Open Water in Winter: An Influential but Underestimated Ecosystem in Northern Boreal Mountain Regions

Abstract

Patches of open water (polynyas) persist throughout six-month winters on many ice-covered lakes in boreal mountain ecoregions of northwestern North America. We explored their distribution, hydrological correlates, and the diversity of species using them from freeze-up to break-up. In headwater drainages, lakes with outflow polynyas were significantly larger than those without, but many small lakes also had polynyas. There was a consistent threshold in upstream catchment size below which outflow polynyas were absent and above which they persistently occurred in downstream lakes. Outflow polynyas depend on winter-long through-flow of water, likely maintained by the hydraulic head of higher elevation ground water in perched water tables in this region of very limited permafrost. Based on camera trapping, two species, the American dipper and river otter, used polynyas heavily throughout winter foraging. Polynyas likely provided crucial forage for at least 9 species of migratory waterfowl (Anatidae) to complete their spring migration or to prepare for reproduction on local lakes. Cameras recorded additional 5 bird and 11 mammal species, as foragers, scavengers, or incidentally. We report previously undocumented significance of these spatially-limited and seasonal polynya ecosystems in expanding the diversity of winter ecological opportunity for numerous species on small to medium-sized lakes.

Keywords

Open water / Winter ecology / Polynya / River otter / American dipper / Migratory waterfowl / Boreal lake

Supplementary Materials

The following supporting information can be found at: https://www.sciepublish.com/article/pii/665, Figure S1:Histograms of relative abundance (number of individual records per day) of semi-aquatic mammals, American dipper, swans, and ducks as recorded by periodically operating camera traps at: (a) site A (2013); (b) site A (2014-15); (c) site B (2014-15); (d) augmented site C (2014-2015). “Swans” were most often Trumpeter Swans (Cygnus buccinator), and “Ducks” includes various species listed in the text. See Methods for how “Individual Records” were calculated from photos. Portions of graphs blocked out in grey are time periods without camera trapping.

Acknowledgments

We thank the Carcross/Tagish First Nation and the Teslin Tlingit Council for the opportunity to work in their traditional territories. We thank the administration staff at Wildlife Conservation Society Canada for assistance in acquiring funding and for their management of financial and logistical processes.

Author Contributions

Conceptualization, D.G.R. and M.C.Y.L.; Methodology, D.G.R. and M.C.Y.L.; Validation, D.G.R. and M.C.Y.L.; Formal Analysis, D.G.R., M.C.Y.L. and P.K.; Investigation, D.G.R., M.C.Y.L. R.R. and P.K.; Resources, D.G.R., M.C.Y.L. and R.R.; Data Curation, D.G.R., M.C.Y.L. and P.K.; Writing—Original Draft Preparation, D.G.R.; Writing—Review & Editing, D.G.R., M.C.Y.L., R.R. and P.K.; Visualization, D.G.R. and M.C.Y.L.; Project Administration, D.G.R.; Funding Acquisition, D.G.R.

Ethics Statement

Ethical review and approval were waived for this study, because camera trapping with automated remote cameras was deemed non-invasive and non-interventionary to the mammals and birds being recorded, and because the jurisdiction of Yukon only requires wildlife research permits for projects involving live-capture and handling of animals.

Informed Consent Statement

Not applicable.

Data Availability Statement

An archive of images captured and data analysed in this study is available as part of the Wildlife Conservation Society Canada’s data storage portal: https://show.pics.io/don-reid/open-water-in-winter(accessed 5 September 2025).

Funding

This research was funded by The Weston Family Foundation and by the T-Gear Foundation, with grants to Wildlife Conservation Society Canada. The APC was funded by the journal.

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

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