Taxonomic Notes
Although the systematics of Eurasian and North African brown trouts (Salmo spp.) remain somewhat disputed, this taxon is well-established as a genetically and morphologically distinct species that is clearly differentiated from members of the Brown Trout (Salmo trutta) complex (Whiteley et al. 2019). It has previously been classified in the genera Acantholingua and Salmothymus (Sušnik et al. 2006; Snoj et al. 2009; Pustovrh et al. 2014).
Justification
Global and European regional assessment: Endangered (EN)
EU 27 regional assessment: Not Recorded
The Ohrid Belvica has a restricted range (extent of occurrence (EOO) c. 386 km2, area of occupancy (AOO) c. 360 km2), which meets the thresholds for the Endangered category under Criteria B1 (EOO < 5,000 km2) and B2 (AOO < 500 km2). It is present at one location where the quality of habitat is estimated to be declining.
Therefore, this species is assessed as Endangered under Criterion B (B1ab(iii)+2ab(iii)).
Geographic Range Information
This species is endemic to Lake Ohrid (sq. Liqeni i Ohrit; mk. Охридско Езеро), located at the boundary between eastern Albania and southwestern Republic of North Macedonia.
Population Information
This species' population size is unknown, but it clearly exceeds 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 somewhat unclear (see 'Habitat and Ecology').
A number of studies report declining abundance since the late 20th century, but this is not supported by quantitative data. For example, fisheries records from Albania indicate that annual Ohrid Belvica landings approximately averaged more than 10 tonnes per year from the 1960s until the 1990s, when they sharply declined to below 2 tonnes per year. However, the Albanian fishery underwent significant changes after 1990, and records from 2022-2023 show that almost 10 tonnes were harvested during the first six months of each year alone. A similar pattern is observed in fisheries records from the Republic of North Macedonia, with landings consistently exceeding 10 tonnes in the majority of years except for the 1990s. The fall in officially-reported landings at this time could plausibly be related to a significant temporary increase in unregulated harvesting (see 'Use and Trade').
In terms of genetic structure, the Ohrid Belvica is significantly divergent from sympatric trout inhabiting Lake Ohrid, which are included in the Adriatic mitochondrial lineage within the wide-ranging Brown Trout (Salmo trutta) complex and are understood to have colonised the lake quite recently.
Habitat and Ecology Information
Oligotrophic and oligomictic Lake Ohrid occupies a steep-sided graben and is of tectonic origin. Its surface area is 358 km2, and it is the deepest lake in the Balkan region, with a mean depth of 164 metres and maximum depth of 289 metres. The lake remains oxygenated even in the profundal zone, but is stratified by salinity below depths of 150 metres and only mixes completely about once per decade. With an estimated minimum age of c. 4 million years, Ohrid is probably the oldest extant lake in Europe.
It is fed primarily by two major karstic surface springs at its southern end plus a series of sub-lacustrine (underwater) springs which are located along the eastern and, to a lesser extent, western shores. All such inflows on the eastern and southern sides originate in the adjacent Lake Prespa (sq. Liqeni i Prespës; mk. Преспанско Езеро; el. λίμνη Πρέσπα) basin, which is located at a slightly higher altitude and drains to Ohrid via subsurface karstic conduits. Four small rivers and numerous intermittent streams also influence the overall water level to a minor extent in spring or during periods of heavy rainfall. Ohrid is drained by the Black Drin (sq. Drini i Zi; mk. Црн Дрим) River, which flows towards the Adriatic Sea after exiting the lake at its northern tip, and it loses significant volumes of water (c. 40%) via evaporation. Due to its relatively limited recharge and discharge regimes compared to its overall volume, it is characterised by a long retention time of c. 83.6 years. The lake's water balance and watershed were artificially enlarged during the 1960s when the River Sateska, which formerly flowed into the Black Drin, was diverted into the lake to increase its potential for hydropower generation. Two large hydroelectric dams were also constructed on the Black Drin main stem immediately downstream of the lake around this time.
The lake contains exceptionally clear water with a Secchi depth of 7-16 metres in the pelagic zone. It is rich in macrophytes, among which the littoral vegetation includes a discontinuous strip of Common Reed (Phragmites australis) extending around 1.5 metres into the water, dense stands of angiosperms (particularly Potamogeton perfoliatus) to depths of c. 4 metres, and a largely continuous dense belt of stonewort (Chara spp.) at depths of 4 metres to c. 11 metres, extending to c. 18.5 metres in places.
The lake’s low-nutrient, high-oxygen environment supports an exceptional biodiversity consisting of at least 1,200 taxa, of which more than 200 are endemic. It is thus among the most species-rich inland water bodies on Earth when surface area is taken into account. The lake is also considered to be a hotspot of endemic salmonid diversity, with up to five recognised species. In addition to the highly divergent Ohrid Belvica, these include four closely-related taxa, the common ancestor of which is likely to have radiated into discrete ecological forms which differ in morphology and reproductive behaviour. The taxonomic status of these forms has been extensively disputed, but for Red List purposes they are currently treated as distinct species comprising Ohrid Trout (Salmo letnica), Ohrid Summer Trout (S. aphelios), (S. balcanicus) and (S. lumi).
