Just in time for the 25th anniversary of Shark Week, conservationists are pushing the U.S. government to declare California's great white sharks an endangered species. In a petition filed with the National Marine Fisheries Service, they argue that great whites of the northeastern Pacific are genetically distinct — and with only about 340 adults remaining, they may already be on the brink of extinction.

"Anywhere in that range presents a very high extinction risk," says Geoff Shester, the California program director of Oceana, one of the organizations that filed the petition. "It's well below most other species that are currently listed as endangered."

Great white sharks are considered vulnerable to extinction worldwide, due to a variety of threats such as shark finning, accidental bycatch and commercial fishing of their prey. They're one of 50 shark species listed as vulnerable by the International Union for Conservation of Nature (IUCN), but California's subpopulation is in especially dire straits, conservationists say, due to its small size and biological isolation.

"They're genetically and behaviorally distinct from other white sharks," Shester tells MNN. "While they are capable of making long-distance migrations, they tend to just go back and forth between the same offshore and coastal sites from year to year. There has been a theory for a while that this population was distinct, but it wasn't until new science came forward in the last two years that it showed no mixing between this population and the other main ones."

The U.S. already outlaws the direct harvest of great white sharks for sale, but Shester says California's great whites are still inadvertently being killed by gillnet fishing in U.S. and Mexican waters. Gillnet anglers may not target the sharks, but their broad nets often snag them anyway as "bycatch," particularly in nursery areas where young sharks tend to congregate at certain times of year.

"Bycatch is the biggest concern right now that has been documented," Shester says. "There are currently no limits on bycatch. A minimum of 10 sharks per year are incidentally being caught, and given their low population numbers and low reproductive output, that could be a major limiting factor in their recovery."

Gillnet fishing in the northern Pacific Ocean. (Photo: ZUMA Press)

On top of bycatch, conservationists are also worried about toxin levels in great whites of the northeastern Pacific. Juveniles off the California coast are contaminated with high levels of mercury, DDT and PCBs, and no one has figured out why. "As top predators, we know they're going to accumulate some of these toxins," Shester says, "but I would not have expected contamination levels to be this high based on that alone. These are the most contaminated sharks in the world."

The petition's timing ahead of Shark Week wasn't entirely coincidental, Shester acknowledges. In fact, Discovery Channel is helping conservationists publicize the sharks' plight, with Oceana board member Ted Danson hosting a Shark Week special Wednesday night ("Great White Highway") that focuses specifically on California's great whites. "We would have done the petition anyway," Shester says, "but we're certainly happy to coordinate it with Shark Week."

Filed jointly by Oceana, the Center for Biological Diversity and Shark Stewards, the petition isn't the first of its kind this summer. Another environmental group, WildEarth Guardians, filed a similar petition in June, aiming to classify the California subpopulation as an endangered species and set aside a "critical habitat" for it. The two petitions are "complementary," Shester says, and taken together, "they show that there are a number of folks concerned about this."

While the ultimate goal of these petitions is to reduce shark mortality, Shester says the first step is to simply gather more data about these little-understood sharks. "One of the primary outcomes with other Endangered Species Act listings is additional prioritization and funding for research," he says. "And we really need to understand the trends for this population. We still don't know some basic biological information."

It remains unclear, for example, how many sharks would constitute a healthy number for this population, which likely began declining centuries ago as humans depleted its prey base. Scientists also lack information about how long it takes to replace a pup caught in a gillnet, whether the sharks suffer from mercury poisoning and whether their food supply is adequate. And even though a California great white "bumped" a kayaker last month, Shester says another goal of the research would be to dispell the myth that sharks and humans are natural enemies.

"While we humans tend to be scared of these sharks, these sharks are our allies in the sense that, as top predators, they keep the oceans healthy," he says. "Just as wolves keep deer populations in check, these white sharks are playing an important ecological role, and they need us to protect them and help them recover."

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Russell McLendon ( @russmclendon ) writes about humans and other wildlife.

Groups push U.S. to save California sharks
California's great white sharks should be federally protected as an endangered species, according to a new petition filed by conservation groups.