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Counting Fish – End of the season

The views expressed are those of the author and are not necessarily those of Scientific American.


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Scientists at the Harte Research Institute for Gulf of Mexico Studies stayed busy this summer completing vertical longline sampling and ROV and diving surveys at artificial and natural reefs off the Texas coast. The work is part of a two-year study to analyze fish life around artificial reefs, which began in 2012.

To date, they’ve completed ROV surveys on all selected 11 artificial reef sites, surveying multiple structures at many sites, and completed most vertical long line sampling, including at standing oil/gas platforms, natural banks, and seven artificial reef sites. “That’s a grand total of 153 gear drops, or 1,530 hooks fished,” reports Jennifer Wetz, HRI fisheries project manager. “We’ve also completed a total of 49 dive surveys on our three core artificial reef sites.”

If setting fishing lines and diving in the Gulf of Mexico don’t sound like hard work, keep in mind that it all has to be done according to protocol, often in less than ideal conditions. (I talked more about the challenges of working at sea in an earlier post).

The study’s overall goal is to understand how fish populations use artificial reefs. The three different sampling methods cover the fact that fish partition themselves out by depth; human divers are best for sampling up to about 90 feet, ROVs and longlines for deeper depths, the former when visibility is good and the latter when it is not.

The study took a serendipitous turn when the Texas Parks & Wildlife Department, which manages the state’s artificial reef program, began creating a new reef (MU775) using several hundred concrete culverts and roughly 500 specially constructed reef pyramids (see a photo of these here). Wetz and company sampled the site before work started, and will continuously monitor it for at least a year, creating the first complete documentation of how marine life colonizes artificial structures.

“We expect to see a lot of occur change quickly as the site goes from barren bottom to structure,” says Greg Stunz, lead scientist on the study. “Then it will more gradually become a climax community, a stable ecosystem that isn’t likely to change much. We’ll document the changes an artificial reef causes, and the differences between reef construction methods. It’s unique in that we get to watch these changes occur.” A reef-less control site nearby will be used for comparison. So far, at MU775 and the control site, HRI scientists have completed 54 gear drops and 54 trap drops (traps are used to sample marine life too small to catch on longlines) for pre-reef sampling.

Why is this work important? “The bigger picture is that artificial reefs are good places to fish, and fishing is a major economic driver in the region,” says Stunz. In addition, artificial reefs could increase the health of the overall marine environment. The seafloor along the Texas coast has very little natural structure habitat, Stunz explains, so artificial reefs increase fisheries production, which enables the fishery to withstand more pressure. Surveys are showing more biodiversity on artificial reefs, equal to or even exceeding natural banks, and more diversity means a sounder and more resilient system overall.

“Across the Gulf of Mexico, one of the reasons red snapper are rebounding is likely because of offshore structures, artificial reefs,” Stunz adds.

He expects that the scientific controversy over whether these structures increase production or merely attract fish may never be satisfactorily settled, although he sees plenty of evidence of increased production. But either way, he points out, people will go fishing on these reefs, and not only will that have a positive effect on the economy, it will also serve to take pressure off of the natural areas. “So, even if we are just aggregating fish, that’s helping to maintain healthy ecosystem.”

For those whose hearts beat faster at the thought of aggregating fish, the TPWD website has an interactive map of artificial reef sites.

The researchers may squeeze in a few more trips offshore, but the season for that is more or less over. Results from the study will be reported at a meeting of the Gulf and Caribbean Fisheries Institute in Corpus Christi, Texas, November 4-8. I plan to attend and report back.

Melissa Gaskill About the Author: A science and environment writer based in Austin, Texas, Melissa Gaskill has a B.S. in zoology from Texas A&M University and a master’s in journalism from the University of Texas. She also has a passion for the ocean and writes about it whenever possible for publications such as Nature News, Men’s Journal, The New York Times, and many others. Follow on Twitter @MelissaGaskill.

The views expressed are those of the author and are not necessarily those of Scientific American.





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