Wild Harris

Sea Lamprey Mouth   (Photo: Wikipedia)

These “vampire-fish” can grow to over a meter long and they suck blood!

Years ago lampreys were thought of as a delicious treat and were a favourite food of Kings and Queens.

Adult sea-lampreys use their sucker mouth and sharp teeth to stick onto fish like cod and drink their blood. In 2010 a swimmer was attacked by a lamprey which stuck onto his back when he was swimming in the English Channel! (He came to no real harm and had a good story to tell his friends).

Wounds on salmon caused by Sea Lamprey  (Photo: Wikipedia)

Sea lampreys are not very common in Harris but have been spotted in rivers close to Leverborough. They spend most of their lives at sea but come into rivers to have young.

Brook lampreys (Lampetra planeri) are smaller relatives of sea lampreys. They spend their whole lives in freshwater and do not suck blood, instead they feed on very small plants and animals and rotting scraps. They have been found in Lewis, not Harris, but biologists might have missed them because they hide in mud and are difficult to spot, - you could be the first to find one here .....

Brook Lamprey    (Photo: Wikipedia)

Special features

Sea lampreys do not have jaws instead they have a round sucker mouth. When they have stuck onto a fish they use special sharp teeth and a razor tongue to scrape through the fish’s skin until they find blood. To let them have a good long drink sea lampreys put a chemical into the blood of the fish that they have attacked. This chemical keeps the blood runny and stops it from making a scab. Most fish that are attacked by sea lampreys die from their injuries. Lampreys even attack huge whales. They do not seem to kill whales but often do leave a hole and bite marks.

When they are in rivers lampreys use their special sucker mouth to pick up stones and make a nest.

Nesting Brook Lampreys    (Photo: Wikipedia)

Lampreys are a very ancient type of fish. They do not have proper bones or scales like most fish, instead their skeleton is slightly soft and their skin is smooth. Another difference between lampreys and other fish is their gills. Instead of single large gill opening, lampreys have seven holes on each side of their head, these are called gill slits.

Sea Lamprey Head and Gill Slits (Photo: Wikipedia)

Life cycle and habitat

Life at sea

Adult sea lampreys spend one to two years at sea feasting on the blood and flesh of large fish and even huge whales and porpoise. This good food makes adult lampreys grow very fast. When they are big enough, usually over 50 cm and up to a kilogram, they are ready to have their young

Life in freshwaters

Adult sea lampreys hitch a ride into rivers by sticking to a trout or salmon that is coming home from the sea in the spring. In this way they get a lift and a meal at the same time! When the trout or salmon get into the river lampreys drop off. They never feed again, in fact their stomachs shrink to nothing.

Just over a year after coming into rivers male and female lampreys get together and use their sucker mouths and wriggling tails to scoop pebbles from the river bed and make a stony nest. Lamprey mothers then lay two hundred thousand eggs and males cover the eggs in sticky milt, which fertilizes the eggs. Adult lampreys bury their eggs to keep them safe. The work of producing young uses up all an adult lamprey’s energy and soon after burying their eggs they die.

The eggs hatch into small lampreys called ammocoetes. These youngsters are blind and look a bit like big worms. Because they are different from adult lampreys, biologists used to think that they were a totally different type of fish.  Ammocoetes drift down river with the water flow until they find somewhere with a muddy bottom. They burrow into the mud and eat small rotting scraps and tiny plants and animals that they sieve from the mud.

Brook Lamprey Ammocete    (Photo: Wikipedia)

After five to eight years of living in the same piece of mud ammocoetes change shape to look like mini adults. In the autumn they leave their river and swim to the sea.

The importance of sea lampreys to Harris

Lampreys are not common in Harris and we do not know if they build nests here. They are probably rare because the water here is rather cold for them. They like clean water and their visits here show that our freshwaters are free from pollution.

Links

http://www.snh.gov.uk/about-scotlands-nature/species/fish/freshwater-fish/lamprey/

http://www.arkive.org/sea-lamprey/petromyzon-marinus

http://news.bbc.co.uk/earth/hi/earth_news/newsid_9281000/9281424.stm