High-Tech Spying on Snapper in Gulf

Sitting on the bottom of the sea 100 feet underwater in the Gulf of Mexico on a cloudy January day, three words come to mind: cold, dark, and lonely.

Think of sticking your face into a bucket of water and ice. Then imagine the water in the bucket is so dark you can scarcely see your hand on the end of your arm. Welcome to Steve Szedlmayer’s laboratory.

Steve Szedlmayer, a professor working out of Auburn University’es Department of Fisheries, readies a receiver to be placed 100 feet beneath the surface of the Gulf of Mexico. The receivers are used to track red snapper fitted with transmitter tags. This device will be installed at a research site 23 miles offshore. (Press-Register/Ben Raines)

The professor, working out of Auburn University’s Department of Fisheries, has been studying red snapper in the Gulf of Mexico since 1990, a 20-year project that has required thousands of scuba dives and allowed Szedlmayer to keep tabs on some individual fish for years. It has also given him unique insight into the ecological impact of the hundreds of artificial reefs off Alabama.

“The basic message is that artificial reefs work. I never believed I’d be saying this 20 years ago. I thought it was a joke. We used to say, ‘Oh my, sinking another ship. Oh what a waste,” Szedlmayer said Thursday. “At this point, I’m convinced that they produce fish, rather than just attract fish.”

That conclusion is inescapable, said Szedlmayer, based on his studies of how long snapper stay on the reefs, what age they arrive at the reefs, what they eat, how quickly they grow and where they concentrate in the Gulf.

The task for Szedlmayer and two volunteer divers — Rusty Hensely and Keith Simmons — last week was to retrieve five expensive underwater receivers and install new ones in their place. The receivers were attached to anchors on the seafloor and suspended with floats so they hung about 15 feet above the bottom. They were designed to record the comings and goings of red snapper fitted with special transmitters on a small artificial reef 23 miles offshore. The

transmitters are surgically implanted in bellies of fish Szedlmayer catches with a rod and reel.

He has been using the array of receivers to track the activities of a group of snapper since August. His data is unique in the scientific world as it provides a 24-hour-a-day log of where individual fish are in relation to their home reef. He can also follow the travels of individual fish from reef to reef by tracking them in real time from the boat with a hydrophone designed to pick up the distinctive pings of the transmitters.

“The precision of the system is incredible. We can track these fish down to their exact position at every moment,” Szedlmayer said. “As far as I know, this system has only been used one other time. I think you will be seeing a lot of other people using it soon.”

Each of the five receivers can record about a million passes by fish. Szedlmayer said it takes about six weeks to fill up the receiver’s memory capacity. That leaves him with roughly 5 million data points to process, a rich trove of scientific information.

But that data comes at a price, namely monthly trips to the seafloor no matter how cold the ocean gets. Most people, scientists included, quit diving in the Gulf in November, when the water temperature drops into the 60s. By January, the temperature hovers around 59 degrees.

The first trick to changing out one of the receivers is finding it. The boat hovers over GPS coordinates associated with a receiver and two divers jump in, swim to the bottom and begin searching. One diver settles to the seafloor and holds the end of a length of rope. Holding onto the other end of the rope, the other diver swims in a circle around the stationary diver and hopes the rope catches on the anchor chain for the receiver. If all goes right, they can usually find the anchored receiver within a few minutes.

But for the diver sitting still and alone on the dark bottom of the Gulf, those can be long and lonesome minutes, with the only sound the gentle burble of exhaled bubbles rising toward the surface.

Szedlmayer has arrays set out on the seafloor in other areas as well, including in shallower water. While he said he can’t draw too many conclusions about the effect of the oil spill on the snapper population at large, he said his research did show that the fish stayed in place on their reefs even as oil drifted over them.

“We’re certainly hoping that we can do an extensive study of whether there was an oil effect or not. One of the aspects we did look at was the age zero fish. We’ve got a long term database on that,” Szedlmayer said, explaining that the young of the year typically settle onto small reefs during the summer.

He said the initial data suggests that there were not a lot of snapper on the reefs that were born this year. Part of the reason, he speculated, was that last year was an extremely productive year for snapper, meaning the reefs were full of 1-year-old snapper.

“The reefs are density dependent. If the house is already full, you can’t let anybody else in, and recruitment was so good last year,” he said. “But, we had cold water upwelling this summer. You had the oil spill. Then you had the extremely high number of age one fish this year.”

In the end, Szedlmayer said, it will take a lot of research to tease apart the effects of those influences. Even then, he predicted, it will be hard to determine what impact the oil spill had.

Click to Watch a Video of Spying on Snapper in Gulf……….

203 Swingle Hall | Auburn, Alabama 36849 | (334) 844-4786 |
Website Feedback | Privacy | Copyright ©