Adaptive trout

Adaptive trout

David Sparks Ph.D.
David Sparks Ph.D.
Summer heat will cause some trout mortality, but halting fishing won't improve the situation

Trout are resilient and even extreme weather rarely has a long-term impact on populations

Wild animals for the most part are well equipped to survive fluctuations in environmental conditions, and trout, Idaho’s favorite fish, are no different. Although they prefer cold water, trout are highly resilient, productive and adaptive. Because of this, short-term fishing regulation changes are unlikely to affect their numbers long-term, even during an extraordinary heatwave. 

Recently, well-intended anglers and angling groups have requested Fish and Game restrict or close fishing during extreme heat because they feel restrictions will reduce fishing-related mortality and preserve more trout for next year when conditions will hopefully improve. 

We are concerned, too. Fish and Game biologists, nearly all of whom are anglers, understand and share their concerns and acknowledge that some heat-stressed fish will die from angling-related mortality. However, basing fishing closures on reduced risk to a relatively small portion of the local trout population is unlikely to change the overall numbers in the near or long term. 

Extensive monitoring efforts have clearly shown that fishing effort and catch rates decline substantially during late summer when hot weather makes air and water uncomfortably warm for anglers and trout, alike.  

Therefore, a relatively low proportion of a stream or river’s trout population has slightly higher mortality associated with angling, and in short, it won’t affect trout abundance the following year, which makes restrictions or closures biologically unnecessary. Regardless, biologists remain committed to monitoring and researching this topic, and assessing whether regulation changes are needed to ensure these cherished resources remain healthy into the future.

Weather or not. River flows and temperatures are probably the two most important environmental conditions for Idaho’s stream and river-inhabiting trout, and we’ve seen some wild fluctuations in recent years. 

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