The Ohrid Belvica occupies sublittoral and pelagic habitats at depths of 40-70 metres, where water temperatures tend not to rise above 10°C throughout the year. It feeds largely on benthic invertebrates and zooplankton, and larger individuals may also prey on smaller fishes.
The maximum recorded lifespan is 12 years, and adult individuals mature at age 3-4+. The principal reproductive period extends from the end of November to the middle of January, when spawning takes place both in the littoral stonewort beds at depths of 4-5 metres, and in the sublittoral zone above patches of fine substrata at depths of 20-40 metres. The latter sites are often distinguished by colonies of the native bivalve mollusc Dreissena presbensis, which are possibly utilised as a spawning substrate. Reproductive activity in the sublittoral is understood to extend into spring, and some individuals may even spawn in June or July. This species' life history has not been studied in detail for around half a century, and it is unclear whether these alternative spawning strategies are indicative of multiple stocks. In addition, its habitat and feeding preferences during the initial growth phase appear to be unknown.
It is understood to be reproductively isolated from other Salmo taxa inhabiting Lake Ohrid, but instances of hybridisation with Ohrid Trout have occasionally been reported. It is unclear if these result from natural processes or refer to individuals reared in hatcheries and released into the lake.
Threats Information
The Lake Ohrid basin has experienced increasing urbanisation (including tourism) and cultivation since the late 1940s. It is thus threatened by the progressive accumulation of anthropogenic nutrients, chemicals and sediment loads from a variety of sources, including untreated domestic sewage, mining and other industry, and agriculture, which are driving increased rates of eutrophication and sedimentation. In the northeastern part of the basin, the Sateska River has become a major source of pollution since it was diverted into the lake. In addition, water abstraction and eutrophication in the Lake Prespa watershed is believed to be responsible for elevated nutrient levels in the southern and eastern affluent springs. These alterations are reflected by increasing phosphorous concentrations in the littoral and pelagic zones, decreasing dissolved oxygen content in the hypolimnion, and reduced water transparency.
A shift to non-endemic algae, macrophyte, diatom, and macroinvertebrate species associated with eutrophication has been observed close to polluted affluents and sewage outflows, but this has not yet resulted in major shifts within the pelagic phytoplankton community. It has been hypothesised that the extensive littoral macrophyte stands, including the stonewort beds utilised by spawning Ohrid Belvica (see 'Habitat and Ecology'), and filter-feeding benthic invertebrates may be acting as a phosphorus sink which buffers the pelagic from eutrophication. Signs of narrowing associated with decreased water transparency have already been detected in the stonewort belt, and should this be lost the extent of Ohrid Belvica spawning habitat would be significantly reduced. The coverage by reedbeds has also decreased due to recreational and residential shoreline development, and further degradation of the littoral vegetation could plausibly drive increased nutrient loading in the pelagic and accelerate the rate of eutrophication throughout the lake.
Increased boat traffic due to tourism, direct abstraction of domestic drinking water and the ongoing capture and pollution of karstic springs are also of concern. Plastics and other solid wastes are regularly washed into the lake because effective landfill sites are limited or do not meet modern standards.
Moreover, under a global warming scenario, the detrimental effects of increased nutrient inputs are projected to intensify. Even a slight increase in the lake's productivity might lead to a complete loss of dissolved oxygen in the profundal zone, while warming water temperatures and increasing eutrophication could interfere with the Ohrid Belvica's food supply, foraging behaviour and reproductive processes.
At least 7 non-native fish species known to exert detrimental pressures on native freshwater fauna through increased competition, predation, transmission of pathogens or habitat degradation have been introduced to Lake Ohrid. Among these, Eastern Mosquitofish (Gambusia holbrooki) was introduced around the mid-20th century in order combat water-borne disease. Rainbow Trout (Oncorhynchus mykiss) was recorded regularly from 1974 to 1994 but now appears to be scarce after the Albanian hatchery from which it originated switched production to native Ohrid Trout. Topmouth Gudgeon (Pseudorasbora parva) was also introduced during the 1970s. Prussian Carp (Carassius gibelio) was first reported in 1983 and is now abundant with annual landings exceeding 20 tonnes, while European Bitterling (Rhodeus amarus) and Pumpkinseed (Lepomis gibbosus) have been established since the 1990s. The origin of Common Carp (Cyprinus domestic strain) in the lake is less clear, but it is currently stocked on an annual basis despite the Ohrid basin being located outside of its native range. Most of these taxa predominantly inhabit littoral and sublittoral habitats and could plausibly predate on the eggs and early life stages of native salmonids, although their impact has not yet been investigated.
There is currently no clear evidence that the Ohrid Belcica is threatened by overharvesting, but conclusive and unambiguous research is required. Abandoned or discarded fishing gear may represent a secondary threat, since nets placed by unlicensed fishers are typically located at known spawning sites and can continue to trap individuals for several months or even years.
