Pond and Lake Management With Focus On Fisheries Management

By Jared Engelbert – BWO Fisheries Science

What is Fish Habitat, and How Much Fish Habitat is Needed?

Merriam-Webster defines habitat as “the place or environment where a plant or animal naturally lives and grows.” So, does this mean that water is habitat since fish live and grow in the water? Let me answer that question by asking you another: Does that mean that atmospheric air is habitat for terrestrial organisms?

Obviously, fish need water to live and breathe, just like terrestrial organisms need air to live and breathe, but I wouldn’t consider either one habitat. Although water quality is a very important factor for a healthy fishery, it is not the topic of this entry.

Fish habitat can practically be anything within the water that a fish uses to hide, forage, stalk, ambush, and the list goes on. Types of fish habitat include aquatic vegetation, rocks, pebbles, trees, buoys, random objects that have fallen in the water, and artificial fish habitat.

What Makes the Best Fish Habitat?

Some might argue that aquatic vegetation is the best type of fish habitat, but I would beg to differ. In temperate regions, which is most of North America, the aquatic vegetation dies off in the winter. If vegetation is the only type of fish habitat in a lake, this leaves little to no cover for the smaller forage fish to hide. Yes, the metabolisms of predator fish species will be lower, but one must think about the predators from above.

Piscivorous birds, such as Cormorants, Herons, Pelicans, and fish-eating mammals (River Otters) can clean house during the cold months when there is not an adequate amount of fish habitat.

The best type of fish habitat is something that has a rigid structure, or “backbone,” with a lot of surface area and high amounts of “interstitial spaces.” Think of an Eastern Redcedar (Cedar) tree. It has strong and flexible limbs covered with small, tightly packed twigs and needles. Once a Cedar tree has been placed in the water, it quickly becomes covered with “periphyton,” which is a conglomerate of beneficial filamentous and planktonic algae, microbes, and detritus that attaches to submerged surfaces. Among this periphyton, there is a smorgasbord of aquatic macroinvertebrates for small fish to feed on.

In a perfect world, one could simply throw in a bunch of Cedar trees and call it good, right? Well, there are a few downsides of the Cedar tree:

1. The small twigs and needles with the high surface area will only last a couple of years before they decompose.

2. The strong, flexible limbs will be decomposed after 3 years.

3. As Cedar trees are added multiple times, nutrients, such as phosphorus, begin to accumulate in the lake.

The third reason is enough to search for an alternative habitat type (in my opinion). The accumulation of phosphorus can cause eutrophication, which can increase the occurrence of harmful cyanobacteria blooms. I have seen a gin-clear nutrient-poor sand pit lake turn into a hypereutrophic green lake due to adding too many Cedar trees for multiple years in a row.

What is the Alternative to Cedar Trees?

The closest thing that resembles a Cedar tree but lacks all of the negative aspects is an “Ugly Tree.” Yes, an Ugly Tree. These Ugly Trees are everything a Cedar tree is but will last forever (at least as long as you or I will live) and do not increase the amount of phosphorus in the system.

Each Ugly Tree is 6 feet tall and 3 feet wide with rigid and flexible limbs that are covered with small needle-like strands of texturized PVC. The small needles are almost instantly coated with periphyton once submerged in the water. This subsequently attracts small baitfish not only for the food but also for the added cover and safe haven from predators.

How Much Habitat is Needed?

To rephrase that question: How much habitat is needed in order to have a net positive effect on the fishery versus it just being a fish attractor? There is a huge difference between a fish attractor and a suitable amount of habitat.

If you have a barren lake void of any habitat, throw out a couple of pieces of habitat, and catch fish around it, you might have a false sense of accomplishment. Research suggests that having 20 to 30 percent of the lake with suitable, high-quality fish habitat creates a predator-prey dynamic that is sustainable with a net positive effect on the health of the fishery.

If there is less than 20 percent coverage, the predators can exploit the forage base, leaving them with a diminished food supply (nowhere for baitfish to hide). If there is more than 40 percent coverage (this scenario happens when aquatic vegetation is extremely dense), the predators can’t feed efficiently because they have to expend extra energy searching for food, and in worst cases, they can’t even swim through the dense stands of macrophytes (too many places for the baitfish to hide). Both scenarios ultimately lead to a stunted predator population.

