Analyzing Artificial Reefs
More fish, or just more fish in one place?
By Melissa Gaskill
The Gulf of Mexico is calm as divers drop one by one off the side of a boat miles from shore. Water stretches in every direction, with nothing else in sight. But as the divers descend beneath the surface, they see schools of red snapper, several of them impressive in size, swimming around an irregular structure resting on the bottom.
This is one of dozens of artificial reefs off the Texas coast, created as part of a Texas Parks and Wildlife Department program. The divers are scientists from the Harte Research Institute for Gulf of Mexico Studies at Texas A&M University-Corpus Christi (HRI). For more than two years, they’ve been analyzing fish and other marine life around 15 of the state’s artificial reefs. Funded by TPWD, “South Texas Artificial Reef Monitoring — Fish Community Assessment Along the Coastal Bend” aims to settle a long-standing debate about these structures: Do they actually increase productivity of the marine ecosystem (the number of fish) or simply serve as gathering points for existing fish and other species?
While numerous studies have documented increases in fish abundance around artificial structures and people catch more fish over and around them, the question hasn’t been definitively answered scientifically. This study, according to principal investigators Gregory W. Stunz and Matthew J. Ajemian, hopes to do so.
Offshore oil and gas platforms in the Gulf have become de facto artificial reefs, providing habitat for a variety of marine life.
“These structures are valuable from a biological standpoint as habitat and economically for fishing,” says HRI Executive Director Larry McKinney. “There is a good case to be made that artificial reefs are in fact new habitat. Our goal is to say definitively yes or no, and that’s clearly what the Parks and Wildlife Department wants to know.”
The answer is particularly important in light of current federal policies that have accelerated removal of offshore oil and gas platforms in the Gulf of Mexico, most of which have become de facto artificial reefs. Federal regulations require a well’s removal once production ceases, and the Department of Interior accelerated the pace of that removal in 2010, largely in response to Hurricanes Katrina and Rita in 2005 and the Deepwater Horizon disaster. In 2010, 221 platforms and other structures were removed; 285 came out in both 2011 and 2012.
Idle offshore platforms pose a risk of leaks or spills, and are more difficult and expensive to remove if damaged or sunk by a hurricane. On the other hand, each of these structures provides two to three acres of habitat for marine life, which makes them popular with fishermen and divers.
The federal government allows companies to convert platforms to artificial reefs rather than remove them. Texas implemented an artificial reef program in 1990, now one of the largest with 67 permitted artificial reef sites. But only 2 percent of decommissioned platforms in less than 100 feet of water and 38 percent of those in waters 101 to 200 feet deep have been converted.
Ultimately, results of the HRI study could support increased participation in the rigs-to-reefs program.
“The study is really important in terms of showing the significant benefit of adding reefs to the region,” says Brooke Shipley-Lozano, chief scientist for TPWD’s artificial reef program. “We hope it will increase conversion of platforms to reefs and get more structures into the program. That is our end goal, to create as much habitat
as possible.”
Counting Fish
The sites analyzed for the study vary in depth, distance from shore and structure, although most are pieces of decommissioned platform jackets (the part of the structure below the water).
In the study’s first year, each site was evaluated for fish species and abundance and differences between site locations and materials used. The second year, researchers looked at vertical and seasonal patterns of fish and how site differences affected those.
Red snapper tend to show up on all types of artificial reefs. This one is being assessed after having been caught at an artificial reef in the Gulf.
Jennifer Wetz, HRI fisheries project manager, says the effort focused on three cutoff platforms between 45 and 55 miles from shore — named MIA7, BAA132 and MUA85. Researchers also sampled natural banks and standing platforms around those sites, for comparison’s sake.
Surveys were conducted by scuba divers and remotely operated vehicles, or ROVs. Divers allow for a wider perspective — they can take in a 360-degree, surface-to-bottom view — but vehicles can go much deeper, potentially surveying all the way to the bottom, typically 200 or 250 feet at the study sites. ROVs also produce video that can be analyzed in the lab (although one of the drawbacks is the staff time required to do so).
TPWD has been collecting data on species and abundance at all of its reef sites, and HRI scientists used the same surveying protocols so that all the data can be combined. The HRI surveys yielded a total of 52 fish species identified from all sites, with 30 species found at one site alone, BAA132.
Researchers also fished the old-fashioned way, with hook and line, to measure fish and collect tissue samples. Wetz reports they dropped a total of 1,530 hooks, catching primarily red snapper. They examined stomach contents, reproductive organs and otoliths (ear bones, which indicate fish age) of the fish caught.
