American Mink on rock

One of the sad facts about becoming a koi keeper is that when you build your koi pond outside, your koi become part of the circle of life. That means your Living Jewels are subject to both the beauty and the danger that nature entails, including predation.

Mink Appearance and Behavior

The American mink (Neovison vison), although not quite as feared as the otter, is equally reviled among koi owners. They can grow anywhere from 18-30” long and weigh 3-5 pounds. They do have some color variation but are primarily dark brown with rounded ears.

Do not be fooled by the Pond Wolf’s “cute” furriness: the mink is a member of the Mustelid (weasel) family and is a koi-killing machine. It can clean out your pond overnight. And once it has discovered the smorgasbord in your backyard, it can return as often as three times a day until there is nothing left. Mink will also kill more than it is capable of eating, even storing leftovers for later consumption.

Similar to other Mustelids, mink are wily hunters. They are intelligent and agile predators, using their faculties to bypass any deterrents that koi owners employ to prevent turning their pond into a drive-thru. Once a mink has found a ready meal, it will come back to your pond repeatedly.

A mink is an excellent swimmer and can dive over 10 feet, so your 6 foot koi pond will not be sufficient to stop it from reaching your deepest-swimming koi. And nets aren’t going to keep mink out either. Neither are wooden fences. Or above-ground ponds.

Mink are primarily nocturnal hunters, making them difficult to spot. Mink capture prey by the throat and will routinely attack targets larger than themselves. They’ve been known to carry off a 2 foot fish. Here is a picture of mink trying to take down a swan!

Mink in the SnowWinter will not deter mink from raiding your koi pond, either. In fact, if your fish go missing in the winter, it may well be a mink that is the problem. Their prized fur is oiled so they are insulated against the cold water. If they can make it under the ice, they can fish underwater for almost half a minute to find a meal.

In summer, your koi might have a chance to out-maneuver the mink. But during winter, koi make a much easier, slower target. And, with its other food sources diminished, mink will come looking for a small reservoir that is well stocked with meals.

Mink Habitats

Mink are found across the United States and Canada. Although they prefer wet environments (swamps, marshlands or close to rivers, lakes and streams) with ample vegetation to slink away in, a mink can rough it in drier areas if there is enough food. However, drier more arid southwestern states (NV, AZ, CA, NM, UT, TX) are not natural habitats of mink.

Mink are more prevalent in rural areas, preferring the quiet life (as well as the extra cover that the thicker vegetations offer). They may be shy, but these koi predators do not scare easily— and even less so when they are hungry.

Mink are solitary, territorial creatures. If you have a mink, it is probably only the one. However, there are anecdotal stories of koi keepers claiming to having been visited by numerous different mink.

How Do I Know That I Have A Mink in My Koi Pond?

When you are missing fish and it’s not because a giant bird is circling overhead, there is a decent chance that you have a member of the weasel family in the neighborhood. They might leave a few scales behind as a calling card when they drag their catch off to a safer space to feed. Mink have also been known to leave a neat stack of their kill, too.

Mink with prey in its mouthIf you live near a water source (like a creek or a stream) and are losing fishi, a mink in your neighborhood might be purloining your koi.

You may also smell something that is akin to a skunk. Like the skunk, the mink can secrete a pretty terrible stench from its anal glands to mark an area or to keep its own predators at bay.

Mink are not particularly careful predators, either. They will disturb anything loose around the edge of your pond (rocks, potted plants, decorative pieces) in pursuit of your koi. They will also leave a murky pond, kicking up sediment, soil or muck in or around the water.

You can also check for tracks. As light as they are, mink will leave small tracks in the snow or mud around your pond. They resemble kitten tracks.

If you happen to find small bite wounds at the back of you koi’s head, it is a telltale sign that you have a mink nearby. They may also pile up kills in a neat row.

Deterring and Preventing Mink Predation

It’s tough to keep a mink away from its meal. They are hardy and courageous creatures that aren’t easily dissuaded, and, if they are, it’s usually not for long.

Many koi keepers will weigh in on how difficult it is to keep a mink out of a pond. They can fit through incredibly small holes. And if there is a hole big enough, rest assured, they will find it. Caulk, foam or find something to plug any gaps you have in fencing

Those that deal with mink problems recommend employing numerous deterrents and layering them to dissuade mink from gaining confidence or becoming accustomed to them.

Additionally, moving your repellents around and not leaving them in the same place will also keep the mink in its place.

Traps

Mink caught in a trapThis is one of the most effective means of addressing your mink problem. Mink are not considered endangered species so trapping is allowed; however, it is often only during a particular season. You will need to check your local codes to see when trapping season is and what you will require if you are trying to trap out of season.

There are numerous types of traps for mink. Research the ones that are most effective for what you are trying to ultimately accomplish.

Mink are wary of anything new, so making it look like part of the environment will be helpful. Cover the wire mesh with dirt or leaves to camouflage and help it look more natural. Additionally, they will be able to detect a new scent, so consider handling the trap and the bait with gloved hands.

Place the traps along the route that the mink take as they are more likely to investigate the meal that you are offering.

If you aren’t comfortable with trapping or aren’t having any success, you can find professional trappers online.

Sound and Lights

Mink have great hearing, and they are able to detect the ultrasonic noises made by its rodent prey. They are also sensitive to high frequencies. Some enthusiasts have used motion-activated sound repellents to good effect.

The same goes for lighting. As nocturnal creatures, mink rely on the dark of night to hunt. A motion activated spotlight can startle them enough to drive them away. It may, however, only be a temporary fix.

Fencing

As with many of the types of deterrents, there are those that have enjoyed success with electric fencing around their ponds and others who have installed it only to have fish still go missing.

Remember to observe the usual protocols to make the electric fencing effective (and also so as not to zap yourself!).

  • Remove debris from around the fencing
  • Employ the correct voltage
  • Use the necessary number of wires
  • Space wires and poles correctly
  • Mark the lines
  • Check it frequently

Chicken wire with holes less than an inch in diameter is sometimes employed by koi owners to fence off the area around their pond, especially the lower part.

In some instances, koi kichi will create a wire covered frame to lay over a pond to stop mink from slipping into the water. This is only as effective as the area it covers however. If there are any spaces around the edges, mink will still get under it.

Dyes

A mink’s visual acuity under water is not as good as on land. Some enthusiasts have enjoyed decent success keeping mink out of a pond by adding a dark-tinted dye to their water to make it more difficult for mink to see the koi underwater.

Motion-Activated Sprinklers

As a water-based predator, mink are not deterred by the water itself, but rather by the rapid and unexpected spray.

Regardless of what methodology you decide to use, get it up and running as quickly as possible as it won’t take long for a mink to decimate a koi population.

As always, prevention will go a long way. And as expensive as it may seem to keep them out, it is nearly always more expensive to get them out once they have gotten in. And the emotional loss is more than all of it.

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