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Lampreys Found In The Lhen Trench 3 December 2007

Brook lamprey by Jenny WheeldonLampreys have been found this year in the Lhen Trench during one of Inland Fisheries’ electrofishing surveys. Although there have been some anecdotal reports of these primitive eel-like fish in recent years, the last official record from a Manx watercourse was in the lower Sulby River in 1981.

Lampreys are very sensitive to pollution, and declined in numbers following the industrial revolution, becoming extinct in many British river networks. Although there has been a resurgence of populations in some UK watercourses in recent years, they are still considered vulnerable and all three British species are included in Annex II of the European Habitats Directive.

Brook, sea and river lampreys have similar freshwater habitat requirements. Spawning takes place in gravel areas similar to those used by brown trout, after which the adults die. After hatching, the larvae, known as ammocoetes, spend several years burrowing in sandy silt and feeding on micro-organisms. Once adult, brook lampreys simply swim up to spawning grounds without feeding. However, sea and river lampreys migrate to saltwater to spend one or two years parasitising other fish by latching on to them with their sucker-type mouths.

During the next fortnight, Karen Galtress, River Management Officer, DAFF, will be setting some traps in the Lhen Trench in the hope of getting a close look at some more specimens. Karen says ‘The two lampreys found in September were not identified to species but if they were river lamprey, adults may be returning from the sea around now.’

‘The Lhen Trench, in many respects, provides good habitat for lampreys. However, the maintenance regime, necessary to provide good land drainage for agriculture, limits the formation and retention of faster flowing areas of spawning gravels. In conjunction with the DoT Land Drainage Section we are hoping to explore the potential for trialling a technique used elsewhere to enhance canalised streams for trout and lampreys, while maintaining capacity to discharge flood flows. The technique, using low-level, alternate deflectors would initially be tried and monitored within one short section. If successful, there may be scope to incorporate other such areas in future years’.

Fisheries Division is also hoping to arrange for a postgraduate student to conduct a study next year to assess the size of the lamprey population in the Lhen and ascertain whether they are using any other Manx streams.

If you think you have seen these fish or would like further information, please call Karen Galtress on 651544/450736.

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