Scientific Sherlocks

These two researchers are gaining clues about the mysterious migraton habits of cobia.

EDITOR’S NOTE: This is part one of a two-part series examining cobia migration patterns. Part two will appear in the September issue.Fisheries researchers have tried for years to learn more about cobia, Louisiana’s brown fish.

For instance, scientists have wondered where cobia come from, where they go, whether or not all cobia migrate, and whether or not you can catch cobia in the wintertime?

Jim Franks and Read Hendon from Gulf Coast Research Laboratory, located in Ocean Springs, Miss., and affiliated with the University of Southern Mississippi, have.

Although these two fisheries biologists have worked together for many years, recently they studied cobia with two different techniques.

Hendon spent his time crunching data and keeping up with the tagged-fish programs for cobia and tripletails, while Franks crunched data on five cobia that the research lab tagged with satellite transmitters.

Although not completed yet, the numbers about cobia have taught us plenty about Louisiana’s brown fish that bite so hard and taste so delicious when on dinner platters.

Tagged-cobia program

Jim Franks started the tagged-cobia program in 1988 by tagging and releasing cobia as well as providing tagging information and tags for anglers all along the Gulf of Mexico.

Outdoorsmen have tagged more than 14,000 cobia since the program’s inception with more than 900 cobia recaptured, about a 6-percent recovery rate.

“In recent years, we’ve been surprised at the number of cobia that we’ve recaptured along the western Louisiana and Texas coast,” Hendon said.

Many anglers had believed that cobia migrated from the Florida Keys to the mouth of the Mississippi River throughout the spring, and then began an eastward migration from the mouth of the Mississippi River back to the Florida Keys in the fall.

However, the latest research indicates that a population of cobias swims far past the mouth of the Mississippi River and actually may swim south to the coast of Mexico before returning to the Keys across the open Gulf.

“Last year, we also saw some unusual movement of cobia,” Hendon explains. “Normally, when we have cobia tournaments in Mississippi and Louisiana, fishermen go to the barrier islands and the shallow rigs on the east side of the Mississippi River.

“However, to find cobia, many of these anglers had to go all the way to the west side of the river. The only thing we could attribute this unusual movement pattern to was the extreme northern extension of the loop current.

“Apparently, when the cobia began their western migration from the Florida Keys, they might have picked up the edge of that loop current at Pensacola and bypassed the Mississippi River and the eastern side of Louisiana, riding that current over to the west side of the Mississippi River.

“The anglers in Florida said it was a late year for them with cobia also.”

Get it and go

Last year, the tagging program also proved that cobia could move quickly across vast regions.

“We had cobia tagged off of Destin, Fla., last spring and then recaptured them one month later far west of the Mississippi River,” Hendon said.

In 2005, the cobia apparently kicked their migration into high gear, possibly using the loop current as a sailboat would use a strong wind to move much faster than they normally would. However, in the summer of 2006, the cobia seem to have moved at a normal pace.

“Catching the loop current may be the explanation of why we have some good cobia years and some years that aren’t as good,” Hendon said. “We may not have fewer cobia in those years. We may just have faster-moving cobia that follow a different route farther offshore during the spring than the years when they run the beaches.”

So far, anglers and researchers have recaptured 25 cobia in 2006, a high number for the Gulf Coast Research Lab; they’ve tagged a total of 254.

Hendon also reports another unusual piece of the cobia puzzle for 2006 as anglers off the Tampa coast still were tagging cobia at the end of June, a time that’s very late for cobia to show up that far south.

“Our main tagging effort is from Apalachicola, Destin and Pensacola, where the Crab Cruncher Tournament in Destin and the Pensacola Cobia Tournament take place,” Hendon said.

The researchers also have seen another surprising development in the tagging program with cobia tagged along the Upper Gulf Coast then recaptured off South Padre Island in Texas, not too far from Mexico.

“The past couple of years, we’ve recorded more cobia that were tagged from Destin to the eastern part of Mississippi being recaptured from Cameron all the way to Galveston and South Padre Island in Texas,” Hendon said. “The reason for this phenomenon may be that more anglers along the Texas coast have started fishing for cobia and/or they are learning more about our tagged-cobia program.

“However, there’s also strong evidence that suggests that a population of cobia may continue past the mouth of the Mississippi River and swim down the coast of Texas into Mexico.

“If you look at a map, you’ll see that not a lot of open Gulf is present that the cobia will have to travel through to go from Mexico to the Bay of Campeche, move to the Yucatan Peninsula, cross the Yucatan Channel, hit Cuba and then have only a short trip to the Florida Keys.”

The researchers have had problems getting information out of Mexico because the cobia tags are written in English. Most anglers can’t read them. Or, if they can read the English tags, they may not have the way to make an international phone call to report the capture of the cobia.

“Until now, we’ve not had any definitive proof that a group of cobia makes this large circle in its migration pattern,” Franks said. “However, I think it’s very likely from the information we’ve received so far that some of the cobia that are tagged on the Upper Gulf are making a complete circle from the Florida Keys west along the Upper Gulf Coast down to Mexico and then back to the Keys.”

Hendon also mentions another possibility — that some cobia actually may ride the loop current from the Florida Keys all the way around the Gulf.

From their research, Hendon and Franks have learned that the cobia have much more complex migration patterns than first believed. Also, different populations of cobia may travel different routes from the Florida Keys to the northern Gulf of Mexico and then back to the Keys.

“The only way we’ll ever know for sure where and how these various populations of cobia travel is by using satellite tags,” Franks said. “These tags will enable us to keep up with the daily, monthly and yearly movements of the different cobia populations. The number of cobia tagged each year has remained constant since the beginning of the program in 1988, as has the number of cobia recaptured.”

Growth of cobia

“The female cobia tends to be larger than her male counterpart,” Franks said. “A 1-year-old female can be from 22 to 30 inches long. A 2-year-old female will be 30 to 44 inches long, and a 3-year-old female will be 32 to 48 inches long. The majority of cobia being caught by anglers are 1- to 3-years old.”

The oldest cobia, an 11-year-old female, that Jim Franks has aged, had a 62-inch length and weighed 110 pounds.

You can help

The more fishermen involved in tagging cobia, an ongoing project, the more scientists can learn and tell us about these unique fish. You can become involved in the cobia-tagging program and receive all your materials free of charge.

“The cobia-tagging program is funded by the Mississippi Department of Marine Resources and the Sport Fish Restoration Program,” Hendon said.

To receive tags and instructions to participate, call Hendon at (228) 872-4202, or email him at read.hendon@usm.edu. He reports that the Gulf Coast Research Laboratory is also doing a study on tripletail and can send you tags and instructions to tag these fish also.

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