Fish don't enjoy heatwaves either...

July 31, 2020 at 4:02 pm

By Director of Fisheries & Hatcheries Francis Brautigam

Is this the new normal?  No, I’m not talking about COVID-19, I’m talking about the abnormally warm and dry summer.  Is this number three out of the last four years? Or is it four out of the last five?  Either way, many parts of Maine are once again suffering from below-average rainfall and varying degrees of drought-like conditions. Anglers are reminded to keep this in mind when fishing for cold-water fish species such as trout and landlocked salmon. Maine is well known for our abundance of coldwater fish populations, yet during a summer like this, our waters can get unusually warm and it can impact fish that are less tolerant of warm waters.

brook trout

In order to beat the heat in streams and rivers, brook trout seek deeper pools that are cooler and better oxygenated. Small, colder tributaries are also locations where these fish will seek thermal refuge. In ponds, they will seek spring holes. When fish are in these situations, they are under stress and more susceptible to predators.

When a stream dwelling brook trout, that has hunkered into a cool 50-degree streamside seep, is hooked by an angler the fish is played out in the main stream where water temperatures may be in the mid 70’s, approaching the fish’s thermal limits. Trout and salmon that reside in our deeper, colder lakes are also impacted by this summer’s weather. A lack of rain and consecutive days with above average temperatures can cause surface water temperatures to be warmer than usual, with some lake surfaces approaching the 80-degree mark. Trout and salmon will stay below the thermocline, where temperatures can be in the 45-55 degree range. A fish caught below 40 feet of water and then brought to the surface may experience a temperature difference approaching 35 degrees! This type of temperature swing can put a great deal of stress on a fish. 

In extreme cases in some shallower and smaller ponds, dry summers can result in fish kills, due to reduced groundwater inputs and less oxygen as it becomes warmer.  (For more information on fish kills and when to be concerned about them, check out this recent blog by MDIFW Fish Pathologist David Russell: When to be Concerned About Finding Dead Fish on Maine’s Lakes, Ponds, and Rivers this Summer.)

During hot summers like this, anglers often wonder what they can do when they are out fishing to help Maine’s trout and landlocked salmon.  I offer the following simple steps:

• Fish earlier and later in the day when water temperatures are cooler.

• Try to limit the time it takes to land your fish, particularly once your fish has entered warmer water. Overplaying a fish can increase stress.

• After hooking a fish, catch and release the fish quickly if you are not planning to keep it.

• Avoid keeping the fish out of the water for pictures or keeping them in warm surface water.

Anglers are also reminded that beginning August 16, the general law for fishing in rivers, streams, and brooks is restricted to the use of artificial lures and flies only. General law length and bag limits apply, except there is a daily bag limit of one landlocked salmon and one brook trout.  Be sure to use MDIFW’s Fishing Laws Online Angling Tool to check for any special regulations on your favorite water!