Glenwood Area DNR fisheries manager Dean Beck has heard of some staggering fish catches over the years coming out of deep depths of water on area lakes.

The anglers are not breaking the law. They are catching and releasing the majority of those fish, but they are likely doing much more damage than they might realize.

“I bristle a little bit when we hear people say, ‘Yeah, we had a 100-fish day and caught them out of 80 feet of water.’” Beck said. “I think, ‘Well, you probably killed 100 fish.’ It is definitely a concern.”

Fish caught from those deeper depths -- often from about 30 feet or more -- can suffer from barotrauma, an injury caused by being pulled out of areas with increased water pressure found at deep depths. Most modern fish species have a gas bladder, and the bladder adjusts to the water pressure when at the deeper levels. When a fish is hooked and pulled quickly to the surface, the bladder expands due to the decrease in pressure.

“They cannot adjust fast enough when being reeled up and out of the water,” Beck said. “In the worst-case scenario, the gas bladder can expand to the point where it pushes their stomach out of their mouth and their eyes are bulging out. Not a good situation. It takes a long time for them to readjust, so they’re laying on top of the surface where they are susceptible to sunburn or gulls and eagles or whatever else is going to pick them off.”

Beck said they definitely encourage anglers who are fishing those deeper waters to plan on keeping what they catch. He also understands that anglers can run into issues with special regulations on certain bodies of water.

Lake Osakis, for instance, has a 15-inch minimum requirement for walleyes, so anything under that length has to be released. The lake also features a popular deep hole that gets down to about 65 feet where anglers will find the walleyes at certain times of the year.

“Anglers would get on them and you could see the fish on the surface after being released,” Beck said. “Too small to meet the 15-inch harvest restriction. Yes, we’re concerned. We appreciate the message of harvest what you need. Maybe if that’s where the fish are and you know you’re having an impact with smaller fish, try something else. Move up, go to different fish in shallower water.”

Panfish like crappies and bluegills will head to some of those deeper depths at certain times of the year, but they generally are more oriented with the vegetation and shallower water.

Beck said most of the lakes in their work area are fertile enough where they stratify in the summer. That creates a warm layer of water on the top and then a cooler layer below.

“That water below typically may not have enough oxygen to support fish, so the fish are right on that thermocline where they’ve got adequate oxygen and the most optimal temperature they can find for comfort,” Beck said.

A species like the walleye prefers cool water. As temperatures warm through the summer, they will move to find that preferred temperature.

“The barotrauma is potentially less of a problem in the summer months when the lakes are stratified,” Beck said. “The bigger problem is going into the fall where water temperature equalizes and you have the fall turnover so it’s mixed. You have oxygen from the top of the water way down to the deep water. That’s where I here some of the fall walleye bite and people saying they caught 100 fish in 80 feet of water. That’s a big concern.”