A Reef Is Born
In the summer of 2013, TPWD began a new reef, MU775, in about 70 feet of water off Port Aransas, using concrete culverts and specially constructed concrete reef pyramids. HRI sampled the site before the work started, again shortly after materials were placed and on a regular basis afterward. This created the first complete documentation of how marine life colonizes artificial structures, and will allow the first-ever comparison of marine life present at the natural site to what comes to the reef.
Concrete structures were placed in the waters off Port Aransas to create reefs in 2013, and researchers have been documenting how marine life colonizes such structures.
“We expected a lot of change quickly as the site went from barren bottom to structure,” says Stunz. “Then we should see more gradual change to a climax community, or a stable ecosystem that isn’t likely to change much. It’s unique that we get to watch these changes occur.”
A reef-less site nearby will be surveyed for comparison.
Preliminary Results
The seafloor along the Texas coast has very little natural structure habitat, so if artificial reefs do indeed increase production, that will help keep Gulf fisheries healthier. So far, the research shows biodiversity on artificial reefs equal to or even exceeding that on natural banks. More diversity means a sounder and more resilient system.
Preliminary evaluation of data on the relative abundance and size of red snapper on standing oil and gas platforms, artificial reefs and natural banks indicates that fish on natural and artificial reefs are larger than those on standing platforms. Snapper species accounted for 26 percent of the total fish abundance at sites surveyed in 2012.
Data from 2013 suggest that reef type — sunken ship or toppled or cutoff platform — does influence fish community structure and abundance. Toppled platforms had the greatest abundance of red snapper, Wetz said, while larger specimens were found around cutoffs. (Anglers will be happy to note that red snapper show up on all types of artificial reefs.) Ninety percent of catches by longlines in deeper water are red snapper, which could reflect the attractiveness of the higher relief of a cutoff versus a toppled platform.
Researchers are still analyzing ROV data to compare how depth, number and age of structures, proximity to other structures (natural and artificial) and distance from shore affect fish communities on an artificial reef. They’ll also be looking at how far from a site those effects carry.
The study has been extended through 2015, with the goal of continuing to monitor and evaluate fish community structure associated with artificial reefs. Wetz says researchers will re-survey study sites to confirm the differences previously observed. The team also will monitor artificial reef sites offshore of Port O’Connor, Port Aransas and Port Mansfield, along with natural banks, standing platforms and unstructured bottom. Comparing data from these various sites will provide better estimates of the value of each in terms of fish abundance. With the number of platforms in the Gulf predicted to decline 29 percent or more by 2023 (as compared to 1999) as removals exceed installations, this data will be especially timely.
McKinney expects that the debate over whether artificial reefs increase or just concentrate production may never be settled to everyone’s satisfaction, but he sees plenty of evidence of increased production.
“Artificial reefs do contribute to ecosystem productivity,” he says. “To me, the question is not whether artificial reefs are an effective [fisheries management] tool. They’re a critical tool. Recreational fishing is a multibillion-dollar industry. Fishing boats can go just about anywhere, and electronic gear find just about anything. We can either help provide a place for people to fish and take pressure off the natural reefs, or allow that pressure to continue. Even if artificial reefs are just aggregating fish, that takes pressure off natural areas and helps to maintain healthy ecosystems.”
Rigs to ReefsThe first offshore drilling platform was installed off the coast of Louisiana in 1937. By 2001, there were 4,043 platforms in the northern Gulf. Removal of nonproducing platforms began in 1973, and the rate of removal accelerated in 2010; about 3,000 were left by March 2013. “Around these platforms are the most desirable fish in the Gulf,” says Larry McKinney, executive director of the Harte Research Institute for Gulf of Mexico Studies. He means red snapper, of course.People started fishing around platforms because that’s where the fish were and the structures were easy to find, especially in pre-GPS days. Recreational fishing is an important part of the economy and lifestyle along the Texas coast; in 2011, saltwater anglers had a total economic output of $3.7 billion in Texas. When oil and gas production began to move farther and farther offshore and to change from fixed to floating structures, artificial reefs were seen as a way to fill the void. Under the state’s rigs-to-reefs program, managed by the Texas Parks and Wildlife Department, owners of a platform scheduled for removal can instead donate it to the program, along with funds equal to half of what it would have cost to remove the structure ($1 million to $7 million or more). The owner caps the well under the structure according to federal regulations, the federal Bureau of Safety and Environmental Engineering approves the reefing plan, and the Corps of Engineers issues a permit. The structure can then be dropped on its side or taken in pieces to a designated reef site. In all, 135 structures have been converted to reefs off the coast of Texas in water ranging from 60 to 305 feet deep, with most in the 150- to 280-foot range. The location of reefs can be found on the TPWD website, www.tpwd.state.tx.us/artificialreefs. |
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