The European Brook Lamprey is considered to represent the more recently-evolved component of a "species pair" alongside the congeneric European River Lamprey (Lampetra fluviatilis).

In genetic analyses, these two species are indistinguishable by single- or few molecular markers, and have been clearly differentiated only through genomic data (Espanhol et al. 2007, Mateus et al. 2013). They often co-occur at breeding sites (e.g., Lasne et al. 2010) and are able to hybridise (Hume et al. 2013; Rougemont et al. 2015). Their larvae are morphologically very similar, but adult European River Lampreys are physically larger than European Brook Lampreys.

These species also differ in their behaviour during the adult life stage in that the European River Lamprey is anadromous and migratory with a parasitic adult stage, whereas the European Brook Lamprey is sedentary in freshwater environments and adults are nonparasitic.

There is evidence that southern subpopulations are genetically more divergent than their northern counterparts, suggesting that the two taxa are undergoing disparate stages of speciation at different locations, with the Iberian Peninsula probably representing a hub of postglacial colonisation (Mateus et al. 2016, De Cahsan et al. 2020).

Their systematics have thus been considered problematic in the past, but the majority of recent publications continue to treat them as separate taxa (e.g., Pereira et al. 2021).

Global and European regional assessment: Near Threatened (NT)
EU 27 regional assessment: Near Threatened (NT)

The European Brook Lamprey does not approach the range thresholds for Vulnerable under Criterion B (extent of occurrence (EOO) < 20,000 km², area of occupancy (AOO) < 2,000 km²) or D2. The population size is understood to significantly exceed 10,000 individuals, hence it does not approach the thresholds for Criteria C or D, and there exists no quantitative analysis which would permit application of Criterion E.

Although no range-wide population trend data exists, a suspected ongoing reduction in abundance based on declining habitat quality might approach or meet the threshold for Vulnerable under Criterion A2 (≥ 30% over the past 12 years = three generations).

As a result of this data uncertainty, Least Concern and Vulnerable are equally plausible Red List categories for the present assessment, and this species is assessed as Near Threatened (A2ce) both globally and for the EU 27 member states.

This species is native to the Northeast Atlantic and Western Mediterranean basins, with isolated subpopulations occurring in the Adriatic Sea basin and upper Danube River system.

In the Atlantic basin, its range extends from the Baltic Sea basin to southern Norway, the North Sea and Atlantic coastlines of the British Isles, France and the Iberian Peninsula, where it is restricted to the upper Nivelle (es. Ugarana) and Deva rivers in Spain plus the lower Douro (es. Duero), lower Mondego, Lis, Ribeiras do Oeste and lower Tagus (es. Tajo; pt. Tejo) rivers in Portugal.

In the Mediterranean basin, it occurs in southern France from the Têt River to the Rhône River, and western Italy from the Serchio River in Tuscany to the Lao River in Calabria. An isolated subpopulation inhabits the Pescara River in Abruzzo, which drains into the Adriatic Sea.

A number of subpopulations are reported to inhabit the upper Danube River in the state of Baden-Württemberg, southwestern Germany. Historical records exist from much further downstream in the Danube system, but these are today understood to correspond to species of the genus Eudontomyzon.

It should be noted that the precise limits of this species' range prior to its 20^th century decline (see 'Population' and 'Threats') are somewhat unclear due to a lack of baseline data. Moreover, some of the available records are likely to correspond to the European River Lamprey (Lampetra fluviatilis), particularly those based on larvae (see 'Taxonomic Notes'). A broadscale approach incorporating entire river systems was therefore adopted to produce the distribution map accompanying this assessment.

This species' population size is unknown, but is understood to far exceed the minimum threshold for Red List criteria (< 10,000 mature individuals). The current population trend has not been quantified, and the number of subpopulations is unclear.

It can be abundant where suitable habitat conditions exist, but has undoubtedly declined since the mid-20^th century and today exists in small, increasingly isolated subpopulations across much of its range.

Abundance has reportedly increased in the Rhine River, Netherlands and western Germany, since the late 1980s (see 'Conservation'). In contrast, ongoing population size reductions based on declining habitat quality are suspected to be ongoing in a number of other countries (see 'Threats').

Like other brook lampreys, this species is nonparasitic. It is a specialised inhabitant of shallow streams with clean, flowing water, soft substrates of sand, silt or mud, and sometimes submerged vegetation.

Its life cycle is characterised by a blind, microphagous larval (ammocoete) phase, which spends several years buried in freshwater sediments of sluggish river and stream reaches. Metamorphosis occurs at the end of this growth stage, at which point individuals develop functional eyes and eventually emerge from the substrate as short-lived, non-trophic adults which spawn and die.

The timing of the annual reproductive period varies depending on location, taking place for example from February to April in France and Germany, March to May in the United Kingdom and May to early July in Finland and Russia. Reproduction generally coincides with water temperatures rising above 9°C, and development of the gonads is accompanied by atrophy of most internal organs and tissues.

