Boy, 9, reels in 8-foot sixgill shark near Burien

When Cosmo Miller begins fourth grade next month, he will have quite a fish tale to share.

Cosmo, 9, caught a 150-pound sixgill shark while fishing in Puget Sound near Burien last week. Using a 30-pound test line, it took him almost an hour to land the big fish and haul it to shore for pictures before turning it loose.

"It was really hard," Cosmo said Monday, "but I had a really big fishing pole."

Cosmo said he had seen smaller sixgill sharks near his grandparents' home in Normandy Park and decided to try to catch one. He said he broke two fishing poles before landing the big one.

He used dogfish, a favorite meal of sixgill sharks, as bait.

Cosmo said it was hard reeling it in, not only because the fish was so big but also because it liked to rest on the bottom of Puget Sound and was a slow swimmer.

He figures the fish was about 8 feet long, about half the size of the 16-foot boat he was fishing from.

Cosmo's father, Howie Miller, said he at first didn't believe the shark story.

"You know about fish stories; you need to have the pictures to prove it," Miller said. "He needs to take them when he goes to school." Cosmo will attend Marvista Elementary School in Normandy Park.

Cosmo's grandfather, Dave Woltz, was with Cosmo when he hooked the shark.

"It was quite a thrill watching a 9-year-old kid pull in that fish," he said. "We had been fishing for about four hours and were ready to come in when all of a sudden he hooks this big thing. His face was beet red and I offered to help him, but he said no."

It's unusual for sixgill sharks to be in such shallow water; Cosmo figures his shark was in about 100 feet of water. They usually are deeper than 300 feet, said Greg Bargmann of the state Department of Fish and Wildlife.

Bargmann says fewer than 100 sixgill sharks are caught each year in Puget Sound. He said a 150-pound shark is small; the average is 400 to 600 pounds and up to 15 feet long; the sixgill shark is one of the largest in the world.

Bargmann said the shark caught by Cosmo was probably between 4 and 8 years old.

Fish and Wildlife, the National Oceanic and Atmospheric Administration and the Seattle Aquarium are studying sixgill sharks and have tagged some as part of their research. Bargmann said his department is studying whether female sharks come into Puget Sound to give birth. Younger sharks stay in the Sound until age 10 or 12, he said.

Shawn Larson, a researcher with the Seattle Aquarium, said she has been doing genetic sampling of the sharks and there seems to be a significant decrease in the number of them in Puget Sound. She believes that's because the juveniles have grown and have moved out of the area without others being born.

Cosmo said he saw a Discovery Channel program about sixgill sharks and immediately recognized what he'd caught. Until then, the biggest fish he'd hooked was a 27-pound salmon.

"When you catch a fish, it fights," he said. "That's why I like to go fishing."

Susan Gilmore: 206-464-2054 or sgilmore@seattletimes.com