By Gloria Dickie, Turtle Island Restoration Network Intern
With 13 major islands and over 100 rocky islets, the Galapagos Islands are a dream destination for many adventurous travelers, but their popularity isn’t limited to the scuba diving crowd.
A new study co-authored by Turtle Island’s Conservation Science Director Alex Hearn reveals the Galapagos Islands are also a major pit stop for migrating whale sharks.
The Galapagos Whale Shark Project is the brainchild of naturalist and explorer Jonathan R. Green in collaboration with Turtle Island Restoration Network, the Charles Darwin Foundation and the Galapagos National Park Service. Between 2011 and 2013, the science team surveyed the whale shark population around Darwin Island, the northernmost island in this biogeographical region.
During a total of 180 dives, teams recorded information about the shark’s size, sex, potential signs of pregnancy, presence of noticeable scars, behavior, and associated fauna. They followed this up with photographic analysis of the area behind the shark’s fifth gill—which serves as a kind of human fingerprint—and prominent scarring. Their data revealed an unprecedented number of whale sharks using the island’s coastal waters as a migration stopover.
“The prevailing thought in the past was that a handful of whale sharks would spend several months at Darwin, but now we know that that the island is visited by several hundred whale sharks, each staying only a couple of days.” Explained Dr. Hearn
More importantly, the majority were large, apparently pregnant females. “Most of these females had big, distended abdomens, which seems to indicate pregnancy. This is the only known place in the world whale sharks in this condition are regularly seen. It’s a mystery why they are here, but we believe Darwin may be a waypoint from which they move into the open ocean to give birth to up to 300 1.5-2 foot young.”
Using high-tech acoustic telemetry tags, researchers tracked the movement patterns of four apparently pregnant individuals around Darwin Island. These tags ‘pinged’ each minute, allowing the sharks to be followed from a small vessel with a directional hydrophone attached to it. The data revealed frequent use of Darwin’s Arch, a natural rock arch located near the main island, but showed no signs of feeding or other specific behaviors, leading scientists to theorize the migration had reproductive purposes. Such usage could have important implications for whale shark conservation.
Since 2002, whale sharks have been listed as vulnerable by the International Union for the Conservation of Nature, largely due to the presence of whale shark fisheries in the Pacific and Indian oceans, most of which have now been closed. However, whale sharks are still taken as by-catch, or illegally. Last year a single slaughterhouse in southeastern China’s Zhejiang province was found to process up to 600 whale sharks annually. Whale shark fins are also highly prized as trophies, and can fetch up to $1,000 each.
Elsewhere, whale sharks can become entangled in fishing gear such as purse seines. In some instances, fishers set their nets around whale sharks in order to catch the fish that swim alongside them. They then drag the shark out of the net and release it, although this may cause injury and even death. This practice is now discouraged or banned in many countries, including the USA, which recently passed legislation banning the setting of nets around whale sharks, to comply with international conservation measures for this species.
With an estimated 695 pregnant females passing through Darwin’s protected waters, the Island could provide essential information to understand the sharks’ reproductive cycles, and in turn, aid conservation efforts.