By Nick Simonson

Late summer brings with it warmer waters, and as temperatures go up, predator fish typically go down in the water column in pursuit of their prey seeking cooler environs until fall settles in.  As those gamefish like walleyes go after baitfish species like smelt, anglers follow suit and put their presentations in those deeper stretches to connect with faster action.  However, angling in depths of 25 feet or more can result in barotrauma, a phenomenon which can injure fish internally due to a change in pressure inside their bodies that can result in immediate or delayed mortality, according to Scott Gangl, Fisheries Management Section Leader with the North Dakota Game & Fish Department (NDG&F).

“Barotrauma is just trauma that fish experience when you pull them up from deep depths, similar to when you’re scuba diving and you get the bends because you’re ascending too quickly. That change in pressure from deep to shallow water can really affect their internal organs,” Gangl explains of the impact on fish.

While some of the effects of barotrauma are noticeable, many injuries can’t be observed by anglers bringing fish out of the depths.  It’s for this reason that catching and releasing fish from depths of 25 feet or more can result in unseen delayed mortality, where the fish appear to swim away in good health, but later die due to unobservable conditions resulting from the pressure change of being brought up through the water column.

“What people see most often is a fish’s swim bladder will overexpand and push its stomach out through its mouth. Fish will have a hard time righting themselves if you try to release them, they won’t be able to swim away because their swim bladder is over expanded. That’s what people see on the outside,” Gangl details, adding, “on the inside, there’s usually some other traumas that occur. There could be gas bubbles in their blood, there could be ruptured veins, ruptured blood vessels, ruptured internal organs, things that could really lead to mortality down the road.  One, two or three days later, that fish might succumb to that mortality.”

In late summer, anglers should take on a selective harvest mindset when their favorite species go deep.  Among the options available to those fishing this time of year include targeting walleyes running deeper and planning to keep all of them that they catch from those depths or alternatively, finding fish up shallower that they can release if desired. Another option for anglers it to target other species such as bass, crappies and bluegills that are up shallower as part of their outing, or after they have their limit of walleyes to mix things up on a particular late summer fishing trip.

“Be aware of it. If you know that you’re going to be seeing fish in deeper water, catching fish from deeper water, know that a lot of those fish probably won’t survive if you release them. So, plan accordingly. You might plan on harvesting the fish you catch, or maybe just alter where you’re fishing. If you are looking at targeting fish in deep water, keep your limit from deep water and then maybe switch techniques and go target fish shallower if you can find them shallower. Fish in shallower water if you want to practice catch and release,” Gangl concludes on angling responsibly in late summer.

Keeping in mind the physical limitations of walleyes and other fish pursuing deeper prey in cooler waters this time of year can help anglers make better decisions to limit delayed mortality from barotrauma.  Plan to keep fish caught from 25 feet of water or deeper, or target fish in the shallows to limit the effects of this phenomenon on the overall populations and health of a fishery. Give other less prone species a shot as well to increase enjoyment of a lake and find fast summer fun along with some keepers for the frying pan.

Simonson is the lead writer and editor of Dakota Edge Outdoors.

Featured Photo: Getting Selective in Late Summer.  Anglers should monitor the depths from which they’re catching fish in late summer and consider keeping those walleyes caught from more than 25 feet deep, or fish shallower to limit the delayed impacts of barotrauma. Simonson Photo.