Lampreys are primitive ‘eel-like’ fish, which unlike true bony fish have no jaw or paired fins. Instead of a jaw, lampreys have a suctorial disk lined with tiny teeth surrounding a mouth. Lampreys feed by sucking onto fish and sucking or rasping away blood and flesh. Fossil lampreys date back to about 280 million years ago, which is 50 million years before the appearance of dinosaurs.
The adult pouched lamprey is about 650 mm long, and marine adults are brilliant cobalt blue in colour with bright greenish lateral stripes. On entering fresh water, adults become drab brown, with males developing a large sac or pouch, which hangs down just behind the mouth. The function of the pouch is unknown.
Habitat and Life Cycle
The pouched lamprey spends most of its adult life at sea, re-entering rivers and embarking upon an arduous upstream migration, during winter and spring, to permanent fresh headwater creeks where it spawns and dies. Larval lampreys spend several years filter feeding from burrows in soft sediments before metamorphosing into their adult form and moving to the ocean in winter.
The lower south west of Western Australia, between Margaret River and Denmark, is home to the pouched lamprey (Geotria australis).
In moving upstream lampreys must negotiate rapids and climb waterfalls, and these days also dams and weirs, in order to reach their breeding habitat. Lampreys are good climbers, using their suctorial mouths to gain a grip on wet surfaces and whipping their bodies upwards to inch their way up and over obstructions. Most of the lampreys’ migratory movements occur on dark nights when water levels are rising and rain is falling. During the early stages of their migration, lampreys are susceptible to blood poisoning and internal bleeding. Many other animals die from injuries and exhaustion incurred while attempting to climb or get around the more hazardous obstructions.
Current Conservation Status
The pouched lamprey is listed as State priority, but is not federally listed.
With an increasing number of obstructions on south west rivers and diminishing habitat due to the clearing of natural bushland, it is important to reduce the lamprey mortality rates associated with obstructions to upstream movement. This is especially necessary where dams and weirs are located below prime lamprey habitat, which is often the case in the karri forest region, and where road and paddock runoff threatens to lure lampreys into danger.
Pouched Lamprey and Climate Change
SWCC Strategic Priority
The Pouched Lamprey is identified as a second order priority asset within SWCC’s NRM Strategy under the Aquatic Biodiversity theme.