Answer:
Salmon populations in the United States is declining due to the following factors:
1. Over-fishing and human activities have put a major influence on the population of salmon.
2. Due to industrialization, urban growth, unplanned farming, deforestation, and pollution would have imparted strains on the stocks of salmon. Apart from this chemical contamination from the industrial run-off and agricultural activities are also declining populations of salmon.
3. Genetically modified fish from hatcheries usually escape and interbreed with wild fish, thus, changing the genetic features of the populations.
4. Construction of hydropower dams is also a major cause of the salmon population declining.
Convection current is current which is caused due to the movement of group of molecules and also called difference in pressure and heat in earth
The convection current circulates in mantle when the earth spins whereas when the earth rotate it causes pull of matter in the mantle of earth.
As a result the earth rotation respond to mantle convection current where it travels.
hope it helps
