Living on the edge... Ecotone...that's the technical, biological word ecologists use for the border where two distinct habitats meet. Images of a terrestrial ecosystem are easy to visualize. For example, hunting pheasants around the edges of old stubble fields. The soft edges of whitetail deer habitat: open fields meeting briars, then goldenrod, followed by scrub brush apples or oaks, depending where you are, then aspens that transition into larger mountain forests.
Diverse terrestrial edge areas that have good plant diversity hold more game.
The concept of edge and the diversity it creates holds true in the watery environment of ponds, too. Increasing edge diversity in water increases the diversity of aquatic organisms. Aquatic habitat diversity becomes more critical when the pond is small.
Small ponds can be productive if a variety of edges are maximized. Pond edge management creates opportunities to increase edge habitat and create a more robust fishery.
First, the physical properties of water and light make a pond interesting because edge areas are horizontal (moving offshore) and vertical (moving deeper). The most productive habitat in the pond is found at the shoreline edge, where the water, air, sunlight, and sediments all come together. This first foot of stable, permanently inundated water and near-shore sediment is where most of the pond production happens. Abundant light penetrates to sediments where submergent plants, attached algae, and emergent plants grow. This base of the food chain feeds zooplankton, insects, other crustaceans, and other consumers.
How can this near-shore zone of plenty be increased? One way to increase the "shoreline development" is by scalloping the shore during construction. Create a "wavy" irregular shoreline. Bait farmers already know that increasing the shoreline area of the pond by scalloping is a secret to getting more bait production from a small pond. Fathead minnows spawn and feed in this shallow, (sometimes) rocky habitat and are partially helped by this shoreline scalloping strategy. Fatheads are a great way to jump-start the forage in a new pond.
Another strategy is increasing benthic (bottom) diversity by having hard and soft bottom features in near-shore waters. Soft sediments are a mix of organic detrital (dead plant) matter and finer inorganic sediments (like silts). These softer sediments accumulate in calm areas not exposed to heavy prevailing winds.
Shallow, calm areas are essential to grow emergent vegetation like rushes, sedges, and cattails. Having a few dedicated areas in the pond meant to grow this type of vegetation is important. This is an area of deposition and accumulation. Driftwood and stumps may drift into this zone (or be intentionally placed). Where this accumulation zone meets the main pond, add some boulders the size of basketballs (or larger) to create a break between a hard and soft bottom. A good spot to do this is on the leeward side of a point that transitions to a cove. Think about a favorite fishing spot where years of wind erosion (and then deposition in the calm water) have done this creative work naturally. Fish will haunt the transitions between hard and soft bottoms.
Vertical, vegetative edge transitions can also be created in ponds. Vegetative "breaks" are created by increasing depth, abruptly causing a rapid decrease in sunlight. As the water gets deeper, light is attenuated (reduced) by back-scattering, reducing the growing power of the light. Since light is the main factor that determines which plants grow (and which ones don't!), depth determines plants. In near-shore waters, emergent vegetation, like cattail, provides dense, close, vertical cover. Small fish such as young-of-the-year sunfish, fathead minnows, and killifish will frequent this zone. This type of emergent zone ends at a depth of about 3 ft., where the pond naturally transitions to submergent plants. This is where the next edge (in 4-6 ft. of water) can be found. Coontail, milfoil, tapegrass, waterweed, and numerous other submergent pondweeds dominate this zone. This zone is critical for sunfish and bass and is the dominant zone associated with fishing in most ponds.
Interestingly, most problems with excessive weed growth also occur here because sufficient light penetrates to the bottom, creating luxuriant plant growth that may become a nuisance.
When planning for the submergent zone of the pond during construction, try for an abbreviated "donut" ring of 4-6 ft. deep water around the pond. This will allow a significant amount of littoral (rooted submergent and floating leafed) habitat around the pond but will not dominate the pond entirely. Floating leaf pond weed, variable pondweed, white and yellow water lily, and other floating leaved plants will grow at the deep edge of this zone. These plants will provide another zone of diversity in the form of cover and shade. Gamefish will increase in number as the cover and shade approach 50% of this 4-6ft—deep zone.
It is important to note that too much cover of one particular type is not beneficial. A monoculture of one plant type (like milfoil) will dominate and choke everything else out. Robust plant diversity and equal amounts of open water in this zone create abundant edge (and great fishing). Don't forget about the edge created by the transitions to open water.
Moving deeper to >7ft. in clean water ponds generally finds a carpet of stonewort or muskgrass, (commonly called Chora). In southern ponds, Chara will grow in the shallowest water as well. This type of algae feels hard and granular and smells musky when crushed. Think of it like a carpet of pale green AstroTurf that may completely cover the pond bottom in depths of 7-12ft. (shallower or deeper in some ponds). Scuds, ostracods, insects, and a bunch of other benthic critters that provide food for perch, sunfish, and crappie are found there throughout the year.
The deep weed edge is the transition between the submergent plants to the Chara (or sometimes Elodea). The overlying open water of the pond (and the next edge) is where some of the best game fishing is found, particularly in the summer.
Want to maximize fishing opportunities in this zone? Put some structure here in the 5-7' contour, creating additional habitat at the deep weed edge. Placing large boulders here will give the pond a trifecta (hard structure, soft bottom, weeds) habitat edge at the open, deep-water transition. Do not waste good rock structure in super deep water (>7ft). We learned this lesson the hard way in our pond. While constructing this 1.3-acre pond, we placed numerous huge boulders in 10-11 ft. of water. Zero smallmouth bass hang out around those deep structures. Instead, all the smallmouth in the pond frequent boulders placed in 4-6ft an additional element of horizontal cover introduced as well. Like what? A 30-foot-long floating dock provides the best shade in the pond and is where a dozen nice smallmouth can be found at this very moment.
Horizontal structure is essential and can be added in the form of docks, swim platforms or simple anchored floating logs in near shore areas over 3-6 feet.
Want a robust, diverse fishery in your pond or lake? Create a variety of depths and bottom types. Habitat diversity creates plant diversity. The food chain, including the fish...will follow. Try to come up with a plan that creates as much vertical edge that makes sense for the goals that you have for the pond. Don't let any one particular habitat type dominate. Plan for a healthy mix of open water and weedy edges. Then, after the pond matures, head down to the dock and catch a fish or two.
Mark Cornwell is a professor of fisheries at the State University of New York in Cobleskill, NY. Based near the Catskill foothills, he feeds the brains of hungry fish students, offering plenty of applied science and hands-on opportunities beyond the classroom. Cornwell also works with select local landowners, collecting data and analyzing ponds, with students receiving the benefit as well. He also assists the college's aquaculture department.
Reprinted with permission from Pond Boss Magazine
