Eel Populations
The assessment of the eel population in the Geisgeil catchment was started in 2008. Part-funded by Scottish Natural Heritage, it is hoped to improve the management of the population within the catchment, as well as providing more of an insight into the ecology this endangered species.
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The long life cycle, along with natural and anthropogenic influences make this species vulnerable to extinction. A pandemic population, the eel does not home on specific rivers but can arrive by currents anywhere in Europe. It is believed that the population has declined by approximately 99% since the 1980's - an alarming statistic. Eels are a popular food in Europe and Asia.
The Trust has undertaken several projects to determine the status and recruitment of eels in the west Highlands whilst raising awareness of the value of eels in Sutherland. An initial survey of west Sutherland elvers provided information on numbers and recruitment in the absence of earlier data. The assessment of eel populations in the Geisgeil catchment started in 2008 with the aim of improving species management through increased knowledge of the ecology of the species and the recruitment of young eels into the system. Another project specifically aimed to develop a standard method for calculating a recruitment index and to estimate the total elver run for each catchment in the area, with the intention of extending the protocol for use by other organisations in similar catchments.
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Eels are ecologically important
- Eels represent about 50% of the standing biomass in most aquatic environments.
- Eels are an important nutrient flux to and from the sea.
- Eels are a keystone species, helping to create a balance as predator, prey and scavenger.
- They are an important prey of many UKBAP list species - including otter, heron, bittern and osprey.
- Due to their slow growth, the eel population within the Highlands may be acting as a reservoir for eels throughout Europe.
The Decline
Evidence suggests that the initial eel decline was the result of stock decline rather than reduced recruitment. There are a number of different possible causes for both stock decline and recruitment decline:
Causes of stock decline
- Loss of habitat - including pollution and over abstraction
- Barriers to migration - structural and also water quality and quantity
- Over fishing
Causes of recruitment decline
- Over-exploitation
- Climate change - changes to oceanographic conditions
- Habitat degradation
- Pollution
- Parasatism
Reports detailing the results of eel projects in Sutherland are available in the archive.
