What on earth is a lamprey!

A brook lamprey caught in a RWF monitoring exercise on the Worth.

We have mentioned lampreys a couple of times in blogs and facebook postings recently, we we though some might be thinking WTF is a lamprey, so here’s a bit more information about them.

So what are Lampreys?
Lampreys are a very primitive form of fish, although scientifically they are not actually classed as fish it is convenient to consider them as such. They look like eels but are jawless, instead of a jaw they have a round sucker mouth with strong rasping teeth. They are boneless,  their skeleton consists of flexible cartilage. They breath through seven gill holes on either side of the head.
There are three species of lamprey living in the UK, the sea lamprey, the river lamprey and the brook lamprey. 

Brook lamprey mouth.

​The sea and river varieties are carnivorous, having the unpleasant habit of attaching themselves to fish with their sucker mouth and boring into the body to eat the blood and flesh, ugh! On the Worth you will be pleased to know that we just have the brook lamprey which is not so disgusting as it feeds by filtering organisms out of the water, in fact it doesn’t eat at all in the adult stage.

How do they live?
Lampreys have two stages, a larval stage and an adult stage. After hatching the larvae drift down stream until they come to a suitable sandy/silty river bottom which they burrow into. They will remain there for five to six years feeding by filtering organisms from the water around the mouth of their burrow. They grow from 3-5mm to 12-15cm before changing into the adult form.

​If that was it most of us would not know we had lampreys in the river, they are normally only seen once they become adult. They metamorphose into adults in July to September and start migrating upstream to their spawning sites where they will spawn in April to May. As the adults do not feed they lose weight during this period and die soon after spawning.

For spawning a group of adults will form a shallow depression in the gravel about 20-40cm across and 2-10cm deep in an area of moderate flow. Here the females will lay about 1,500 eggs to be fertilised by the males.  ​

Spawning lampreys.

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Heron eating lamprey.

Spotting lamprey.
Now is probably about the best time to see lamprey as it is spawning time, so if you are out by the river keep an eye out for these eel like fish. They are particularly vulnerable to predators at this to time so you might see a heron or goosander taking them. If you do see any please let us know. We have seen a few in our work in the river this season but are always interested in finding out more about them.

​One of the problems lampreys face on the river (as well as the herons!) is the number of weirs. These act as a barrier to migration and may be limiting the population, mind you this also applies to other fish such as trout and grayling. River Worth Friends are keen to have some of these weirs removed if possible.

Main top photographer copy write of RWF member John Tickner.
Lampreys spawning - Dr Will O'connor.
Heron with lamprey - Clive Daelman.
If you want to know more there is a good exploration of all three UK species here.