Dick Waller, Bruce Comyns and Jim Franks, USM marine biologists at the Gulf Coast Research Laboratory here, are more than 100 miles off the coast of Mississippi today (through Saturday) searching for newly hatched larvae of the giant bluefin tuna.
Bluefin tuna can reach up to 10 feet in length and can weigh up to 1,400 pounds. Prized by both the commercial and recreational fishing communities, these ocean giants can spell big money. A 444-pound bluefin caught in January 2001 brought in $391 per pound at a Tokyo fish market auction.
At several days of age, however, giant bluefin larvae are not giant; they are about the size of a pencil eraser. Not much is known about exactly where bluefin adults spawn, conditions favorable for spawning and what contributes to the survival of the young. What is known is that these giants generally spawn in the northern Gulf of Mexico and the Mediterranean Sea.
"In the Gulf of Mexico, there is apparently a spring run for spawning purposes," Waller said. "While there is no regular monitoring technique, looking at the numbers of larvae gives us an indication of the number of adults coming into the area to spawn."
Waller is Mississippi's coordinator for the Southeast Area Monitoring and Assessment Program, a partnership among federal and state agencies and universities. The biologist has spent years sampling resources in the Gulf from Key West, Fla., to Brownsville, Texas.
"To cover a large geographical area with consistency from year to year, we sample on a set grid pattern, taking samples at those same spots every year," Waller said. "What we are doing now is supplementing the (grid pattern of the) spring plankton survey by going to the ocean fronts and eddies that others identify for us."
Satellite imagery is providing clues for finding the fronts where water masses of different temperature or salinity meet or eddies that spin off from a water mass that differs from the surrounding water. Ocean fronts also play a role in the formation of large mats and "weed lines" by sargassum, a floating brown algae found in the western Atlantic and the Gulf.
The sargassum mats and weed lines are potential habitat for the bluefin larvae. Through exploration using remotely operated vehicles, video, divers, and a variety of sampling gear in a related study supported by the Mississippi Department of Marine Resources, the team has already collected more than 8,700 fish representing at least 90 different species associated with the sargassum.
"We will be sorting and identifying the fish from this trip at the GCRL," Waller said. He said another piece of the puzzle will come from Dr. Bill Richards of NMFS in Miami. "He is one of the leading experts on tuna larvae. The sizes we are catching are very small and hard to identify, and he will confirm our identifications. We are also providing specimens to other researchers for DNA work. That would tell them from which population the bluefin tuna are coming.
"It is easier to assess inshore habitat," Waller added. "But when you are dealing with animals that spend their whole life cycle offshore, it is harder to find answers: how do their larvae grow up, where do their juveniles hide? We want to know exactly where and why."
By Linda Skupien