The lampreys belong to an ancient order of vertebrates, the Agnathans or 'jawless fishes'. The skeletons of lampreys are of strong flexible cartilage and it is no comprised of bone. A round, sucker-like disc surrounds the mouth which, in adults, carries rasping teeth. Most, but not all, species of lamprey are parasitic on other fish. Lampreys occur in temperate waters in both the northern and southern hemispheres. The three lamprey species present in UK (brook lamprey Lampetra planeri, river lamprey Lamprey fluviatilis and sea lamprey Petromyzon marinus)
Brook lampreys are an entirely freshwater species, and unlike other British lamprey species, do not feed on as adults. They are the smaller of the British lamprey species, reaching a length of 15-19 cm. Despite being freshwater-resident, brook lamprey do, however, undergo limited spawning migrations. Some of these movements may be passive, such as the downstream drift of larvae to sandy/silt nursery areas. Here they remain for up to five years before metamorphosing into adults. Active upstream migrations of pre-adults and adults occur through the winter and, on reaching suitable gravel spawning areas, these fish hide among cover until spawning takes place during April-June. All of these adults die after spawning.
River lamprey are larger than brook lamprey, reaching a size of 30-50 cm. They are anadromous and migrate from their coastal feeding grounds into freshwater, to get ready to spawn, during the autumn and spring. Autumn migrants are sexually undeveloped while spring migrants enter from the sea in spawning condition. River lamprey migrate upstream at night and the adults rest in cover during the day. Spawning takes place between April-May on pebble/gravel substrates. Populations that are purely freshwater-resident are rare in Europe, but one exists in Scotland. This unique dwarf-river lamprey form is found in Loch Lomond. As its name suggests, this dwarf form is smaller than its sea-going conspecific, only reaching a size of 25 cm.
Sea lamprey are the largest of the three species, reaching a size of approximately one metre in length. After spending 18-24 months feeding at sea, adult sea lampreys migrate into rivers during the spring and early summer. They spawn between the months of May-July in areas of pebble and cobble substrate.
How do lamprey reproduce?
All lamprey species spawn in gravel substrates, not unlike those used by salmon and trout. Brook and river lampreys spawn slightly earlier than sea lamprey. On reaching their spawning ground, lamprey construct a 'nest' in which to lay their eggs - this is best described as a pit in the river and excavated material is piled up at the downstream end. Brook and river lamprey spawn in a 'ball' which may comprise up to 50 individuals. Sea lamprey, by contrast, spawn in much smaller numbers.
After hatching, the young lamprey larvae, known as ammocoetes, drift downstream with the current. These larvae settle in suitable areas of nursery habitat - areas that comprise fine, soft substrate in well oxygenated, slow flowing water. The ammocoetes feed on fine particulate matter such as diatoms, algae and bacteria. Ammocoetes may stay in this substrate for up to five years (or up to eight years for sea lamprey) before they transform into pre-adults and, in the case of river and sea lamprey, start their migration to the the sea during late autumn (sea lamprey) and late winter-early summer (river lamprey). Brook lamprey do not migrate to sea, spending their entire life in freshwater.
Are they threatened?
Good water and substrate quality (particularly in spawning areas) is important for all lamprey species, and all species are threatened throughout their range by habitat degradation. Physical barriers can pose particular risks to anadromous river and sea lamprey, but other freshwater-resident forms can be negatively impacted if new in-stream structures are created. There is no commercial value for brook lamprey, but in some areas of Europe, river and sea lamprey are exploited commercially for food. Historical fisheries existed for river lamprey in Britain, famously resulting in the death of an English monarch, but now, only one small-scale fishery exist for this species. These fish are used to supply the angling bait market.
The conservation status of lamprey
- Brook Lamprey Annex II of the EU Habitats Directive Appendix III of the Bern Convention.
- River Lamprey Annexes II and V of the EU Habitats Directive Appendix III of the Bern Convention and are on the UKBAP Priority List. The dwarf river lamprey form is a conservation feature in the Endrick Water Site of Special Scientific Interest in Scotland, giving it protection under the Wildlife & Countryside Act 1981 (as amended).
- Sea Lamprey Annex II of the EU Habitats Directive Appendix III of the Bern Convention and are on the UKBAP Priority List.
Despite their conservation status within Europe, sea lamprey are regarded as a serious non-native pest in the Great Lakes of North America. There, this species causes considerable damage to the sport fishery that exists there and millions of dollars are used to control sea lamprey numbers every year.
Last updated on Monday 24th September 2012 at 16:38 PM. Click here to comment on this page