National Lamprey Survey of Scotland (2003-2005)
141 catchments throughout mainland Scotland, Orkney and Shetland and Western Isles were surveyed by electrofishing for larvae, confirming lamprey presence in most rivers with previous records and identifying 17 catchments with previously unknown populations, extending the known range of all species.
Lampreys were present in 65 of the 141 catchments and at 342 of 710 survey sites.
Lampreys were absent from all survey sites on Orkney and Shetland and from those areas of west Highlands north of Loch Carron. Distribution was patchy in east Sutherland, Caithness and Easter Ross, but several previously unrecorded populations were identified. Lampreys were present in most rivers south of the Great Glen.
Sea lamprey were present in 13 catchments, river lampreys in 20 and brook lampreys in 51. Unidentified Lampetra species were present in a further 13.
Sea lampreys were the rarest species in both records and survey. They have been recorded in 35 rivers, although their continuing presence in some of these is uncertain. Although scarce, sea lampreys are widespread with extant populations in all regions excepting Orkney and Shetland and, perhaps, Western Isles where occasional adults are seen but breeding is unconfirmed.
The survey identified several catchments with previously unrecorded river lamprey populations, particularly in south Argyll. River lampreys have now been recorded in 42 mainland rivers. There are no records from any of the islands. River lampreys are largely restricted to rivers south of the Great Glen.
Brook lampreys were the most common species in both records and survey. Their presence has now been confirmed in all regions excepting Orkney and Shetland. Single, isolated populations were present on Lewis, Skye and Islay. The species is common south of the Great Glen. Distribution is patchy in the far north of Scotland and they are absent from the far north-west.
The three lamprey species present in UK (brook lamprey Lampetra planeri, river lamprey L. fluviatilis and sea lamprey Petromyzon marinus) are listed on Annex IIa of the Habitats Directive, reflecting concern over widespread declines across their European range. Five Scottish rivers known to hold good populations of lampreys have been selected as candidate Special Areas of Conservation (cSAC). Records of lampreys outside these rivers are relatively scarce. More information on lamprey distribution is required to assess how representative are the cSAC rivers, and to provide a baseline against which future population trends may be measured. In addition, protection of lampreys outside the cSACs clearly requires an awareness of their presence.
Semi-quantitative, timed electric fishing was used throughout. Surveyors fished over patches of suitable habitat for 5 minutes using smooth DC. Lamprey ammocoetes and transformers attracted from the substrate were captured in dip nets. The numbers of five-minute samples taken from each habitat unit varied with the area of suitable lamprey habitat, more samples being taken from larger habitat units than from small units. Total time fished was recorded. On completion, the area covered was measured in order that a minimum density could be calculated.
Lamprey habitat units were scored as either optimal or sub-optimal using the simple two-point key used by Harvey & Cowx (2003). This defines optimal habitat as stable, fine sediment (silt/sand) to a depth of 15 cm or more, in slow flowing well oxygenated water, often with fine layer of organic detritus. Sub-optimal habitat is characterised by a patchy or shallow covering of fine sediment among larger substrates.
Lampreys were anaesthetised using 2-phenoxy ethanol and were examined on white measuring boards. All lampreys were identified to the lowest possible taxonomic level and measured to the nearest mm. Surveyors were required to complete pro-forma field sheets.
National Lamprey Survey of Scotland , SNH (2020)
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