Danube Salmon
Tagged: animal, animals, cat, fish, invertebrate, mammalHucho hucho
( image )
Unlike its oceangoing cousins, the Danube salmon lives, breeds, and dies in the inland waters of the Danube River, where it is exposed to habitat destruction and environmental pollution. Salmon are majestic fish, and the Danube species is the largest of all. While the Danube salmon lives in rivers, many species live at sea. On reaching maturity, sea-dwelling salmon undertake a migration of epic proportions to the river in which they were spawned. Compelled by instinct, each fish battles against unbelievable odds-sometimes including rapids or even falls-to reach the mouth of its home river to spawn. The female digs pits in the gravel in which to lay her eggs, which take about five weeks to hatch. Although the life cycle of sea-dwelling salmon is physically challenging, its migratory habits have helped safeguard its success as a species. Juveniles that manage to negotiate the journey from their spawning grounds to the sea stand a better chance of reaching maturity than those that stay in the rivers of their birth. Unlike the Danube salmon, sea salmon avoid exposure to the pollution or irreversible habitat alteration that can occur in rivers as a result of environmental disasters.
International Pressures
The Danube River flows through 12 countries inhabited by a total of more than 70 million people. Enforcement of environmental controls is therefore complicated. Some problems are historical, relating to industrial sites that were built before environmental legislation had to be taken into account. Others are political, where one country is not bound by the environmental laws of another. Both situations apply to the Danube, along which there are approximately 1,700 industries, many producing wastes that are known to be toxic. Aquatic organisms cannot survive the levels of toxicity and must find new areas or perish. Escape is not always possible, and the result is often the destruction of many thousands of creatures and their habitats.
Pollution Crises
In 2000 a dam leaked cyanide from a Romanian gold mine into the Tiza River, a tributary of the Danube, killing all forms of aquatic life for 250 miles (400 km) downstream. In Hungary alone about 85 tons of dead fish were removed. Some environmentalists claimed that the whole ecological system of the river had been wiped out by the spillage. By early February 2000 cyanide was detected at the confluence of the Tiza with the Danube, and it was feared that the poisoning might cause the extinction of the Danube salmon. The outcome has been less devastating, but the situation illustrates the precarious future faced by the Danube salmon. Such pollution crises are serious enough to threaten the existence of any Danube species. In the case of the Danube salmon there are other significant threats, including overfishing, water extraction for a wide range of industrial and other uses, and river alteration (primarily channeling and damming). The Danube salmon is being pressurized from many quarters, to the extent that its long-term survival looks uncertain. Repeated attempts to introduce hatchery-bred stocks into a number of watercourses have been largely unsuccessful. However, in 1968 stocks were introduced from Czechoslovakia into Spanish waters, well outside the species’ natural range. Over the years the stocks have become established. Restocking might not be the answer to the Danube salmon’s problems, but it could be an essential lifeline.The Danube salmon (also known as the European sabnma, Danube trout, and European river trout) is the largest of all the salmons, and faces an uncertain future.
Danube salmon (European salmon, Danube trout, European river trout)
- Family: Salmonidae
- World population: Unknown; estimates are low
- Distribution: Rivers of Danube basin; introduced elsewhere in Europe, U.S., Canada, and Morocco
- Habitat: Deep, well-oxygenated regions of fast-flowing water; also found in backwaters at temperatures of 43-64°F (6-18°C)
- Size: Up to 6.5 ft (2 m). Weight: over 220 lb (100 kg)
- Form: Similar to salmon (Salmo salar), but slimmer, large head and jaws. Greenish back, silvery sides with diffused pink sheen, white along belly. Numerous small star-shaped black spots on back, gradually decreasing in number down body
- Diet: Adults feed on other fish, amphibians, reptiles, waterfowl, and even small mammals. Juveniles feed predominantly on invertebrates
- Breeding: Spawning March-May after migration to shallow, gravelly areas with fast-flowing, oxygen-rich water. Female excavates nest with tail and (with help of male) covers fertilized eggs. Hatching period 5 weeks
- Related endangered species: Satsukimasa salmon (Oncorhynchus ishikawai); carpione del Garda (Salmo carpio); Ohrid trout (S. letnica); ala Balk (S. plarycephalus); Adriatic salmon (Salmothymus obtusirostris); beloribitsa (Stenodus leucichthys leucichthys)
Comments
Got something to say?