Marine Biologists Make New Discoveries About Offshore Oil Platform EcosystemsPublished: June 15, 2009
Many of California’s offshore oil drilling platforms will reach the end of their useful productivity in coming years, and state agencies involved with managing ocean resources are expected to decide within the next year or so about how these platforms should be decommissioned.
Under the direction of CSULB marine biology Professor Christopher Lowe, research by three of his master’s degree students who are graduating this year may lend valuable insight to policy makers in their platform decommissioning discussions. Lowe recently presented a summary of these projects to the California Ocean Protection Council meeting.
According to Lowe, current state regulations require oil companies to completely remove the platforms and restore the seafloor to its original state. “The way they do that is to drop charges down the legs and explode it at the base so they can separate it from the seafloor, then they can lift and cut it,” Lowe said. “But the problem is that the explosions kill everything that has a swim bladder that lives within a kilometer of it.
“But research within the last 10 years has shown that there are species of rockfish around these platforms that aren’t found anywhere else because they’ve basically been fished out elsewhere—fish like cow cod, canary rockfish and bocaccio, which at one point were threatened species in California,” he continued. “The only place that you find large numbers of adults is around these platforms.”
Student Kim Anthony recently became a senior marine biologist for Southern California Edison. Her study, funded by the Minerals Management Service of the U.S. Department of the Interior, examined a possible mitigation tool, Lowe said.
“In the Santa Barbara Channel offshore of Ventura, we acoustically tagged 79 platform-associated rockfishes and lingcod and translocated them from three different platforms to the Anacapa Island State Marine Reserve to test whether they would home back to their platforms of capture, up to 11 miles away, or take residency at their new location,” Anthony explained. “In a reciprocal experiment, 19 fish were translocated from a natural reef to one of either two platforms, one-half to three-and-a-half miles away. Automated acoustic receivers stationed around Anacapa Island, Santa Cruz Island, and each of three oil platforms recorded the presence of tagged individuals over the duration of the study, which was 620 days.
“About 25 percent of the translocated fish to Anacapa Island homed back to the platforms from which they were originally caught,” she reported. “Fish that homed did so quickly, taking on average from one to 15 days. The remaining took up residency at Anacapa Island or moved out of the range of detection. Some individuals moved from Anacapa Island to Santa Cruz Island, inside the Scorpion State Marine Reserve.”
The Santa Barbara Channel is about 400 to 500 meters (about 1,300 to 1,640 feet) deep in the middle, and the fish were typically moved about six to 12 miles. “The homing distances for lingcod, vermilion and brown rockfishes are the farthest yet reported,” Anthony said. “After they homed, several fishes made long-distance movements between platforms, and between platforms and natural habitat, including going back to Anacapa. Cumulative distances that many of the fishes traveled exceeded 19 miles. The use of acoustic telemetry for this study has demonstrated that rockfishes and lingcod appear to be using natural and platform habitat concurrently and their home ranges may be much larger than previously thought.”
Lowe believes a platform’s vertical structure and abundance of places to hide or attach offers an appealing environment to a rich variety of sea life, from plankton and mussels to a variety of fish species. Moreover, “The fact that these platforms are geographically isolated may reduce the rate at which individuals leave because it’s a little risky moving somewhere else,” and facing natural predators. Security regulations also keep fishing and dive boats away from the platforms.
Although Santa Barbara Channel platforms have been studied by a number of scientists, no one had examined fish populations around the platforms off Long Beach and Huntington Beach until now. CSULB student Chris Martin of Huntington Beach undertook research funded by the California Artificial Reef Enhancement (CARE) program.
“What we actually found out was that the fish assemblages are completely different compared to Santa Barbara,” Martin said. “We have a lot more of the warm temperate species, the kelp forest species. You find a lot of Garibaldi, which is the California state fish; sheephead, cabezon and a lot of species that are economically important as well. Cabezon and sheephead have been the focus of the live fish fishery when the rockfish fishery collapsed. Not only have we seen extremely high densities of them on these platforms, but they’re very large.”
He also observed fish nesting and protecting egg masses, “so it’s likely that these platforms are suitable breeding habitat for some species which may be producing a lot of larvae to coastal areas,” he said. He added there might be an ecological significance to having a protected community of high quantities of large fish that reproduce in significant numbers. “Meanwhile, if we want to take the platforms out, it might be more detrimental than leaving them in.”
He also looked at the fishes’ depth preferences. There are a variety of decommissioning options in addition to complete removal. One option would be to cut the top of the platform off to a depth of 85 feet below the surface to meet Coast Guard regulations that enable ships to safely pass over the sites. “We found that there were a number of species that prefer the warmer surface waters of the offshore platforms, and removing the tops of the platforms to 85 feet might eliminate important habitat for some of these species,” Martin said.
“We believe our data will help managers make the right decisions on what to do with platforms once they are scheduled for decommissioning,” Martin continued. “If they wanted to preserve the habitat and cut the platforms off at 85 feet, you’ll lose habitat for some species, but at least it won’t eliminate all the habitat for fish.”
In another study of the Long Beach and Huntington Beach platforms funded by USC Sea Grant and the California Ocean Protection Council, CSULB student Carlos Mireles of Long Beach examined site fidelity and depth utilization of cabezon, sheephead, grass rockfish and kelp rockfish at platforms Edith and Eureka using similar acoustic telemetry methods as Anthony. Edith is in water about 150 feet deep and Eureka is in about 700 feet.
Over a year and a half, he looked at how long fish stayed at each platform as well as the depths they used over time. “This is basically to characterize the platform as habitat—how do they perceive the structures as vital habitat to them? Does it meet all of their resource needs?” he said.
“Some of the things that we’re seeing is that some individuals are utilizing these structures all the way to the bottom. One of our platforms is in 700 feet of water and one of the species, cabezon, is actually going all the way to the bottom, which is deeper than has been seen before. In addition, all four species studied use the horizontal supports of the platform like seafloor habitat. So, platforms are acting like high-rise buildings for these fishes.”
Water temperature plays another role in fish behavior around the platforms, Mireles said. “For one of our species, when the water temperature warms, they go deep to 100-300 feet, then as the temperature gets cold again, they come up to the shallower areas, so we’re seeing a temperature effect on the vertical movement for two of the species. The other two species don’t seem to be affected much by temperature.”