1) Daur Pearl Mussel

Dahurinaia dahurica Middendorff, 1850
Order: Unioniformes – Freshwater Mussels
Family: Margaritiferidae – Pearl Mussels
Status: Rare species

Identification features:
This species has a fairly large and thick shell. The outer surface is dark brown, with some areas being almost black. The nacreous (inner) layer is white with a slight pinkish hue. Shell dimensions: length 105–218 mm, height 32–69 mm, thickness 25–40 mm, and weight up to 840–1000 grams.

Distribution and habitat:
Lives in rivers, streams, and small lakes within the Onon and Khalkh river basins. It has a restricted distribution.

Lifestyle:
Occurs in clear, clean waters of mountainous areas, particularly in sandy or fine gravel sections of rivers and lakes. Reproduces during July–August. Tiny larvae develop on the gills of fish.

Population and threats:
Population size and overall distribution have not been determined. Growth and development are slow. Natural factors such as river pollution, increased turbidity during floods, and the occasional drying up of lakes and ponds lead to mortality and population decline.

Protection status:
Listed as a rare animal in Annex 7 of the Mongolian Government Resolution, and included in the Red Book of Mongolia. Some of its habitat is partially included within nationally protected areas.

Conservation measures:
Study its biological and ecological characteristics. Protect the sandy and fine gravel habitats in rivers and lakes where it resides from all types of pollution.

2)Cockscomb Pearl Mussel

Cristaria plicata Leach, 1815
Order: Unioniformes – Freshwater Mussels
Family: Unionidae – River Mussels
Status: Rare species

Identification Features:
This is one of the largest mussels found in Mongolia. It has a thick and strong shell with a triangular “wing” sticking out from the top edge. The shell is brown with dark stripes on a greenish background. The shell length is between 200 and 240 mm. The total height, including the wing, is 140 to 180 mm (about 150 mm without the wing). The shell thickness is around 60 mm, and it can weigh up to 300 grams.

Where It Lives:
This mussel lives in Lake Buir. Since the 1960s, its numbers have dropped a lot because many get caught accidentally in fishing nets. It is now rare, especially in places where fishing is common. Its habitat is limited.

Lifestyle:
It lives on muddy or sandy bottoms in slow-moving water areas like bays and shallow parts of rivers and lakes. It usually stays at depths of 1.5 to 2 meters. As it moves along the sandy bottom, it leaves a noticeable trail.

Population and Threats:
Changes in the lake’s water levels make it hard for young mussels to survive. Adult mussels often get caught in fishing nets by accident, which lowers their population.

Protection Status:
This species is officially listed as rare by the Mongolian government and is protected in Lake Buir and nearby wetlands under international agreements. It is also included in Mongolia’s Red Book of endangered species.

Conservation Actions:
Efforts to protect this mussel include studying its biology, protecting its habitat through national or local laws, releasing mussels caught accidentally in fishing nets back into the water, banning fishing in breeding areas, and educating people about its conservation.

3)Selenga River Pearl Mussel
Anodonta sedakovi Siemaschko, 1848
Order: Unioniformes – Freshwater Mussels
Family: Unionidae – River Mussels
Status: Rare species

Identification Features:
The shell is broad, somewhat elongated, thin, and fragile, with a relatively high dome. The outer surface is greenish to yellowish-brown with faint dark grooves. The inner nacre is white with pale yellow spots. Shell length is approximately 92 mm, height 51 mm, and thickness 33 mm.

Distribution and Habitat:
This species is found in the Selenga, Orkhon, and Tuul river systems.

Lifestyle:
It lives buried in muddy and sandy bottoms of calm, slow-moving bends and sheltered areas of rivers. It is also found in small isolated lakes and ponds.

Population and Threats:
Due to water pollution, the species has become very rare in the Tuul River, particularly from Ulaanbaatar to Ulkh Bay.

Protection Status:
The species is listed as rare in the annex of the 2012 Mongolian Government Resolution and included in Mongolia’s Red Book.

Conservation Measures:
A detailed study of the species’ biology and ecology is necessary. Measures should focus on reducing pollution and improving water quality in the rivers it inhabits, especially in the Tuul River area. Special attention must be paid to protecting water quality. In some rivers within the Arctic Ocean watershed where populations have disappeared or declined, active breeding and restocking efforts should be undertaken.

4) Mongolian Pearl Mussel
Middendorffinaia mongolica Middendorff, 1851
Order: Unioniformes – Freshwater Mussels
Family: Unionidae – River Mussels
Status: Rare species

Identification:
The shell is hard, elongated, and slightly compressed. The outer surface is dark brown, while the inner layer is pale yellowish-white with a bluish tint. The shell length ranges from 30 to 80 mm.

Distribution and Habitat:
This species has been found in Russia’s Chita region and in Mongolia’s Onon, Balj, Khalkh, and Nömörög river basins, inhabiting rivers and streams.

Lifestyle:
It lives in fast-flowing rivers with sandy or gravelly bottoms, usually at depths up to 1.5 meters in mountainous and steppe river valleys. Reproduction takes place from early June to August. After 20 to 40 days, larvae detach from the mother mussel and float freely in the water before attaching to the gills of host fish, where they develop until maturity.

Population and Threats:
Population size and distribution have not been well studied. The species is very rare and occurs only in limited areas. Growth is slow. Pollution, increased turbidity during floods, and reduced oxygen levels cause deaths among larvae and sometimes adult mussels.

Conservation Status:
Listed as a rare species in the 2012 Mongolian Government Resolution and included in Mongolia’s Red Book. Its habitat is partially protected within the Mongol Daguur and Nömörög Strictly Protected Areas.

Protection Measures:
Further study of the species’ biology and ecology is needed. Protecting water quality in the Onon, Balj, Khalkh, and Nömörög river basins is essential to its survival.