Sometimes, I get caught up in the advice I give people. The same advice is often given repeatedly; eventually, it may come out like a pond recipe or, worse yet...a rule. Advice on what kind of pond to build, how deep to make it, structures to add, and what fish to stock may be so routine that they set themselves up as rules. Getting out of the usual routine and challenging, reinforcing, or flat-out rejecting typical could be a good plan.
Simple ponds require simple instructions because (generally) they are simple habitats resulting in short food webs. Larger, diverse bodies of water have (generally) more complex habitats, resulting in more niches and leading to a more complicated food web. The advice gets a bit more complicated as the food web gets more complicated.
More rules.
Enter the differences between ponds and lakes. Without getting into a lengthy discussion about definitions of ponds vs. lakes, let's just agree that a pond is smaller, shallower, and less complex than a lake. A lake is larger, deeper, and likely more diverse. The lack of habitat diversity in small ponds limits the number and types of fish it can support.
There is simply not enough habitat complexity or space.
Can you build complex habitats in small ponds? Yes, but not a lot of it. Space becomes limiting as predators (particularly Largemouth) dominate that space and limit fish diversity.
Naturally nutrient-poor, small waters have a limited ability to produce a large fish biomass. High-elevation ponds with small watersheds have limited time to pick up dissolved nutrients. The rain water that falls has no time to run through weathered soils and dissolve solids.
Building blocks in the water, such as calcium, magnesium, and chloride (and others), are the dissolved solids from which the pond food chain is built. Without these dissolved solids, the food chain is anemic. Think of these nutrients as the Legos of Life. The food chain is where those nutrients end up in the form of plants, plankton, other invertebrates, forage fish, and finally predator fish or rough fish.
In this part of the country, upstate New York, small ponds at higher elevations are also cooler. Here the forage fish are often golden shiner and native pumpkinseed (bluegill are introduced and not native). Much of the debate comes when a predator is added. Is it better to stock Largemouth or Smallmouth bass? Largemouth bass grow very slowly because the growing season is relatively short; the water temperature only makes it over 70°F for a few weeks a year.
Typically, these small, nutrient-poor ponds' cool temperatures and lack of complexity call for Smallmouth bass. Additionally, Largemouth can be problematic because they will overpopulate, overeat, and then eliminate forage.
Smallmouth are more likely to produce a self-sustaining balanced pond in a small pond. Smallmouth are better behaved than Largemouth. Largemouth overeat prey and the pond becomes bass-on-bass quickly.
Drumroll please, herein lies the exception to the rule.
Recently, a colleague approached me with a unique question. He asked (somewhat incredulously), "Can you tell me...why are the Largemouth bass in my pond so big?"
I have never had a similar question postulated! Smiling, I asked him, "Is this a problem?" He answered, "No, it's a great problem to have, but I don't understand it!" The family-owned pond is a high-elevation 10-acre pond that they rarely fish in. But when they do fish it, the pond produces several big bass in the 5-lb class—Hmmmm... 51b pound largemouth...not too shabby for any New York pond.
Time to investigate; no arm twisting is needed.
Some SUNY Cobleskill fisheries students were challenged to determine the root cause of this big bass "problem." The class will perform water quality, plant, plankton, and fishery surveys in a typical lake survey.
After a quick trip to the lake, water quality results confirmed the suspicion that the total dissolved solids were low (33mg/L) leading to a low conductivity (40pS/cm). The alkalinity or buffering ability of the water that relies on carbonates was also low (<17mg/L). The hardness or the concentrations of calcium and magnesium were low (<17mg/L). These low results were typical for high-elevation, small mountaintop lakes with almost no watershed. These readings should be in the 100-200 (or more) range for better fish production. This mountaintop (small watershed) lake was low in nutrients.
The plant survey indicated a shallow lake with a maximum depth of 7 feet. The lake was carpeted with waterweed (Elodea canadensis), a nice native plant that grew across the entire lake bottom. There were few floating leaf plants, save some small patches of floating leaf pond weeds (Potomogeton natans).
