Low oxygen levels in dead zone may do harm to popular bait fish
The study results are only partial and preliminary, but they are tantalizing nonetheless.
A Port Aransas scientist has found evidence that low oxygen levels in an area off Louisiana known as the dead zone could be hurting reproduction in croaker - an important baitfish in recreational fisheries in the Gulf of Mexico.
Peter Thomas, a professor at the University of Texas at Austin Marine Science Institute, emphasized that his findings are only preliminary and still need to be confirmed with further study he plans to do next year.
UTMSI scientists aboard the Longhorn research vessel conducted research in the dead zone in August and October. The dead zone is an area of the Gulf of Mexico off Louisiana where low oxygen levels for years have flushed away and even destroyed marine life. The dead zone seasonally waxes and wanes in size, growing some summers to an area about the size of New Jersey.
Scientists say the root cause of the dead zone lies with nutrients, especially nitrogen, that come from sewage and fertilizer that constantly are washing down the Mississippi River and then out into the Gulf. Algae, which feeds on nitrogen, then grows at a stepped-up pace.
Dead algae is eaten by massively multiplying bacteria, consuming huge amounts of oxygen. Lack of oxygen kills shellfish, and fish move to waters with more oxygen.
UTMSI scientists are studying whether the parts of the dead zone with moderately low oxygen levels have long-term effects on reproduction in various kinds of sea life. That includes croaker and copepods - tiny crustaceans that exist in the billions throughout the world's oceans and play vital roles in the marine food chain.
The scientists took samples at various sites in the dead zone in August and October.
Thomas, a professor who specializes in marine toxicology and reproductive physiology, said he found evidence there were about half as many females as males at one site. If further research confirms that ratio, it would be an important finding, Thomas said.
"It would suggest that (low oxygen in the water) might skew the sex ratio, which could affect the reproduction of young croaker," he said. More sampling in the dead zone in next year could either confirm the finding or show the sample was an anomaly.
Male-to-female ratios were much closer to 50-50 at the other three areas where croaker samples were taken, Thomas said.
Previous studies in other areas of the world have shown a decreased number of females in waters with low oxygen, Thomas said.
Scientists still are in the process of evaluating samples of mud containing benthic organisms and don't have even preliminary findings to
talk about yet, said Ed Buskey, a UTMSI research professor who handled benthic research in the dead zone research mission.
The Oct. 2-6 mission was the last research voyage scheduled for the Longhorn. UTMSI plans to sell the vessel soon. Under their grant, UTMSI scientists are slated to do more dead-zone research missions in August and October next year. They likely will do that aboard the Pelican - the research vessel of the Louisiana Universities Marine Consortium, known as LUMCON.
The researchers are hoping to do additional research in the dead zone in 2008.