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!
Winter 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.
If 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
This 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.
Over the last 10 days (end dec 2019, early Jan 2020) my pond has been decimated of fish; both koi and goldfish. Specifically about three koi 15+ inches, two about 9” and half dozen or so babies about 6”. The three dozen or so goldfish missing were a combination of pretty fantail and more common goldfish. As of yesterday all that remains are two of the larger koi and three or so small goldfish.
Background:
Live in Cleveland OH. Just three miles out of downtown with a city zip code
Have had this large pond for about 5 years now.
Completely net it over the winter. We thought to mostly keep out leaves/debris. Used planks and heavy landscape stone to hold netting in place
NEVER had an issue during winter. Spring/Summer though we’ve done battle with heron
Yard fenced/gated
We could find NO point of entry into the pond. Nothing, that we could see, was disturbed
Thought we ‘maybe’ saw a few scales in the deeper end but not 100%. Doesn’t really matter…..we know they’re dead.
I give much of this detail to make a point that this (whatever is it) can happen to anyone, anywhere, anytime. We’re quite sad as we’ve thoroughly enjoyed the process of training to hand feed, moving fish eggs for protection and have both koi and goldfish babies over the year. Even had some pvc in pond for fish to hide in.
We’ve now taken the “hoops” from the pond and laid the netting on the waters surface and “secured” the net best we can. I set three rat traps with salmon on them. As of this writing it’s day two and none have been snapped. Not sure whether we’ll restock. I want to but we’ve lost four years of history and though it’s nature doing what nature does – I feel bad for the fish.
Any thoughts or suggestions would be of interest.
We are very sorry to hear about these tragic losses. If the fish are missing from your pond and you are finding no evidence of remains, it is likely due to a predator. Blue Herons and raccoons are usually at the top of the koi fish predators most wanted list and can be a nuisance year around. You can read more about these two via the links below.
https://nextdaykoi.com/koi-fish-facts/koi-predators-heron/
https://nextdaykoi.com/koi-fish-facts/koi-pond-predators-raccoons/
Perhaps someone else reading this could provide additional suggestions.
Thank for your reply.
We’re pretty convinced it’s something stealthy (ie mink) because as I mentioned the pond is totally covered by netting and zero notice of disturbance. So a bird can’t get in and a clunky coon wouldve left a calling card nor swam down 4’ to catch/kill the fish. It’s all too late. Now need to decide if pond gets ripped out and becomes a swimming pool or the pond simply becomes a water garden. We don’t want to go through this again…..and the poor fish.
We understand. Again, we are sorry that it appears something got to them. We hope you come to a conclusion about your pond soon.
We live in Hinckley–just a few miles south of you–and our neighbors have seen a mink in the creek behind our property. Our small pond has a variety of hideouts for the fish: these include a cement mixer tub with holes and numerous 2″ and 3″ PVC mazes. Earlier in the summer (early July ’20 the fish (Koi, goldfish, shebunkin, minnow) were terribly spooked by something and, fortunately, nothing went missing. I then installed a fishline fence around the perimeter, purchased a couple of ultrasonic deterents (waste of $, imo) and a motion-activated sprinkler. I also play talk radio throughout the night. I trapped one baby racoon in the middle of summer, but never a mink. After a few months the fish finally became less skiddish (it is now 25 Sept 2020) but, unfortunately, something really spooked them last night. They are refusing to come to eat when I knock on the rocks…..my next line of defense will be a couple of bright motion-activated flood lights. I hope you have had a great summer enjoying your pond, and good luck to all Koi enthusiasts!
Wow! I have the exact same story from New England. At first it was a Heron, easy to deter with fish line and a few motion activated things, then 2 raccoons humanely trapped one day after another and driven a far distance to be released. But one winter even with the pond frozen over every single koi and gold fish was gone, small large it didn’t matter. Except my largest which I called jaws because it must’ve been 2.5 feet long. One day I caught a glance of the suspect, a mink skipping across the snow, but by then it was too late. After 6 years of maintaining and loving my expensive koi, I gave up, had it filled in and built a putting green.
We have a mink that just killed my 6 lb koi 3 of them over the winter… very upset.. forget trapping. If I see the thing again the the gun is coming out..
I just lost an entire koi pond of about 30+ koi ranging from 5in babies to large multi-pound koi. Some I had for more than 2 decades. I live in NJ and the attacks happened in early Feb 2020. No ice at all. Very sad as these fish would swim right into your hand to be fed. Large butterflies, fantails and rather beautiful coloring on all. 2 of the largest survived the first night attack. One swam inside my filter box to escape and the other went far up my stream. Everything is covered with frames and netting for the entire winter. It didn’t matter to the mink.
I even put alot more netting held with heavy rocks to protect the 2 survivors after the first attack. It didn’t matter. 2 nights later my survivors were gone without a trace. Netting will not stop them. I’ve had traps out for the last 4 nights but only caught a large raccoon. My pond is too deep for a raccoon to be a threat. I’m sure the mink will return but now I have alot more traps with sardines for bait that should be to irresistible. At least I hope so.
Very sorry to hear about the trouble you’ve had with the Mink. It does not sound like it will be easily deterred. We hope the traps are successful in protecting your remaining koi from harm though.
