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 a cross-appointed faculty member in the School of Natural Sciences at Laurentian University and my research program includes supervision of undergraduate and graduate research projects.  My research laboratory is in the Vale Living with Lakes Centre on the shores of Ramsey Lake. 

I conduct research on reproductive ecologies of fishes, food web structure and contaminant dynamics in northern aquatic ecosystems, and assessment of aquatic biodiversity at the landscape scale. 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) fish biodiversity recovery in the historical acid deposition zone of northeastern Ontario, and iii) interaction of maternal effects and environmental factors in shaping fish reproductive success.

Publications (last 6 years)

McMeans, B.C., P.A. Cott, T.A. Johnston, P.J. Blanchfield, M.M. Guzzo, and R.A. Cunjak. 2023. Winter as a defining season for Canadian fishes, pp. 485-507  In  Hasler, C.T., J.G. Imhof, N.E. Mandrak, and S.J. Cooke  (eds.)  Freshwater Fisheries in Canada,  American Fisheries Society, Bethesda, MD, USA.

Kluke, C., G.L. Lescord, B. Kielstra, A. Lock, T.A. Johnston, S. Bhavsar, and J.M. Gunn. 2023. Spatial patterns and environmental factors related to arsenic bioaccumulation in boreal freshwater fish of Ontario, Canada.  Canadian Journal of Fisheries and Aquatic Sciences 80: 628–641.

Lescord, G.L., T.A. Johnston, D.E. Ponton, M. Amyot, A. Lock, and J.M. Gunn. 2022. The speciation of arsenic in the muscle tissue of inland and coastal freshwater fish from a remote boreal region.  Chemosphere 308: 136140.

Johnston, T.A., G.L. Lescord, M. Quesnel, P.-L. Savage, J.M. Gunn, and K.A. Kidd.  2022. Age, body size, growth and dietary habits: what are the key factors driving individual variability in mercury of lacustrine fishes in northern temperate lakes?  Environmental Research 213: 113740.

Ponton, D.E., J. Ruelas-Inzunza, R. Lavoie, G.L. Lescord, T.A. Johnston, J. Graydon, M. Reichert, C. Donadt, M. Poesch, J.M. Gunn, M. Amyot. 2022. Mercury, selenium and arsenic concentrations in Canadian freshwater fish and a perspective on human consumption intake and risk.  Journal of Hazardous Materials Advances 6: 100060.

Presello, A.J., J.L. Smith, T.D. Drew, K.K. Loftus, T.A. Johnston, C.C. Wilson, and T.E. Pitcher. 2021.  Induction of free-flowing gametes in order to establish a reintroduction broodstock of bloaters (Coregonus hoyi) for Lake Ontario.  Advances in Limnology 66: 363-379.

Johnston, T.A., A.J. Harry, R.D. Montgomerie, M.D. Wiegand, G.A. Spiers, J.M. Casselman, and W.C. Leggett.  2021. Maternal effects on embryonic survival and development in walleyes of Lake Nipissing, Ontario.  Transactions of the American Fisheries Society 150(6): 777-791.

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 123: 107349.

Johnston, T.A., J.J. Montgomery, G.L. Lescord, K.A. Patterson, L.C. Haslam, K. Tremblay, G.E. Morgan, H.K. Swanson, N. Commanda, S.D. Kaufman and J.M. Gunn. 2021. An isotopic analysis of food web structure and trophic interactions in Lake Nipissing, Ontario. Ontario Ministry of Northern Development, Mines, Natural Resources and Forestry, Science and Research Branch, Peterborough, ON. Science and Research Technical Report TR-45. 62 p. + appendices

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.