Species
Sturgeons
Find out about the threats facing Europe's sturgeons and what Fauna & Flora is doing to save these critically endangered...
A significant proportion of the world’s wildlife moves from place to place, sometimes once in a lifetime, sometimes several times a year. Many move to new feeding grounds when their food supply dries up. Others travel to breeding grounds. Some relocate to escape the cold – or the heat. These movements may be seasonal or spontaneous. Long distance or short. Solitary journeys or mass migrations.
Fragmentation of their natural habitat – whether that’s a river, a forest or a grassland – is one of the biggest threats to migratory species – and indeed any species that needs to disperse. For terrestrial and aquatic animals alike, these barriers to their movements can mean the difference between life and death for individuals, and between extinction and survival for their species.
Juvenile sturgeon in Georgia © Tamar Edisherashvili / Fauna & Flora
A juvenile sturgeon caught in Georgia's Rioni River, which is one of Europe's last refuges for these critically endangered migratory fish.
What is habitat fragmentation?
Habitat fragmentation takes many forms. A vast forest wilderness crisscrossed by a new road network and turned into a series of isolated pockets of habitat. Destruction of a hedgerow that serves as a natural corridor connecting two areas of woodland. Erecting a fence that cuts a savannah landscape in half. Constructing a dam across a major river.
All these human interventions that block access or reduce range have a negative impact on wildlife.
How does habitat fragmentation affect biodiversity?
Fences blocking traditional saiga antelope migration routes in Central Asia and restricting access to traditional grazing grounds can lead to mass starvation.
New roads that cut through the territories of wide-ranging carnivores such as the African wild dog, European brown bear and Iberian lynx expose them to the dangers of speeding traffic as they cross the tarmac.
Widespread deforestation forces African forest elephants to venture into open areas and farmland – increasing the threat to people and animals posed by human-wildlife conflict.
Saiga on the move. © Albert Salemgareyev / ACBK
A saiga herd on the move to new grazing grounds
Freshwater species affected by habitat fragmentation
Migrating salmon have to make one of nature’s toughest journeys. They spend most of their life at sea but return to the river of their birth to breed, heading upstream to the very same spawning grounds where they were born. To reach them, they need to negotiate fierce rapids, high waterfalls and hungry bears. Today, they also face increasing numbers of man-made obstacles.
Dams and other physical barriers pose enormous threats to wild salmon – and to other migratory fish such as sturgeon.
What are the main causes of freshwater fragmentation?
One of the biggest causes of river fragmentation is the creation of man-made barriers that inhibit the natural flow of water or the free movement of freshwater species. These include dam construction, road building, chemical pollution, and unsustainable levels of water extraction for irrigation.
What impact do dams and other barriers have on freshwater wildlife?
Some of the adverse effects of river fragmentation are well-known. Large dams that block the path of migratory fish, and prevent them from reaching their spawning grounds, are an obvious threat to their survival.
Other impacts are less immediate, such as the long-term isolation of populations across a river system, which prevents gene flow and leads to inbreeding.
An additional problem is the speed at which this fragmentation has taken place. Human-induced changes have been too rapid, leaving freshwater species with no time to adapt to the new conditions.
The impacts of fragmentation on freshwater ecosystems are also being magnified by other indirect threats such as climate change.
Stung Atay dam construction in 2012 in Siamese crocodile habitat. © Jeremy Holden / Fauna & Flora
Construction of Stung Atay dam at the heart of the critically endangered Siamese crocodile's freshwater habitat in Cambodia.
Europe’s rarest fish
The critically endangered asprete, was almost wiped out by the construction of Romania’s largest hydropower complex, which had a serious impact on the only three rivers where the species was known to occur. The asprete has since disappeared from the Argeș River and in its tributary, Râul Doamnei. Fortunately, a small watercourse was retained downstream from the dam built on the Vâlsan river, enabling the fish to survive here. Even here, the presence of several weirs and other obstacles continues to threaten the asprete’s future in this stretch of river.
Among other conservation activities, Fauna & Flora and in-country partner Alex Gâvan Foundation are pressing decision-makers to remove four weirs that are preventing the free movement of the asprete and other fish species towards favourable habitat for living, feeding and breeding.
Asprete in the Vâlsan river, Romania. © Alex Găvan Foundation
Asprete in Romania's Vâlsan river, the only known refuge of Europe's rarest fish.
Sturgeon on the brink
Poaching has historically been the main threat to the survival of Europe’s sturgeons. But a significant new threat recently surfaced in Georgia’s Rioni River, one of the last strongholds of these critically endangered fossil fish. The proposed construction of a new hydrodam upstream from Fauna & Flora’s project site would have a potentially disastrous impact on the Rioni – and deal a death blow to the recovery prospects of the river’s flagship fish species.
Bizarrely, the original environmental impact assessment made no mention of the sturgeon. The proposal met with widespread disapproval within Georgia, including mass demonstrations in major towns and cities. Construction has now been suspended, and Fauna & Flora continues to engage diplomatically with those in charge, while working with local partners and communities to combat other threats to Rioni’s precious sturgeons.
Vartsikhe Dam on the Rioni River. The Rioni is the last sturgeon stronghold in the Eastern Black Sea region. © Stephanie Foote / Fauna & Flora
Vartsikhe Dam on the Rioni River, the last sturgeon stronghold in the Eastern Black Sea region.
Slender hope for the gharial
The gharial is a critically endangered freshwater crocodile found only in Nepal and northern India. Damming and water extraction in its dwindling river habitat have caused a precipitous decline in its population. The Girijapuri barrage is a prime example of the problem. Built in 1976, this dam left the world’s second-largest breeding gharial population isolated in a 20-kilometre stretch of the Girwa River.
In 2023, a team of conservationists funded by the Conservation Leadership Programme, the long-running initiative co-managed by Fauna & Flora, published details of a little-known and unprotected gharial population that they discovered downstream of the barrage. It appears that juvenile gharials are being flushed downriver when the barrage gate is opened during monsoon floods. The team is now recommending urgent intervention to address the threats faced by gharials on both sides of the barrage.
The gharial is a critically endangered crocodilian endemic to the Indian subcontinent. © Gaurav Vashistha / CLP
The gharial’s narrow snout and needle-sharp teeth are ideal for catching and holding onto its fish prey. This critically endangered crocodile is threatened by fragmentation of its river habitat.
Siamese crocodile rescue
At the start of the new millennium, the proposed construction of hydroelectric dams upstream from one of the Siamese crocodile’s key strongholds in Cambodia represented an existential threat to this recently rediscovered and critically endangered reptile. Loss of its wetland habitat, commercial hunting and farming, hybridisation with other croc species in captivity and accidental entanglement in fishing gear had already taken a severe toll on the Siamese crocodile.
Among the many activities that Fauna & Flora and our partners have carried out to safeguard the future of this species, we have minimised the risk posed by dam construction by identifying suitable alternative sites for the release of captive-bred Siamese crocodiles as part of an agreed national reintroduction programme that aims to reinforce the wild population.
Siamese crocodile. © Jeremy Holden / Fauna & Flora
Siamese crocodiles in Cambodia are being reintroduced to freshwater habitats that are free from the threats posed by major dam construction.
Freshwater flagships
Species such as the Siamese crocodile, gharial, asprete and Europe’s sturgeons are standard-bearers for their threatened freshwater habitat. One quarter of the world’s critically endangered species are found in fresh water. Please support our efforts to protect them.
Donate todayA trio of scientists combing a stretch of the Vâlsan River during the asprete survey. © Alex Găvan Foundation
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