Unknown territories: discovering the Revillagigedo Islands – Oceanographic
While I was ostensibly foreman, in reality Mauricio Hoyas – or “Doctor Shark” – was in charge. Mau is the most active shark specialist in Mexico and has tagged over 300 sharks in Revillagigedo National Park alone. Together with Frida lara who completed his doctorate on shark movements in the archipelago, and Alejandro González, the director of the National Park, we had a wonderful team.
During the first 20 hours of our trip to Revillagigedo the seas were high and heavy. Most of the crew lay on the deck, wrapped in towels, their faces drained of blood and a Dulux swatch of greens and yellows. By the third night, the sea went down and we awoke to a quilt of gently rippling blue. The flying fish caught by our bow jumped out of the water and propelled themselves to the surface using wing-shaped pectoral fins. Tiny black petrels hovered on the surface with their bat-like flight patterns, tapping the water with their feet to cause the plankton to feed.
Perhaps the most abundant shark species around the Revillagigedo Islands is the Silver Tip. It is a beautiful shark, with clean lines, extremely hydrodynamic and with crisp silver or white lines along the dorsal and pectoral fins. The silvertip is pugnacious in personality. They swim directly over you, before pulling away at the last second. It is a large, slow growing species, but here most were young, not much more than puppies. It turns out to be a silvery-tipped nursery, and further into the deep blue the adults congregate.
As young, Silver Tips feed primarily on benthic prey (which inhabit the bottom) such as stingrays, stingrays, and octopuses, but as they grow they will feast on other predators, such as scads, trevally, trevally, tunas, wahoos and other sharks. These in turn feed on smaller fish which can themselves feed on plankton, and this plankton bioaccumulates poisons like mercury. Each step in the chain results in a higher concentration of these deadly pollutants. Even though we’re 720 kilometers off the Mexican coast, the silver tips here are still loaded with industrial pollutants that we dump into the sea. When I asked Maurizio what would happen if you ate silver tip sharks here, he told me. explained that this would be “really bad” because his “studies have shown that the mercury levels are really high”. “If you are a pregnant woman you cannot eat predatory fish, and eating any of these silvertips could kill you,” he added.
Our primary focus of the Revillagigedo Expedition is the exploration of the underwater features around the remote island of Clarion. The westernmost island of the archipelago, it is 24 hours of steam from the nearest tiny seamount. With Alejandro on our team, we received the unique permission to explore the non-diving sections of the coastline and use DPVs; vehicles powered by divers or scooters.