As we are celebrating Leighton Moss' 50th anniversary this year, I am focussing once a week on an important element of the site. I was having a few technical issues over the weekend, so this one is actually for last week (you will be treated to another later on this week). Privileged visitors have recently been getting great views of one of our larger residents, the otters, so I thought I would fill you in on these fabulous mammals.....
Otters are awesome! They are members of the Mustelid family and so are related to the likes of weasels, stoats and badgers. The word 'otter' comes from the old English word 'oter' or 'otor' which is derived from the same place as the word 'water', which is of course where they spend large parts of their time. They eat mainly fish, but will also take water insects and birds to supplement their diet.
Young otter at Leighton Moss by Dave Hall
Male otters are called 'dog' otters, females are referred to as 'bitches' and their young are therefore 'pups', just like dogs. Their home is called a 'holt'. Otters are prgnant for around 60 to 86 days. After one month, the pups can leave the holt and after two months, they are able to swim. The pups live with the family for approximately one year and then are often cast out to make room for the next year's pups.
Otters are a protected species as they were almost wiped out by a number of contibuting factors including hunting and water pollution. Now thanks to the ban on hunting them, and the cleaning up of many of our waterways, otters are now present in every county in the country once more.
So how have they fared at Leighton Moss?
Otters were historically present on site here from the beginning, but by the mid-90s, they had sadly disappeared. This was due to huge declines in fish stocks. Because Leighton Moss is in a valley bottom, water runs into the reserve from the surrounding farmland and brings with it nutrient rich sediment. Over time, this builds up in the pools, making the water shallower. Shallow water heats up easily on warm days which, when combined with the high nutrient levels, causes algal blooms (algae is sort of an aquatic plant that spreads over the water surface). When algae dominates in this way, it blocks out light from the pools making them a less desirable place for aquatic plants, insects and the fish that feed on them. This then also has a knock on effect on the wildlife that eats them too, such as herons, bitterns and otters.
The problem needed some specialist kit to solve it. In 2004, thanks to some European funding, we were able to bring in a huge floating digger to remove the silt. This large digger was originally developed in America for managing the vast swamp areas there. As you can see from the photo, it is no ordinary digger. If a normal digger were to try and drive into the pools at Leighton Moss, even with caterpillar tracks, it would sink if it hit a softer area. However, as the photo shows, this digger's caterpillar tracks have huge floatation devices, so if it hits a soft bit, it simply floats up and doesn't get stuck. This machine removed the sediment from Lilian’s pool, Grisedale pool and the ditch network that runs through that part of the site. It was then pumped out onto a farm on the edge of the reserve, where, because it is so rich in nutrients, it acted as a fertilizer when ploughed back in.
Floating digger by Robin Horner
The effect of the work was almost instantaneous. The aquatic plant populations increased, which caused coot numbers (which prior to the work had declined) to rise. Aquatic invertebrates rose in numbers, fish stocks recovered, and in 2006, less than a year after the work was completed, otters returned to the site, and have bred almost every year since.
Thanks to some funding from Higher Level Stewardship, we were able to bring the digger back in December last year, to give the Public and Lower hide end of the reserve the same treatment. The work was completed in March this year and we are really pleased with the results.
The otters have been spotted regularly out and about down at the Public and Lower hide end of the reserve over the last few months. We have a large male who will have a much larger territory than just Leighton Moss. Then there is a female, and each year they generally have two pups. Once the pups come out in the summer, they can be quite active in the day and are often spotted fishing. The main fish they eat here are eels.
Otter swimming by Phil Boardman
When you are heading down the causeway, beyond Public hide there is a bridge over the main dyke. This dyke is a bit of a motorway through the reserve for our otters. There are two large stones other side of the bridge on the edge of the dyke where you will often see signs that the otters have passed through there - their poo (known as spraint). If you have never seen an otter here, or indeed anywhere, here are a few tips to help you try to find one...
Good luck!