June 25, 2020 2 min read

We are getting to that time of year where water temperatures are starting to peak. At Cheeky, we avoid fishing trout water during the summer that gets too hot. You probably already know that hot water temperatures put stress on fish. However, you may be surprised by just how deadly fishing for cold water fish in the heat may be.

Release Mortality Rates

Montana is a well-known example of actually enforcing this rule. When water temperatures exceed 73 degrees in some areas, fishing is restricted to only the morning, during a time period when fish are less prone to thermal stress. Multiple studies have been conducted by state agencies that confirm the efficacy of these protections.

A 2008 Montana study compared release mortality rates of local game fish caught on fly in cool (<68 °F), warm (68 to 73°F), and hot water (>73°F). Findings suggest that release mortality rates increase with water temperature increases. For rainbow trout, release mortality went from 0% in cool water, to 9% in warm water. In hot water, release mortality rates of up to 16% were recorded.

For brown trout, release mortality rates rose from 0% in cool and warm water to 4% in hot water. Mountain whitefish exhibited the most sever differences. In cool water the release mortality rate was 0%, but in warm water, the mortality rate rose to 20% and in hot water, the rate was recorded at 28%. The findings of this study also indicate that fish caught early in the morning are more likely to survive than those caught in the evening, after a stressful day of hot water temperatures.

A 2017 study performed by the Michigan Department of Natural Resources of fish caught and released on conventional gear found that release mortality rates were as high as 43% when surface water temperatures exceeded 50 °F. However, in cooler water temperatures, release mortality rates dipped to around 15%.

While these findings are specific to certain fish species in specific locations, on a broader level, the results are clear: fish are more likely to die after being caught and released in stressfully hot water. 

What You Can Do

Though local regulations may not prevent you from fishing during periods of hot water temperatures, we suggest following the general rule of thumb to stay away from water that is over 70 degrees. Instead, look for water that stays cool year-round, or limit your fishing to very early hours. Carrying a small thermometer with you makes it easy to figure out water temperatures. If you are fishing in warmer water, limit the time spent fighting the fish by using heavier gear and a tighter drag. Leave the fish in the water at all times and reduce handling the fish to a minimum. Forgo the pictures, and make sure to thoroughly revive the fish during the release.