British whitefishes
The taxonomic status of Coregonus subpopulations inhabiting the British Isles has not been definitively resolved since a series of endemic species were described between the early 19^th and early 20^th centuries.

Among these, C. clupeoides is most closely related to C. pennantii Valenciennes, 1848 from northwestern Wales and C. stigmaticus Regan 1908 from northwestern England. A number of recent studies have demonstrated that there is little morphological or genetic support for considering these as distinct taxa when they are compared with one another (Etheridge et al. 2012, Crotti et al. 2020).

In the United Kingdom, all three are treated as junior synonyms of the congener Coregonus lavaretus (Linnaeus 1758), the name of which has since the mid-20^th century been applied to a widespread complex of polymorphic whitefish populations occurring across northwestern Eurasia (Crotti et al. 2021). However, the systematics of this putative assemblage and the native range of C. lavaretus remain questionable (see further discussion below).

C. clupeoides is currently regarded as valid for global Red List purposes following Fricke et al. (2024), and the present global assessment should be considered equivalent to the most recent Scottish national assessment for C. lavaretus (Nunn et al. 2023).

European ciscoes and whitefishes
At the regional scale, the systematics of European ciscoes and whitefishes (Coregonus spp.) has also been the subject of considerable debate since the turn of the 21^st century, with little indication of a definitive outcome.

It is widely accepted that non-anadromous members of this group have repeatedly undergone adaptive radiations in boreal, subarctic and perialpine lakes (Douglas et al. 1999, Østbye et al. 2005, Kahilainen and Østbye 2006, Harrod et al. 2010, Hudson et al. 2011).

Subpopulations inhabiting these systems largely diversified in the wake of the most recent glacial period 10,000-15,000 years ago. They are typified by parallel patterns of divergence in traits associated with foraging (i.e., gill raker counts, benthic vs. pelagic feeding ecology), physiology (i.e., growth rate, habitat depth partitioning) and reproductive ecology (i.e., reproductive timing and spawning habitat).

Up to six different sympatric forms sometimes referred to as “morphs”, "ecomorphs" or "ecotypes" have evolved in some perialpine lakes, and these radiations might be even more diverse in a few large systems of northeastern Europe (Præbel et al. 2013, Doenz et al. 2018, Bitz‐Thorsen et al. 2020, Öhlund et al. 2020).

However, there exist significant differences in opinion regarding the taxonomic status of these forms.

In northern Europe, including the United Kingdom, all except a handful of Irish subpopulations are usually regarded as belonging to two widely-distributed species; Coregonus albula (ciscoes) and C. lavaretus (whitefishes), with the latter also frequently referred to as the "Coregonus lavaretus species complex” (Etheridge et al. 2012, Wanke et al. 2017, Häkli et al. 2018, Crotti et al. 2020). Within this comparatively uniform taxonomic concept, the catch-all English vernacular name “Vendace” is typically used for C. albula while "Common Whitefish" or "European Whitefish" are applied to C. lavaretus.

Conversely, researchers and fisheries authorities based in Central Europe have tended to treat the different forms as distinct taxa, leading to the recognition of more than 60 species across the European region (Kottelat and Freyhof 2007, Selz et al. 2020, De-Kayne et al. 2022, Selz and Seehausen 2023). Under this diverse taxonomic concept, the name “Vendace” is restricted to its original usage for the United Kingdom endemic Coregonus vandesius and the native range of C. lavaretus is limited to its type locality of Lake Bourget in France.

With the above in mind, it appears unlikely that the striking phenotypic diversity exhibited by members of this genus will ever be adequately represented by a single accepted taxonomic system. The Red List currently follows the nomenclature provided by Fricke et al. (2024).

