It was a common sight last weekend at docks and marinas, offshore anglers reaching into their fish boxes and hauling out one of the most sought fish caught off the South Carolina coast.
It was one of the first weekends where smaller boats could sneak offshore and dolphinfish - more commonly referred to as dolphin or mahi-mahi - were out there in good numbers.
Dolphin are probably the most sought-after fish for offshore anglers, and with good reason said Don Hammond, who heads the privately funded Dolphinfish Research Program (dolphintagging.homestead.com).
"It's the number one caught fish along the Atlantic Seaboard and Gulf of Mexico. Everyone loves the dolphinfish," Hammond said, citing their abundance as well as their desirability by seafood lovers.
Hammond has been studying dolphin for the past 13 years, four years while working as a fisheries biologist with the S.C. Department of Natural Resources and the last nine after retiring from DNR. Anglers wherever dolphin are found have been tagging the delectable fish in the name of science. The project is funded by individuals and DNR provides technical assistance and data analysis, among other things.
"What we've shown clearly is this is an international fishery," he said. "When we began this study science didn't even have hard data to confirm there was a south to north migration of fish up the East Coast. Not only have we shown there is a migration from south to north, starting at the Florida Keys all the way to New York, but the fish off our coast also are caught throughout the Caribbean. We share a common stock."
Scientists know dolphin are extremely fast-growing, but like humans their growth rate varies.
Hammond said scientists have documented that dolphin can grow as much as 2.67 inches per week while they are small, less than a meter long. They may weigh as much as 40 pounds in the first 12 months of life. Dolphin begin to mature sexually as small as 14 inches fork length (measured from head to fork of tail) and by the time they are 24 inches fork length all dolphin are sexually mature.
"You're looking at a fish that is three to five months of age," Hammond said. "Compare that to the red drum (the most popular inshore saltwater species) and they do not begin to mature sexually until they are 4 years of age. In all the age growth studies done on dolphin, there's only been one fish that was documented to be 4 years old. The oldest (and therefore largest) dolphin is typically three years old and there are darn few of those."
Hammond said dolphin are "virtually an annual crop."
He said studies have show there is a total annual mortality rate of 99.7 percent.
"For all the fish that are spawned in a given year, less than three-tenths of one percent will survive until the following year," he emphasized.
At first glance, those numbers would suggest overharvest is a real danger, but Hammond said it's unlikely that would happen because dolphin range over such a wide area and they spawn 12 months out of every year.
"Somewhere in the North Atlantic, there is dolphin spawning going on," he said.
There are catch limits - 10 per person per day or 60-fish maximum per boat - and in Florida, Georgia and South Carolina there is a 20-inch minimum fork length size limit.
In South Carolina dolphin season is generally considered April through October and Hammond said it's a progression. The fish anglers now are seeing are usually five to 20 pounds, what he calls middle-age fish, generally 6 to 12 months old. As the season continues, typically later May into June, the middle-age fish start to decrease in numbers but the larger 30- to 50-pound bulls begin to show up. As the larger fish move out, they are replaced with smaller fish.
Hammond said 13 fish tagged in his study have been recovered in the Caribbean. Their average time at liberty is eight months and all the fish that have been recovered were 3- to 6-month fish.
Tagging results, whether recreational efforts or satellite tags, show preferred temperatures and movement up and down the water column and also have revealed interesting things about the speed at which dolphin can move.
"The fastest we've documented is 130 miles from one day to the next. We've seen other travels where there was sustained travel in excess of 90 miles a day, where a fish went from Islamorada (in the Florida Keys) to Oregon Inlet (the heart of North Carolina's Outer Banks), a distance of 890 miles in nine days," Hammond said.
"That sounds mind-boggling to most people, but it's actually slow. I say that because a 2-by-4 (piece of lumber) thrown in the Gulf Stream will cover more ground than that fish. The Gulf Stream is moving at five miles per hour so in 24 hours that's 120 miles. The reason fish travel slower is that they are always facing into the current looking for that baitfish being swept to them.
"Dolphin have no place to be at a set time. They are perfectly at home anywhere the water quality and temperature is correct and there is plenty of food. Plenty of food is the essence of their life and where they're found."
North Carolina and Florida combined account for 91 percent of the dolphin caught by fishermen, each at just over 45 percent. Hammond said South Florida is where the heaviest tagging activity in his study takes place and he attributes that to the closeness of the Gulf Stream. Florida accounts for 60 percent of the fish tagged in his program. North Carolina anglers account for only eight percent of the fish tagged.
He said South Carolina has tagged as many as 28 percent of the fish but that has dropped off, something he said is probably because people are making fewer fun trips because of the cost of fuel.
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