Summer Flow and Arctic Grayling System Capacity
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Species Common Name
Arctic Grayling
Latin Name (Genus species)
Thymallus arcticus
Stressor Name
Summer Flow
Specific Stressor Metric
Average August Flow Standardized as % of Mean Annual Discharge (MAD)
Stressor Units
% of MAD
Life Stage
Geography
Upper Peace River Basin (British Columbia)
Detailed SR Function Description
This function was adapted to be used for Arctic Grayling in the Upper Peace River Basin by Hagen et al. (2026) from Rosenfeld and Enright (2025). The original flow-ecology relationships developed by Rosenfeld and Enright (2025) were based on data from 25 different streams in 6 different countries for multiple salmonid species (including European Grayling).
Hagen et al. (2026) justifies summer flow as a stressor for Arctic Grayling as so:
"Flow is a master variable controlling the quantity and quality of stream habitat, but which is also
affected by human activity (Poff et al. 1997; Rosenfeld and Enright 2025; Tenant 1976). Summer
streamflow is thought to be an important factor affecting Arctic Grayling system capacity. In Arctic
tundra streams, higher summer discharge has been associated with increased growth of subadult/adult
Arctic Grayling (Deegan et al. 1999). Reduced stream flows in the Big Hole River, Montana, are
coincidental with reduced grayling abundance and distribution (Federal Register, 2010). Potential
linking mechanisms are dewatering of spawning sites, loss of connectivity among spawning, rearing,
and refuge sites, and reduction of habitat volume intensifying competition and predation. In Alberta,
altered surface and groundwater flows linked to agriculture, grazing, resource extraction, and
recreational development are also considered threats to the species (Alberta Environment and Parks and
Alberta Conservation Association 2015). Within the Williston watershed, low summer streamflow has
also been suggested as a potential stressor. Large numbers of Arctic Grayling fry have consistently been
captured and observed stranded in pools isolated from the main channel after water levels dropped in
summer (e.g., Cowie and Blackman 2003, 2004, 2007). "
Hagen et al. (2026) adapted data from Rosenfeld and Enright (2025) to estimate the effect of summer flows on Arctic Grayling system capacity using the following logic:
"To model expected impacts of summer streamflow on Arctic Grayling system capacity, we utilized
mean discharge estimates for the month of August, which were computed from recent discharge records
at Water Survey of Canada streamflow gauging locations in study watersheds. August represents the
core of the summer growth period in rearing habitats for both adult and juvenile Arctic Grayling
following declines from freshet flows, but prior to emigration to overwinter locations. The stressor
response curve is defined in terms of streamflow levels standardized as percentages of mean annual
discharge (MAD). Inflection points of the dome-shaped stressor-response curve are based on the
Rosenfeld and Enright (2025) predictions for system capacity in relation to MAD, which estimate
optimal flow at 57% of MAD with confidence intervals 36% to 96% MAD, with the steepest rate of
decline between 13% and 0% MAD."
Hagen et al. (2026) justifies summer flow as a stressor for Arctic Grayling as so:
"Flow is a master variable controlling the quantity and quality of stream habitat, but which is also
affected by human activity (Poff et al. 1997; Rosenfeld and Enright 2025; Tenant 1976). Summer
streamflow is thought to be an important factor affecting Arctic Grayling system capacity. In Arctic
tundra streams, higher summer discharge has been associated with increased growth of subadult/adult
Arctic Grayling (Deegan et al. 1999). Reduced stream flows in the Big Hole River, Montana, are
coincidental with reduced grayling abundance and distribution (Federal Register, 2010). Potential
linking mechanisms are dewatering of spawning sites, loss of connectivity among spawning, rearing,
and refuge sites, and reduction of habitat volume intensifying competition and predation. In Alberta,
altered surface and groundwater flows linked to agriculture, grazing, resource extraction, and
recreational development are also considered threats to the species (Alberta Environment and Parks and
Alberta Conservation Association 2015). Within the Williston watershed, low summer streamflow has
also been suggested as a potential stressor. Large numbers of Arctic Grayling fry have consistently been
captured and observed stranded in pools isolated from the main channel after water levels dropped in
summer (e.g., Cowie and Blackman 2003, 2004, 2007). "
Hagen et al. (2026) adapted data from Rosenfeld and Enright (2025) to estimate the effect of summer flows on Arctic Grayling system capacity using the following logic:
"To model expected impacts of summer streamflow on Arctic Grayling system capacity, we utilized
mean discharge estimates for the month of August, which were computed from recent discharge records
at Water Survey of Canada streamflow gauging locations in study watersheds. August represents the
core of the summer growth period in rearing habitats for both adult and juvenile Arctic Grayling
following declines from freshet flows, but prior to emigration to overwinter locations. The stressor
response curve is defined in terms of streamflow levels standardized as percentages of mean annual
discharge (MAD). Inflection points of the dome-shaped stressor-response curve are based on the
Rosenfeld and Enright (2025) predictions for system capacity in relation to MAD, which estimate
optimal flow at 57% of MAD with confidence intervals 36% to 96% MAD, with the steepest rate of
decline between 13% and 0% MAD."
