Are there otters on the river worth?

Picture courtesy of Rob Withey

Looking for otters

We have been thinking about otters recently.

Otters are quite difficult to spot, they are very furtive  and not usually out and about during the day, their active time is between dusk and dawn. So the presence of otters is often established by what they leave behind rather than seeing the animal itself, what they leave behind are faeces and foot prints.

​​About three years ago, when RWF was just getting going, we found what we think were otter droppings, known as a spraint, below the dual carriageway bridge at Aireworth Grove. Otter spraints consist of the remains of the otter diet so will have fish bones and scales, there will often be crayfish remains. Mink droppings (scats) are smaller and do not have so much fishy remains but ​more fur and feathers. Mink scats have an unpleasant odour while otter spraints smell more pleasant, some say a mix of lavender and fresh fish!

Otter usually leave spraints in prominent positions as territory markers. Picture courtesy of Wild Life Survey Unit Ltd

Mink print at Pitt Street.

​​More recently we got quite excited by a footprint spotted under the bridge at Pitt Street a few weeks ago, however on consideration we decided it was more likely a mink rather than otter as there were only four toes showing.  Although mink have five toes one is set back and does not usually show on prints, otters usually have five showing on the print. Also the claws were more pronounced than one would expect for an otter, plus the prints were small for an otter.

​A couple of weeks ago we thought we had found what may be the decomposed body of an otter near Kinara Close, it had been in the river a while and was pretty disgusting! On further examination it turned out to be a goat’s skin!

​So two recent disappointments. Then RWF member, John Tickner, who likes nosing around the nooks and crannies of the river, spotted these prints under Vale Mill at Oakworth. The first ones we think are rat (small and pointy) or possibly mink, but the other two look very much like otter, they are bigger, otters prints are about 2” across, and show five toes.

Rat prints.

We reckon these are otter prints....

....and these to.

​So we think that otters are present on the Worth. However it is unlikely that they are resident here, more likely they pay us regular visits from their resident territory on the River Aire. 

Otter on the Aire at Marley, photographed by RWF member John Tickner (copyright John Tickner).

Have you seen an otter on the Worth or think you have seen signs of otters? Please let us know, we are keen to build an understanding of their presence on the river.

Arguments about otters

​Why are RWF so obsessed with otters? I hear you ask! Well otters were present in many rivers in the British Isles until they went into a steep decline in the latter half of the twentieth century, mainly due to the use of organochlorine pesticides in agriculture which polluted the rivers and got into the otter’s  food chain. With the outlawing of these pesticides in the early 1990’s and also the ban on hunting in 19768 otters have made an astonishing comeback, we would like to think that the River worth could be part of the comeback of this iconic species.
​
We know  there are advantages and disadvantages to the return of the otter and can now almost hear the cries of outrage from some in the angling community who think the otters are stealing “their fish”.

Otter doing what it does best - catching and eating fish.

​Let's look at the advantages first.

• Firstly there are a lot of signal crayfish in the Worth and otters love crayfish so that’s a plus to start with. Signal crayfish are an invasive species that was introduced to the UK in the 70’s and is now out competing the native white clawed crayfish, it is prolific throughout Yorkshire. They can have a big impact on river ecology, they burrow into the riverbank leading to erosion, they also eat the eggs of resident fish such as trout and grayling.

Signal crayfish - an American invader - emerging from the Worth. Picture courtesy of Aire Rivers Trust.

• Research has found that the presence of otters can limit the numbers of another American immigrant, the mink. This is good news for the local water voles. Water voles have been in decline for some years, a study showed a decline of 30% in ten years. This is partly due to predation by mink which were imported for fur farming in the 1930’s, following the establishment of escapees they have spread throughout Britain. Being smaller than Otters they 

American mink - often seen on the Worth. Picture from NatureScot

          are able to pursue the poor water vole into it’s burrow.

• Other research has shown that the presence of top predators such as otters has a beneficial effect on the whole ecosystem.

otters and anglers

Large barbel taken by an otter. Picture from Angling Trust

​The only disadvantage is that otters do like to eat fish, which can upset some anglers. Seeing some posts on social media it seems that to many anglers the only good otter is a dead otter. We at RWF think the argument is a bit more nuanced than that. A recent study has found that the majority of the otter's diet consists of smaller fish such as minnows, bull heads and stone loach. This does not mean that otters do not take larger fish but that they are not likely to be stripping a river of it’s large fish such as barbel as anglers claim. This article from Martin Salter of the Angling Trust makes just this argument.
​

Otter fence - you have to remember to shut the gate! Picture courtesy of Farm & Country Fencing Epping

​Carp fisheries present a different problem. Being heavily stocked with large fish they are like a Macdonalds for otters. The environment agency provide grants for fencing fisheries, it is also possible under licence to catch otters that breach security and release them outside the fence. This provides some protection for the big carp.
However it could be that anglers have had it too easy! They are used to landing huge barbel and carp and having bulging keep nets of smaller fish but perhaps this is unnatural in a balanced environment. They 

​may have to accept that this will not be a commonplace in an environment shared with a top predator.

​It could be that if anglers lower their sights a little they may not have such stupendous catches but they will see they are sharing the river with a magnificent beast. 

Picture courtesy of Wildwood Trust