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Monday, May 10, 2021
BUENOS AIRES, May 22 2009 (IPS) - Thousands of visitors are drawn every year to Argentina’s southern Patagonia wilderness region to fish in glacial lakes and crystal clear streams and rivers. But the trout and salmon that they have come to find are not native species, and pose a threat to local biodiversity.
“Despite our recommendations, trout continue to be introduced into lakes and rivers in Patagonia, and we have seen in the latest bird counts that the decline in some aquatic species has been catastrophic,” naturalist Claudio Bertonatti, a museum curator and a member of Argentina’s Fundación Vida Silvestre (Wildlife Foundation), told IPS.
Trout and salmon were introduced in Argentina in the early 20th century for recreational fishing in lakes and rivers in the southern provinces of Río Negro, Neuquén, Chubut, Santa Cruz and Tierra del Fuego. The species, which readily adapted to local conditions, breed without human intervention.
But as fishing tourism grew, fish farming took off. Of a total of 2,500 tons of fish raised every year in Argentina, 70 percent are rainbow trout (Oncorhynchus mykiss), one of the most sought-after species by sports fishers.
According to the International Union for the Conservation of Nature (IUCN), trout are among the world’s 100 most damaging invasive species. Once they have adapted to their new environment, trout deplete native species. Nevertheless, fishing seasons and limits are set to preserve them in Argentina’s southern provinces, to avoid a decline in tourism.
Although Argentina ratified the Convention on Biological Diversity, which commits countries to make efforts to prevent, control or eliminate invasive alien species, that is not always possible, a source at the Secretariat of the Environment and Sustainable Development, who preferred to remain anonymous, told IPS.
Such apparently conservation friendly measures in fact run counter to legislation that stipulates that the state must combat alien species, he said.
The source said the argument that exotic species must be preserved because they bring revenue in to provincial government coffers is not valid, because such protection actually violates the Convention on Biological Diversity, which is national law in Argentina. But the damage continues.
The theme of the International Day for Biological Diversity, May 22, this year was invasive alien species.
According to the United Nations, since the 17th century, at least 40 percent of all animal extinctions for which the cause is known were the result of invasive species.
Alien species deplete native species by modifying local ecosystems, competing for resources and transmitting pathogens.
They also aggravate poverty due to their impact on agriculture, forests, fisheries and the natural systems “that underpin millions of livelihoods in developing countries,” says the U.N.
In Patagonia, trout have led to a decrease in tadpoles and frogs, crustaceans and native fish like the Patagonian smallmouth perch (Percichthys trucha) and the Patagonian silverside (Odontesthes microlepidotus).
They also threaten the survival of water birds, such as the hooded grebe (Podiceps gallardoi), a fragile native species.
The hooded grebe, which was only discovered in 1974, said Bertonatti, lives on lakes on the plateaus of the Patagonian province of Santa Cruz. In 1979 it was declared a protected species in the entire province. There are an estimated 3,000 to 5,000 grebes on 130 lakes in the province.
Aves Argentinas (BirdLife International’s local partner) and Asociación Ambiente Sur, two local environmental groups, reported that the preliminary results of the bird counts and inspections they have carried out, “far from being encouraging, sounded the alert on the future of this species and its habitat.”
The NGOs called for the urgent design of an action plan to keep the species from going extinct. “The hooded grebe is in critical danger,” they said.
Trout eat the eggs and chicks of this species, which has no defence mechanism against the alien species of fish that invaded the lakes only a few decades ago.
But the grebes are not only threatened by trout. The expansion of tourism and mismanagement of waste have led to a mushrooming of garbage dumps that attract the kelp gull (Larus dominicanus), a native bird that also feeds on grebe eggs and young.
According to Bertonatti, there is no one single reason for the decline of South America’s rich biological diversity, but a number of factors that come together to undermine a species or an ecosystem. In this multiplicity of factors, the invasion of an alien species can be the final death blow, he said.
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