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Brook Trout and Lake Trout, coldwater species are found in many lakes, ponds, and streams within the Adirondacks. They require cold, well oxygenated waters that are clean, to survive. With the increasing in overall temperatures, I felt it was time to explore the impact that these rising temperatures would have on our fish populations.
Fish, except large pelagic predatory species, for the most part, maintain a body temperature that are in relation to the water that they live in. They rely on an external heat source (ectotherms.) Ectotherms have lower metabolic rates and require less energy for basic activities, thus can survive on less food. These fish species experience environmental changes to temperatures seasonally and have cellular and subcellular mechanisms for adapting. These mechanisms are genetic. The effect of temperature on biochemical and physiological processes drives fish to select environments that allow for optimal functioning. These temperature preferences can be so strong, that a fish will not leave cooler waters to feed on prey that are located in warmer surface waters. These temperature preferences change as the fish grow. Waters that are suitable for juvenile fish are generally not adequate for adults, thus forcing the adults into deeper colder waters. This can cause decreased localized food sources, overcrowding and diseases.
As the temperatures rise, there is increased evaporation and decreased water levels. This can lead to increased algal growth, and then increased bacterial action that leads to decreased oxygen levels in the colder parts of lakes making them inhabitable to Trout and other fish species. Lake Trout would be forced to move outside of their optimal temperature zone. The decreased water levels would mean that Brook Trout would loose access to portions of streams during summer months. This coupled with the already reduced habitat connectivity from undersized or perched culverts could have a significant impact on our native Brook Trout.
The above outcomes are not do to drastic temperature rises, but from as little as a couple degrees. Studies have already indicated that bodies of water within the Adirondacks have increased water temperatures and are showing increased algal growth and decreased oxygen levels.
To put it in perspective: Brook Trout function best at water temperatures at or below 65 degrees F. They can tolerate brief periods of between 24-48 hours at temperatures up to 72 degrees F. Even a few hours at 75 degrees F, Brook Trout will die. Lake Trout need waters that remain at or below 50 degrees F to survive.
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Thanks for the article! Please, if you know, provide the temperature ranges for Rainbow and Brown trout as these are popular stock species even if non native.
Rainbows and especially Browns can tolerate water temperatures up to the low 70’s fairly well. When temperatures start getting above 70 all trout start searching for cooler water. Fishermen in the 19th Century used to mark spring holes in Adirondack lakes because they knew that’s where the fish would be during hot weather.
A well-known Pennsylvania trout fisherman, Joe Humphries (who taught fly fishing at Penn State) used to say that if the water is 80 degrees, don’t expect to find trout. They will be congregated where cooler waters enter the streams and lakes. In summer, a stream thermometer can be an important tool.
Two resources that may be of interest:
1. Lake Trout and Climate Change in the Adirondacks – http://www.nature.org/adirondackslaketrout
2. Rethinking Culverts – https://www.youtube.com/watch?v=vWtVFsOOFW8
“This can lead to increased algal growth, and then increased bacterial action that leads to decreased oxygen levels in the colder parts of lakes making them inhabitable to Trout and other fish species.”
I’d have thought the hypoxic conditions would render the affected areas uninhabitable to trout.
Cerise,
You are correct. That was a typo. It does make the area uninhabitable. The decreased oxygen levels (hypoxic conditions) will greatly impact fish populations. It renders the areas uninhabitable to trout as well as other cold water species. The physiological stress placed on the fish makes them more susceptible to disease and predation as well.
Great article and timely! In addition to cold water (less than 55F), Lake Trout need well oxygenated water which can be depleted in bottom waters with extended lake stratification due to climate change. According to the Nature Conservancy Report (Thill 2014), Lake Trout have been extirpated from 75 lakes where they were once reported, with 102 potentially still containing Lake Trout. I would argue our prospects for maintaining Brook Trout in some of the Adirondack waters is much greater because we have the ability to improve culverts and provide upstream passage, and Brook Trout are highly dependent on groundwater inputs that help maintain colder areas of streams. It will be much more challenging to find natural ways to maintain oxygen in our deep cold lakes to provide optimal Lake Trout habitat. Winter conditions should also be considered with milder winters more energetically demanding to trout than the more traditional cold winters. Time is of the essence to find ways to preserve these iconic Adirondack fish!
Preferred temperature ranges (for optimal growth and feeding) for Rainbow Trout are 12-18C (53-64F), with approximately 25C (77F) the lethal maximum; Brown Trout range from 12-19C (53-66F), with 27C(80F) the lethal maximum temperature.