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Tom Johnston

Research Interests

I am a fish and fisheries ecologist with the Science and Research Branch of the Ontario Ministry of Natural Resources and Forestry and my research informs and supports fisheries management in Ontario. I am also an Adjunct Professor of Biology at Laurentian University and my research program includes supervision and co-supervision of undergraduate and graduate research projects. My research laboratory is located in the Vale Living with Lakes Centre on the shores of Ramsey Lake.

Specifically, my research examines trophic and reproductive ecologies of fishes, and food web structure and contaminant dynamics in northern aquatic ecosystems. This research is primarily field-based, and covers a wide range of lakes and rivers from across northern Ontario. Current research projects in my lab are examining: i) variation in trophic niche positions and dimensions of fishes with respect to ecosystem conditions and community composition, ii) the relative effects of growth rate and food web position on variation in fish mercury bioaccumulation, iii) interaction of maternal effects and environmental factors in shaping fish reproductive success, and iv) assessment of fish biodiversity at the catchment scale in recovering waters of the historical acid deposition zone of northeastern Ontario.


Publications (last 6 years)

Johnston, T.A., A.D. Ehrman, J.J. Montgomery, and H.K. Swanson. 2021.  Dietary and non-dietary contributions to among-individual variation in carbon and nitrogen isotopic composition of lake trout.  Ecological Indicators, In press, doi: 10.1016/j.ecolind.2021.107349.

Johnston, T.A., J.M. Casselman, and W.C. Leggett. 2021.  Sex-based divergence in isotopic compositions of north temperate freshwater fishes.  Hydrobiologia 848: 873-884.

Thomas, S., S. Melles, R. Mackereth, T. Tunney, C. Chu, C. Oswald, S. Bhavsar, and T.A. Johnston. 2020. Climate and landscape conditions indirectly affect fish mercury levels by altering lake water chemistry and fish size.  Environmental Research 188: 109750.

Johnston, T.A., M.D. Wiegand, R.L. Szmydala, L.R. Porteous, J.M. Casselman, and W.C. Leggett. 2020.  Sex-based differences in fatty acid composition of adult walleye.  Ecology of Freshwater Fish 29: 654-664.

Patterson, K.A., T.A. Johnston, L.C. Haslam, W. Keller, G.L. Lescord, M.J. Heerschap, R.A. DeJong, H.K. Swanson, P.A. Lennox, C-L.B. Chetkiewicz, C.M. O’Connor, J.W. Warmbold, J.L. Bailey, B.A. Edwards, M.T. Arts, C.J. Chenier, A.W. Sumner, R.W.K. Tang, B.A. Branfireun, N.E. Jones, S.P. Bhavsar and J.M. Gunn. 2020. Fish and aquatic sampling activities in the Hudson Bay Lowlands Ecozone of the Far North of Ontario: 2008-2018. Ontario Ministry of Natural Resources and Forestry, Science and Research Branch, Peterborough, ON. Science and Research Technical Report TR-41. 54 p. + appendices.

Johnston, T.A., K.A. Patterson, L.C. Haslam, S.J. Scholten, J.M. Gunn and C.D. Wren. 2020. Limnological and fish community surveys of Tadenac Lake and Tadenac Bay (Georgian Bay, Lake Huron), 2011–2014. Ontario Ministry of Natural Resources and Forestry, Science and Research Branch, Peterborough, ON. Science and Research Technical Report TR-39. 39 p. + appendix.

Sumner, A.W., T.A. Johnston, G.L. Lescord, B.A. Branfireun, and J.M. Gunn. 2020. Mercury bioaccumulation in lacustrine fish populations along a climatic gradient in northern Ontario, Canada.  Ecosystems 23: 1206–1226.

Lescord, G.L., T.A. Johnston, M.J. Heerschap, W. (Bill) Keller, F.M. Southee, C.M. O’Connor, R.D. Dyer, B.A. Branfireun, and J.M. Gunn. 2020.  Arsenic, chromium, and other elements of concern in fish from remote boreal lakes and rivers: drivers of variation and implications for subsistence consumption.  Environmental Pollution 259: 113878.

Mozzon, C.M., G.L. Lescord, P.-L. Savage, and T.A. Johnston. 2020.  The trophic niche of sculpins (Cottus spp.) in forage fish assemblages of boreal lakes. Journal of Fish Biology 96: 92-101.

Lescord, G.L., T.A. Johnston,  B.A. Branfireun, and J.M. Gunn. 2019. Mercury bioaccumulation in relation to changing physicochemical and ecological factors across a large and undisturbed boreal watershed.  Canadian Journal of Fisheries and Aquatic Sciences 76: 2165-2175.

Johnston, T.A., A.D. Ehrman, G.L. Hamilton, B.K. Nugent, P.A. Cott, and J.M. Gunn.  2019.  Plenty of room at the bottom: niche variation and segregation in large-bodied benthivores of boreal lakes.  Canadian Journal of Fisheries and Aquatic Sciences 76: 1411-1422.

Lescord, G., T.A. Johnston, B. Branfireun, and J.M. Gunn.  2018.  Percentage of methylmercury in the muscle tissue of freshwater fish varies with body size and age and among species. Environmental Toxicology and Chemistry 37: 2682-2691.

Johnston, T.A.  2018. Egg size and lipid content of lake trout, Salvelinus namaycush, in the wild and in captivity. Canadian Journal of Fisheries and Aquatic Sciences 75: 2123-2135.

Lescord, G., E. Emilson, T.A. Johnston, B. Branfireun, and J.M. Gunn. 2018. Optical properties of dissolved organic matter and their relation to mercury concentrations in water and biota across a remote freshwater drainage basin.  Environmental Science and Technology 52: 3344-3353.

Johnston, T.A., N.P. Lester, and B.J. Shuter. 2016. Recruitment, pp. 830-845  In Craig, J.F.  (ed.)  Ecology of Freshwater Fisheries,  John Wiley and Sons,  West Sussex, UK.

Johnston, T.A., M.C. Prévost, L. C. Haslam, and P.A. Addison.  2016.  Life history variation within and among naturalized rainbow trout populations of the Laurentian Great Lakes.  Journal of Great Lakes Research  42:  861-870.

Haring, M., T.A. Johnston, M.D. Wiegand, and T.E. Pitcher.  2016.  Differences in egg quantity and quality among hatchery and wild- origin Chinook salmon (Oncorhynchus tshawytscha).  Canadian Journal of Fisheries and Aquatic Sciences 73: 737-746.

Persaud, A., A. Luek, W. Keller, F.C. Jones, P. Dillon, J.M. Gunn, and T.A. Johnston.  2015.  Trophic dynamics of several fish species in lakes of a climatically sensitive region, the Hudson Bay lowlands.   Polar Biology 38: 651-664.

Stasko, A.D., T.A. Johnston, and J.M. Gunn.  2015.  Effects of water clarity and other environmental factors on trophic niches of two sympatric piscivores.  Freshwater Biology  60: 1459-1474.

Cott, P.A., A. Schein,  B.W. Hanna, T.A. Johnston, D.D. MacDonald, and J.M. Gunn.  2015.  Implications of linear developments on northern fishes.  Environmental Reviews  23: 177-190.

Johnston, T.A., and C.C. Wilson.  2015.  Comparative ecologies of domestic and naturalized rainbow trout in northern Lake Huron (Ontario, Canada).  Ecology of Freshwater Fish  24: 338-354.