Global and European regional assessment: Vulnerable (VU)
EU 27 regional assessment: Not Recorded

The Powan is endemic to Europe, where it is restricted to a number of lakes in western Scotland, United Kingdom. It has a restricted extent of occurrence (EOO) of c.1,685 km² and an area of occupancy (AOO) of c.100 km²), which meet the thresholds for the Endangered category under Criterion B1 (EOO < 5,000 km²) and Criterion B2 (AOO <500 km²). The quality of habitat is estimated to be undergoing continuing decline, and the species occurs in eight threat-defined locations.

Therefore, this species is assessed as Vulnerable under Criterion B (B1ab(iii)+2ab(iii)).

This species is endemic to Loch Lomond and Loch Eck in western Scotland, United Kingdom.

Additional subpopulations resulting from benign introductions are established in Loch Sloy and Carron Valley Reservoir, both of which are artificial accumulation lakes located within the Loch Lomond catchment. It has more recently been translocated to the Allt na Lairige, Lochan Shira, Loch Glashan and Loch Tarsan reservoirs, where reproduction is also taking place (see 'Conservation'). The translocated subpopulations are included in the present assessment since the known intent of the introductions was to reduce the extinction risk of the taxon, the occupied sites are geographically close to the natural range, viable offspring have been produced, and at least five years have passed since the translocations took place.

Loch Sloy, Allt na Lairige and Loch Tarsan could not be included on the range map accompanying this assessment due to their small size.

This species' population size is unknown, and the current population trend has not been explicitly quantified.

The Loch Lomond subpopulation is understood to have experienced a significant reduction since the 1980s. It was formerly abundant in the lake, but the results of hydroacoustic surveys carried out since the mid-2000s indicate that it has become comparatively scarce.

The effective size of both subpopulations is estimated to be relatively small, suggesting that they may possess a limited ability to adapt to future environmental change.

Loch Lomond is the largest freshwater lake in Great Britain by surface area, and was formed after the last glacial period. It has a maximum depth of 191 metres and three main basins comprising a deep and narrow oligotrophic northern basin, a wide and shallow mesotrophic southern basin and a small mid-basin with intermediate physical characters.

Loch Eck is also post-glacial in origin, but is much smaller with less-complex bathymetry than Loch Lomond, and comprises a narrow, steep-sided basin with a maximum depth of 42 metres.

There is substantial evidence to demonstrate that the two resident subpopulations differ markedly in aspects of their morphology, parasite loading, feeding ecology and life history.

For example, in Loch Lomond this species feeds intensively on zooplankton from May to September, and for the remainder of the year consumes only small quantities of benthic prey such as chironomid larvae and sphaeriid clams. In contrast, the Lock Eck subpopulation feeds predominantly on zoobenthos throughout the year, and stops feeding only during the annual reproductive period.

The two subpopulations exhibit morphological differences that appear to be driven by these divergent feeding strategies. In particular, individuals from Loch Lomond exhibit traits associated with a pelagic diet, i.e., a comparatively longer, shallower head, large eye and superior mouth, while those from Loch Eck display benthophagous traits such as a deeper head shape and inferior mouth. In addition, individuals from Loch Eck tend to be smaller-bodied with a slower growth rate and lower parasite load than those from Loch Lomond.

The majority of male individuals reach sexual maturity at age 2+ and most females at age 3+. Both sexes mature earlier in Loch Eck than in Loch Lomond.

The annual reproductive period extends from mid-December to early February and lasts for a maximum of four weeks, with the precise timing dependant on environmental cues that may be related to the lunar cycle.

Reproductive males form aggregations at spawning sites located in shallow water several weeks prior to females, which arrive independently as they become ripe and leave immediately post-spawning.

In Loch Lomond, spawning takes place on offshore gravel banks or along shorelines, whereas in Loch Eck it is believed to occur in the vicinity of macrophytes such as Quillwort (Isoetes spp.) and Water-Milfoil (Myriophyllum spp.).

The incubation period is relatively extended and the eggs hatch in spring, with mortality in the first year of life believed to be > 99%.

