GULF OASES
Man-made structures might provide vital habitat for highly migratory species
The deployment of artificial reefs is often a contentious subject, but in the Gulf of Mexico, these man-made structures are considered ocean oases, supporting a variety of resident marine life and even migratory species such as tuna and marlin. For anglers, these structures are go-to spots and provide an exciting fishing experience. Scientists also recognize the importance of these habitats, and are curious about how the structures might affect the migration and distribution of a variety of fish species.
WORLD’S LARGEST ARTIFICIAL-REEF COMPLEX
The ninth-largest body of water in the world, the Gulf of Mexico is also home to the largest artificial-reef complex.
Offshore oil and gas exploration began in the late 1940s off Louisiana with the installation of the first oil and gas platform, and by 1983, more than 4,000 had been installed throughout the GOM. These platforms are some of the most productive habitats, providing vertical relief that historically had been scarce, especially in the western Gulf, which predominantly consists of flat, natural plains of clay, mud and sand. Structures—such as ships and concrete bridge components, along with these platforms—provide a habitat network throughout much of the northern Gulf. However, as many nearshore platforms are reaching the end of their production lifetime, the GOM will continue to see these platforms decrease in the coming years, expanding them to deeper waters.
IDLE IRON
In the 1970s, legislation was introduced to address the growing oil and gas infrastructure in the Gulf. Commonly called the Idle Iron Act, this plug-and-abandonment policy requires inactive platforms to be dismantled and responsibly disposed within one year of their termination to mitigate risks to both the environment and navigation safety. Severe weather has toppled and severely damaged platforms and associated infrastructure, leaving the structures weakened and at risk of leaks from wells that could cause potential damage to the ecosystem and negatively impact saltwater anglers in the long term.
In 2005, hurricanes Katrina and Rita hit the Gulf of Mexico, destroying 115 platforms and damaging 52 more along
with 183 pipelines. Coupled with the Deepwater Horizon disaster of 2010, enforcement of the Idle Iron legislation and platform removal was accelerated. Between 2010 and 2015, 813 platforms and structures were removed, and outcry from both the angling and scientific communities led to the National Artificial Reef Plan, which was introduced to recognize these structures’ importance, and the pressure to remove idle structures was reduced.
Incorporating many of the remaining structures into state-run reefing programs will help retain this habitat in the future and solve issues related to environmental risks and liability. Angler groups were among the first to realize the importance of such structures, were instrumental in slowing the Gulf’s platform removal and can also be integral in garnering attention for other fishery-related issues. After all, anglers are often a source of unequaled information regarding the distribution and movement of fishery resources.
PLATFORMS AND MIGRATIONS
Although most anglers fishing on artificial reefs are targeting resident species such as grouper and snapper, these structures are also important to migratory fish such as tuna and billfish. The use of oil and gas infrastructure as migration stepping stones provides a place for fish to feed before making the next leg of their journey, or act as a meeting point to increase the chance of encountering other individuals.
Recent research focuses on the interactions of pelagic species and these platforms, and how these structures influence behavior, diet and movement patterns. Residency around platforms varies by species from tight to loose association, and prey species have been shown to have a tighter association and longer residency period around these structures than the predatory fish.
Yellowfin tuna have been observed to spend a wide range of time at the floaters. Some hang around from hours to months, and some demonstrate residency to the same floater for multiple years. By making direct movements from one floater to another, this indicates that they were not wandering the open ocean or coming
Yellowfin tuna have been observed to spend a wide range of time at the floaters.
upon the floater by happenstance, but rather, these fish might know the locations of these structures, using them as stop-offs during their movements.
To date, research has focused mostly on the impact of artificial reefs in the commercial fisheries for migratory species. Recent technological advances now allow vessels to communicate in advance with fishery-deployed artificial reefs to determine which structure is holding increased quantities of fish, and has been the concern of many anglers and scientists as catches are increasing with less effort. This could mean populations may be vulnerable to overfishing, even though the GOM’s pelagic longlines are set away from platforms because they are adrift in currents and must avoid entanglement.
Assuming commercial-fishing methods do not change, research has shown that it is unlikely that these species have increased vulnerability around the floaters. However, proposals have been submitted to shift commercialfishing methods from longlines to green-sticking, or even to a standardized troll-based approach, which would allow commercial fishing closer to platforms, possibly increasing the vulnerability of the species that frequent them.
The shift of oil and gas exploration from coastal waters to deeper offshore waters means interactions with pelagic species are likely to increase. The understanding and implications behind migratory-species interactions with artificial reefs is still largely uncertain, but new advances in technology and improved location accuracy of satellite and electronic tags allow for more-detailed migration and behavioral patterns to be uncovered.
The Center for Sportfish Science and Conservation, along with anglers throughout the Gulf of Mexico, are partnering to deploy new and improved satellite tags to further understand the connection between these artificial reefs and highly migratory species.