Distribution
Lampreys live mostly in coastal and fresh waters, although some species (e.g. Geotria australis, Petromyzon marinus, Entosphenus tridentatus) travel significant distances in the open ocean, as evidenced by their lack of reproductive isolation between populations. Some species are found in land-locked lakes. They are found in most temperate regions except those in Africa. Their larvae (ammocoetes) have a low tolerance for high water temperatures, which may explain why they are not distributed in the tropics.
Lamprey distribution may be adversely affected by over-fishing and pollution. In Britain, at the time of the conquest, Lampreys were found as far upstream in the River Thames as Petersham. Reduction of pollution in the Thames and River Wear has led to recent sightings in London and Chester-le-Street.
Distribution may also be adversely affected by dams and other construction projects disrupting migration routes, obstructing access to spawning grounds. Conversely, the construction of artificial channels has exposed new habitats for colonisation notably in North America where Sea lampreys have become a significant introduced pest in the Great Lakes.
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