Quantifying lost and inaccessible habitat for Pacific salmon in Canada's Lower Fraser River
Date
2021
Authors
Finn, Riley J. R.
Chalifour, Lia
Gergel, Sarah E.
Hinch, Scott G.
Scott, David C.
Martin, Tara G.
Journal Title
Journal ISSN
Volume Title
Publisher
Ecosphere
Abstract
Loss of connectivity caused by anthropogenic barriers is a key threat for migratory freshwater
species. The anadromous life history of salmonids means that barriers on streams can decrease the amount
of habitat available for spawning and rearing. To set appropriate targets for restoration, it is important to
know how different populations have been impacted in terms of the location and extent of historically available
habitat that has been lost or has become inaccessible. Using mapped and predicted barriers to fish passage
in streams and diking infrastructure, the amount of both floodplain and linear stream habitat that
remains accessible today was estimated for 14 populations of salmon in the Lower Fraser River, British
Columbia, Canada’s most productive salmon river. To place these estimates within a historical context, the
floodplain area was estimated using vegetation records from the 1850s, and lost streams were estimated
using a digital elevation model-derived stream network. To bolster areas where little mapping has been
done, current barrier data were used to predict locations likely to have barriers. Accessibility to floodplain
was poor across the entire region with only 15% of the historical floodplain remaining accessible. Linear
stream habitat ranged in accessibility from 28% to 99% across populations based on mapped barriers. Inclusion
of predicted barriers revealed an additional 33 km of potentially inaccessible stream habitat and the
modeled stream network located approximately 1700 km of stream length that has been completely lost.
Comparing habitat accessibility and barrier density against the assessed status of populations revealed
insights useful for understanding the impact of barriers on spawning and rearing and guiding the allocation
of restoration effort. Applying methods for addressing missing data, such as lost streams and unmapped barriers,
was essential for estimating the accessibility of habitat within a historical context.While much emphasis
has been placed on the role of marine conditions in wild Pacific salmon recovery, the magnitude of habitat
loss in the Fraser cannot be ignored and suggests it is a major driver of observed salmon declines.
Description
Keywords
anadromous species, barriers, connectivity, conservation planning, culverts, dams, flood control, fragmentation, habitat loss
Citation
Finn, R. J. R., Chalifour, L., Gergel, S. E., Hinch, S. G., Scott, D. C., & Martin, T. G. (2021). Quantifying lost and inaccessible habitat for Pacific salmon in Canada’s Lower Fraser River. Ecosphere, 12(7), 1-20. https://doi.org/10.1002/ecs2.3646.