Counting Fish: Longlines, Lionfish and Liberty Ships

It?s been a busy week for scientists in the Gulf of Mexico

Multi-beam map of MU 616 Liberty Ship Reef on the seafloor of the Gulf of Mexico. Credit: Schmidt Ocean Institute

Last week, scientists dropped longlines at artificial reef sites off the Texas coast, pulling up some nice-looking red snapper, gray snapper and triggerish. No fish and chips for dinner, though; these specimens were measured, weighed and contributed various tissue samples for research. Meanwhile, using a multi-beam acoustic array onboard the R/V Falkor, other researchers created a 3D map of an artificial reef made from sunken Liberty Ships. These ships carried supplies during World War II, and were sunk in five locations around the Gulf of Mexico in the 1970s. Also onboard, an ROV team hard at work surveying fish populations at artificial reef sites, and looking to repeat earlier documentation from another site, MU A-16, of invasive lionfish near the Texas coast.

These scientists, from the Harte Research Institute for Gulf of Mexico Studies at Texas A&M University-Corpus Christi, along with colleagues from TAMU College of Science and Engineering and the University of Georgia, are spending a couple of weeks on the R/V Falkor, owned by the private Schmidt Ocean Institute.

Longlines

The longline-wielding fisheries folks are studying, among other things, how best to deal with barotrauma, which affects survival of fish that are caught and released. Many popular recreational fish such as snapper live near the seafloor. When these fish are hooked and reeled to the surface, the rapid change in pressure expands their swim bladders, displacing other organs. The increased buoyancy can make it difficult for a released fish to resubmerge, and even if a fish does return to depth, the lingering effects of barotrauma may make it more vulnerable to predators or eventually kill it. Catch-and-release is intended to allow us to enjoy recreational fishing without decimating populations of target fish, but if the animals don?t survive the process, this approach obviously won?t work.

Researchers will be investigating the effectiveness of venting, or inserting a needle into the swim bladder to de-inflate it. Venting isn?t always done properly; some fishermen mistakenly puncture the esophagus, which can protrude from the fish?s mouth, rather than the swim bladder. Other organs may inadvertently be punctured, or infection introduced. The researchers are also looking at the effectiveness and practicality of using a weighted hook to return fish to an appropriate depth, so the bladder can naturally return to normal.

Lionfish

Lionfish, native to the Indo-Pacific have been common since about 2000 in Florida?s waters ? locals hold lionfish derbies and it?s pretty much open season for spearfishing for the invaders ? and have gradually worked their way across the Gulf of Mexico. In August, 2011, the spiny predators were first documented at the Flower Garden Banks National Marine Sanctuary, 100 miles south of the Louisiana coast. Lionfish are aggressive feeders, prolific spawners, and have no natural predators in the Gulf of Mexico and Caribbean, so can negatively effect marine ecosystems where they?ve invaded. As I explained in previous posts, HRI scientists are conducting ROV surveys as part of a two-year study to assess fish communities on artificial reefs. On September 21, ROV cameras captured the first evidence of lionfish off the coast of Texas (this video also shows the challenges of maneuvering the ROV!). Additional documentation of the extent of the lionfish invasion in this part of the Gulf will be a sort of two-fer from the ROV work.

Liberty Ships

Liberty Ship artificial reef sites were created by the Texas Parks and Wildlife Department to provide important habitat for numerous fish species and other marine life ? and great opportunities for fishermen and scuba divers. But, as discussed in previous posts, there is some debate about whether artificial reefs such as these actually increase the productivity of an ecosystem ? adding biomass in the form or more fish and other marine life ? or just serve as gathering places by providing shelter and a sort of underwater cafeteria. The HRI study, funded by TPWD, is intended to help settle that debate.

?The multi-beam maps will allow us to accurately locate the structure that exists on these sites,? says Greg Stuntz, chair of Fisheries and Ocean Health and HRI and lead scientist on the artificial reef study. ?The maps also give us an idea if the structure is broken up, how it?s oriented, and how far away structures are from each other. Knowing precise locations will aid us in the future if we want to evaluate ideal placement of artificial reef structures. For instance, is there a certain distance apart that most affects fish size, abundance and growth?? The scientists will import the maps created on the Falkor into GPS onboard other vessels and use them when fishing, diving and surveying on those structures in the future.

While the best weather for dive surveys has past for this year, I still hope to accompany HRI researchers on at least one expedition next year. Good thing it?s a two-year study.

Previously in this series:

Counting Fish: Gulf of Mexico Artificial Reef Survey
Counting Fish: on the artificial reefs
Counting Fish: well, thanks Isaac, no counting fish this week

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