Green Sunfish Overpopulation - Ask Extension
Hi. I purchased a home with a 1/4-1/3 acre pond 2 years ago. I have battled the usual duck week, algae, muck, etc. put in aerators and have finally go...
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Green Sunfish Overpopulation #760439
Asked July 07, 2021, 1:29 PM EDT
Hi. I purchased a home with a 1/4-1/3 acre pond 2 years ago. I have battled the usual duck week, algae, muck, etc. put in aerators and have finally gotten the pond hopefully healthy again. My concern now is the population of fish. I have caught over 100 green sunfish less than 6 inches long in the last 3 weeks. 43 in one day! No other fish species have been caught. Have been researching, and have found conflicting information. Some say to add predator fish (ie Medina Soil and Conservation), such as bass, others say renovation, killing all fish and starting over. I have abundant wildlife, and would hate to disturb the ecosystem I have. Your guidance would be very much appreciated!!!
Medina County Ohio
Expert Response
This is really unfortunate news, dmalson77. Green Sunfish are ivery cool animals . . . in the expanse of wild waters. They can wreck small, managed ponds.
The problems Green Sunfish pose to managed ponds are manifold: (1) Most fishes are gape-limited predators, certainly most native to Ohio. Green Sunfish mouths are relatively much larger than other sunfishes (Lepomis spp.) at similar length. They are thus much more competitive for food resources than other longer sunfishes would be. (2) Sunfishes are aggressive, and Green Sunfish are especially so. In larger numbers, with their big mouths, they can substantially suppress other fish populations, especially sunfishes. (3) They are prolific in making a lot of babies. Given these characteristics, they can quickly dominate ponds where close proximity forces them into competition with other species.
You can try to suppress their numbers by stocking substantial numbers of the largest Largemouth Bass that you can afford to buy or that local hatcheries have available. However, top-down eradication via predation isn't likely, and the situation may eventually degrade again as remaining Green Sunfish rebuild their population. Also, so long as a viable population of Green Sunfish remain, you aren't likely to establish a fishery for other Lepomis sunfishes in a small pond.
The most likely reliable "fix" is to contract eradication of the population using a registered fish toxicant (usually rotenone: only licensed applicators can legally apply such pesticides) and subsequently restocking to initiate the fishery you'd like to have. Unfortunately, that will be expensive and (as you've surmised) is certainly very intrusive. Still, the pond is essentially a managed artificial environment and will recovery relatively quickly in response to your actions to follow.
Sincerely sorry to bear this news. Please stay in touch if more info comes to light.
Luck!
Eugene
The problems Green Sunfish pose to managed ponds are manifold: (1) Most fishes are gape-limited predators, certainly most native to Ohio. Green Sunfish mouths are relatively much larger than other sunfishes (Lepomis spp.) at similar length. They are thus much more competitive for food resources than other longer sunfishes would be. (2) Sunfishes are aggressive, and Green Sunfish are especially so. In larger numbers, with their big mouths, they can substantially suppress other fish populations, especially sunfishes. (3) They are prolific in making a lot of babies. Given these characteristics, they can quickly dominate ponds where close proximity forces them into competition with other species.
You can try to suppress their numbers by stocking substantial numbers of the largest Largemouth Bass that you can afford to buy or that local hatcheries have available. However, top-down eradication via predation isn't likely, and the situation may eventually degrade again as remaining Green Sunfish rebuild their population. Also, so long as a viable population of Green Sunfish remain, you aren't likely to establish a fishery for other Lepomis sunfishes in a small pond.
The most likely reliable "fix" is to contract eradication of the population using a registered fish toxicant (usually rotenone: only licensed applicators can legally apply such pesticides) and subsequently restocking to initiate the fishery you'd like to have. Unfortunately, that will be expensive and (as you've surmised) is certainly very intrusive. Still, the pond is essentially a managed artificial environment and will recovery relatively quickly in response to your actions to follow.
Sincerely sorry to bear this news. Please stay in touch if more info comes to light.
Luck!
Eugene
Thank you so very much for responding Eugene, even with not so nice news. It is what it is, and I don't discourage easily. I've tried to find a registered fish toxicant applicator in Medina County to at least get an idea as to cost, and cannot locate one on the internet. Do you have an avenue or list available? I also thought about building and using large fish traps along with trying to find large mouth bass (which were not available in the spring of this year it seemed). Would I still be continually fighting a losing battle? Thanks! Debra
Oops. Sorry for delay, Debra. I'm not sure how I missed that you'd reopened this thread.
