Paul Nelson: Bemidji area lakes experience dramatic warming
Seasons often change on a dime in the Bemidji area. After a long, cold winter and a cool, wet spring, summer arrived suddenly this past week, almost like someone had flipped a switch.
The lakes are warming fast with air temperatures in the upper 70s and low 80s this past week. Surface water temperatures started the week in the low 50s, with most lakes rising into the 60s in less than a week’s time.
The most accurate measurement of water temperatures in the lakes occurs first thing in the morning, before direct sunlight hits the water.
What matters most is how much heat the lakes are able to hold overnight, not how much can the first few inches of water spike during the day in direct sunlight with light winds.The first few inches of surface water in the lakes heats during the day and then mixes with the cooler water below at night. For fishing purposes, the truest measure of surface water temperature is the temperature the lakes are able to hold overnight.Spring peak is the name often used to refer to the short part of the walleye calendar when the big female walleyes are fully recovered from the spawn and ready to go on a feeding binge.The spring peak usually occurs about the same time the lakes are able to hold 60 degrees overnight for the first time, which is close to the point most local lakes are right now.Walleyes have been spreading into the lakes and the schools of walleyes are no longer concentrated close to the spawning sites.Most walleyes are still using shoreline connected structure, especially on the larger lakes where there are plenty of good feeding options along the shoreline.On smaller walleye lakes, all bets are off. Walleyes will go to the best feeding areas right away, regardless of location. There can be walleyes feeding on humps on small lakes on opening weekend.Walleyes in larger lakes usually work their way to the outside edges of shoreline connected structure before some fish start jumping off the shoreline and moving to mid-lake structure.Some walleyes stay on shoreline connected structure much of the summer, with many fish moving back and forth as their feeding options change.The fish instinctively seem to know what is coming next. The next big thing after the spottail shiner spawn is the insect hatches in the mud basins of the lakes.Millions of insect larvae of dozens of species are busy feeding in the mud basins of the lakes, getting ready to hatch into mature insects (some species have multi-year life cycles).The end game of most aquatic insects is to rise to the surface and molt, turning into flying insects so they can complete the mating portion of their life cycle.Many walleyes and perch, along with many other species, will head to the mud basin to eat the insects as they emerge from the mud or prey on the other species of fish eating the insects.New weed growth in the lakes has been minimal so far this spring. Most vegetation in the lakes died over the long winter. The only remaining cover on the shallow flats has been the occasional rock pile or the mats of chara which stay green all year long.Once the cabbage and coontail weeds start to grow, the areas of new weed growth will be like magnets to any fish on the shallow flats.Anglers are still catching walleyes along shoreline structure in 7 to 9 feet of water but more fish have been moving to the outside edges of shoreline structure, using slightly deeper water.Jigs and spottail shiners have been the baits of choice for most walleye anglers this spring but some anglers have also been catching walleyes on live-bait rigs with minnows or leeches.Bass fishing opened this past weekend, with most bass still in pre-spawn mode and just starting to move onto their spawning beds.Crappies and sunfish have also moved into the shallows to feed before they are ready to spawn. Most members of the sunfish family (which includes crappies and bass) spawn when the surface water temperatures reach the mid 60s.