Marine Scientists to Investigate Effect of Gulf of Mexico ‘Dead Zone’ on Fish Populations

Nov. 10, 2009

AUSTIN, Texas — Whether a large area of low oxygen water called the "dead zone" in the northern Gulf of Mexico could cause declines in environmentally and economically important fish populations is the subject of a new study by University of Texas at Austin marine scientist Peter Thomas.

Thomas and colleagues at several universities have received $2 million in funding from the National Oceanic and Atmospheric Administration (NOAA) to study the effects of hypoxia (low oxygen) on fish reproduction and model the impacts of hypoxia on the size of fish populations in the area, which is off the coast of Louisiana east of the Mississippi River.

"There has been a striking increase over the past 20 years in the size of the dead zone during the summer," says Thomas, professor of marine science at the University of Texas Marine Science Institute in Port Aransas. "But the long-term effects of its increase on the size of fish populations are unknown."

Marked suppression of reproduction in Atlantic croaker has already been documented at several hypoxic sites in the northern Gulf of Mexico.

In an initial study, Thomas found that male and female Atlantic croaker collected from hypoxic waters in Florida's East Bay near Pensacola had little ovarian and testicular growth, low egg and sperm production, and low levels of reproductive hormones during a time a year when they would normally be increasing in preparation for reproduction.

Recently, similar decreases in egg and sperm production and reproductive hormones were observed in croaker collected over a much larger area from the dead zone off the Louisiana coast.

Recent model simulations have predicted that this kind of decrease in reproduction can lead to population declines.

However, Thomas says that researchers need to obtain more precise information on the nature and extent of reproductive impairment of croaker throughout the dead zone, and further refine the croaker population models to increase their accuracy and utility as a fisheries management tool.

"Our goal is to provide resource managers with predictions about the impacts of hypoxia on fish populations that they can incorporate into their management decisions," says Thomas.

The Dead Zone varies in size, but can extend to 8,500 square miles (roughly the size of New Jersey) in some years. Incidences of seasonal coastal hypoxia have been increasing in oceans worldwide, largely the result of increased agricultural and industrial run-off.

Thomas will be working with Kenneth Rose and Dubravko Justic from Louisiana State University, Kevin Craig at Florida State University and Thomas Grothues at Rutgers University. The grant is part of NOAA's Gulf of Mexico Ecosystems and Hypoxia Assessment Program.

For more information, contact: Lee Clippard, College of Natural Sciences, 512-232-0675; Peter Thomas, Department of Marine Science, 361-749-6768.