Northern Lamprey (Petromyzontidae)

When it comes to longevity, there is one species on the Weald Moors that makes the ancient peatland landscape’s heritage seem like the mere blink of an eye. Lamprey belong to a group of fish that are among the most primitive of all vertebrate life with a lineage that stretches back at least 450 million years…

ID: lamprey and eels are often mentioned in the same breath and while both species possess a long, slender body, the similarities between each are limited. Unlike most true fish, lamprey do not have a hinged jaw but, instead, a mouth encircled by a round, sucker-like disc, and strong, rasping teeth (which are used by certain species to attach themselves to fish, which they then feed on). They also lack scales and bones, possessing a skeletal structure comprised entirely of cartilage. Completing the otherworldly picture, the lamprey profile includes a single nostril (located on top of the head) and a row of seven distinctive gill pores directly behind the eye on each side of the head.

In the Field: Britain is home to three lamprey species: Sea, River and Brook. The largest of the trio, Sea Lamprey (Petromyzon marinus) can reach up to 100 centimetres in length and, as the name might suggest, tend to inhabit coastal waters and larger rivers and streams — although much remains unknown about their exact movements. River Lamprey (Lampetra fluviatilis) and their smaller cousins Brook Lamprey (Lampetra planeri) are more closely related and typical of smaller rivers and streams, such as those found on the Weald Moors. While River Lamprey have disappeared from many watercourses in modern times, Brook Lamprey (which measure around 12-16 centimetres in adulthood) remain the most widespread and abundant species in our waters, where they can spend up to six years living as larvae. Adult Brook Lamprey are also distinct because, unlike River and Sea Lamprey, they do not eat but simply move straight to their breeding grounds to spawn and die.

How Are They Doing? Adult River Lamprey grow to maturity in coastal estuaries and their numbers appear to have been badly affected by the numerous obstacles that block passage to and from their spawning grounds further upstream in many of our waterways. Brook Lamprey, on the other hand, continue to survive in many places where their larger cousins have long since disappeared. This may be explained by the fact they do not undertake a long migration and can live out their entire lives in relatively short stretches of water. However, for both species the presence of gravel and silt in river and stream beds is vital for both egg-laying and the creation of nursery areas for growing larvae. Activities such as dredging and channelisation work can be hugely detrimental to these habitat features and lamprey numbers may also be badly hit where water levels are liable to regular fluctuations from drainage and abstraction.

On the Weald Moors: lamprey have been recorded in the River Tern at Crudgington and it is entirely possible they may be present in the smaller tributaries that flow through the Weald Moors, too. If you wish to investigate further, Brook Lamprey (which are perhaps the most likely species to be present on the moors) are at their most visible during April and May, when they move by daylight into the clear, shallow waters in which they establish their communal nesting sites. Any areas with plenty of small stones and gravel will be especially worthy of attention. It is here that lamprey build their nests, by moving small stones around with their mouths — a trait that has earned them the alternative name of ‘stone suckers’. Often visible in large numbers, many lamprey unsurprisingly fall victim to predatory birds at this time of year, so searching for hunting heron, ducks and gulls may also prove worthwhile.

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