Cross-section of the earstone, or otolith, from a totoaba shows the annual rings that researchers use to learn about the fishs history.
Adult totoaba otolith collected from an Indian midden. Specimen courtesy of Scripps Institute of Oceanography, La Jolla, Calif.
During their tender youth, both the endangered fish species totoaba and the commercially important gulf corvina require the brackish water habitat provided by the shrinking Colorado River estuary, report researchers.
Although overfishing has been implicated in the decline of both species, commercial harvesting isn’t the only reason for the two species’ decline, the finding suggests. Since 1960, diversion of Colorado River water for human uses has greatly reduced the amount of fresh water that reaches the Gulf of California, thereby reducing the brackish-water estuary, the region where river water and ocean water mix.
"It’s the first time that we’ve been able to substantiate that these fish are using Colorado River water," said Kirsten Rowell, the aquatic biologist who led the research team. "We provide evidence that both of these fish need brackish water in their youth, but today the northernmost part of the Gulf of California is more saline than the open ocean."
Mari N. Jensen | University of Arizona
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