Study author, Heidi Swanson, holds one of her research subjects.

Research in Action—New findings show that in certain populations of lake trout found in Canada’s Far North, specifically, four Arctic lakes in the West Kitikmeot region of Nunavut, up to 27 percent of individuals make annual migrations to marine environments.* Researchers used a technique called otolith microchemistry, which involved examining changes in chemical composition in the otoliths (small ear stones) along a “timeline” that represents a fish’s life. Certain chemical signatures indicate movement to saltwater.

Life in extreme northern rivers and lakes can be harsh, and food is often scarce. Much like their close cousin, the Arctic char, a proportion of the population of lake trout studied were shown to migrate into the ocean each summer, where it is believed food is more plentiful. Fish that migrated were in better condition than permanent freshwater residents. Mean age of first migration to salt water for lake trout was 13 years, older than for Arctic char, which migrate at 5 years. This is likely because lake trout need to be larger and older to tolerate higher salinities.

*Swanson, H., and 6 co-authors. 2010. Anadromy in Arctic populations of lake trout (Salvelinus namaycush): otolith microchemistry, stable isotopes, and comparisons with Arctic char (Salvelinus alpinus). Can. J. Fish. Aquat. Sci. 67:842–853.

Example of strontium profiles across a life “timeline” in a lake trout otolith (ear stone). Each year, the otolith grows, forming annual bands. In resident fish, strontium levels were relatively level with low annual amplitude oscillations throughout the fish’s life. In marine migrating (anadromous) lake trout, first movement to saltwater is shown by an increase in strontium levels and higher amplitude annual oscillations. For this fish it occurred at an estimated age of 17 years.

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