One year after the biggest oil spill in American history, researchers study whale sharks to shed light on long-term devastation.
It’s the first feeding season after the Deepwater Horizon disaster, and marine biologist Rachel T. Graham is looking for sharks in the crystal-blue waters off the coast of Belize. In this sliver of reef, schools of large fish – primarily snapper and jacks – show up, as usual, after the full moon. But what’s missing are the dozens of white-spotted whale sharks that feed on the eggs the fish lay. This year, only a handful of sharks show – and the ones that do behave strangely. “They looked really hungry, feeding more frantically than usual,” says Graham, a whale shark expert with the Wildlife Conservation Society who has studied the creatures in Mexico and Belize since 1998. “Like they just couldn’t wait to get food.”
The latest causes for concern for the whale sharks, which are overfished, poached, and have a declining food stock, are the 200 million gallons of oil and almost two million of chemical dispersant BP put in their path. “We have pictures of whale sharks in the middle of the oil spill,” Graham says. “We know that surely some died from oil coating their gills. Other may have ingested oil and dispersant, and who knows what that might have done.” The sharks, which have been deemed vulnerable (one step away from endangered) by the International Union for Conservation of Nature for years, are in danger. With their long, meandering migrations – from Belize to the US, Baja to the Philippines – they are hard to track and count, and there are few people dedicated to studying them. To save the sharks and their troubled ecosystem, Graham and other researchers are tracking them, raising awareness, and trying to influence policy.
Even before the spill, whale sharks had it tough. Plankton levels have declined globally for at least a decade for numerous reasons, including pollution, temperature change, and ocean acidification, which eats through plankton’s plates of calcium carbonate. Ship traffic and overfishing of spawning species also threaten whale sharks, as does the lucrative trade of shark fins and meat for the Asian market. To top it all off, whale sharks are slow to mature and bear few young.
In a typical year, these slow-moving sharks – the largest living fish species that weigh up to 79,000 pounds – follow schools of fish, sucking in great quantities of spawn and plankton at the ocean’s surface off the Mississippi Delta and the coast of Mexico’s Yucatan Peninsula in summer, and near Belize and Honduras in the spring. Although researchers spotted whale sharks in the oil during the spill, there hasn’t been a single confirmed death-by-oil-spill of a whale shark; they sink when they die, and couldn’t be tracked due to restrictions on boats during the spill. So instead, researchers like Graham track the living – and hold out hope for the species.
Graham plunges into the warm, plankton-filled, pea-soup green waters off Isla Holbox, Mexico, with a mask, snorkel, fins and a six-foot-long pole spear, which holds a long dart with a $2,000 satellite tag attached. She looks for the spotted shimmer of the whale sharks moving in the cloudy waters. While these sharks don’t chomp their food like predatory sharks, instead filtering it through their tiny teeth, they’re still dangerous – the massive tails that make up a third of their body length could knock Graham out in an instant. She kicks carefully through the water, doing her best not to get in between the animals and their dinner as she dives down under the sharks to sex the animal so she can tag proportionate numbers of males and females. With her target selected, she closes in, hooking her thumb through the rubber tubing at the end of the spear and pulling it taught. She lets go, sending a dart and tag through the back skin of the whale shark, which doesn’t seem to notice.
The tags transmit data that help reveal where whale sharks go, what depths and water temperatures they prefer, light levels – which can be used to determine latitude and longitude – and how far and fast they travel. This knowledge has, in recent years, started to paint a picture of whale shark behavior, which helps scientists recognize changes in patterns, and problems.
This picture is key to assessing damage done to the sharks and the ecosystem on which they rely. Tags tell scientists that a whale shark, for example, might feed in Mexico and the northern Gulf, or travel from Belize to Cuba, or Florida, important information that helps policy makers and managers of natural resources make informed decisions.
Gauging the health of an ecosystem as big as the Gulf’s is not something scientists can do overnight. Oil entered the food chain in a big way last year, but how deep it went and whether it persists in marshes and sediments are unanswered questions. Some experts believe the spill reduced quantities of plankton and fish spawn in the Gulf, which may explain the feeding-frenzy behavior Graham observed off the coast of Belize. The plume from Deepwater Horizon overlapped with the Gulf’s infamous “dead zone” - an oxygen-deprived area where little can live, created by agricultural runoff from the Mississippi River.
Perhaps the greatest hope for the shark is tourism. Graham estimates the economic impact of whale shark tours for the area around Placencia, Belize, in the millions of dollars. Tourism also offers protection to whale sharks, as the physical presence of guides and tourists helps to keep poachers at bay. And public sentiment, inspired by whale shark encounters, can change shipping routes, similar to those made in the North Atlantic to protect right whales. All you have to do is see them, says Graham. “These are animals that evolved over millions of years, reaching perfection in predatory form,” she says. “Floating near a 10-ton, 40-foot-long wild thing in its natural environment can be a life-changing experience.”
Where to Swim with Whale Sharks
Belize: Avadon Divers, Placencia
Baja: Baja Expeditions, La Paz Mexico
Cancun: EcoColors Tours, Cancun, Mexico
First published in Men’s Journal Vol 20 No. 09, Sept 2011.