The use of dynamite by fishermen is one hypothesis being put forward by Costa Rican fishing regulators to explain the massive deaths of dozens – and possibly hundreds – of Eastern Pacific green sea turtles on Central America’s Pacific coast.
The endangered turtles began appearing on the shores of northwestern Costa Rica over the weekend, and many of them did not exhibit any physical damage. On Wednesday and Thursday, the Nicaraguan conservation group Paso Pacifico found 28 dead turtles off the coast of San Juan del Sur, just north of where the Costa Rican turtles where found. None of the Nicaraguan turtles showed signs of physical damage, and all but one was an Eastern Pacific green sea turtle.
According to Luis Fonesca, one of the biologists investigating the case, two turtles have already been examined with inconclusive results. Costa Rica’s National University is currently conducting an analysis to determine the causes of death, but several theories top the list.
Dynamite or longline fishing
According to Roberto Umaña, head of the Costa Rican Fisheries Institute (Incopesca) in the northwestern province of Guanacaste, and Roger Blanco, head of investigations for the Guanacaste Conservation Area, local fishermen have reported several cases of the use of dynamite by Nicaraguan fishermen near Costa Rica’s northern Pacific coast.
“There were turtles found swimming in circles in the water,” Umaña told The Tico Times. “I don’t know how a bombing would affect a turtle, but confusion like that seems to make sense.”
Didiher Chacón, of the Wider Caribbean Sea Turtle Network (Widecast), also said that a number of the turtles had sustained blows to the head.
According to Lisa González, national director of Paso Pacifico in Nicaragua, the use of dynamite for fishing is increasing in central and northern Nicaragua, and one case was reported in San Juan del Sur last September.
“Right now the goal is to eliminate as many causes as possible,” González said. “The easiest thing is to look into human causes like dynamite or longline fishing.”
A sudden influx of mahi mahi to the Pacific coast has increased the number of longline fishermen currently operating in Costa Rican waters. The presence of hooks and lines on some of the turtles initially led investigators to suspect longliners as the culprit, but only a small number of the carcasses found showed possible signs of fishing interaction.
“It is certainly possible that some of these turtles were killed from longline fishing,” said Blanco, “but that has been a persistent threat for some time. Most of these turtles don’t have hooks and were likely killed by something else.”
Chemical or natural causes
The lack of physical damage in many of the turtles along with the fact that they are nearly all the same species of turtle has led investigators to suspect a chemical or natural cause.
“Olive Ridley turtles are extremely common in this area,” Blanco said. “If it was just dynamite or fishing then we would expect to see a few of that species as well, but they are almost all green turtles.”
Dead sea turtles without any physical damage have been turning up along the coasts of Mexico and all of Central America for months. Massive deaths have been reported in Guatemala and El Salvador. Though some of these deaths were later attributed to red tide, which does not occur in this part of Costa Rica, a turtle-killing disease could be afflicting the entire region.
“Some of the turtles looked at have strange microorganisms in their stomachs,” Blanco said. “Right now we can’t determine anything, but it is definitely being looked into.”
Though some have speculated that radiation from Japan’s Fukishima disaster could be to blame, Fonesca said experts are not pursuing that angle. Based on research from the University of Massachusetts Dartmouth and the Woods Hole Oceanographic Institute, scientists estimate that it would take at least five years for the radiation to spread to the Western hemisphere, meaning that marine animals would not be affected until 2016.
UPDATE 12:53 p.m. on Nov. 12:
Officials spotted a large brown patch of water with a cluster of dead turtles inside during a fly-over mission late Thursday. A group of officials traveled to the site by boat on Friday to collect samples for testing. Tests revealed that the cause of death for some of the turtles was due to the red tide.