Britain's jawless wonders: brook lamprey ecology and taxonomic status.

Lampreys (family Petromyzonidae, ‘stone-suckers’) belong to the Agnatha, (‘jawless’), the most primitive of all living vertebrates. They have no lower jaws and the mouth is surrounded by a round sucker bearing circles of rasping teeth. They are eel-like in shape but have neither paired fins nor scales and their skeletons are entirely cartilaginous. There are three species of lamprey in Britain: brook (Lampetra planeri), river (Lampetra fluviatilis) and sea (Petromyzon marinus), but having seen L. planeri nest-building in a nearby river (the R. Itchen in Hampshire), it is this species that I want to focus on here.

Brook lamprey (Lampetra planeri) nest-building in the River Itchen, Hampshire, UK.

L. planeri  is the smallest of the three British species at 13–15 cm long. The teeth are blunt and less developed than in the other more predacious species, and it does not feed as an adult. Larvae (‘ammocoetes’), are semi-translucent and dull grey-brown in colour, though a 'golden' form does exist with reduced pigmentation. Larvae occur in suitable silt beds, mainly in running water but sometimes in large numbers in silt banks in lakes. Although not common, it is the most abundant and widespread British lamprey and its distribution can be seen in the maps below for the National Biodiversity Network (NBN); the larger-scale map shows Hampshire and surrounding areas. However, due to a decline in several parts of Europe, it has some legal protection including being long-listed in the UK Biodiversity Action Plan.

British distribution of L. planeri (from NBN as of 6th Jan 2011)

Distribution of L. planeri in and around Hampshire (from NBN as of 6th Jan 2011)

Usually cryptic and nocturnal, L. planeri (like most lampreys) are rarely seen except at spawning time (April & May) when they move into shallow, clear water during daylight to start their complex, communal nest-building activities - the photo above was taken in April 2009. As spawning approaches, adults move from silts and migrate upstream at night, often in large numbers, until they reach suitable spawning grounds. These are areas of small stones and gravel in flowing water where the current is present but not too strong. When the water reaches 10–11ºC they tend to spawn at the lower ends of pools, just where the water is starting to break into a riffle. The nest may be constructed by a dozen or more adults moving stones with their suckers and is normally an oval depression 20–40 cm across and 2–10 cm deep. Females produce about 1,500 eggs each and hatched larvae (3–5 mm long and blind) drift downstream to burrow in suitable areas of silty sand. The adults die soon after spawning. Larvae live for around 6½ years in Britain, filtering fine organic particles from the silt. Metamorphosis occurs during July to September, after which they are more silvery, though the back remains dark. They also develop teeth and full vision, though adults do not feed.

Upstream migration can only occur in the absence of barriers, either natural (e.g. waterfalls) or man-made (e.g. dams, weirs or polluted areas). Little is known about their requirements in terms of water quality and quantity, though some limited pollution appears to be tolerated if it does not lead to substrates being smothered. They need suitable conditions (e.g. substrate type) in spawning areas and nursery habitat, and rivers should not be changed to produce excessive cover or fast flow. Channelisation and some aspects of management for angling (e.g. dredging of pools and construction of weirs) has been damaging to lampreys, mainly through habitat destruction, with potential impacts from use as bait. The removal of riffles and associated spawning gravels, and the dredging of silt beds can entirely eliminate lampreys from a river. Similarly, water abstraction and land drainage can produce unstable habitats with variable water levels which flood and disturb spawning gravels and nursery silts at some times and dry out at others. Climate change is likely to produce similar problems, with heavy rain in the autumn and winter, and drought in the summer.

Also, although L. planeri and L. fluviatilis are generally treated as separate species, there is some genetic evidence that this might not be the case. Schreiber and Engelhorn (1998) found very little difference in the DNA content between both species suggesting L. fluviatilis may just be an anadromous form of the relatively 'stationary' L. planeri, with gene flow inferred between them. Their taxonomic relationship and status is still a matter for debate although further research continues to suggest that they may not be truly separate species. For example, Lesne et al. (2010) show a high incidence of communal spawning of the two species in a French river, suggesting that they are less reproductively isolated than previously believed.

From a practical conservation perspective, L. planeri (whether or not it is a species separate from L. fluviatilis) does have some key requirements, but nothing that a little more considerate and thoughtful river/habitat management shouldn't be able to provide in abundance, and which would in turn help mitigate the likely effects of climate change.

References

Lasne, E., Sabatié, M., & Evanno, G. (2010). Communal spawning of brook and river lampreys (Lampetra planeri and L. fluviatilis) is common in the Oir River (France) Ecology of Freshwater Fish, 19 (3), 323-325 DOI: 10.1111/j.1600-0633.2010.00428.x

Schreiber, A., & Engelhorn, R. (1998). Population genetics of a cyclostome species pair, river lamprey (Lampetra fluviatilis L.) and brook lamprey (Lampetra planeri Bloch) Journal of Zoological Systematics and Evolutionary Research, 36 (1-2), 85-99 : 10.1111/j.1439-0469.1998.tb00781.x

Further reading

• More on lamprey ecology can be found here.
• An identification guide to British lampreys can be found here.
• A guide to monitoring lamprey can be found here.