It’s hard to believe that more than a year has passed since the Deepwater Horizon oil spill in the Gulf of Mexico. In the meantime, we’ve seen the tar balls recede and the plumes of oil dissipate, and from what we hear in the news, oil-damaged ecosystems are slowly returning to normal. But one question that keeps coming up is, “just what is normal?” It turns out that for many Gulf species, including the iconic and beloved sea turtle, too little is known about populations, growth rates, or breeding patterns to answer that question with any certainty.
Unfortunately, this isn’t the first time that scientists have lacked the critical data they need to monitor ecosystem responses to an environmental disaster. In the wake of the Exxon Valdez oil spill, evaluating the effects on wildlife was difficult because of limited information. Now, more than 20 years later, we’re in the same position again. A 2010 National Research Council report, Assessment of Sea-Turtle Status and Trends: Integrating Demography and Abundance, outlined exactly why so little data exist and what would be needed to properly assess the impacts of the spill on Gulf ecosystems.
Assessing Sea Turtle Populations
The first problem is getting an accurate count of population sizes. Sea turtles migrate long distances between seasons and at different stages of their lives, which makes counting them in any particular geographic region difficult. Most monitoring today relies mainly on counting nests and females on beaches. However, this doesn’t give a complete picture of population numbers, because adult females can take decades to reach sexual maturity, do not nest every year, and represent only a small fraction of the total sea turtle population.
Simple counts of nests also fail to provide any information on trends in the abundance of sea turtles or on the causes of changes in population. For example, the nesting of loggerhead turtles on Florida beaches has been monitored since 1989 (shown right). Until 1998, nest numbers increased; but more recently, the number of nests has declined rapidly. Many factors could account for this decline, from environmental changes to increased accidental capture in trawling nets. But without more information, specific causes cannot be determined.
For those and other reasons, the long-term effects of the recent Gulf oil spill on sea turtle species cannot be completely evaluated, and the success of restoration plans remains unknown.
What Information is Needed?
The National Research Council report identifies several important pieces of information that could help increase information about sea turtle populations.
Because sea turtles migrate—sometimes leaving an area for many years—scientists must piece together what might have happened to the animals during that time. The report concludes that it is important to also look at the different ages of the turtles within populations and to integrate those data with what is known about sea turtles’ birth rate, survival, growth rate, and age at maturity. This information would help scientists figure out if the oil spill impacted some sea turtle populations or some age classes within a population differently than others. New tools in genetics, such as DNA markers, can help to identify individual sea turtles and associate them with a particular population. Scientists then can use that information to determine whether sea turtles that swam in waters affected by the oil spill came disproportionately from some sites, perhaps already depleted, as opposed to others, possibly more robust.
The report also noted that all too often, the information collected by one research organization is not accessible to other researchers because the methods for collecting and analyzing data are not standardized or because of issues with data ownership and sharing. Incentives to encourage data sharing, for example through funding, would make it easier for researchers to gain access to all the necessary information.
Another issue is the permitting process for such research. Even before the Deepwater Horizon spill, sea turtles were listed as endangered, meaning that special permits were required to carry out research. However, most sea turtle researchers agree that the permitting process is a greater obstacle to research than is necessary to protect sea turtles and can delay or hamper important research projects and conservation efforts.
Getting accurate assessments of sea turtle populations will require interdisciplinary research among experts on topics such as population genetics and genomics, statistics and bioinformatics, One way to provide this information would be to launch interdisciplinary training in these topics for fisheries and conservation professionals.
Looking to the future, we can’t rule out another oil spill or other environmental disaster. But with some work, we’ll be better prepared to assess and understand changes in wildlife and ecosystems, and design plans to restore habitats, before the crisis occurs. Let’s hope that the Deepwater Horizon spill – the largest offshore oil spill in U.S. history – was the impetus we needed to get there.