Fish takes scientist on 8,000-mile journey

Don Hammond, director of the Dolphinfish Research Program, prepares to release the fish after attaching a 180-day satellite tag.

The Dolphinfish Research Program headed by former S.C. Department of Natural Resources biologist Don Hammond of James Island hit the research jackpot with a fish that was tagged on June 3, 2014.

Hammond affixed satellite tags to two dolphin caught off Charleston aboard the My Three Sons, owned by Hunter Edwards and captained by Michael Mattson. The tags, made available through a grant by the Guy Harvey Ocean Foundation, were programmed to monitor the fish’s movements for six months; previously, satellite tags used in the study had been programmed for 30 days of information.

One of the two fish tagged aboard My Three Sons covered more than 8,000 miles from the time it was tagged off Charleston until the tag popped up Dec. 3, 2014, near the Dominican Republic; the other tagged fish lasted just 36 hours before being consumed by a predator.

So how does Hammond know the other fish was taken by a predator?

“I attached the tag to the fish and the way we attach it it’s not coming loose. Something had to cut that tag loose,” Hammond said.

Hammond said in previous studies they have actually traced the predator while the tag passes through the fish’s digestive tract. He said one thing the tags record is light intensity and “when the light goes out for 36 hours, 72 hours, that’s a pretty good indication something happened to that tag. All of a sudden it floats to the surface and records daylight again.”

The odds are stacked against dolphin from the beginning. Hammond said the current estimate of total mortality is 99.7 percent. They are found worldwide in tropical and sub-tropical waters.

“In other words, only three-tenths of one percent of all the fry that hatch out in a year will survive past 12 months of age,” he said. Hammond said every bluewater predator feeds on dolphin. Eighteen satellite tags programmed for 30 days were used during the first phase of the study and only three fish were able to carry them the full 30 days.

“These tags cost $4,000, then there’s an additional $1,000 cost for satellite time to get the data back. It makes you nervous when you throw $4,000 into the ocean,” Hammond said.

The Dolphinfish Research Program began in 2002 while Hammond was working with DNR. When he retired after a 35-year career, Hammond took the study to the private sector, which he said was appropriate because by then it was readily apparent that the dolphin fishery is not a state fishery, it’s an international fishery.

One of the challenges of the Dolphinfish Research Program is that the current tags must be used on at least a 20-pound fish so that it does not alter the fish’s swimming behavior and make the fish a target for predators.

“We would like to see (the tags) miniaturized further so we can put them on smaller fish,” Hammond said. “We’re actually monitoring the geriatric segment of the dolphin population.”

The well-traveled fish was tagged 62 miles southeast of Charleston. The information took 23 days to upload to satellites.

And as far as Hammond knows, that fish — probably now a trophy 40-pounder — is still swimming. The satellite tag is gone, but there’s also a conventional external streamer tag affixed to the fish, something Hammond would dearly love to get back.