Unio delphinus 

Scope: Global & Europe
Language: English

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Taxonomy [top]

Kingdom Phylum Class Order Family
Animalia Mollusca Bivalvia Unionoida Unionidae

Scientific Name: Unio delphinus Spengler, 1793
Taxonomic Notes: This species was recently spilt from Unio pictorum in Spain, and hence there is little data under this name. It was assessed for the Andalusian Red Book under the name Unio cf pictorum. Araujo et al. (2009) reviewed the status of the species and fully documents other synonyms.

Assessment Information [top]

Red List Category & Criteria: Near Threatened ver 3.1
Year Published: 2011
Date Assessed: 2009-05-23
Assessor(s): Araujo, R.
Reviewer(s): Aldridge, D., Van Damme, D., Seddon, M.B. & Cuttelod, A.
Unio delphinus is the more common and distributed Unio species in the western part of the Iberian Peninsula . Nevertheless, as all the naiads, its reproductive cycle is highly specialized and relies upon a fish. Moreover, juvenile naiads are very demanding in terms of water and sediment quality. These two factors combine to see a decline in the overall populations, with loss of recruitment. In addition, the anthropogenic alterations suffered by water bodies in the last decades (water transfer, water detraction, river channelling and dredging, impoundments etc.) have had serious consequences on aquatic ecosystems and the negative impact of these disturbances on the richness and density of naiad species has been demonstrated (Araujo et al. 2009). the species is considered to be close to meeting the 30% loss of populations over the last three generations, and hence is listed as Near Threatened (NT), almost meeting criteria A2c.

Geographic Range [top]

Range Description:This species is restricted to the Iberian Peninsula (Portugal and Spain), where it is found in the  rivers draining Spain and Portugal, towards the Atlantic Ocean (Araujo et al. 2009). It is present in at least a hundred 10 x 10 km2 in the region.
Countries occurrence:
Portugal; Spain
Additional data:
Range Map:Click here to open the map viewer and explore range.

Population [top]

Population:There is little data prior to 2000 to establish population trends, but the species is believed to be declining. 20-30% loss of populations over the last three generations (30-45 years, based on a generation length of 10-15 years).
Current Population Trend:Decreasing
Additional data:

Habitat and Ecology [top]

Habitat and Ecology:The species is found in all kind of rivers and streams with permanent water, in sandy, gravel or muddy substrate at the shores and slopes under the tree shadow, but also in sunny sandy beaches. It can live in lakes (Ruidera lakes). In the dry seasons, specimens survive in isolated populations which take refuge in pools together with the fish.
Continuing decline in area, extent and/or quality of habitat:Yes
Generation Length (years):10-15

Use and Trade [top]

Use and Trade: This species is not used.

Threats [top]

Major Threat(s): Its habitat is threatened by changes of hydrologic regime of the streams due to dams and impoundments. The loss of host fish populations is also impacting the species, as well as the water pollution resulting from nitrate run-off from intensive farming and some water pollution from industry.

Conservation Actions [top]

Conservation Actions: This species is listed on the Spanish and Andalusian Red Lists of Invertebrates.  - Spanish Red List of Invertebrates: Near threatened  (Verdu and Galante 2009). Andalusian Red List of Invertebrates: Vulnerable A4ce;B1ab(iii)+2ab(iii) (Barea-Azcón et al. 2008) . Water catchment management schemes and pollution monitoring are required to improve the conditions in the rivers, as well as restocking host fish populations and ex-situ breeding to provide juveniles for restocking populations in the rivers that are declining.

Classifications [top]

5. Wetlands (inland) -> 5.1. Wetlands (inland) - Permanent Rivers/Streams/Creeks (includes waterfalls)
suitability:Suitable  major importance:Yes
5. Wetlands (inland) -> 5.5. Wetlands (inland) - Permanent Freshwater Lakes (over 8ha)
suitability:Suitable  major importance:Yes
5. Wetlands (inland) -> 5.7. Wetlands (inland) - Permanent Freshwater Marshes/Pools (under 8ha)
suitability:Suitable  major importance:Yes
2. Land/water management -> 2.1. Site/area management
2. Land/water management -> 2.3. Habitat & natural process restoration
3. Species management -> 3.4. Ex-situ conservation -> 3.4.1. Captive breeding/artificial propagation

In-Place Research, Monitoring and Planning
In-Place Land/Water Protection and Management
In-Place Species Management
In-Place Education
12. Other options -> 12.1. Other threat
♦ timing:Ongoing    
→ Stresses
  • 2. Species Stresses -> 2.3. Indirect species effects -> 2.3.3. Loss of mutualism

7. Natural system modifications -> 7.2. Dams & water management/use -> 7.2.11. Dams (size unknown)
♦ timing:Ongoing    
→ Stresses
  • 1. Ecosystem stresses -> 1.1. Ecosystem conversion
  • 1. Ecosystem stresses -> 1.2. Ecosystem degradation
  • 2. Species Stresses -> 2.1. Species mortality

9. Pollution -> 9.1. Domestic & urban waste water -> 9.1.2. Run-off
♦ timing:Ongoing    
→ Stresses
  • 1. Ecosystem stresses -> 1.2. Ecosystem degradation
  • 2. Species Stresses -> 2.1. Species mortality

9. Pollution -> 9.2. Industrial & military effluents -> 9.2.3. Type Unknown/Unrecorded
♦ timing:Ongoing    
→ Stresses
  • 1. Ecosystem stresses -> 1.2. Ecosystem degradation
  • 2. Species Stresses -> 2.1. Species mortality

Bibliography [top]

Araujo, R., Reis, J., Machordom, A., Carlostoledo, Madeira, M. J., Gomez, I., Velasco, J. C., Morales, J., Barea, J. M., Ondina, P. and Ayala, I. 2009. Las Nayades de la peninsula Iberica. Iberus 27(2): 7-72.

Barea-Azcón, J.M., Ballesteros-Duperón, E. and Moreno, D. 2008. Libro Rojo de los Invertebrados de Andalucía. Consejería de Medio Ambiente, Junta de Andalucía, Sevilla.

IUCN. 2011. IUCN Red List of Threatened Species (ver. 2011.2). Available at: (Accessed: 10 November 2011).

Verdú, J. and Galante, E. 2009. Atlas de los Invertebrados Amenazados de España (Especes en peligro critico y en peligro). Direccion General para la Biodiversidad, Ministerio de Medio Ambiente, Madrid.

Citation: Araujo, R. 2011. Unio delphinus. The IUCN Red List of Threatened Species 2011: e.T195510A8975648. . Downloaded on 16 October 2018.
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