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NEWPORT, Ore. – A pilot project to evaluate the feasibility of re-establishing native oysters in Oregon – without damaging native eel grass, a protected plant species – has completed its third year and researchers say tests conducted in Netarts Bay near Tillamook show positive results.

Oyster seed, called “spat,” planted in test plots in 2005-06 survived through three full years and established larvae on shells placed in the bay. The outplanted oysters had active reproductive tissue indicating colonization may have begun, and larvae were also found on some other nearby structural material. Genetic testing confirmed that it was Ostrea conchaphila, the native variety known as the Olympia oyster, which had been planted two years earlier.

“So far, things look encouraging,” said Jessica Miller, an ecologist with Oregon State University’s Coastal Oregon Marine Experiment Station. “The oysters have survived their ‘outplanting’ and established themselves. We would like to go back out in the spring and check on their progress one more time because there are still a lot of questions that need to be answered, such as whether naturally produced larvae are surviving and reproducing on their own.”

The Olympia oyster was found in many Oregon and Washington estuaries until over-harvesting and habitat loss through development all but wiped out the species. During the height of these harvests in the 1890s, some 130,000 bushels of oysters were annually shipped from the Pacific Northwest to California and within 20 years, 90 percent of these native oysters had disappeared.

Researchers speculate that the remaining oyster populations may have succumbed to increased silt generated by 20th-century logging and mill operations, which either killed them outright or covered their beds and destroyed their habitat. They have not returned in discernible numbers to Oregon estuaries.

The Olympia oyster, which is smaller than the commercially grown Pacific oyster, is highly prized for its distinctive flavor. Originally the oysters grew from Baja California to Vancouver Island, and were found in three Oregon bays – Yaquina, Netarts and Coos Bay.

The project to re-establish them was begun by The Nature Conservancy in 2005. Dick Vander Schaaf, the group’s coast and marine conservation director in Oregon, got permission and funding from NOAA to establish a pilot study in Netarts Bay, where OSU has a research lease, but delays in the approval process stretched out the start of the research project until 2006.

The Whiskey Creek Shellfish Hatchery donated its services to raise the native oysters and owner Sue Cudd used local adult oysters to provide more than 50 million microscopic larvae for the project that will be continuing through 2009. Efforts this year are focusing on increasing the restoration work beyond the pilot study by planting out four times as many oysters as had been done in previous years.

In 2006 Miller and her colleagues, including master’s student Pamela Archer, spread out 400 bags of shells with oyster seed attached. Half of the bags contained tiny oysters the size of a grain of sand that were raised in 2006; the other half were from the 2005 brood year and these year-old oysters had grown to the size of a quarter. The bags were deposited in two plots in different densities, so the researchers could gauge the impact of the oysters on eel grass.

“We were looking a number of things in the study,” said Miller, who is an assistant professor of fisheries and wildlife at OSU and works at the Hatfield Marine Science Center in Newport. “In addition to growth and reproductive success, we wanted to see if there were outplanting practices – such as certain shell densities – that would minimize impact to the native eelgrass present in the study area. What we found was that at low and medium densities, the short-term impact is negligible. But at higher densities, there appeared to be at least a short-term effect, including a reduction in eelgrass density compared to control areas with no oysters.

“So any strategies for re-establishing native oysters should consider the issue of population density and impacts on vegetation,” she added. “Given that both the oyster and eelgrass are native and co-existed in our local estuaries, the potential for localized and possible short-term loss of some eelgrass should not necessarily prevent efforts to re-establish the native oyster.”

Oysters are filter-feeders that often improve the water quality of estuaries and can add habitat diversity to the ecosystem. Some researchers believe that establishing oyster reefs helps migrating juvenile salmon by creating protective channels, though few definitive studies have been done.

The researchers hope to evaluate the Netarts Bay site again in early spring and check the oysters for growth, reproduction, and possible predation by crabs. Natural reproduction may have been negatively affected by an outbreak of the Vibrio virus, which had a major impact on Pacific Northwest oysters in 2007.