What is killing hundreds of Central American sea turtles?
Hundreds of dead sea turtles have appeared in Central America’s Pacific this year and, for the most part, no one knows why.
The Environment and Natural Resources Ministry (MARN) in El Salvador registered 114 dead sea turtles from September to October, while Guatemala’ s National Council of Protected Areas (CONAP) recorded 115 mysterious deaths for the year. Nicaraguan nongovernmental organization Paso Pacífico confirmed the deaths of at least 40 in the country’s southern Pacific and have heard unconfirmed reports of dozens more.
Among the dead species are the critically endangered leatherbacks and Eastern Pacific green sea turtles. Costa Rican turtle experts confirmed that deaths of this magnitude could severely affect the population.
Though theories abound, scientific evidence is insufficient for experts to determine the causes with certainty.
The latest mass death was discovered last week when at least 30 partially decomposed turtles washed up on Costa Rica’s northwestern shores. Though an official count doesn’t exist, fishermen reported seeing hundreds of rotting turtle carcasses in deep waters.
Because of the state of decomposition in most of the turtles, scientists have been unable to reach a final conclusion as to the cause of death, but a fly-over and subsequent water test confirmed the appearance of a normally harmless type of red tide.
“In this case it seems like an indirect contamination,” Antonio Pora, director of the Costa Rican Fisheries Institute’s (Incopesca) red tide committee, told The Tico Times. “We found jellyfish in the turtle’s stomachs and those jellyfish were contaminated by a micro-algae.”
Red tide, or an algal bloom, is a rapid surge in the population of microscopic algae in an area. Certain kinds of red tide can kill off huge numbers of marine species at once. Red tide is nothing new to the Costa Rican Pacific, but this particular type, Pyrodinium bahamense, does not normally appear in concentrations high enough to kill wildlife.
Scientists from the University of El Salvador’s Marine Toxins Laboratory also believe that the same type of red tide could have killed their country’s turtles in September. Pyrodinium bahamense was the confirmed cause of death for 206 El Salvadoran turtles in 2005.
According to Poras, high concentrations of the toxin in this type of red tide can also affect humans. The consumption of contaminated mussels killed three people in the 2005 incident in El Salvador and red tide experts fear that it could happen more frequently.
“The only thing we can do is issue a warning and ban people from eating shellfish,” Poras said. “We issued a warning for the country six months ago.
Though many algal blooms are natural occurrences, increases in their frequency and concentration have been linked to temperature oscillation events like El Niño, which Central America experienced last year. Scientists and environmentalists also say that increases in red tide could be caused by human wastewater disposal.
“If we don’t change the way we treat the water in coastal communities then we are going to have frequent red tides,” said Didiher Chacón, Costa Rica’s director for the Wider Caribbean Sea Turtle Network (WIDECAST). “The proliferation of this algae is not very compatible with eco-tourism.”
While environmentalists and marine experts remain preoccupied by the possibility of increasingly toxic algal blooms, it is unlikely that all of this year’s dead turtles were killed from toxins.
In both the recent Costa Rican case and the September El Salvador case, scientists were unable to conclusively prove that the turtles actually died from the red tide. In Costa Rica biologists only found contaminated jellyfish in some of the turtles, had a very small sample size and did not test the water until five days after dead turtles began appearing. In El Salvador red tide experts did not test the water until two weeks after the turtles began dying, confirmed Salvadoran environmental group Ecological Unity and the University of El Salvador.
“There was an irresponsible environmental response to the incident,” Ecological Unity spokesman Alfredo Carías told The Tico Times. “They declared that it was red tide before they even did any tests.”
Longline fishing, a common turtle-killer, is responsible for at least several of the mass deaths. In January, 280 olive ridley turtles were killed in a longline fishing accident, and officials at Guatemala’s CONAP believe fishing could be responsible for the deaths of many of the turtles in their waters. Dynamite fishing was a suspected cause of death for a number of turtles in Nicaragua in September.
While both Chacón and Carías acknowledge that toxins are extremely likely, they say that the lack of systems to confirm the causes of these mass deaths makes it difficult to coordinate a possible response.
“At the national levels we are not prepared,” Chacón said of the region. “People who do the analysis normally know little about turtles and marine issues so they are unprepared as well. We need to develop mechanisms to confirm these causes and then to prevent them.”
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