news from the waterfront by Tim Matson
The Case of the Missing Fish
A while back I was visiting a weedy pond to put together a cleanout plan. Before I left, the owner mentioned another concern. “Last summer we stocked 100 trout and they seemed to be doing fine,” he said. “We fed them, no sign of fish kills. But after the spring thaw when the ice melted, no fish! Not a ripple, even when we threw in fish chow. Do you have any idea what happened?”
“Could have been a dozen things,” I said, and ran down the basic plot lines for most missing fish mysteries.
The most common culprit is an animal predator. I asked the usual questions: had he seen any heron activity, kingfishers, mergansers, otters, mink, cormorants? Nope, he hadn’t, but then again his family kept the place as a second home, and they weren’t always there to keep watch.
Okay, I said, it could have been any one or more of those fish thieves feeding while you were away. Or some two legged predators, the kind that carry a fish pole.
Just to make sure the fish hadn’t followed an urge for spawning and exited the pond downstream, we checked the spillway. But it was a screened standpipe, with no other pond overflows, so I crossed that possibility off the list.
Of course the truth is, he would never really know what happened. I did suggest that if he planned to stock more fish, he would do well to bone up on fish thievery protection. And to be realistic, be aware that an untended pond is an easy predator target. Even when you’re on site, otters and mink can do a lot of damage to a fish crop and go undetected, especially under ice. When that’s the problem, trapping may be necessary.
What follows is a basic survey of fish predators, and fish protection tactics.
Birds are one of the most common fish predators, and the easiest to identify. Herons like to stalk shallow pond edges and catch fish and frogs with their sword-like bill. They are large birds, pretty easy to spot (especially when they come flying in looking like extras from Jurassic Park), and even after they’ve departed their large three toed footprints may be easy to spot in shallow water. Herons have been known to clean out a good sized fish crop in short order.
Kingfishers are smaller birds that sound like flying castenets when they swoop in and perch in tree branches near the pond. From there it’s a short dive into the pond to spear their prey and return to ground or tree for the feast. I believe they also like crawfish, as do herons. When I find crawfish shell debris on my swim raft, I know birds have been at work.
Mergansers, cormorants, and even osprey, also like to feast in ponds.
Bird protection runs the spectrum from underwater pond design features to airborne devices, and a bunch of stuff in between. Ponds intended for fish rearing will usually benefit from rather deep shoreline slopes, which can discourge heron stalking, as well as keeping fish out of shallow edge areas where they may be easy to strike. Rafts and piers provide cover for fish trying to avoid predatory birds. Deep water habitat such as stone rubble, sunken trees, and other constructed fish shelters, also offer fish protection. Decoy alligator heads anchored in the water are also reported to scare off predators.
Louis Warlick, a commercial fish grower I know in Randolph, Vermont, recommends establishing watercress beds at shallow pond inflow areas, where trout like to gather for food and spawning; the watercress mats provide the fish protective cover. (Peak Pond Farm 802-728-5065)
There are numerous devices that can be setup on the pond shore to discourage bird attacks. Fish farmers will often rig up an electric fence line around the pond edge to deter herons. As anyone who’s used an electric fence knows, it’s important to keep the grass near the line mowed to prevent a short circuit. Nets over the pond are sometimes used by professional growers, but need maintenance, proper mesh sizing to prevent inadvertant fish trapping if the net hits water, and may make the pond awkward for other uses.
Fish predators have their own predators of course, and fish growers use a variety of critter decoys to scare off birds. I’ve used balloons with owl faces, complete with moving eyes, to scare off kingfishers and other predatory birds from eating my rainbow trout. Even more realistic decoy owls with wings that flap in the breeze are available. Other decoys include 3-D coyotes that move in the wind, and faux foxes.
Birds are also scared off by reflective tapes hung near a pond, or over the water. (There’s a berry farmer just down the road here who uses these tapes to keep birds from eating his raspberry crop, and you may be familiar with them as fruit and vegetable crop protection.)
OTHER CRITTERS, OTHER DEVICES
Noise making machines can also be deployed to scare away predatory birds and other critters. They include devices that make loud noises at random intervals, which may scare off herons and other fish predators. Some machines are designed to operate at sub sonic levels, so they won’t be a nuisance to you or your neighbors. Other devices emit sounds similar to geese in distress, which won’t save your fish (geese are vegetarians), but might deter these waterfowl from fouling your pond and shoreland. Rotating flashing lights can also be used to scare off birds. These may be especially useful at night or in low light situations when reflective ribbons are not working, or when winds are flat and not animating animal decoys.
Bird-X offers a comprehensive selection of devices to help protect your fish crop as well as deter mess making geese, all without harming the animals. Which is nice, considering that many birds are a valuable part of wildlife ecology, as well as protected species and illegal to kill. The folks at Bird-X suggest that you’ll get the best results from critter deterrents if you mix several different types, and move them around periodically.
Before signing off, and lest you get the wrong impression from this lengthy litany of animal repellants, I happily admit to getting lots of pleasure from watching a variety of critters visit my pond. Geese stopping by briefly during migration; kingfishers and herons occasionally stalking crawfish and frogs; wild ducks and turkeys, deer, moose, etc. I think of my pond as a wildlife habitat as well as a swimming and skating pond, as I know a lot of other pond owners do. But if I were losing pricey stocked trout to bird predators, or if the geese decided to move in long term, I’d be checking out repellants. And remember, fish can also be raised in protective cages, but that requires feeding and maintenance; we’ll cover cage culture in a future Pondology. Happy hooking.