Identification and distribution of subtidal and intertidal shellfish populations in Tillamook Bay, Oregon

Graduation date: 1996EXECUTIVE SUMMARY\ud An increase in the commercial and recreational harvest of clams in Tillamook Bay, Oregon, coupled with a general lack of knowledge about the bay's ecology, served as the impetus for a shellfish survey undertaken in the summer of 1995. Commercial clam harvest has increased twelve fold since 1978 (Carter et al 1994). Recreational harvest has nearly tripled since 1993, although it is still far below the recreational harvest from the early 1970s (Johnson pers corn 1995). The 1995 survey served as a precursor to a more extensive survey to be completed in 1996, and was designed to provide a qualitative assessment of clam distribution in the bay. By identifying those areas of the bay that support relatively dense populations of commercially and recreationally important species of clams, this report will assist in the design of the 1996 survey. It encompassed the northern half of the bay, and provided additional information about substrate\ud type, flora, and fauna in the surveyed areas.\ud Methods were modeled after Hancock et al (1979) and consisted of identifying 92 sampling stations throughout the northern half of the bay. The 92 stations were selected to provide a variety of substrate type and depth. Two SCUBA divers used a two square foot sampling ring placed randomly at each station to identify an area that was then excavated to a depth of two feet\ud using hand rakes. Clams found within the sampling volume were identified, measured, and in some cases, sent to Oregon Department of Fish and Wildlife (ODFW) for size measurement and age class analysis. Data collected from this study and from previous studies suggests that the overall abundance of clams in Tillamook Bay has remained relatively stable or increased over the past 20 years. The exception to this observation is with the population and biomass of gaper clams (Tresus capax), which has declined substantially since the late 1970s. Densities of the other three commercially and recreationally important clam species appear to have generally increased, and it is appears that biomass has increased nominally. The average size of individual clams has decreased.\ud The density of clams appears to be linked to the type of substrate, and substrate preference differs between species of clams. A wide variety of flora and fauna, and a prevalence of juvenile finfish and shellfish appear to indicate an ecologically productive estuary. However, natural and human-caused impacts such as sedimentation and agricultural runoff pose a threat to the bay's ability to continue providing food, recreation, and economic benefit to the communities dependent upon the bay. The paper concludes by briefly discussing the current and the future management of the clam resource in Tillamook Bay