A similar Gulf oil spill happened in 1979.
The story has a familiar ring: A semi-submersible offshore rig in the Gulf of Mexico drilling an exploratory well miles below the ocean floor. Problems with the drilling mud. Crude oil and natural gas at high pressure (6.7 lbs per square inch) forced up through the well casing. A failure of the blowout preventer. A huge explosion, rupturing the well casing. More than 1.2 million gallons of oil a day boiling up out of a bore hole into the sea.
It was June 3, 1979. The well was called Ixtoc I, a project of PetroleÃ³s Mexicanos (PEMEX) in the BahÃa de Campeche, 50 miles off the northern coast of the Yucatan Peninsula, 500 miles south of Brownsville, Texas. By the middle of June, an oil slick covered more than 1,100 square miles of the Gulf. PEMEX officials and contractors struggled for nine months to get the flow of oil under control. Before the well was sealed, an estimated 138 million gallons had escaped.
It will be months, even years, before researchers begin to quantify the effects of the Deepwater Horizon spill. While we wait for analysis, the aftermath of Ixtoc is about the only indicator we have of the possible effects of a major oil spill on the marine environment, coastal habitats and wildlife in the Gulf.
Examining the Evidence
Here's what we know about Ixtoc: More than 8.4 million gallons of oil washed up on Mexican beaches, and another 3 million gallons came ashore along 162 miles of beach in the United States. Most of this oil came in during the summer and early fall before the peak of waterfowl migration, but the leak continued through the winter, threatening millions of ducks and other birds that winter along the Gulf coast from Louisiana to YucatÃ¡n. It's interesting, then, that only 1,400 birds were found with oil on feathers or feet -- most of them wading birds and terns. No ducks were found with oil on their feathers.
Researchers from Texas A&M University-Corpus Christi studied shorebirds on Texas barrier islands and beaches as the oil came ashore in August 1979. They reported that numbers of birds on the beach "were much lower during the period of oil contamination than before the spill or during the same period a year later€¦" The percentage of oiled birds "was low (less than 10 percent) and few dead birds were found." The researchers speculated the drop in numbers "may have resulted from reduced food supplies or from shifts to uncontaminated areas."
Early reports from biologists who monitored birds after the Deepwater Horizon spill suggest that most birds were getting out of the oil's way, much like birds seemed to do after the Ixtoc spill. Given a choice, the ducks that began arriving on the Gulf coast in September might have avoided any oil left from the Deepwater spill. If the Deepwater well remains sealed, the risk of large rafts of diving ducks running afoul of huge oil slicks appears to be quite low.
The TAMU-CC researchers raise another more subtle possibility: a shortage of food. After Ixtoc, a group of biologists representing the United Nations Environmental Program went to the Bay of Campeche to survey the impact of the spill.
"The populations of crabs were almost totally eliminated over a wide area," they reported. "(However), the abundant beach clams as well as other mollusks of the sand beaches did not exhibit any drastic mortality following the spill." Researchers speculated that larval shrimp could have been poisoned over nearly 6,000 square miles -- an area equal to 2.5 percent of the Mexican part of the Gulf.
The combination of hard information and speculation makes it hard to guess how the Ixtoc spill might have affected meat-eating ducks such as lesser scaup. And since no one bothered to look for impacts in populations of other shoreline invertebrates like crayfish and insects, there is no way of knowing whether the bluebills that visited the Yucatan during the winter of 1979-1980 were short of groceries or not.
The UN team did report exceptionally large blooms of plankton in the bay. The oil might have acted as fertilizer for some of these single-celled floating plants, or it might have killed off populations of single-celled grazers and mollusks that ordinarily feed on the tiny plants. Studies near the spill showed that heavy slicks of relatively fresh oil could kill stands of sea grasses, but the plants seemed to resist damage from a small dose of oil or exposure to tar mats. It's worth noting that the plants that survived contact with the oil absorbed some components -- concentrations of these hydrocarbons were six to 15 times as high in grasses that had been exposed to oil as they were in nearby grasses that had not.
The information suggests redheads and ring-necked ducks probably didn't face a food shortage in the Bay of Campeche after the Ixtoc spill. It also suggests birds feeding on vegetation in the area might have eaten some oil as well.
In the late 1970s, the U.S. Fish and Wildlife Service tested hen mallards to find out whether oil in their diets affected their ability to lay viable eggs. A diet that included 2.5 percent south Louisiana crude reduced the number of eggs a hen could lay by half. A diet with only 0.25 percent oil didn't affect the number of eggs she laid or the viability of the eggs. This study suggests that exposure to high concentrations of oil might affect production, while exposure to lower levels would not. While Ixtoc might have affected production in a few ducks, the estimates of continental populations of redheads and bluebills don't show any drop in the early 1980s that might be attributed to the spill.
What We Can learn
The similarities between Ixtoc and Deepwater Horizon are significant: Both events were underwater spills in the Gulf of Mexico that released a lot of oil and lasted a long time. The bacteria and plankton that consumed much of the oil at Ixtoc are at work on the Deepwater spill -- conditions of temperature and salinity are broadly the same, at least at the surface.
The differences are less obvious but might prove to be noteworthy: The Ixtoc I wellhead was in 160 feet of water; the Deepwater Horizon wellhead was in 5,000 feet of water. Corexit dispersant was used only on the surface in the Ixtoc case, while on the Deepwater spill, 700,000 gallons of Corexit were injected into the stream of oil at the wellhead. Most of the oil from the Ixtoc spill came ashore on sandy beaches, while much of the Deepwater oil is coming ashore on highly productive coastal marshes, where vegetation and structure might prove to be far more sensitive. And the coast of Yucatan and eastern Mexico, while important to North American waterfowl, aren't nearly as important as the northern Gulf Coast of Texas, Louisiana, Mississippi and Florida.
Considering the size and potential environmental impacts of the Ixtoc I spill, the effort to understand its effects seems curs
ory, and the information we gleaned remarkably incomplete.
What a pity. If we had provided enough funding and manpower for a systematic analysis of the Ixtoc aftermath, we might at least have had a clearer understanding of the nature and extent of the dangers posed by the Deepwater Horizon blowout. It's bad enough to run uncontrolled experiments on a landscape scale -- it's even worse when we don't bother to record the results.
Chris Madson is an avid waterfowl hunter from Cheyenne, Wyo.