Wednesday, March 29, 2006

When Dissolved Oxygen Levels Fall, the Proportion of Male Fish Rises (Which is Bad News for the Female Fish)

Anyone concerned with Long Island Sound knows about the problems caused by low levels of dissolved oxygen (or hypoxia), a condition that is widespread in the western end of the Sound in summer. Hypoxia has been linked to the lobster die-off of 1999; hypoxia caused the massive fish kills of 1987; hypoxia causes all kinds of physiological stresses; and hypoxia turns what otherwise would be a habitat teeming with life into a dead zone.

A study released today indicates the there might be another problem linked to hypoxia. It creates an overabundance of male fish:

Aquatic dead zones, infamous worldwide for suffocating fish, may also be transforming female fish into males, according to research published today on ES&T’s Research ASAP website … The study not only has dire implications for fish populations: It also hints that hypoxic conditions—water containing less than 2.8 milligrams of oxygen per liter—may be interacting directly with the hormones of the reproductive system, experts say.

The study was done in a lab, published in but scientists think that the same affects might be occurring in nature, depending on when and where fish reproduction and development takes place.

According to the study, which is being published in Environmental Science and Technology, 1 million square kilometers – or 386,000 square miles – of coastal waters are hypoxic. If you click through the maps on this Connecticut DEP site, you’ll get an idea of how much of the Sound suffers from dissolved oxygen concentrations of about 2.8 milligrams per liter or less – in August, basically everything off Westchester and Nassau counties, and Greenwich and Stamford, Connecticut

Environmental Science and Technology Online has a story about it here, and AP wrote about it (and Newsday picked it up) here.

Meanwhile, Connecticut legislators still haven’t passed a bill that would put money in the state Clean Water Fund for nitrogen-removal at sewage treatment plants (nitrogen being the component of sewage that causes hypoxia); New York City forced a renegotiation of its nitrogen-removal agreement that extended its deadline by three years; and Westchester County has yet to announce its nitrogen removal plan.


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