Function Derivation
Based on data from other species; Empirical data (standardized to ecosystem response); Expert opinion (to adapt to Arctic Grayling system capacity)
Transferability of Function
This function is broadly and adaptable and transferable amongst salmonid species. The original flow-ecology relationships developed by Rosenfeld and Enright (2025) were based on data from 25 different streams in 6 different countries for multiple salmonid species.
Source of stressor Data
This stressor-response function was adapted to Arctic Grayling system capacity by Hagen et al. (2026) from data in Rosenfeld and Enright (2025).
Stressor Magnitude Data
Gauging stations (Water Survey of Canada gauges in study watersheds)
PoE Chain
altered surface and groundwater flows (agriculture, resource extraction, etc), reduced summer streamflows, reduced habitat volume, loss of habitat connectivity
Function Type
continuous
Stressor Scale
linear
References Cited
Alberta Environment and Parks and Alberta Conservation Association. 2015. Status of the Arctic
Grayling (Thymallus arcticus) in Alberta: Update 2015. Alberta Environment and Parks. Alberta
Wildlife Status Report No. 57 (Update 2015). Edmonton, AB. 96 pp.
Cowie D.M. and B.G. Blackman. 2007. Arctic grayling (Thymallus arcticus) Fry Surveys in the Nation
River, 2004. Peace/Williston Fish and Wildlife Compensation Program Report No. 314. 27 pp plus
appendices.
Cowie, D.M. and B.G. Blackman. 2004. 2003 Arctic grayling (Thymallus arcticus) fry surveys in the
Ingenika River. PWFWCP Report No. 291
Cowie D.M. and B.G. Blackman. 2003. 2001-2002 Arctic grayling (Thymallus arcticus) Fry Surveys in
the Omineca and Osilinka Rivers. Peace/ Williston Fish and Wildlife Compensation Program Report
No. 276. 18 pp plus appendices.
Deegan, L.A., Golden H.E., Harvey C.J. and B. J. Peterson. 1999. Influence of Environmental
Variability on the Growth of Age-0 and Adult Arctic Grayling. Trans, Am. Fish. Soc. 128(6): 1163-
1175.
Federal Register. 2010. Endangered and Threatened Wildlife and Plants; Revised 12-Month Finding to
List the Upper Missouri River Distinct Population Segment of Arctic Grayling as Endangered or
Threatened. Federal Register / Vol. 75, No. 173 / Wednesday, September 8, 2010 p. 54708-54753
Hagen, J., Stamford, M., Bottoms, J., & O’Connor, B. (2026). The past and future of Arctic Grayling in the upper Peace Basin: A synthesis of long-term learning for recovery planning. Prepared for the Fish and Wildlife Compensation Program – Peace (FWCP Project No. PEA-F26-F-4354-DCA).
Poff, N.L., Allan, J.D., Bain, M.B., Karr, J.R., Prestegaard, K.L., Richter, B.D., Sparks, R.E., &
Stromberg, J.C. 1997. The natural flow regime: A paradigm for river conservation and restoration.
