In the Pacific coast of Costa Rica, hammerhead sharks spend their nights feeding on squid and their days healing their wounds near underwater aid stations where other fish symbiotically cleanse their injuries. Their vision is poor, but their curiously shaped heads sense the magnetic waves emanated by an underwater mountain ridge that is advancing towards Costa Rica, and which has been identified as the source of many of our earthquakes.
The findings above come from the tagging of hammerheads over the last few years, as reported by Michelle Soto of national newspaper La Nacion.
Marine biologists and conservation activists in Costa Rica have been tagging Sphyrna lewini hammerhead sharks that swim near Isla del Coco since 2004. This investigative project conducted by the Sea Turtle Restoration Program (PRETOMA in Spanish) involves genetic analysis of the hammerheads, which is accomplished by taking a biopsy from under the dorsal fins of the sharks.
Tagging of hammerheads, until now, was mostly focused on transmitter devices that the sharks carried in their muscle tissue. These electronic tags transmit a 90 Mhz sound wave that is picked up by a network of buoys extending from Costa Rica to the Galapagos archipelago. The tags are shot by divers armed with spear guns. While the sharks are in their aid stations being nibbled on by Naucrates ductor (pilot fish), they go into a soporific state that allows divers to move in and shoot the transmitters into the sharks. About 180 sharks have been tagged in this manner.
The new tags also allow divers to collect a biopsy specimen that is sent to a genetic lab. The electronic tagging has thus far revealed that the hammerheads in Isla del Coco migrate back and forth from the Galapagos. These are the same sharks that swim and feed in the territorial waters of Colombia and Ecuador. Genetic analysis will confirm whether these are the same hammerheads that swim in the Golfo Dulce of the Osa Peninsula. The ultimate goal is to consider if fishing and other human activities in these areas should be regulated to protect the sharks.
Tagging of hammerheads has prompted Costa Rica to approach the governments of Colombia and Ecuador and ask to them to join in mutual conservation policies or treaties. Other countries like Honduras have agreed.
Costa Rica was recently praised by organizations like the Humane Society and Defenders of Wildlife for her protective stance towards Sphyrna lewini hammerhead sharks. Marine conservation groups have been calling on our government to adopt this stance since 2010, and at the recent Convention on International Trade in Endangered Species representatives of Costa Rica called for protection of her emblematic species, which is under serious threat of extinction due to factors such as overfishing and shark fin trafficking.
A recent study in the journal Conservation Biology underscores the need for protection of many shark species in the Pacific:
“We estimate that reef shark numbers have dropped substantially around populated islands, generally by more than 90 percent compared to those at the most untouched reefs”, said Marc Nadon, lead author of the study and a scientist at the Joint Institute for Marine and Atmospheric Research (JIMAR) located at the University of Hawaii, as well as a PhD candidate with Dr. Jerry Ault at the University of Miami’s Rosenstiel School of Marine & Atmospheric Science. “In short, people and sharks don’t mix.”