In Loch Lomond this species was formerly the favoured prey of the Eurasian Otter (Lutra lutra), Grey Heron (Ardea cinerea), Great Cormorant (Phalacrocorax carbo), Northern Pike (Esox lucius) and European River Lamprey (Lampetra fluviatilis), but there is evidence to suggest that all of these species have altered their trophic ecology to feed primarily on the non-native Eurasian Ruffe (Gymnocephalus cernua) since its introduction to the lake (see 'Conservation').

Some tributaries of Loch Lomond have been dammed for domestic water supply and the development of hydroelectric schemes, leading to concerns over the water level of the lake.

An upward shift in trophic status has also been detected, with increased nutrient enrichment concentrated mainly in the southern basin which is surrounded by agricultural land plus several towns and villages.

The lake is also impacted by human recreation, e.g., hydrocarbons from leisure boats, especially during the summer.

A series of blue-green algae (Cyanobacteria) blooms have been reported in Loch Eck since the early 2010s, but the phenomenon has not yet been studied in depth.

Since the 1970s, a number of non-native fish species have become established in Loch Lomond, among which the Eurasian Ruffe is of particular concern. It is an opportunistic, largely benthivorous predator and unlike the native fish species present in the lake continues to feed intensively throughout the winter, when it is believed to prey heavily on Powan eggs, e.g., in one study it accounted for c.64% of those eaten.

No non-native fish species are currently established in Lock Eck, but their introduction represents a plausible future threat.

Warming of the lakes due to climate change also constitutes a major ongoing and future threat for this cold-water adapted species.

This species has in the past been exploited on a commercial basis, e.g., during the two World Wars, but has not been used or traded since the mid-20^th century.

Recreational angling is permitted on both Loch Lomond and Loch Eck, but this species is not targeted.

This species is included (as Coregonus spp.) in Appendix III of the Bern Convention.

At the national scale it is included (as Coregonus lavaretus) in Schedule 5 of the Wildlife and Countryside Act 1981 and Schedule 3 of the Conservation (Natural Habitats, &c.) Regulations 1994, and is listed as a priority species of conservation concern in the U.K. Post-2010 Biodiversity Framework and the Scottish Biodiversity List.

Loch Lomond and Loch Eck both lie within the Loch Lomond and Trossachs National Park. The lower reaches of the affluent Endrick Water and four islands in the southeastern portion of Loch Lomond together comprise a Ramsar site under the Convention on Wetlands of International Importance (site no. 73), and Lock Eck is designated a Site of Special Scientific Interest.

The introduced subpopulations established in Loch Sloy (formerly a natural lake that was impounded and enlarged during the 1940s) and Carron Valley Reservoir were intentionally translocated to create "refuge" subpopulations for conservation purposes. In 1988, a number of adult fish were transported directly from Loch Lomond to Loch Sloy, and from 1988-1990 gametes were annually stripped from reproductive individuals captured in Loch Lomond resulting in the release of thousands of fry at both sites. There is evidence that the introduced subpopulations have diverged in some aspects of ecology, morphology and life history, although no clear signals of reduced genetic diversity have been detected.

The divergence in genetic structure, morphology, ecology and life history exhibited by the two natural subpopulations has led to them being considered as distinct units in terms of management. Between 2009 and 2011, efforts were made to establish two new refuge sites for each subpopulation. These actions were driven by plans to modify the Loch Sloy hydroelectric plant, plus the lack of an existing refuge site for the Loch Eck subpopulation. Eggs and fry from Loch Lomond and Loch Sloy were introduced to the Allt na Lairige and Lochan Shira hydroelectric reservoirs, and adults and fry from Loch Eck were transferred to lochs Glashan and Tarsan. Subsequent sampling has revealed that reproduction is taking place at all four locations.

The taxonomic status of British Coregonus species is in need of a definitive review, but there exist a number of complications (see 'Taxonomic Notes').