The Fish Professor- Making a Stocking Correction

 The fish population in your pond is dynamic and always moving, shifting, and changing. There are reproduction booms, predators eating prey, fish harvested for the frying pan, and mortality from natural causes. As pond managers, we do the best we can to understand these factors to match goals we set for our pond—within reality. Even though the goals may be well defined, the fish in the pond may not follow the perfect plan. When Mother Nature throws you a curve ball, you may need to adjust and take some corrective action including the possibility of an alteration to the stocking plan.

First, we need to be aware there is a problem, which requires information. As an example, think about a 2-acre pond with Largemouth bass mixed with Smallmouth bass with a primary goal to have catchable populations of both species—in good numbers—and bass big enough to bend the rod, with enough excess to eat one if you hook it too deeply. Left alone and unmanaged, with these two different species in your pond, the Largemouth will likely take over and eliminate Smallmouth. Worse, if there are few baitfish and sunfish to buffer predation of Largemouth on bronzebacks, the Smallmouth population will decline and domination by Largemouth will happen faster. Track your fishery. Catch some fish and capture information on and sizes and numbers of Smallmouth and Largemouth to collect important information needed to make critical decisions for managing this fishery. Keep a diary of fish caught. If anglers are catching more Largemouth than Smallmouth, and the Largemouth are larger, then they are on the verge of dominance. 


What to do? 

Fish out (cull) some Largemouth bass in the 8-14” range and eat them. Invite friends and family over for a tasty Largemouth fish fry. Try ceviche, it’s tasty. Then stock some Smallmouth bass! How large should they be? At least 10-12” and at 25/acre. If you can’t buy Smallmouth so big, stock more numbers and expect some attrition. But, culling Largemouth first is important. Remove as many Largemouth as you can catch. Why? Because you won’t catch them all during the cull—and the Largemouth will be back. Plus, in 2-3 years you will have the same Largemouth problem again. There is a caveat here, though. It’s okay to be a little bit selective while culling. Remember, aggressiveness is an inherited trait. If you cull most of your aggressive-nature bass, you can influence the population where culling is even more difficult. It’s okay to select bass according to body condition and aggressive behavior. Catch a fat, mean one and release it.

Should fathead minnows be added on top of bass? In my opinion, and in most cases, no.  It’s a waste of money. Stocking fathead minnows on top of bass just temporarily feeds bass with no hope of establishing the minnows. Further, 90% of the minnow biomass is lost as only 10% of the minnow energy goes to bass growth. Essentially, bass eat 10 pounds and grow one. Note: if you are fine with this financial and biomass loss, then do it—after all, I feed other pets every single day. The juice just isn’t worth the squeeze.

In this situation, corrective stocking of sunfish in spring may help the situation. Stocking large sunfish (I like pumpkinseed here in the north) in the spring before spawning can help buffer predation. The large sunfish should be able to avoid predation and pull off a successful spawn.

What about stocking bluegill? As we have discussed in these pages before, bluegill are really the only fish that will expand their population in the face of Largemouth bass predation.  Rarely are Largemouth bass well behaved. They eat everything. 

Have or get information on bass-bluegill catches. If bluegill are overpopulated and stunted, and there are only a few big Largemouth, the bluegill are on top and eating bass fry, limiting Largemouth recruitment. Solution: corrective stocking of a few more bass. How many? Not many in a small pond. Maybe stock ten to twenty-five 10” largemouth per acre to knock down those stunted bluegill. And, what if there are millions of stunted 8-10” Largemouth and only a few large bluegill (which is a VERY common problem around here)? Cull every Largemouth possible, and then correctively stock 100 large bluegill per acre. That size bluegill can be found. If they are smaller than ¾ the size of the average Largemouth bass, the stocking may not help because the bass will just eat them. If bass are stunted at 8-10”, stock bluegill that are at least 6” to give them a chance.

Let’s move from bass and panfish to trout. In a trout pond in the north, as many as 50% of the trout will die in a typical year. A 2-acre pond, 12 feet deep, and stocked with 100 trout in 2018 will likely only have 25 trout left in 2020. Will the trout spawn on their own in the pond, replacing themselves? No, not likely. A self-sustaining trout pond would have a specially designed spawning box, and the trout to stock is a brook trout. Brookies are the species that will use the spawning box reliably. Successful trout reproduction requires aerated, cold water percolating through clean gravel to incubate eggs. Unless a pond has a nice gravely stream flowing into the pond, trout need to be maintained through a regular stocking program. Why do the trout die in such large numbers? Two reasons primarily—heat stress and low dissolved oxygen. Trout need cold, well oxygenated water all the time and in most North American ponds, this zone of cold, oxygen rich water is in short supply in the summer. Generally, this means the pond needs to have a large volume of water with good oxygen AND a depth greater than ten feet.  The larger the volume of cold, oxygenated water there is, the more trout that can survive. Another confounding factor, warm water holds less oxygen. This means in summer when water temperature increases, dissolved oxygen decreases by the physical nature of water itself. My pond is 10’ deep and I can over-summer trout every other year. Every two years they all die.  Why? It’s too warm (>70°F) even in a high elevation of 1650’ in my upstate New York pond.  So, if I want trout, I need to restock when they die. Knowing that they are likely to perish, I might stock (my favorite!) large tiger trout (>12”) in the Fall so that we can immediately enjoy them. If they die, it will likely be in August of the following year, so we can have fun catching them for most of the year before they have a brush with heat death. And, if they make it to September, I am good for another year. Bonus.  

If the goal is to stock trout on top of trout, replacing larger fish that are aging out and dying, revisit the example above. We started with 100 trout that were stocked at 12” and after Year-1 they are likely 14-15”. Plan to stock at least 25 more 12” fish that year if there is no harvest. If the goal is to wait until Year-2, plan to stock 50-75 trout. Depending on the pond, waiting until Year-3 or 4 may result in total replacement of all 100 trout. In most ponds, trout die and should be considered a put-grow-and-take (or die) fishery whose numbers are kept up by a regular stocking plan. Rainbow trout are usually the most available trout for stocking and are a great option because they are usually well trained to a feeder. Brown trout can be more aloof and can create feeding problems. Monitor the fish closely and adjust every 1-3 years depending on your pond.

Sometimes corrective stocking just means adding the RIGHT fish. I was recently at a beautiful local pond that was green with planktonic algae. The only goal the owner had was a pond that was clean and clear to swim in and enjoy. The owner did not give one hoot about fish.  Not one! But the owner also hated the green water. A quick shore seine netting revealed millions of small golden shiners. An abundance of planktivorous fish (such as these shiners) can crash a zooplankton population, causing a decrease in water clarity, making it green. This pond’s green water was caused by a lack of zooplanktonic grazing. Too many baitfish? Stock a predator. In this case, we recommended 50 ten-inch Smallmouth bass to knock down, but not eliminate, the golden shiners. Adding the smallies brought balance to the plankton-prey-predator relationship. In this case, adding Smallmouth to a pond that had none helped water clarity by allowing the zooplankton grazer population to expand and graze the algae. Sometimes subtle changes in the food web where nutrients are locked up, make a pond look completely different. A correction of the addition of 50 ten-inch Smallmouth turned a green pond into a clear one over the course of a year.

Corrective stocking can bring a pond back into compliance with the stated goals, and it might even bring back some natural balance to the pond. The limiting factor to corrective stocking is the access to good information. Keep good records of catches. Have the water quality monitored by a professional. Above all, pay attention. Are fish starting to stunt? Are trout starting to disappear? Is water turning green or excessively clear? Corrective stocking may be part of the solution. 

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