The Long Read: Are otters depleting fish stocks at Banbury Reservoir?

Grimsbury Reservoir, Banbury. NNL-180805-130517009
Grimsbury Reservoir, Banbury. NNL-180805-130517009

Despite their cuddly appearance otters are ferocious predators sitting near or on top of the freshwater food chain.

For the past five years Banbury anglers have seen a rise in the number of fish found dead at Grimsbury Reservoir, located off Hennef Way, as a result of otter predation.

Grimsbury Reservoir, Banbury. NNL-180805-130528009

Grimsbury Reservoir, Banbury. NNL-180805-130528009

The signs of an otter attack are unmistakable. Larger fish are disabled by the otter biting off parts of the fish’s fins, the otter can then kill the fish but will only target the organs, particularly the liver as potential meals.

Fish carcasses with these telltale signs of otter predation have been appearing on the banks of Grimsbury for many years.

A former BDAA committee member, who wished to remain anonymous, said: “The otter problem has probably been going on for five years. We knew of six fish that had perished in about 12 months. But that is six fish you know of because they have been washed up on the bank.”

The reservoir is owned by Thames Water which, in turn leases it to the Banbury and District Angling Association (BDAA) which takes care of the day-to-day running, the collection of day fishing fees and the security of the water.

A fish at Banbury Reservoir with the telltale signs of otter predation NNL-180805-151346001

A fish at Banbury Reservoir with the telltale signs of otter predation NNL-180805-151346001

Anglers familiar with the reservoir, however, feel the BDAA have been reluctant to address the otter predation issue despite fish stocks reducing.

The cost to replace large carp and other species of fish can run into the thousands of pounds so anglers felt the need to protect them was high.

In 2016, over two years after anglers had raised concerns about otter predation, the BDAA contacted Embryo Angling Habitats which specialises in otter proof fencing solutions for lakes and reservoirs for a quote to otter proof Grimsbury Reservoir.

BDAA chose not to go with Embryo, instead installing what many anglers consider to be a less effective alternative.

The former committee member added: “It has always been fenced but it doesn’t go into the ground so obviously there’s big gaps underneath it.

“I spoke to them about the cost of replacing lost carp versus the cost of fencing it and being able to sustain their income.”

He added: “Because it is already fenced all it needs is a skirt to go all the way around. Proper otter fencing goes two feet down and two feet out, in the shape of the letter ‘L’.

“There’s big holes either side of the gates that me or you could get through let alone an otter.”

Banbury and District Angling Association spoke to the Banbury Guardian about the issues raised by anglers concerning Grimsbury Reservoir.

Club secretary Pete Upton said: “My side of the story is that about two years ago the then bailiff phoned me up and said there was about ten dead carp down there.

“We had people look at it and they said it was a classic sign of an otter attack, the way they were half eaten.

“Several of the carp fishermen said we want to do something about this or else we’ll be devastating the place and they’re not going to come.

“So we made the decision to spend £12,000 to have an otter fence. The green fence was there already and this company came in and dug a trench all around with a mini digger and put in this fence, under the ground like you’re supposed to.”

He added: “Most of the carp fishermen down there have said they are pleased we put in otter fencing.”

The reservoir is also home to the Banbury Cross Sailing Club which creates potential problems the BDAA have no control over.

Mr Upton said: “That gate from the club house isn’t even our gate. People who use the sailing club don’t care (about otter access). They’re just going to open it and if it’s not rolled back they’re not going to worry about that.”

Otters are, however, not the only predator depleting stocks at Grimsbury Reservoir as another species is becoming a problem.

My Upton said: “Our biggest problem is cormorants. They have eaten all the roach and perch down there. In the late summer when they come back there will be seven or eight cormorants there.

He added: “We’ve done what we could. Unless you have a full-time man down there living on site I don’t know how you can stop these things.”

Matty Perring has been fishing at Banbury’s Grimsbury Reservoir for many years.

Matty has bagged a 29lb 4oz carp and many others that break the 20lb barrier.

In recent years, however, Matty too has seen evidence of increased otter predation .

Matty said: “They’ve been down there for a while. It must be four years they’ve been there.

“They have taken a lot of fish out of there.

“The first we heard of it was when Aynho got decimated, the lakes at Aynho. The owner paid to put a fence up and there’s a few local lakes that have put fences up.”

The relationship between angler and otter is more complex than simply us against them as Matty explains: “I’m not against otters, I think they have every right to be here as everybody else.

“People see them as cute and cuddly and people see us as just catching a fish, dragging it in and then putting it back.”

Matty is, however, unimpressed with the BDAA’s attempts to otter proof Grimsbury Reservoir.

He said: “You’ve got two huge gaps by the gates so they’re using the gates like everybody else.

“In order for them to fence that it will cost around £40,000 so I don’t blame them for not doing it.

He added: “It’s a lot of money and they’re only a small angling association, it might be beyond them. They seem to think they have done the best they can.”

Not only do otters remove prized fish from the reservoir, their presence has a knock-on effect to fish behaviour.

Matty said: “What happens when a predator is in the water is the fish habits will change so it will make it harder to fish.

“They’ll shoal up tight and change their feeding habits.”

He added: “It is a shame because there’s some cracking fish in there. You could see the carp were successful, you could see the young ones coming through.

“There’s still carp in there but it’s nowhere near like it was.”