattern of the likelihood of capturing resident coastal cutthroat trout in our standard sampling protocol based on the river temperatures.

Figure 5.  Longitudinal pattern of the likelihood of capturing resident coastal cutthroat trout in our standard sampling protocol based on the river temperatures observed in 2012 and 2013 (green and red, respectively) and longitudinal pattern of river temperature in 2100 if river temperatures increase by 2°C (3.6°F).

Longitudinal pattern of the likelihood of capturing common carp, a warm-water non-native fish species, in our standard sampling protocol based on the river temperatures observed in 2012 and 2013.

Figure 6. Longitudinal pattern of the likelihood of capturing common carp, a warm-water non-native fish species, in our standard sampling protocol based on the river temperatures observed in 2012 and 2013 (green and red, respectively) and longitudinal pattern of river temperature in 2100 if river temperatures increase by 2° C (3.6° F).

Conclusions

The Willamette River has recovered greatly from past water pollution and river channel modifications, but it faces many threats in the future. Population in the region is expected to continue growing rapidly. Land development continues to see increasing demands for urban and residential lands while agricultural and forest industries are fighting to protect their land base. Much of the new development pressures are in the valley along the mainstem Willamette River and its floodplain. Streams and river temperatures already approach the lethal limits of native cold-water fish species, especially in the lower river near the major urban centers. Many miles of streams in the basin are listed by environmental agencies as water quality impaired because of water temperature. The climate in the basin is projected to warm by 1.0 to 3.4° C (2 to 6° F) by the middle of the century. Our results suggest that the likelihood of occurrence of native cold-water species, such as juvenile Chinook salmon, would decrease substantially if future river temperature increases by 2° C (3.6° F) or more.

One of the greatest challenges is to create a scientifically sound vision of the new river, a river that is changing because of its altered flow regimes and sediment supply, a river that is changing because of social changes in the towns and communities along its banks (Wallick et al., 2013). Water management authorities are facing increasing demands to store water in reservoirs and withdraw more water during low flow seasons when the needs of the aquatic ecosystem also are most acute. Flood control reservoirs already have reduced sediment transport to the mainstem by 60%, and peak flows in the river are reduced roughly 30 to 70%. The momentum of current trends and uncertainty of future changes make it critical for our region to anticipate the future Willamette River.

Related Links & Publications

Contributors to WW2100 Fisheries Research

  • Stan Gregory, OSU Fisheries and Wildlife (lead)
  • Josh Williams, MS Student, OSU Fisheries and Wildlife (Graduated: 2014) 

References

Wallick, J. R., Jones, K. L., O’Connor, J. E., Keith, M. K., Hulse, D., & Gregory, S. V. (2013). Geomorphic and Vegetation Processes of the Willamette River Floodplain, Oregon—Current Understanding and Unanswered Questions. US Geological Survey Open File Report, 1246. http://pubs.usgs.gov/of/2013/1246/pdf/ofr2013-1246.pdf

Williams, J. E., Giannico, G. R., & Withrow-Robinson, B. (2014). Field guide to common fish of the Willamette Valley floodplain. Corvallis, Or.: Extension Service, Oregon State University. http://ir.library.oregonstate.edu/xmlui/handle/1957/50100

 

Web page author: S. Gregory
Last updated: October 2015