Let’s Do the Math

For a 1-acre pond with depths ranging between 0 and 8 feet (entire pond is shallow enough to not stratify), an acre is 43,560 square feet. Twenty percent of 1 acre is 8,715 square feet. A cluster of 10 Ugly Trees has an effective range of approximately 400 square feet (20’ x 20’). That means a total of 20 Ugly Tree Habitat Clusters would be the recommended amount of habitat to add to a 1-acre pond.

Using the same calculation, with Cedar trees, you would have to add 200 medium-sized Cedar trees every 3 to 5 years. With artificial habitat, you only have to do it once.

Placement is Key

Now that we have covered the best types of fish habitat and how much is needed, let’s talk about placement. This is just as, or even more important than, the previously mentioned topics. If you spend a ton of time and money on fish habitat and just go out to your pond and toss it in the Mariana Trench, it was a complete waste of your time and effort. Proper placement is key.

Where should the fish habitat be placed? In the water… Yes, that is the first step. But where in the water?

You must understand a little bit of limnology for this one, so I will get you up to speed. In most small impoundments during the early summer, a phenomenon called “stratification” takes place. This is when warm water is on top (epilimnion) and the cooler water is on the bottom (hypolimnion). The area between the two layers is called the “thermocline.” The thermocline acts as a barrier, limiting gas exchange and mixing between the layers. The epilimnion is where photosynthesis occurs, which produces dissolved oxygen (fish need it to live). Not all, but most ponds have almost no oxygen below the thermocline (usually 6 to 8 feet deep depending on water clarity, depth, wave action, and surface area).

Can you see where I’m going with this? Fish habitat is useless if it is below the thermocline. Before any habitat enhancement projects, I create a bathymetric map using a depth finder unit equipped with sonar logging capabilities. There are multiple software programs that you can use to do this. I focus on adding habitat in areas around the lake that are less than 8 feet deep. This is usually the shoreline or littoral area, but occasionally there are mid-lake humps and peninsulas that provide exceptional areas to add fish habitat.

Arrangement of Fish Habitat

Now that you know what depths to place the habitat in, I will briefly go over arrangement. Clusters of fish habitat with gaps in between each cluster have proven to work very well. Place 8 to 10 trees or Ugly Trees closely together (I like to put 4 Ugly Trees jammed together in the center and make a circle around the middle 4 with the other Ugly Trees). Leave a 20’-30’ gap in between each habitat cluster for fishing lanes. Add enough habitat to cover 20 to 30 percent of the lake. This is what it takes to provide enough fish habitat to have a noticeable and positive effect on your fishery.

The Role of Natural Habitat

Natural habitat, such as aquatic vegetation, is also a key component of a healthy ecosystem. Aquatic vegetation (or macrophytes) provides excellent cover for small fish, reduces erosion, and filters the water column. Littoral vegetation (marginal, emergent, and submergent) protects the shoreline from erosion and decreases the amount of suspended particles generated from wave action. Allowing aquatic vegetation to establish and grow along the shoreline is always a good management practice. Keep in mind, not all macrophytes are equal.

I won’t go into detail on all of the good and bad (invasive) species of macrophytes, but a few species that I would highly recommend are: American Pondweed (Potamogeton nodosus) and Eelgrass (Vallisneria americana) for submerged plants; American Water Willow (Justicia americana), Squarestem Spikerush (Eleocharis quadrangulata), Pickerelweed (Pontedaria cordata), and Smartweed (Polygonum sp.) for marginal plants.

In Summary

Providing a diverse habitat mosaic that includes seasonal aquatic vegetation and permanent habitat with a rigid framework (artificial fish habitat) will create an environment suitable for a productive fishery. Having 20 percent of the pond or lake with artificial habitat and 10 percent coverage of aquatic vegetation will most definitely maximize the productivity of the fishery. If the macrophyte community exceeds the recommended coverage, control methods might be necessary.

Collectively, {proper fish habitat, diversity, and coverage} is just one variable of the complex equation we call fisheries management. Other important factors, such as water quality, pond construction and design, predator-prey dynamics, supplemental feeding programs, user enjoyment, etc. will be covered in other entries. Feel free to check out our YouTube page for more content: @bluewingoutdoors4639