The Lake Where You Live

Another DNR research project provides evidence that wood in the water is a key to healthy lake fisheries.

Several years ago the DNR did an experiment on Little Rock Lake in Vilas County, removing about 75% of the sunken logs and branches from one of the lake’s two lobes to see how the fishery would respond.

After four years the researchers observed that the yellow perch population collapsed in that lobe of the lake — the perch lost spawning habitat and the young that hatched were more vulnerable to predators. Largemouth bass, with few perch to feed on, began to eat their own young, and their growth rates declined.

More recently, the DNR tried the same basic experiment in reverse on 90-acre Sanford Lake, also in Vilas County. Gregory Sass, a fisheries research team leader, and Max Wilkinson of the UW Stevens Point fisheries research unit, shared the results during the Wisconsin Lakes and Rivers Convention earlier this month.

In 2018 the research team added some 140 full-canopy conifer trees to the northern shore of the lake, which had a diverse fish population but relatively low productivity. They then monitored the response of the various species.

The biggest change was a sharp increase in the bluegill population. The team attributed that to the trees providing a refuge from predators — the branches and pine needles creating a nearly impenetrable barrier — and so greater survival of new year classes of those fish. The rock bass population increased slightly; smallmouth bass and perch stayed about the same.

Walleyes declined somewhat, but the researchers said that probably had little to do with the addition of wood and simply reflected a general trend toward a decrease in walleyes within Wisconsin’s ceded territory — essentially the northern third of the state. 

The team will continue to monitor the lake’s fishery for about eight more years while planning for two more significant “tree drops” somewhere within that span.

And why does wood in the water have such a positive influence on fish populations? One reason is that it provides a safe haven for newly hatched and juvenile fish, which otherwise can be gobbled up by predators.

Another reason is that the wood itself provides its own food chain. As it starts to absorb water and decay, a layer of periphyton (algae, microbes and organic matter) builds up on the surface. Small invertebrates including insects then feed on that material. In turn, they provide a feast for the juvenile fish taking shelter among the branches. 

And then along come the adult fish, from panfish on up to the apex predators like bass, walleyes and northern pike. Versions of this food chain drama can play out around any wood lying in the water.

As we develop lake shorelines, the wood in the water tends to get removed to make way for piers and swimming areas. To help make our fisheries healthier, we can reverse that process by dropping shoreline trees into the water (or simply leaving those that fall on their own), or by working with our lake associations to install a cluster of whole trees (fish sticks).

When it comes to fishing, the saying holds true: It’s the wood that makes it good.

Ted Rulseh is a writer, author and lake advocate who lives on Birch Lake in Oneida County. His new book, “Ripple Effects,” has been released by UW Press. You can learn about it by visiting his website at https://thelakeguy.net.