commercial fisheries are often held responsible for the decline of fish population worldwide. A study in the us has found that changes in the flow of a river are also a major cause. It affects growth. The study by researchers of University of Arizona says diversion of river water for multi-purpose projects such as dams ends up reducing water flow downstream of the river and in estuaries.
EndangeredCommonly called totoaba (Totoaba macdonaldi) and the first commercially important fish in the Gulf of California, the endangered fish variety was the subject of the Arziona researchers" study. Totoaba is a large, endemic species that spawns only in the Colorado river"s estuary. Commercial totoaba fishery, however, crashed in 1975 and overfishing was blamed for the fish"s decline. The study, however, says that since 1960, diversion of Colorado river's water for other uses, including the Hoover dam on the river, reduced the amount of fresh water that reached the Gulf of California. This increased salinity of the estuary, which affected breeding of totoaba and other marine organisms in the estuary.

To understand how diversion of water affected the fish population, the researchers compared the growth of otoliths