Use and Trade Information
Lake Ohrid supports a long-established commercial fishery, and the Ohrid Belvica is of considerable economic importance alongside Ohrid Trout, Skadar Bleak (Alburnus scoranza), European Eel (Anguilla anguilla) and the non-native Eurasian Carp (Cyprinus domestic strain). It is typically eaten fresh or dried and is viewed as a local delicacy. It is increasingly marketed by the local tourism sector, which has led to rising demand and market prices since the turn of the century.
During the period 1960-1990, a joint Ohrid fisheries commission managed issues of transboundary concern such as quotas per country, minimum landing sizes, closed seasons and stocking measures. This authority no longer exists, although collaboration continues at political and research levels.
In the Albanian portion of the lake, the local fishery was administrated by a state enterprise employing around 35 fishers until the fall of communism in 1991. This was followed by a period of deregulation during which an estimated 800 authorised and unauthorised fishers operated on the lake (see 'Population'). Since 2002, a dedicated Fisheries Management Organization issues a maximum of 110 licenses at any given time.
Prior to 1994, the Republic of North Macedonia fishery was managed by two state-owned companies, but is today governed by a private firm which employs around 50 fishers. The current concession was granted following a total fishing moratorium, which was in place from 2004-2012 due to fears of overharvesting.
Annual Ohrid Belvica commercial landings apparently vary, but an average yield of at least 10 tonnes per country has been reported consistently since the 1960s except during the 1990s. However, these figures do not account for unauthorised harvesting, which has been widespread since regulations were first introduced and mostly takes place during the spawning season, when the fishery is officially closed (see 'Conservation'). Gill nets are the most widely-used gear by both licensed and unauthorised fishers, but purse seines and long lines are also employed.
A hatchery-based supportive breeding programme for the Ohrid Trout has been established at the Hydrobiological Institute Ohrid in the Republic of North Macedonia since 1935. Experimental hybridisation with Ohrid Belvica reportedly took place during the 1950s, but it is unclear whether any hybrid individuals were subsequently released into the lake.
Conservation Actions Information
The North Macedonian portion of Lake Ohrid has been included in UNESCO's list of World Heritage sites since 1979. A bilateral agreement between Albania and North Macedonia resulted in establishment of the Ohrid Watershed Management Committee in 2004 and the Ohrid-Prespa Transboundary Biosphere Reserve in 2014. At the national scale, a number of additional protected sites have been created around the lake, including the Pogradec Aquatic and Terrestrial Protected Landscape and Drilon National Monument in Albania, and the Lake Ohrid Monument of Nature and Galičica National Park in North Macedonia. In April 2021, Lake Ohrid was added to the Ramsar Convention on Wetlands of International Importance (site 2449).
Fisheries management plans have been developed in both Albania and the Republic of Macedonia since the 2000s. Current regulations covering the Ohrid Belvica include minimum landing sizes (30 cm in Albania, 22 cm in Republic of North Macedonia) and closed fishing seasons (November 1 to January 31 in Albania, December 1 to March 20 in Republic of North Macedonia). Annual quotas were established in Republic of Macedonia during 2011, since when the permitted commercial offtake has risen from 1-12 tonnes per year, and recreational offtake from 400-900 kilogrammes. Steps have been taken towards the harmonisation of these legal frameworks in order to supervise the fishery on a collaborative basis, which may involve reinstatement of the joint fisheries commission (see 'Use and Trade'). Points of concern include improved control of unauthorised harvesting, establishment of new annual landing quotas for both countries, a review of stocking procedures to include analysis of their effectiveness, modernisation of existing hatchery facilities, and an update of approved fishing gear types.
Recommendations for the design of a transboundary fish monitoring programme were made following a multi-species stock assessment carried out from 2013-2015, but it is unclear whether these were subsequently implemented. These surveys took place in the littoral zone and thus did not target the preferred offshore habitat of the Ohrid Belvica.
In 2018, a pilot study investigating the presence of lost, abandoned or discarded fishing gear in the North Macedonian part of the lake resulted in the removal of more than 12,000 metres of nets from the lake.
Improved wastewater treatment measures are required to prevent the ongoing eutrophication of Lake Ohrid. Since the late 1980s, around 65% of domestic wastewater produced in the Republic of Macedonia is collected by a ring system and transported to a treatment plant near the town of Struga, from where the effluent is pumped into the Black Drin River. However, the system was never fully-completed and is thus partly dysfunctional. In Albania, a wastewater treatment plant was installed at the urban centre of Pogradec in 2006, but the phosphorous-rich effluent is discharged directly into the lake. Moreover, most rural communities still lack access to proper wastewater facilities, and continue to release untreated effluent into the lake or its tributaries.
Protection and restoration measures for the littoral zone and its macrophyte community has been recommended as a potentially effective measure to protect the pelagic from increasing nutrient levels. Restoring the original course of the Satesca river has also been proposed.
A deeper understanding of the Ohrid Belvica's demographics (population size and trend), life history (particularly diet preferences, locations of nursery zones and key spawning sites, the possible existence of multiple stocks with divergent reproductive strategies, and the impact of non-native species) and response to the ongoing threats would undoubtedly prove beneficial in the design of any structured management plan.
