Understanding larval billfish

billfishbabyResearchers are catching young billfish, some less than .20 of an inch in size, to understand where the marlin and sailfish caught in Texas come from.

“Surprisingly, they all start off really small,” said Dr. Jay Rooker, professor and McDaniel Chair of the Marine Fisheries Department at Texas A&M Galveston. “The smallest we catch are 3 to 4 millimeters, and the biggest ones in our nets are 20 to 25 millimeters.”

Once researchers catch the fish in the net, a variety of information can be pulled from the fish by extracting the otolith ear bone.

“You can pull an ear bone out and count up the rings like you would with a tree,” he said. “Say that individual fish is seven days old — you could count seven rings.”

Other pieces of information are compared together so scientists can learn how to best take care of the billfish population, which equals more fish for anglers.

“We’re doing a lot of life history studies, with distribution and abundance and where we find them,” Rooker said. “We relate this to oceanographic features so we can identify suitable nursery habitats.”

Rooker said they do catch marlin, but the majority are sailfish.

“We started sampling from Texas over until Louisiana, and have found we tend to get the highest concentrations of catches right on the western margin,” he said. “Our catch of sailfish is higher than other areas that are supposed to be good spawning areas.”

Dr. Benjamin Walther, assistant professor at the University of Texas Marine Science Institute, said the process is lethal, but provides invaluable information to understanding the species. Part of the research aims to see where exactly the fish are spawning — whether that be in Texas waters or the Atlantic.

“We can’t put a tag on larval billfish, so the otolith method can be very powerful,” he said. “It turns out that when fish live in different bodies of water they have different chemical compositions, and some of those signatures are recorded in the otolith.

“The signature of their birthplace is stamped into the otolith for life.”

According to Walther, the information is beneficial for anglers because it is extremely important for the effective management of the species.

“You need to know what it is you’re managing, and if you’re managing mixed stock you need to take account of the fatality and fishing done in the whole area,” he said. “Understanding those kind of mixing dynamics is extremely important for a good management plan.”

Walther said the information they compile may be shared with conservation groups to help the species management, such as the Coastal Conservation Association of Texas.

Robbie Byers, of the Texas CCA, said they are not currently funding larval billfish research, but said the information does help the association.

“We can use that information on what laws to support,” Byers said. “We are certainly involved in pelagic research, but as far as billfish larvae here in Texas, we aren’t right now.”