Taxonomic Notes
In some published literature, this species is treated as a subpopulation of the Bourget Whitefish (Coregonus lavaretus) or a member of the "Coregonus lavaretus species complex", and referred to by the English vernacular names "Common Whitefish" or "European Whitefish" (see below).
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 21st 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, 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.
In the absence of a region-wide consensus, the Red List continues to follow the taxonomy provided by Fricke et al. (2024).
Justification
The Traun Whitefish is endemic to Lake Traun, Austria. The species has a restricted range (extent of occurrence (EOO) c. 33 km2), which meets the threshold for the Critically Endangered category under Criterion B1 (EOO < 100 km2). It occurs in one location where the quality of habitat is estimated to be undergoing continuing decline and the number of mature individuals is inferred to also be undergoing continuing decline.
Therefore, this species is assessed as Critically Endangered under Criterion B (B1ab(iii,v)).
Geographic Range Information
This species is endemic to Lake Traun (de. Traunsee) in the Salzkammergut region, upper Danube River system, Austria.
Population Information
This species' population size is unknown, but it is understood to exceed the minimum threshold for Red List criteria (< 10,000 mature individuals).
The current population trend has not been explicitly quantified, but abundance is inferred to be declining based on a marked reduction in commercial landings since around 2010. Environmental research indicates that this may be related to Lake Traun's recent recovery from industrial salinisation (see 'Threats').
Habitat and Ecology Information
Lake Traun is a perialpine, oligotrophic lake formed after the last glacial period. It has a maximum depth of 191 metres and is connected to nearby lakes Hallstatt (de. Hallstätter See) and Wolfgang (de. Wolfgangsee) via the Traun and Ischl rivers.
Current knowledge suggests that the relatively small-bodied Traun Whitefish predominantly occupies the profundal zone at depths of 40-60 metres. Maximum lifespan is c. 6 years and individuals become sexually mature at age 2+. The lengthy annual reproductive period extends from mid-October to early March when spawning occurs in the littoral zone.
Threats Information
Lake Traun was polluted by the discharge of waste materials from local salt and soda works from the early 20th century until production ended in 2005. No negative impact of these dissolved salts on aquatic species inhabiting the lake has ever been detected. This phenomenon has been linked to the rapid washing-out of pollutants due to the high discharge of the affluent Traun River, while the relatively shallow depth at which the wastes were released may have prevented their buildup in the hypolimnion.
However, the lake's recovery from salinisation has had a more damaging impact on stratification and deepwater oxygen concentrations. After industrial pollution ceased, the lake rapidly became meromictic with a substantial decrease in dissolved oxygen throughout the hypolimnion. The development of hypoxia is likely to have significantly reduced the available habitat for deepwater aquatic fauna such as the Traun Whitefish and is plausibly responsible for the recent decline in abundance.
This species is potentially threatened by resource competition and/or introgressive hybridisation with non-native whitefish from Lake Constance and the Baltic region, which have been routinely introduced to Lake Traun for decades in order to boost the local fishery. Some of these fish derive from a commercial strain of the Maraena Whitefish (Coregonus maraena) developed in the Czech Republic during the 19th century, which has been reared in Austrian hatcheries since the 1950s and used for stocking the lakes of the Salzkammergut region under the local name "Maraene". This strain is possibly introgressed with the North American Lake Whitefish (Coregonus clupeaformis).
Genetic analyses have demonstrated that little to no introgression between the Traun Whitefish and stocked individuals has occurred, and this is probably attributable to spatial and/or temporal reproductive isolation.
Stocking with native whitefishes, referred to locally as "Coregonus sp.", "Salzkammergut Reinanke" or "Renken" has also taken place in Lake Traun, and the risk of artificial hybridisation and introgression between the Traun Whitefish and lineages inhabiting lakes Wolfgang (de. Wolfgangsee) and Hallstatt (de. Hallstätter See) cannot be discounted.
The species is the focus of a fishery.
Other non-native species which have been introduced to Lake Traun and could potentially impact native fishes through predation include European Eel (Anguilla anguilla), Eurasian Pikeperch (Sander lucioperca) and Rainbow Trout (Oncorhynchus mykiss).
Additional threats include the degradation of littoral habitats for urban development and future shifts in the temperature regime of Lake Traun due to climate change.
The lake became increasingly eutrophic due to human activities during the mid-20th century. This process may have previously exerted an effect on whitefish population structure and selection but is not currently considered to represent a threat (see 'Conservation').
Use and Trade Information
Whitefishes comprise an important cultural element in the Salzkammergut region, where they are widely served in restaurants and marketed fresh, frozen or smoked as "Salzkammergut Reinanke". The Lake Traum Whitefish is typically skewered ("Stecklerfisch"), grilled and eaten whole. It is targeted by a long-established commercial fishery, but only a small number of fully professional fishers still operate.
Unlike sympatric whitefishes, this species is not reared in hatcheries or artificially stocked.
Conservation Actions Information
This species is included (as Coregonus spp.) in Appendix III of the Bern Convention and Annex V of the European Union Habitats Directive. Lake Traun is surrounded by several protected areas, but none of them include aquatic habitats.
In 2021 a fishing ban extending from 2022-2025 was established as a response to the declining Lake Traum Whitefish stock.
Investment in wastewater treatment facilities since the 1970s has driven an improvement in water quality of the lake, which has returned to its former oligotrophic state.
The lake continues to undergo recovery from industrial salinisation, and research predicts that full vertical mixing and re-oxygenation of the hypolimnion will occur in the near future. These developments are likely to benefit the Traun Whitefish, and annual population monitoring is strongly recommended.
A ban on stocking the Baltic whitefish strain in Lake Traun has also been proposed in order to remove the threat of hybridisation.
This species is not well-studied, and a deeper understanding of its demographics (population size and trend), life history, and the driver(s) of its recent decline would likely prove useful in the development of a structured management plan.