Study: Chesapeake Dead Zones Impact Deep-Water Fish

Low-oxygen zones have a more serious impact on fish in the Chesapeake Bay's deepest waters than previously thought, according to a decade-long Virginia study

The study conducted by the Virginia Institute of Marine Science and published in May's issue of the Marine Ecology Progress Series magazine found the so-called dead zones impact the abundance of species including the Atlantic croaker, white perch, striped bass and summer flounder, according to a release.

The dead zones are caused by nitrogen runoff from fertilizer, as well as sewage and other sources that fuel algae blooms. The dead zones in the Chesapeake tend to peak in mid-summer, according to the release.

“The drastic decline we saw in species richness, species diversity, and catch rate under low-oxygen conditions is consistent with work from other systems," Andre Buchheister, a doctoral student at The College of William and Mary who authored the report, said in the release.

Buchheister said the fish in the study avoided water with less than 4 mg of dissolved oxygen per liter due to "physiological stress." That's double the traditional level used to define hypoxia and just over half of normal coastal oxygen levels, he said.

However, the institute's release noted, the effects of the dead zones are balanced "to some degree" by the nutrients' impact on fish at other water levels of the bay, and the algae growth promotes the growth of other fish and predators.

The team conducted the study on fishes caught and released using trawl nets in 48 trips from 2002 to 2011 at 3,640 sampling stations throughout the bay, according to a release.