Well, I don't know that the cause is wholly lost (although it may be regarding the possibility of viable fisheries for other species of Lepomis-genus sunfish). If there is to be hope in a situation as you've described, it would likely be in establishing and sustaining a bass population, restocking if there's evidence that they're not doing well. Unfortunately, because of intraspecific competition, large numbers of Largemouth Bass might never grow well . . . but they may be able to keep a Green Sunfish population in check. Fewer fish (if they can't effectively spawn and recruit in the presence of a large Green Sunfish population), would likely exhibit better growth, but would need to be restocked with greater frequency. It's complicated and hard to know how it would play out without actually running the "experiment" on your site.
Even if local hatcheries don't have Largemouth Bass in the spring, most who raise them should by fall. Many soil and water conservation districts (SWCD) will have Largemouth Bass available through an annual fish sale. Medina may as well.
There are a couple issues regarding trapping Largemouth Bass. In general, the black basses (genus Micropterus, of which largemouth is one) tend to be wary of traps. Large numbers don't trap easily unless from habitats where their densities are abnormally high, i.e., where they're crowded. The other is that Largemouth Bass are managed and regulated as game. You cannot trap them frompublic waters without a specialized collection permit (which aren't issued to the general public). You are welcome to harvest them on a recreational license using rod and reel, but you're then limited to the catch limits specified in Ohio's fishing regulations. (Note that if you have a friend with an isolated, private pond, the previous statements don't necessarily apply. Have at it.) Lastly, be mindful of moving wild fish. That always comes with some risk, even if slight, of introducing disease to your pond. That risk is less with fish purchased from hatcheries that deliberately manage against disease.
I can't personally know of all the locally active pesticide applicators around the state. As an absolute last resort, I do have a list of all the state's pesticide applicators that are specifically licensed to apply products to water. That list isn't really practical for public consumption because (1) it was extracted at my request about six years ago (it's not something I do every day) and (2) it includes everybody so licensed; that might be an individual who only works for a single golf course, residential property manager, etc. I would recommend starting by asking Medina SWCD if they know of local applicators. Because I've mentioned their utility a couple times above, https://medinaswcd.org/
Do stay in touch if I can be of any service as this unfolds. You're always welcome to use my direct contact info below.
Best,
Eugene
Well, I don't know that the cause is wholly lost (although it may be regarding the possibility of viable fisheries for other species of Lepomis-genus sunfish). If there is to be hope in a situation as you've described, it would likely be in establishing and sustaining a bass population, restocking if there's evidence that they're not doing well. Unfortunately, because of intraspecific competition, large numbers of Largemouth Bass might never grow well . . . but they may be able to keep a Green Sunfish population in check. Fewer fish (if they can't effectively spawn and recruit in the presence of a large Green Sunfish population), would likely exhibit better growth, but would need to be restocked with greater frequency. It's complicated and hard to know how it would play out without actually running the "experiment" on your site.
Even if local hatcheries don't have Largemouth Bass in the spring, most who raise them should by fall. Many soil and water conservation districts (SWCD) will have Largemouth Bass available through an annual fish sale. Medina may as well.
There are a couple issues regarding trapping Largemouth Bass. In general, the black basses (genus Micropterus, of which largemouth is one) tend to be wary of traps. Large numbers don't trap easily unless from habitats where their densities are abnormally high, i.e., where they're crowded. The other is that Largemouth Bass are managed and regulated as game. You cannot trap them frompublic waters without a specialized collection permit (which aren't issued to the general public). You are welcome to harvest them on a recreational license using rod and reel, but you're then limited to the catch limits specified in Ohio's fishing regulations. (Note that if you have a friend with an isolated, private pond, the previous statements don't necessarily apply. Have at it.) Lastly, be mindful of moving wild fish. That always comes with some risk, even if slight, of introducing disease to your pond. That risk is less with fish purchased from hatcheries that deliberately manage against disease.
I can't personally know of all the locally active pesticide applicators around the state. As an absolute last resort, I do have a list of all the state's pesticide applicators that are specifically licensed to apply products to water. That list isn't really practical for public consumption because (1) it was extracted at my request about six years ago (it's not something I do every day) and (2) it includes everybody so licensed; that might be an individual who only works for a single golf course, residential property manager, etc. I would recommend starting by asking Medina SWCD if they know of local applicators. Because I've mentioned their utility a couple times above, https://medinaswcd.org/
Do stay in touch if I can be of any service as this unfolds. You're always welcome to use my direct contact info below.
Best,
Eugene