Does anyone know……once your pond is completely cleaned out by some predator, guessing a mink, do they move on and far away or once close are they always close? Asking because trying to determine if I want to restock and start over. And yeah…..if it happened once it could happen again but I had 4 fortunate years of no winter predator in my covered pond. Thx
Thank you for sharing your experience. We are very sorry to that a possible mink cleaned out your pond. We would have recommended covering your pond or maybe setting up a motion sensor activated device. Unfortunately, mink are fairly clever predators. Perhaps someone else on this thread could offer some advice on how to further prevent losses from the pond.
Unfortunately they do return. I had beautiful Koi that were kllled three times. I double netted my pond but that did not work. I had a night light and that did not work either. I noticed the mink came during a storm. We live on a lake so they are literally right in our backyard! My husband and I deflated. I have cried so much about our loss those poor innocent fish were all killed. Luckily we got outside to bury their bodies so when the mink returned they could not find them as they had scattered our fish all in different hiding spots. We are not sure we can go through this again. Really angers me because we can’t even enjoy having fish in a pond because of these nasty good for nothing creatures. So sorry for everyone’s loss I know exactly how you all feel. It is devastating but they return!!!!!
I know I am responding to an old post, but wondering what you ended up doing. I had 20 18” koi disappear in December 2018. I suspect a mink but never saw it. Pond was securely netted with no signs of disturbance. I just wanted to cry. I was afraid to restock, but was given 2 koi in 2020 & prayed they would not suffer the same fate, because I love my pond & didn’t want to fill it in (my husband’s threat). They are still around, and this summer I was lucky to be given 8 12” koi. They aren’t as beautiful as the ones I lost, but they didn’t cost me anything. I may think about purchasing next year & pray that whatever took them 5 years ago will not come back. I can’t believe I was this patient & that my husband hasn’t filled it in.
Having lost around ten fish to a heron and defeated it with a frame of thin branches and chicken wire, we now have been targeted by a nocturnal swimming predator that’s not an otter!
Sept. 18th I moved ALL the survivors into a tank, had to drain the pond to catch them. Then built a heavy duty frame over the whole pond and chicken netted the lot right down below water level.
Lost 27 fish in the tank! Ammonia/oxygen levels I guess.
Been raided again since as the mink has wriggled through tiny spaces in rocks. Went in the pond in my wetsuit and found the exit which I stuffed with wire. Down to very few shy fish, one with massive wounds to the tail.
Have a motion sensor halogen lamp pointing towards the likely access trail and a basic wildlife IR camera.
Determined to fight to the last and try to save the survivors who’ve been through hell as I raised them from fry and they all have niknames.
Pest control due out on tuesday as mink are ‘vermin’ here in UK.
Will gradually reinforce the net deffences if the predator will slow down its efforts long enough!!
We took a different approach. Since our koi pond had an irregular shape it made it almost impossible to put up a physical barrier to keep mink and other predators out. So we decided to put the fish in a confined environment. I bought an 8’ piece of 18” diameter plastic culvert pipe. I made mesh screens for each end that can slip in from the top. When the fish start going dormant, we round them up and put them in the culvert pipe and close up the ends. Worked great the first year! For the second year we did a slight re-model and added skylights (screens) to the top so that we could see the fish and they would have a little daylight. Total cost was about $120 and a few hours of my time. We store the pipe in the backyard during the summer months.
If you would like photos, I would be happy to send them.
I have a koi pond in my backyard and had around 20 large koi as long as 28”for about 5 years. No problems then one fall and early winter my pond was cleaned out by mink. I gave up on the koi because I have a small creek behind my house with bike trails on both sides of the stream. Well this last fall someone gave 42 koi around 20” long. I had problems as soon as the weather turned colder here in Iowa. I lost 10 fish in less then 10 days and even saw the mink in the daytime going after the fish. I finally built a cage 4’x 3’ x 2’ out of pvc and heavy plastic fencing. That saved the koi for now. I’ve started setting traps out in the last 2 weeks and have caught 2 mink and 1 raccoon.
I have a koi pond and much to my surprise a mink was at the edge of the pond in the middle of the afternoon. I must have not chased him away in time because he got 5 of my 16 fish. Perhaps it happened the night before. I thought that mink were nocturnal. Any thoughts.
Also, is there any thing that they hate the smell of that will keep them away?
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We had a goldfish in our pond that was at least 14 years old (Megladon) and about 50 other goldfish – gold, black, frilly white. We have successfully fended off herons, owls, hawks and coons for years with double netting staked over the shallow end while in the deep end (5 feet) the fish hid under the shelf of the waterfall and the lilies. We have motion sensing lights too- as well as two loud dogs. We had a few wet footprints one night and most of the fish were gone. Put a second net over the deep end overlapping them weighted with rocks and plants thinking it was a coon. Nope, mink, and we lost Meg….We have about a dozen fish left (mostly black) and with the warmer weather, netting thoroughly staked down, coyote urine and letting the dogs out in the middle of the night, we are holding on. Breaks my heart though to where I don’t want the pond any longer because I can’t stand to see a family member like Meg die.
I’ve lost many families of koi through the years to mink. The only successful protection I’ve had is to build a cage. We use small chicken wire coated with rubber to eliminate rust and contamination. We frame with PVC and lower into the deepest part of the pond.
I have given up on trapping mink. It seems impossible unless I am present when they appear.
Good Luck
I had my pond for 14 years & never had a problem until December 2018 when my 20 18” koi just disappeared. We are sure it was a mink because the pond was very well netted & it was winter. Although the netting showed no disturbance, I understand mink are very good at what they do…otherwise, it was “Scotty, beam me up”.