Dave Barlow © Cleveland Naturalists’ Field Club. 7th April 2024
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The Otter (Lutra lutra) on the River Leven
North Yorkshire
Derek E Capes
Abstract
The frequency of otter sprainting activity has been monitored each month over a period from 2002 to 2011, at a series of sites on the River Leven and some of it’s tributary streams in North Yorkshire.
The note describes the method employed and gives results in terms of annual totals and variations.
Other miscellaneous data is given, including likely fish prey items and some data on road traffic accidents involving otters in the area.
Some speculative comments are made on possible otter movements between several other adjacent river systems, and the need for more sophisticated studies to investigate this possibility.
1. Introduction
I first became interested in surveying for otters in the late 1970’s after hearing a talk by Gordon Woodroffe describing his work on the Yorkshire Esk, and wondering if there were any otters on the River Leven which runs through my home village of Great Ayton. From February 1979 to February 1981 I did a total of 52 site visits, involving 9 sections of the river but encountered just 3 signs of otter. Twenty years later, my retirement in 1999 coincided with the launch of the Northumbrian Otters and Rivers Project so I decided to get involved, as following reports of an increase in signs generally, I was curious to see if the same applied locally. Initially, I monitored a few sites around the village on a routine basis, including other sites as and when time permitted. Then the idea was born to commit to a longer term survey, covering a wider area. A number of sites were selected to be monitored each month. Foot and Mouth restrictions curtailed activity in 2001, so the survey started in January 2002, and continued until December 2011.
In North Yorkshire, a project was undertaken by Woodroffe (1) and others, to introduce rehabilitated animals to several sites on the River Derwent system and to the River Esk to reinforce small existing populations. This took place between 1990 and 1993, and subsequent monitoring over several years showed an increasing number of otter signs, and evidence that breeding had occurred. There was the distinct possibility that otters may have dispersed more widely, and a survey of 17 sites largely covering the length of the Leven and some of it’s tributaries was carried out in May 1995 by Woodroffe and Winter (2) found 4 of the sites positive (23.5%).
In February 1998, O’Hara surveyed the Leven (3)and found 5 positive sites from 13 examined (38.5%), all of these positive sites being located in the lower stretches of the river.
The rest of this detailed article can be found here
2 Background
The otter population of Britain, and especially England, fell dramatically from the mid 1950’s, largely due to the introduction of organochlorine pesticides in agricultural practices. Once the problem had been identified and appropriate remedial action taken, the decline halted. Otter numbers started from a very low base, to make a slow recovery. In some areas, re-introductions from captive bred stock were carried out. Recovery continued, but at different rates throughout the country as young animals dispersed into their own territories.
