This species is referred to as a subpopulation of the Arctic Cisco (Coregonus autumnalis) in the majority of published literature but is here treated as a valid taxon as per Fricke et al. (2024).

At the regional scale, the systematics of European ciscoes and whitefishes (Coregonus spp.) has 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 been recorded in perialpine lakes, and these radiations might be even more diverse in some 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, the majority of 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. Irish subpopulations are included within the pan-Arctic Coregonus autumnalis (Arctic Cisco).

In contrast, 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. Irish subpopulations are regarded to comprise the endemic species C. pollan.

In the absence of a region-wide consensus, the Red List continues to follow the taxonomy provided by Fricke et al. (2024).

Global and European regional assessment: Vulnerable (VU)
EU 27 regional assessment: Endangered (EN)

The Irish Whitefish has a restricted range (extent of occurrence (EOO) c. 12,912 km², area of occupancy (AOO) c. 760 km2), which meets the thresholds for the Vulnerable category under Criterion B1 (EOO < 20,000 km²) and Criterion B2 (AOO <  2,000 km²). It is present at five locations where the quality of habitat is estimated to be declining.

Therefore, this species is assessed as Vulnerable under Criterion B (B1ab(iii)+2ab(iii)) at the global and European regional scales.

In the EU 27 member states, the EOO (3,028 km²) and AOO (148 km²) meet the thresholds for the Endangered category under Criterion B1 (EOO < 5,000 km²) and Criterion B2 (AOO < 500 km²). It is present at three locations where the quality of habitat is estimated to be declining and is assessed as Endangered under Criterion B (B1ab(iii)+2ab(iii)).

This species is endemic to Ireland, where it is currently present in five fluvial lake systems, comprising Lough Allen, Lough Ree and Lough Derg in the Shannon River system, Lough Erne in the Erne River system and Lough Neagh in the Bann River system.

Records from the 19^th century suggest that it was at that time present in loughs Derravaragh and Iron in the Shannon River system and Lough Garadice in the Erne River system, among which the latter currently forms part of the Shannon-Erne Waterway canal.

This species' population size is unknown, but it exceeds the minimum threshold for Red List criteria (< 10,000 mature individuals). The current population trend has not been quantified. Overall abundance is understood to have declined significantly since c. 1970, based on a combination of anecdotal reports, fisheries bycatch data, and netting/hydroacoustic surveys.

The largest extant subpopulation inhabits Lough Neagh, where it was estimated to comprise c. 25% of overall fish biomass during the early 2000s. Major shifts in the structure of this subpopulation linked to a loss of older individuals were detected during the 1990s, leading to several years characterised by weak recruitment.

Subpopulations formerly inhabiting loughs Derravaragh, Iron, Garadice and upper Lough Erne have been extirpated, and abundance in lower Lough Erne is currently understood to be low.

The Lough Allen subpopulation was discovered during the mid-2000s, and recent (2013-2016) surveys suggest that abundance is relatively high compared with other lakes in the Shannon River system.

There exist reports that the Irish Whitefish was abundant in loughs Ree and Derg prior to the mid-20^th century. Surveys conducted in 2010 suggest the Lough Ree subpopulation may be larger than previously understood, but nevertheless comprises < 1% of overall fish biomass in the lake.

This species mostly inhabits large post-glacial lakes. It has on occasion been observed in the main stems of the Shannon, Erne and Bann rivers, and may even spawn in the Shannon upstream of Lough Derg.

Lough Neagh is the largest lake in the British Isles by surface area but is relatively shallow with a maximum depth of 25 metres. It was formerly mesotrophic but is today hypertrophic, and is perhaps able to support a relatively large Pollan subpopulation due to significant wind-driven mixing which results in only transient thermal and oxygen stratification (see 'Threats').

The maximum depth of the remaining four inhabited lakes ranges from 31 metres in Lough Allen to 65 metres in Lough Erne.

Lough Erne comprises two basins, of which the upper basin is currently eutrophic and the lower basin meso- to eutrophic.

Lough Allen is the least-affected by human activities and has consistently remained in an oligotrophic state. The trophic status of loughs Ree and Derg has fluctuated between mesotrophic and eutrophic since the 1980s, with a current tendency towards the former.

The Pollan occupies benthopelagic habitats in cool, deep water, and during warmer months of the year undertakes diel vertical migrations related to foraging. It feeds predominantly on zooplankton, particularly copepods and cladocerans, but also takes larger prey including chironomid larvae and the crustacean Mysis salemaai. It exhibits slight differences in feeding ecology depending on location. For example, in Lough Neagh insects are taken at the water surface during periods of calm weather. The typical lifespan is c. 5 years and individuals become sexually mature at age 2+. The annual reproductive period extends from December to January, when spawning takes place on well-washed banks of coarse stony substrata in shallow (≤ 3 metres depth) littoral habitats. Reproductive males typically aggregate at spawning sites several weeks prior to females, which arrive independently as they become ripe and leave immediately post-spawning. The incubation period is around two months, and the eggs hatch in spring.

