Lamprey

(Lampetra fluviatilis)

Order: Petromyzoniformes Family: Petromyzonidae

Fotos: Ari Saura

Description: The lamprey belongs to the class Cyclostomata. Its vertebral column is made of soft cartilage, not bone, and it has a cylindrical body and smooth skin. At the pre-adult and adult period, the lamprey has a round suction cup mouth ringed with little horny teeth. and seven rounded gill slits behind the eyes. The lamprey has only median fins. When mature, it is normally 25−35 cm long.

Origin and distribution: Ancestral lampreys were living in the sea over 500 million years ago. In Europe, the range of the species extends from Italy to southern Norway and the Baltic Sea. In Finland, the lamprey is encountered in the Baltic Sea and rivers running into it and, as a land-locked form, also in some lakes. At least 40 rivers, notably those discharging into the northernmost Gulf of Bothnia and the eastern Gulf of Finland, support spawning runs of lamprey. The land-locked form occurs in three main water courses.

Reproduction: Mature lampreys usually ascend rivers in August and September, although they do not actually spawn until May or June of the following year. Once in the river, lamprey fast for the rest of their life, the intestine having already atrophied before the spawning migration. Lampreys die soon after spawning. The eggs are sheltered by gravel for two or three weeks. Lamprey larvae spend their first years in silt and sand-bottomed river banks.

Diet, growth and migrations: Larval lamprey feed mainly on micro-organisms among decomposing plant material. The larval period lasts 4−6 years, at the end of which the larvae undergo metamorphosis and their internal organs are radically rearranged. The lamprey is an anadromous species that moves into the sea along with the spring flood. The size of migrating larvae ranges from 9 to 16 cm. The sea and lake phases are, however, not well known. The sea phase usually lasts from spring to the autumn of the following year. In their first summer, young lampreys move over quite a large area and feed on bottom fauna and fish. They attach themselves to the side of fish, and feed on their skin and muscles. Lamprey suction marks have been seen on herring (Clupea harengus membras), sprat (Sprattus sprattus), smelt (Osmerus eperlanus) and vendace (Coregonus albula).

Fishing and catches: The lamprey is a delicious and valuable fish, and is widely appreciated in Finland, notably in Ostrobothnia and Satakunta. An estimated 2-3 million lamprey are caught in the sea every year using traps and lamprey fyke nets made of willow branches or nowadays often of nylon netting. Although the flesh of the lake lamprey is as good as that of the sea form, there is no tradition of lake lamprey fishing in Finland, most likely because of the small size and low numbers of the lake form.

Vulnerability, threats and management: The building of hydro-electric power plants, cleaning and terracing have depleted lamprey stocks in almost all Finnish rivers. In some dammed rivers, stocks have been maintained by transporting spawning migrating fish to waters above the dams in the autumn. In a new management strategy recently adopted, larvae are reared and released soon after hatching. Larvae production could be enhanced in cleaned river stretches by reconstructing river channels.

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