BioScience, 47: 769–784. https://doi .org /10 .2307 /1313099
Rosenfeld, J. S., & Enright, D. (2025). Developing generalized flow ecology relationships for stream salmonids: Providing a clearer empirical basis for minimum flow regulations. Transactions of the American Fisheries Society, 154(2), 162–178. https://doi.org/10.1093/tafafs/vnaf001
Tennant, D. 1976. Instream flow regimens for fish, wildlife, recreation and related environmental
resources. Fisheries 1: 6–10. https://doi .org /10 .1577 /1548- 8446(1976)001<0006:IFRFFW>2 .0.CO;2
Grayling (Thymallus arcticus) in Alberta: Update 2015. Alberta Environment and Parks. Alberta
Wildlife Status Report No. 57 (Update 2015). Edmonton, AB. 96 pp.
Cowie D.M. and B.G. Blackman. 2007. Arctic grayling (Thymallus arcticus) Fry Surveys in the Nation
River, 2004. Peace/Williston Fish and Wildlife Compensation Program Report No. 314. 27 pp plus
appendices.
Cowie, D.M. and B.G. Blackman. 2004. 2003 Arctic grayling (Thymallus arcticus) fry surveys in the
Ingenika River. PWFWCP Report No. 291
Cowie D.M. and B.G. Blackman. 2003. 2001-2002 Arctic grayling (Thymallus arcticus) Fry Surveys in
the Omineca and Osilinka Rivers. Peace/ Williston Fish and Wildlife Compensation Program Report
No. 276. 18 pp plus appendices.
Deegan, L.A., Golden H.E., Harvey C.J. and B. J. Peterson. 1999. Influence of Environmental
Variability on the Growth of Age-0 and Adult Arctic Grayling. Trans, Am. Fish. Soc. 128(6): 1163-
1175.
Federal Register. 2010. Endangered and Threatened Wildlife and Plants; Revised 12-Month Finding to
List the Upper Missouri River Distinct Population Segment of Arctic Grayling as Endangered or
Threatened. Federal Register / Vol. 75, No. 173 / Wednesday, September 8, 2010 p. 54708-54753
Hagen, J., Stamford, M., Bottoms, J., & O’Connor, B. (2026). The past and future of Arctic Grayling in the upper Peace Basin: A synthesis of long-term learning for recovery planning. Prepared for the Fish and Wildlife Compensation Program – Peace (FWCP Project No. PEA-F26-F-4354-DCA).
Poff, N.L., Allan, J.D., Bain, M.B., Karr, J.R., Prestegaard, K.L., Richter, B.D., Sparks, R.E., &
Stromberg, J.C. 1997. The natural flow regime: A paradigm for river conservation and restoration.
BioScience, 47: 769–784. https://doi .org /10 .2307 /1313099
Rosenfeld, J. S., & Enright, D. (2025). Developing generalized flow ecology relationships for stream salmonids: Providing a clearer empirical basis for minimum flow regulations. Transactions of the American Fisheries Society, 154(2), 162–178. https://doi.org/10.1093/tafafs/vnaf001
Tennant, D. 1976. Instream flow regimens for fish, wildlife, recreation and related environmental
resources. Fisheries 1: 6–10. https://doi .org /10 .1577 /1548- 8446(1976)001<0006:IFRFFW>2 .0.CO;2
Stressor Response csv data
arctic_grayling_summer_flow_sr_curve_0.csv
(272 bytes)
| Stressor (% MAD) | Mean System Capacity (%) | SD | low.limit | up.limit |
|---|---|---|---|---|
| 0 | 0 | 0 | 0 | 0 |
| 12.3 | 62.63 | 0 | 62.63 | 62.63 |
| 40.43 | 100 | 0 | 100 | 100 |
| 89.65 | 99.64 | 0 | 99.64 | 99.64 |
| 150.29 | 54.8 | 0 | 54.8 | 54.8 |
| 199.51 | 40.21 | 0 | 40.21 | 40.21 |
| 199.51 | 40.21 | 0 | 40.21 | 40.21 |
| 299.71 | 14.95 | 0 | 14.95 | 14.95 |
| 400 | 0 | 0 | 0 | 0 |
Stressor Response Chart
Mean Response
±1 Standard Deviation
Upper/Lower Limits