Clams and Other Shellfish
Clams and Other Shellfish
Background
There are two clam species in the Coquille River estuary which are fishery resources. These are the softshell clam, Mya arenaria, and the gaper clam, Tresus capax. Softshells were introduced to the Pacific coast in the 1870s by oystermen bringing oyster seed stock from the Atlantic coast. Softshell clams are now found in most estuaries in Oregon, and have become the dominant large intertidal clam species in coastal river-dominated estuaries such as the Coquille, Siuslaw and Umpqua. These estuaries apparently never supported the abundance of native bay clam species found intertidally in the more marine influenced estuaries. Softshell clams are more tolerant than native clam species of the reduced salinity levels which commonly occur in the Coquille River estuary in winter. The Coquille River estuary supports the southernmost populations of softshell and gaper clams in Oregon.
Softshell clams prefer a mud-sand substrate but can also be found in areas containing a rock-mud misture. They are found at a depth of 6 to 12 inches in the substrate and they filter feed on plankton. They reach sexual maturity at a size of about one inch, are summer spawners and have a free-swimming larval period of about 2 to 5 weeks depending on water temperature. Softshell clams can grow to nearly 6 inches under conditions, and 10 year-old clams have been observed in the recreational harvest.
The distribution of softshell clams the Coquille River estuary is centered in the intertidal areas of Bandon marsh, located between Bandon and the highway 101 bridge on the east side of the bay. Only a few sparse pockets of clams exist on the opposite (north spit) side of the bay, probably due to the predominantly sandy sediment of the intertidal habitats there. Softshell clams have been observed as far upstream as Randolph Slough (river mile 6) and as far downstream as the south jetty tideflat. ODFW has conducted intertidal surveys of most of the Bandon marsh, recording distribution and density of softshell clams, sand shrimp and three species of tideflat vegetation. Moder