PAUL NELSON FISHING: 'Fish are simple creatures'
Surface water temperatures are now in the mid to upper 60s in the Bemidji area, with early summer fishing patterns taking over the lakes.
Crappies, sunfish, largemouth and smallmouth bass have all finished spawning and have moved off to the edges of deeper weeds or other heavy cover.
Walleyes and other species are more concentrated into specific areas when they are spawning. Once they are done, it’s like the crowd dispersing after a movie (if you can remember what that was like) with fish heading in every direction.
Fish are simple creatures. They only dwell on food and safety, eat and don’t get eaten. Early summer patterns have all species of fish spreading out into the lakes and populating areas that best suit their needs.
Oxygen can be a major limiting factor for fish later in the summer, but not right now. Oxygen levels are high at all depths, with lakes beginning to stratify by temperature and starting to develop a thermocline.
There are a lot of fish moving toward deeper water because of the insect hatches in the mud basin. It's not just perch and walleyes that take advantage of the insect hatches, it is also suckers, tulibees, whitefish, crappies, sunfish and many species of minnows.
Clouds of insect larvae emerging from the mud basin are so thick they are visible on sonar. The insect larvae emerge from the mud and form into huge masses that look like clouds, right before they head to the surface to molt and become adults.
Most fish eat insects some of the time, while others eat them for a major part of their diet.There are tens of millions or more insects in many lakes, which is enough biomass to set up a food pyramid in deep water.
That’s the way a food pyramid works. There is a huge base of food at the bottom, with things that eat the insects on the next layer and larger predators on top of them.
Fish are opportunistic. Their whole life is centered around food and safety. Larger predators go to areas where insects are hatching to feed on the fish, not the insects,
A healthy lake will have several options for each species in different parts of the lakes. Rusty crayfish are a good example, with large populations in infested lakes.
Rusty crayfish are an invasive species, but they offer walleyes, perch, bass and northern pike a plentiful food source, along with minnows and small fish located in the same areas.
Oxygen levels will become an important factor later in the summer, once the water column is stratified by temperature and a thermocline forms in deep lakes.
The big demand for oxygen below the thermocline starts with the insect hatches. The insects draw many species of fish below the thermocline, where the fish begin to use up the oxygen supply. It is like a big bait cooler full of water and minnows with no bubbler.
The water column will stratify by temperature, with the warmest water on the surface and the coldest water on the bottom. The thin layer between the cold water and the warm water is called the thermocline.
The thermocline is dense enough to be visible on sonar and can act like a barrier for the fish. Water above the thermocline keeps mixing from wave action and has high oxygen levels because all the vegetation is located above the thermocline, which is the primary source of oxygen.
The water below the thermocline stops mixing and has a finite amount of oxygen. Fish respiration and decomposing plant and animal matter begin to use up the oxygen until at some point, many lakes have too little oxygen below the thermocline to support fish.
Fish are more spread out early in the summer than at any other time of the year. Anglers need to find a pattern the fish are using and then figure out how to catch them.
Many walleye anglers have switched from jigs and minnows to live bait rigs with larger chubs, leeches or nightcrawlers.
Paul A. Nelson runs the Bemidji Area Lakes Guide Service. Guided trips for 2020 can be booked by calling or texting (218) 760-7751 or by email at firstname.lastname@example.org.