Marine Biologists Make Discoveries About Offshore Oil Platform Ecosystems

Many of California’s offshore oil drilling platforms will reach the end of their useful productivity in coming years, so 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 students may lend valuable insight to policy makers in their platform decommissioning discussions. Lowe presented a summary of these projects to the California Ocean Protection Council meeting in April.


According to Lowe, 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. 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 said. “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.


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. 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. 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.

“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.”

Fall 2009 Issue

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