CHATHAM — The 50 pound severed tuna head drifted in the water off the back of the M/V OCEARCH like a decaying chew toy, dripping blood and oil, begging for a great white shark to come up out of the ocean and give it a taste.
Standing on the back deck, Captain Bob Yates bangs a clever down on a small herring, splitting it in two. He collects a handful of fish bits with his hands and throws them into a stained plastic bucket.
Mike McCallister, a 28-year-old research biologist from the University of North Florida , takes the bucket from Yates and pounds the fish into a thick paste with a shovel.
It is just after 10 a.m. and the two men, one a seasoned fisherman, the other a young scientist from Florida, are building a chum trail, hoping to coax a great white shark out of the deep.
“You get one person back here, it gets boring and tedious after a while,” McCallister said, throwing another clump of mush out. “I enjoy doing it. It helps pass the time.” Full story for BostonGlobe.com subscribers.
Javier Panzar can be reached at email@example.com.