Beginning in 2008, scientific divers have been conducting an ongoing US Forest Service underwater survey of lakes along the Oregon coast to note the presence or absence of native Oregon Floater mussels (Anodonta oregonensis). Since the melting of the Ice Age glaciers 6,000–14,000 years ago, these freshwater lakes have been alternately joined and separated due to the changing sea levels, sediment influx and dune formation. They are known as depression lakes because they have formed in depressions in the sand dunes.
View Cleawox Lake.8.3.10 in a larger map
In the Anodonta life cycle, larvae called glochidia must attach to a host fish for several weeks before dropping to the lake bottom to mature. This is a commensal relationship, meaning that it affords a positive outcome for the mussel and has little effect on the host fish. Comparison of genetic markers from the DNA of mussels and fish collected by divers from the various lakes will reveal patterns of past and present connectivity between the lakes. Analysis of the DNA will also help scientists better understand the evolutionary lineage of each of the lakes. It will also confirm the species identity of the mussel, since recent research has shown that identification of mussels based on shell characteristics can be unreliable.
Volunteer scientific divers Jim and Chris Pendergrass joined Siuslaw National Forest Asst. Fisheries Program Manager Mike Northrop on August 3 to dive Cleawox Lake, 4 miles south of Florence in Honeyman State Park. Unfortunately no Anodonta were sighted in 2 dives in the arm of the lake by the north picnic area. However USGS ecologists Bob Hoffman and Jason Dunham were on hand along with a team of Youth Conservation Corp teens and collected numerous fish from the same location with minnow traps and a seine net. Specimens included native threespine stickleback and coastrange sculpin as well as non-native white crappie, largemouth bass, bluegill, golden shiner, and yellow perch. Presently, the population status of Anodonta in Oregon is thought to be good, but information is lacking (thus work like this).
In previous survey dives, the mussels were collected from Lily Lake, Alder Lake, Dune Lake (all north of Florence), Carter Lake, Threemile Lake (both south of Florence) and Coffenberry Lake (north of Astoria). During dives in Erhart Lake, Loon Lake (both north of Florence) and Lost Lake (south of Florence), Anodonta were absent. It was somewhat puzzling that no Anodonta were found in Cleawox Lake despite the abundance of possible host fish for the Anodonta glochidia. Further dives may be planned to search different areas of this lake for the mussels.
Thanks to Jason Dunham for scientific fact checking and to Lorne Curran for assistance in posting this blog.