Prior to the diversion of water upstream in the Colorado River, this species was the most common mollusk in the estuary. It constituted 80-90% of the clams throughout the delta and was so abundant that heaps of the shells formed ridges that stretched for miles. The density of clams has been reduced from 25 to 50 per square meter to three per square meter. The clam has been largely replaced by several thicker-shelled species of Venus clam (Chione spp.). These previously minority species now account for 95% of the clams in the area.
The increase in salinity of the water and decrease of nutrient input from the river as a result of diversion and use of water led to the decline of the clam, which is now endangered and only found in a few isolated locations, including Isla Montague, the largest island at the mouth of the Colorado river. The clams are not harvested and are not affected by pressure from fishing.
Studies of the clam have been used to infer the original extent the estuary in the absence of earlier survey data. Shells of the clam became sharply less prevalent about 65 km south of the river's mouth, constituting only 25% of shells in this area, and becoming rare to absent at a distance of 80 km. These observations have been used to infer that the mixing zone of river and sea water probably extended as far as 65 km south of the river's mouth. Isotope analysis of oxygen in the shells of the clam have also been used to independently estimate rates of salinity, and the results from this approach were found to correspond with observations of the prevalence of the clam shells, and also to agree with numerical models proposed in the past.
Read more about this topic: Mulinia Coloradoensis
Other articles related to "conservation history, conservation":
... 1988 Endangered (IUCN Conservation Monitoring Centre 1988) 1990 Endangered (IUCN 1990) 1994 Endangered (Groombridge 1994) 1996 Critically Endangered (IUCN 1996) ...
Famous quotes containing the words history and/or conservation:
“Let us not underrate the value of a fact; it will one day flower in a truth. It is astonishing how few facts of importance are added in a century to the natural history of any animal. The natural history of man himself is still being gradually written.”
—Henry David Thoreau (18171862)
“The putting into force of laws which shall secure the conservation of our resources, as far as they may be within the jurisdiction of the Federal Government, including the more important work of saving and restoring our forests and the great improvement of waterways, are all proper government functions which must involve large expenditure if properly performed.”
—William Howard Taft (18571930)