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Shark beached at Admirals Cove draws researchers’ interest
The gleaming eye of the dead animal washed up on the beach caught the attention of the marine mammal stranding volunteer.
The vivid, aqua-green circle was unlike like the eye of a harbor porpoise, seal, whale or any other marine mammal. Coupeville resident Sandy Dubpernell – a volunteer with the Central Puget Sound Marine Mammal Stranding Network – realized the creature was a shark.
And while most shark species have five gill slits, this one was different; it had six gill slits.
The stranding network does not usually respond to calls dealing with strandings of fish or other non-mammal species. But Dubpernell was happy to volunteer her time to investigate this unusual discovery of a six-gill shark.
She had received the call about the ravaged carcass that local resident said had been damaged by youths who had been playing around with it.
When Dubpernell arrived, she found a large piece of driftwood shoved through the dead shark’s mouth and out through a gaping wound in its side.
According to Jeff Christiansen, biologist with the Seattle Aquarium, the waters of Puget Sound provide a nursery for this unusual, 200-million-year-old shark species. The importance of the local environment is to the young and growing baby sharks has yet to be determined, he said.
Based on analysis of tissue samples, scientists believe the sharks in Puget Sound are related – an extended family estimated at about 8,000 adult sharks.
The six-gill shark is more commonly found cruising the ocean’s depths, but researchers have tagged a number of the creatures so they are able to learn more about these fish.
The seven-foot, four-inch long shark that washed ashore on Whidbey Island was a juvenile. Although its gender could not be determined, adult male was ruled out. The dead fish had undeveloped reproductive organs and was either a female or a young, immature male.
Female six-gills can grow as large as 14 feet long; the smaller males grow as long as 10 feet. Their large size makes them one of the world’s top 10 largest predatory sharks.
But this species is no threat to humans and, like all sharks, plays an essential role in marine ecosystems.
As top-level predators, sharks shape food webs and the loss of such predators has proven to have profound effects on the number and diversity of other species.
Humans, however, are a threat to them. It is reported that in just three years (2006 to 2009), 1,341 six-gills were killed as by-catch in longline fisheries.
With shark populations on the decline around the world due to over-fishing, Washington state prohibits fishing for six gills. And while this shark stranding is an unusual occurrence for Whidbey Island, Christiansen said immature sharks sometimes wash up on beaches during crabbing season in the Puget Sound region.
“Even the smaller juveniles are powerful creatures capable of breaking into crab traps,” Christiansen said.
But gulping down the Vexar bait pouch – a plastic mesh material – often used in the traps can lead to internal damage that ultimately results the predator’s demise.
An animal autopsy, a necropsy, of the Admirals Cove shark was not conducted before the carcass floated away, so its cause of death is unknown. A necropsy would have determined if the bait pouch was still lodged inside the animal.
The Washington Department of Fish and Wildlife is currently monitoring the numbers of six-gill sharks that die as a result of ingesting this type of bait, Christiansen said.
If the numbers grow, they may require gear modifications or impose restrictions to prevent more six-gill deaths, he said.
Dubpernell said that if she encounters one of these specimens again, she is prepared to put to work the dissection skills she has gained from responding to marine-mammal strandings.
“I have done a lot of porpoise necropsies before,” she said.
After consulting with Christiansen at the aquarium following the shark’s discovery, Dubpernell said she now knows what to check for.
The body of the Admirals Cove shark washed out with the tide, but it may not be the last time that Whidbey Island residents encounter this particular carcass.
As the body decomposes, gas will fill the body cavity and the dead shark will rise to the surface – where it could return to the shore.
That would be good news for scientists who want to learn more about the health of the waters surrounding the Puget Sound. Christiansen said he would like to get a tissue sample, and would be willing to send someone up to Whidbey to collect it.
The other option is to find some intrepid volunteer to do the job.
“If we can’t send someone up, we can give information over the phone on what to do,” Christiansen said.
Beachcombers, fishers, divers and anyone else who might spot a six-gill shark, dead or alive, should contact the Washington Department of Fish and Wildlife at 360-902-2200 or the Seattle Aquarium at 206-386-4379.
An online reporting form is also available at seattleaquarium.org/page.aspx?pid=1100.
How to help
Sightings of six-gill sharks –dead or alive – should be reported to the Washington Department of Fish and Wildlife at 360-902-2200 or the Seattle Aquarium at 206-386-4379. File a report online at seattleaquarium.org/page.aspx?pid=1100.