How Fish Respond to Cold Water Temperatures

[PeterSL]

'KeepFishWet' has reviewed some of the relevant science  https://www.keepfishwet.org/keepemwet-news-1/2021/1/19/winter-fishing

LESSONS FROM SCIENCE ON ICE FISHING

There have been a handful of studies examining the impacts of ice fishing on fish. Despite the differences between ice fishing and, for instance, fly fishing in open water, there are some parallels we can draw, especially in regard to how fish react to angling at very cold-water temperatures. Two trends that stand out and one aspect that needs to be examined further are:  

1)    During winter, fish have a muted physiological stress response and mortality rates are generally lower. The stress response measured by examining blood concentrations of glucose, lactate, and cortisol (read here for more information) often decreases at lower water temperatures. By holding walleye in a pen, this study was able to show that all fish were still alive 24 hours after angling. This is good news for anglers — fish are less physiologically impacted by angling during the winter.   

2)    Although stress responses are often diminished at lower water temps, they can also be prolonged and/or delayed. A study on northern pike, found that it took 45 mins to 4 hours to see changes in blood chemistry following the angling event. As a comparison, in warmer water temperatures we often see these types of changes within minutes. During the winter, this means that fish may not incur the physiological impacts of angling until hours after they are released, and these impacts may last hours longer. We often say that just because you saw your fish swim away does not mean that it’s ok, and this is even more relevant at colder water temperatures.   

3)    While not specifically addressed, several of the studies also point out some of the potential impacts of air exposure during winter fishing. One study noted that fish showed signs of freezing damage to eyes and gills. Very cold air temperatures and windchills could cause damage even during brief air exposures. 

Recommendation: If the guides on your rod are freezing up, consider how delicate gill tissue might respond to air exposure. Just one more reason to Keep Fish Wet.  

Until we have some more conclusive science on the impacts of winter fishing at cold temperatures, it behooves us to employ the precautionary principle and extra careful when fishing during cold temperatures. Returning fish to the same lie where you hooked them, limiting fight time, using barbless hooks, and minimizing air exposure are all important actions that anglers can take to help create better outcomes for fish after release.