Munched marine mammals signal sharks on the prowl

Sharks, including this nearly 16-foot specimen from the 1940s, are normal members of the local marine ecosystem.

PACIFIC OCEAN — In at least one telling of the story, a local surfer was out looking for waves in the ocean off Oregon’s Fort Stevens State Park around this same time several years ago.

He’s resting on his board when he feels a massive jolt. He looks back. A chunk of his board, a bit of tail and fin, is missing. He glances to the side just in time to see a large great white shark roll by him. It seems to look at him — he can see one dark eye. And then it’s gone.

Stories about large sharks travel faster than the sharks themselves. Though NOAA identifies great whites as “the top shark species implicated in unprovoked fatal attacks throughout the world,” encounters with them by humans are rare. Especially out here.

In recent weeks, however, four sea animals have been found dead from large shark bites on Clatsop County, Ore., beaches.

The Northern Oregon/Southern Washington Marine Mammal Stranding Network responded to two adult harbor seals, one adult Steller sea lion and a 7-foot striped dolphin that were all believed to be close to shore after being attacked.

Following a necropsy, Oregon’s Seaside Aquarium, which coordinates with the stranding network to pick-up animals from area beaches, said that in each instance the animals appeared to have died as a result of attacks by a large shark, either a great white shark or a broadnose sevengill shark. White sharks can reach up to 21 feet in length and weigh up to 4,800 pounds; broadnoase sevengill sharks are significantly smaller, usually less than 10 feet long, and sometimes themselves are the prey of white sharks.

Given recent attacks on the marine mammals and during an ongoing large diatom bloom, which may make the local ocean water murky, ocean swimming is not recommended.

Though rarely seen by humans, great white and sevengill sharks are no strangers to this area.

In 2005 and 2006, state and federal scientists tagged 32 broadnose sevengill sharks (16 males and 16 females) in the Willapa Bay and Grays Harbor estuaries, fitting them with acoustic transmitters.

Over three consecutive years, the scientists studied the movements of these sharks. The study, published in 2012 in the Journal of Fish Biology, showed the sharks “exhibited a distinctly seasonal pattern of estuary use, inhabiting the estuaries during the summer months and moving to the open coast during the winter.”

From October 2005 through September 2007, researchers detected tagged fish from Puget Sound to Mission Beach at San Diego, Calif. Most of these pings occurring during the autumn and winter, though the sharks didn’t linger.

Previously, the scientists said they’d had only the most basic knowledge of these sharks’ movement patterns, making it difficult to manage policies around them and as well as difficult to understand their role in coastal and estuarine food webs.

“The work presented here reveals that [broadnosed sevengill sharks] move over the continental shelf off Washington and Oregon during the winter,” the study stated. Those years of study also revealed an annual spring migration from coastal habitats into estuaries. The sharks spent long periods of time in these estuaries during the summer and, individually, based on size and sex, seemed to be loyal to specific spots in the estuary.

According to information provided by NOAA, great white sharks are distributed sparsely along the coast. While shark attacks on humans have been recorded primarily close to shore, from San Miguel Island in southern California to farther north, in spots off Cannon Beach, Ore.

Shark researchers used to think great whites spent most of their lives in coastal waters but more recent research shows the opposite: Great whites are ambitious travelers who can travel across great distances — though why and often where are still unanswered questions. A study published by marine scientists based out of California institutions in the early 2000s showed that great white sharks travel across vast stretches of open ocean.

But human encounters with sharks — especially large species like great whites — are rare. “Jaws” is still only a movie, a fantastic story built around an imagined “what if.” And while at least one NOAA division studies great whites off the California coast, there is little research on the species’ movements farther north off Oregon and Washington.

Still, there are definitely seasons when there is more activity below the waves.

As fall salmon runs sweep toward the Lower Columbia River, sea lions bark loudly again in the Port of Astoria’s east mooring basin, diving after fish near the Astoria Megler Bridge, and sharks roam the near ocean water.

Over the years, there have been scattered reports of large sharks (likely great white sharks) chomping on the ends of surfboards or showing a slice of iconic fin above the waves in Oregon and Washington. In Oregon, where more of the reports originate, few of these cases have resulted in serious injuries or death.But they have made people reevaluate when and where and if they still want to dip into the ocean.

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