This species requires well-washed beds of gravel and small cobbles with fast-flowing water and nearby backwaters for successful spawning and larval development. Depending on location, adults may migrate distances not exceeding a few kilometres to reach their spawning grounds.

Spawning usually takes place within a "nest", most often comprising a bowl-shaped indentation excavated from the substrate with a rim of stones deposited immediately downstream. However, in some cases larger groups participate in mass-spawning and turning of gravel over a patch several metres wide without forming conspicuous depressions.

Spawning itself involves the male attaching to the head of the female and wrapping his tail around her body, at which point the gametes are released. However, alternative spawning strategies such as sneaker males and the release of gametes without pairing have been reported. Fertilisation is external, and fecundity has been reported to vary from 1,000-2,000 eggs per individual female.

Although the nests formed during courtship and spawning have typically been described as shelters constructed to protect the eggs and yolk-sac larvae, recent evidence suggests they may actually function as structures to facilitate downstream egg dispersal.

Hatching occurs c. two weeks after egg deposition, and one to three weeks later the larvae emerge from the spawning substrate and drift downstream to settle in sheltered areas, where they bury into silt beds.

Once settled at a site, the head of each larva protrudes above the substrate with its mouth directed towards the current in order to trap drifting food particles. The larvae are believed to be generalist feeders, filtering algae such as desmids and diatoms, detritus and miscroscopic animals from the water column, although some benthic organisms may also be consumed.

The larval stage lasts 2.5-4.5 years, depending on location, and tends to be more extended at northerly latitudes. Metamorphosis begins during the summer or early autumn, and the initial mobile, non-feeding subadult stage is known as the macropthalmia. Spawning takes place the following spring.

As a result of this species' freshwater life cycle and ability to undertake short spawning migrations it is able to penetrate further upstream and colonise relatively smaller habitats than the European River Lamprey, often above artificial or natural obstructions that the latter is unable to pass.

This species' decline has been driven by an interacting series of anthropogenic factors.

In particular, river and stream engineering projects designed to manage seasonal flooding, connect river systems for transport and exploit water for agricultural, domestic and industrial purposes have been ongoing since the 19^th century.

For example, the construction of dams, weirs and other barriers has blocked upstream migration routes, caused subpopulations to become fragmented, and hindered natural flow and sedimentation processes. The extent of suitable habitat for egg deposition and larval development has thus been significantly reduced throughout the European Brook Lamprey's range.

Several other forms of habitat modification are considered to negatively affect this species. Extraction of sand and other sediments from riverbeds can directly destroy ammocoete habitats, while dredging can drastically modify important spawning sites. Regulation of channels and banks may eradicate entire subpopulations through the loss of vital river features such as riffles and silt beds. Certain land management practices have resulted in increased soil erosion and siltation of gravel beds used for spawning.

Widespread pollution from agricultural, domestic and industrial sources has further reduced the extent of habitat. There exist numerous documented instances of European Brook Lamprey subpopulation declines or extirpation events due to poor water quality, e.g., the upper Danube River in Germany. Adults can be negatively affected by pollution barriers during their spawning migrations, eutrophication due to increased nutrient loads can cause spawning beds to be smothered by algae, and ammocoetes are probably sensitive to high concentrations of environmental contaminants.

At some sites, intensive stocking with predatory salmonids such as Brown Trout (Salmo trutta) or Rainbow Trout (Oncorhynchus mykiss) for recreational fisheries is understood to have contributed to declining abundance through predation of ammocoetes.

Increasing temperatures due to climate change could drive shifts in range, alter migration patterns and impact physiological processes, but this has not been studied in depth.

This species is not used or traded.

This species is included in Appendix III of the Bern Convention and Annex II (except in Estonia, Finland and Sweden) of the European Union Habitats Directive.

It is nationally-protected and/or assessed as threatened in the National Red Lists or Red Data Books of a number of countries within its range.

Numerous subpopulations occur within the boundaries of protected areas, many of which are included in the European Union's Natura 2000 network.

Its conservation been of interest since at least the late 1980s, when dedicated management programmes were already underway in Germany, the Czechia and perhaps elsewhere.

The subpopulation inhabiting the Rhine River appears to be recovering from its earlier decline due to improvements in water quality and connectivity that have occurred since the international Rhine Action Programme was launched in 1988.

Since the European Union Habitats Directive was adopted in 1992, most member states to which the European Brook Lamprey is native have designated Special Areas of Conservation (SACs) for its specific protection. Information regarding direct management efforts is scarce, however.

It is recommended that future research efforts should focus on establishing this species' population trend across its entire range, understanding the effects of poor water quality on its life cycle, investigating the factors that might result in successful habitat improvements (e.g., barrier removal, passage solutions), and examining the potential effects of climate change.  In practice, such efforts will be most efficiently coordinated at local, national or regional scales.

Some subpopulations exhibit marked genetic divergence, and this should be taken into account when considering conservation actions, particularly those that involve translocation or use of hatchery stocks.