Predator Control – Otters: Unwanted Visitors

What does over four miles of fencing have to do with koi? Our story started a year ago in early November. By that time we had culled through over 5,000,000 fry and grown our (fish) crop of koi, butterfly koi and goldfish as much as we could until spring when the water warms. We had invested many, many man-hours and fed tons of food to get the crop to this point. The “keepers” are in the mud ponds, settling in for the winter, and awaiting harvest in February when the culling and sales will resume. At this point we knew what was in each pond, based on stocking densities, feeding rates, and the size of the ponds.

Last February, we started harvesting for the second cull and found that many ponds had produced only 40 to 50 % of what they should have. Some ponds were missing over 90% of fish stocked! All that time and money spent on food, only to discover that so many of our fish were missing. We’ve always lost some fish through the winter, primarily to Blue Herons, but this was ridiculous.

We soon discovered what the problem was – river otters. Both North Carolina and Virginia have re-introduced them into the wild over the last few years. In the words of one wildlife official, “they’ve done quite well.” It turns out that otters are virtual fish eating machines. If you’ve ever observed them at the local zoo, you’ve seen that they are constantly on the move. All that activity burns a lot of calories, and for otters, those calories come from fish.

The otter can weigh up to 50 lbs. and need to eat at least 25% of their body weight each day to survive. For some perspective, that would be 600 – 3˝ koi or 80 – 6˝ koi per day! As you can see, it doesn’t take many otters to devastate a fish crop. All of our ponds drain into adjacent creeks and rivers where otters live and travel, so we were an easy mark. You can’t much blame them for making themselves at home. They’ve spent their life catching only bass and trout in the river and then they suddenly discover a koi farm where there are wall-to-wall fish of every size and color. Apparently our farms had become a gathering place for otters from miles around.

The next question we asked ourselves was “What do we do now?” We were able to trap a few during their season, but not enough to make a difference. So after much discussion, we decided that if we were going to stay in the fish business we would have to fence them out. Our research showed that otters are pretty wily animals and can climb over or dig under most fences, especially when there is an all-you-can-eat buffet on the other side. So we took the plunge and invested in over four miles of 4´ tall, 3˝ mesh fencing. We added four strands of 7000-volt electric fence wire, one as close to the ground as we could get, another 6˝ above that and two more at the top.

As of this writing, it seems to be working. We’ve seen otter tracks leading up to the fence and none on the other side. We’ve seen evidence of one attempting to dig under, but he was deterred and gave up.

We’ve had customers report that otters have wiped out their display ponds in one night. So if you have any kind of pond relatively close to a creek or river, beware of the otter!

About the Author
Randy LeFever is President of Blue Ridge Fish Hatchery, one of the largest Koi and goldfish farms in the US. He has been involved in the production and distribution of high quality koi and Butterfly Koi on a national basis for over 30 years. He’s credited for naming and introducing Butterfly Koi to the US market in the 1980’s.

Blue Ridge Fish Hatchery
4536 Kernersville Rd.
Kernersville, NC 27284
1-800/334-5257
Fax 336/784-4306
Email: staff@blueridgefishhatchery.com
Web: blueridgekoi.com