This species is threatened by eutrophication, which was initially driven by point-source discharge of domestic wastewater and subsequently by diffuse agricultural pollution.

In deep lakes, this process typically leads to oxygen depletion in the hypolimnion, and a subsequent reduction in the extent of available foraging and refuge habitats, which can be exacerbated due to thermal stratification in summer.

A limited commercial fishery still exists in Lough Neagh; small-scale commercial or semi-commercial fisheries which formerly operated in Lough Erne and the Shannon lakes have been inoperative since 1994 and the 1960s, respectively. In Lough Neagh, age 0+ individuals are taken illegally and used to bait long-lines for European Eel (Anguilla anguilla). Recreational angling is permitted on all five lakes, but this species is not typically targeted.

Increased algal growth and sedimentation associated with eutrophication may also increase Irish Whitefish egg mortality or cause the loss of entire spawning sites, while nutrient enrichment can interfere with individual growth rate, fecundity and age at maturity.

Eutrophic conditions also favour a number of non-native fish and invertebrate species which are considered detrimental to native fish communities. Among these, the Common Roach (Rutilus rutilus) is likely to compete for zooplankton resources since it thrives in nutrient-rich conditions, and has become established throughout Ireland since the mid-20th century.

In addition, introduced predatory fishes such as Eurasian Perch (Perca fluviatilis) and Northern Pike (Esox lucius) are likely to consume some Irish Whitefish individuals, although the extent of their impact is unclear.

The Zebra Mussel (Dreissena polymorpha) was unintentionally introduced to the Shannon-Erne system during the early 1990s and represents a major plausible threat due to its consumption of phytoplankton and ability to alter zooplankton abundance, community structure and composition. It may also colonise Irish Whitefish spawning sites and negatively impact reproductive success.

The Quagga Mussel (Dreissena bugensis) was detected in the Shannon River system during 2021 and is believed to be driving significant food web alterations affecting pelagic fishes in some other European waterbodies, e.g., Lake Constance.

The Asian Clam (Corbicula fluminea), which has a broadly similar life history to the mussel species, was first observed in the Shannon River during 2010 and in Northern Ireland in 2016.

The Bloody-Red Shrimp (Hemimysis anomala) has been present in the Shannon River since 2008 and can alter freshwater ecosystems by consuming zooplankton and competing with native mysids. Research has demonstrated its ability to prey on Irish Whitefish eggs and larvae.

Water abstraction may expose gravel beds and reduce reproductive success, and land drainage leading to siltation of downstream lakes can lead to clogging of spawning sites.

Increased water temperatures driven by climate change represent a plausible ongoing and future threat, and could further reduce the extent of suitable habitat due to the development of anoxic conditions in deep water during summer stratification. Warming of the lakes may also impact this species' winter spawning behaviour and overall reproductive output.

A limited commercial fishery still exists in Lough Neagh, from where c. 450 tonnes per year were being exported annually around the turn of the 20^th century. Small-scale commercial or semi-commercial fisheries which formerly operated in Lough Erne and the Shannon lakes have been inoperative since 1994 and the 1960s, respectively.

In Lough Neagh, age 0+ individuals are taken illegally and used to bait long-lines for European Eel (Anguilla anguilla).

Recreational angling is permitted on all five lakes, but this species is not typically targeted.

The Irish Whitefish is not presently reared in hatcheries or stocked anywhere within its range.

This species is included (as Coregonus spp.) in Appendix III of the Bern Convention and Annex V of the European Union Habitats Directive.

At the national level it was assessed (as Coregonus autumnalis pollan) as Vulnerable for the Republic of Ireland's most recent (2011) National Red List, and is included in the National Fisheries Act (as "Pollen"). In Northern Ireland, it is included in Schedule 3 of the Conservation (Natural Habitats, &c.) Regulations 1994 (as Coregonus spp.) and is listed as a priority species of conservation concern in the United Kingdom's Post-2010 Biodiversity Framework (as Coregonus autumnalis).

Lough Derg and Lough Ree are included in the European Union's Natura 2000 network (sites IE0004058 and IE0004064), and lower Lough Erne includes a number of small protected areas. Lough Neagh has also been included in the Natura 2000 scheme (site UK9020091), and is a Ramsar site under the Convention on Wetlands of International Importance.

The Lough Neagh commercial fishery is regulated by a close season plus gillnet mesh size and minimum catch size limits.

Measures to improve wastewater treatment since the 1990s have been linked to an improvement in water quality at some locations, e.g., Lough Derg.

A standardised sampling protocol for Irish Whitefish conservation assessments has recently been developed with the support of Inland Fisheries Ireland and the Irish Research Council.

In 1995, the United Kingdom Biodiversity Steering Group published an action plan for Northern Irish subpopulations which included a range of suggested management actions, none of which were subsequently implemented.

Proposed future research topics include investigating the genetic relationships between subpopulations, in addition to understanding their respective abundance, habitat use, prey selectivity, recruitment success and the location of spawning sites.

The potential for artificial rearing in hatcheries and the creation of "refuge" subpopulations through translocation to additional sites has also been suggested, but no feasibility analysis has been carried out.

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