Two great white sharks were spotted off the coasts of Florida and Georgia on Sunday. Ocearch, a non-profit organization performing research on the great whites, is on a first-name basis with these sharks: Katharine is a 14-foot, 2,300-pound shark, and Mary Lee, a 16-footer, weighs in at 3,456-pounds. Both sharks were originally tagged off the coast of Cape Cod, Katharine in 2013, and Mary Lee in 2012.
Ocearch studies great white sharks and other large apex predators all over the globe, generating data on the movement, biology and health of the sharks to inform conservation efforts, and to enhance public safety. The Ocearch website boasts a “shark tracker,” – a map of the world interspersed with dots where the huge predators have “pinged” – that is, surfaced for long enough to have the tags on their dorsal fin caught by tracking satellites.
Why is it important to study sharks? Well, in an ironic twist of nature, sharks are not only highly dangerous to humans, but are also what’s known as “keystone species,” or apex predators. As such, they help maintain the balance of entire ecosystems. Eradication of the sharks, many of which are already considered endangered, would result in the complete collapse of the delicate food web. Sharks are hunted for food worldwide – the Chinese eat shark fin soup, and also use shark fin medicinally for its reputed anti-cancer properties. Environmentalists are concerned that the taking of sharks is threatening the shark population. Also they condemn “finning” – the practice of cutting the fins off and throwing the shark back into the ocean to drown.
The great white sharks spotted off the Florida and Georgia coasts had previously been caught and extensively tested, fitted with tagging devices and released back into the ocean. When the sharks are caught, the research team has about 15 minutes to collect samples, measure the animal’s length and weight, and mount several devices on the dorsal fin for tracking fine and broad scale movements. SPOT tags enable the study of critical nursery, feeding, and breeding areas for the highly migratory great white sharks including areas where human and sharks may come into contact. The sharks are also fitted with accelerometer data-loggers (ADLs), used to record the animal’s body movements and posture during swimming. PSAT tags – called “pop-off” tags – also track shark movements, gauging location, water temperature, depth and seasonal feeding movements. Acoustic tags, small sound-emitting devices, track sharks in multiple dimensions, but the receivers must be in relatively close range to detect the signal.
Blood samples are taken, to study the reproductive status of the shark, by measuring hormone levels. Stress physiology is also assessed as the animals are captured and tagged. The researchers look at food consumption including type of food and contaminates. The sharks are checked for parasites, and length and weight are taken. Female sharks are subjected to Ultrasound analysis, to assess their reproductive status. Fin clips are taken for DNA analysis, to look at relatedness and dispersal of the sharks, which will assist in population management. The DNA will also help researchers understand the sharks’ diet to help with ecosystem management. Muscle biopsies, ultrasound, and hormone assessments assist with the discovery of breeding areas, which in turn, are critical to effective conservation measures.
Sharks are apparently only minimally stressed during this procedure. Data collected from the tags indicate that the animals recover and are swimming strongly 2-4 hours after being returned to the ocean. Long-term survival and long-distance migrations post-catch, show normal function and reproductive cycles.
Studies undertaken in the course of the OCEARCH expeditions have resulted in 40 research papers currently in preparation or completed. These studies form the basis for making informed policy decisions on shark conservation efforts. Additionally, swimmers in the warm Florida and Georgia waters can enjoy a measure of comfort, knowing that at least two of the great white sharks have been spotted and accounted for.
By Laura Prendergast