The shallow depth of this pond was very concerning. Essentially, this lake was an over-deepened wetland that was in danger of winterkill due to the high organic input from the plants and shallow depth. The decomposition of the plants under the ice in winter causes the water under the ice to go completely anaerobic, killing the fish.
A depth (around 10ft) is generally required to store enough oxygen for fish to make it through until spring. This pond was shallow. But...the relatively shallow depth allowed complete mixing during the ice-free season by the wind. This lake does not stratify, allowing the existing limited nutrients to be well utilized.
The plankton survey indicated a community dominated by small rotifers and very few large copepods. There were almost no water fleas (such as Daphnia). Water fleas are great fish food. But they were not present due to lack of hardness in the water. Or, they were simply getting eaten by small fish.
The fish community was surveyed using an electrofishing boat. The fish told a bit of a different story. Honestly, the results were surprising. Only four species composed 100% of the catch. These were brown bullhead, golden shiner, pumpkinseed, and Largemouth bass. Some big bass larger than 20 inches were brought to the net. This fishery was a very simple system that was working perfectly.
The major niches were well represented by typical species doing their job well. Bullhead, a benthic omnivore occupied the bottom zone, eating invertebrates. The benthic zone in this pond was EXTENSIVE, and the bullhead probably played an outsized role. The golden shiners were large, numerous, and all one size (6-10"). Shiners occupied the semi-open water planktivore niche. The pumpkinseed were numerous with a good size structure and occupied the invertebrate picker niche in the rooted plant zone. Bass have a hard time chasing down big shiners in open water.
The bass rounded out the piscivorous predator niche. Largemouth bass were acting as well-behaved top predators.
Two questions remained. Why were the bass so big in an unproductive pond? And, why were bass not overeating the prey (as is the general rule in most simple-not-diverse and large) in this pond?
Let's take the last question first.
The main prey item for bass in this pond are pumpkinseed sunfish, then golden shiner, then small bullhead and, lastly, small bass. It's likely in that order of importance, depending on the time of year.
The bass (likely) shift predation on these prey items as they grow, shifting between prey items that are the perfect size. These prey fish have just enough cover to run and hide (in plants), so the Largemouth cannot be 100% successful in eating them all. Small pumpkinseed and golden shiner are eaten almost as they are produced. This results in a good population of large ones who are the next year's spawners. In most uniform habitat, small Largemouth bass ponds, the most common problem is that Largemouth overeat prey, resulting in bass-on-bass scenario. In this pond, just enough prey (including small bass!) makes this pond work. The prey fish buffered each other.
Secondly, why are the bass so big? Three reasons. First, this pond was not that small. Typically greater than 10 acres and sometimes even larger depending on the beaver. If they get into the pond (as they do frequently), they create new flooded habitat (and greater diversity). Second, the big bass were old. How old? Very old! The 20" bass collected in the survey were all 12-15 years old. These large bass are eating their young, reducing the number of medium-sized bass. This cannibalism frees up more groceries for larger bass. In other words, more food for larger fish.
Essentially, the largest bass in the pond are culling the smaller ones. Lastly, these fish were unharvested. Many times, the largest fish in a system are removed by anglers. Since this pond is 100% private and only fished by the family, they control the harvest. The harvest here is zero and could resemble the closest thing to an unfished, untouched, self-sustaining, balanced population of fish that I have studied. It was really cool to see an unproductive water, with so few species doing so well.
When we presented the landowner with the above explanation, it came with a warning. This pond appears to be a unique, rare, and fragile ecosystem that could quickly change if the balance of the food web were altered. The limited amount of nutrients supports a well-structured fishery that is old and slow-growing. If the family allowed fishing and harvested most of the larger bass, this would eliminate the dominant predator and would likely push the system toward stunted fish.
What about my advice (and exception to the rule?) of stocking Smallmouth instead of Largemouth in small ponds? This pond was an exception but a notable one. It was large enough, private enough, and had JUST enough habitat diversity to keep the predators and prey in a natural balance.
Keeping Largemouth bass as a well-behaved top predator in a simple pond system is hard to do—and rare. In this case, the best thing the landowner can do is leave it alone!
Keep doing more of the same, and keep the pond exceptional.
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
