Dames & Moore Inc. and Biosonics. 1994. Salmon Migration Study Manchester Naval Fuel Pier, Manchester, Washington. March-June 1993, Report to US Navy.

REGION: PNW SPECIES: juvenile chum salmon

STUDY OBJECTIVES: Impact Assessment. Determine whether, upon encountering the fuel pier, outmigrating juvenile chum salmon ignore pier, alter their course to deeper waters, delay migration, or encounter predation.

METHODS: Observational: inferential data from combined visual observations and hydroacoustics technology. Hydroacoustic soundings did not positively identify fish species or direction of travel. Rather, juvenile salmonids were identified by a specific sounding pattern. Migration patterns were inferred from trends in hydroacoustic data indicating fish presence and/or absence at specific sites or combined sites. Pierside observations noting fish presence, numbers, swimming direction, and behavior were recorded from six locations corresponding to specific areas covered by hydroacoustic transducers. Empirical: seining catches at offshore and nearshore sites were compared to observational and hydroacoustic data.

OBSERVED BEHAVIOR: It was inferred from the combined observation/seining and hydroacoustics data juveniles continued to migrate east to west and west to east parallel to the shoreline rather than offshore movement to the south. Most observations and catches (79% of catches) were at the nearshore stations with very few found at offshore stations with movement offshore dependent upon size. Fish caught at nearshore stations were most often 60-80 mm in length, while fish caught offshore were normally 90 mm or larger.

OBSERVED LIGHT REACTIONS: It was inferred that the pier's shadow did not appear to alter migratory patterns.

COMMENTS: Migratory behavior east to west and west to east were believed to be dependent upon preferred prey resource availability in eelgrass beds on both the east and west sides of docks. No significant stalling or movement offshore was apparent. No direct evidence of increased predation presented. Although 13 predators were identified in the area, there was no determination of increased or decreased levels of predation in relation to the pier.

The physical design ( i.e. pier height and width, piling number and type) and consequent shadow casting capacity of this pier diminishes its impact on nearshore prey habitat. The design of this pier limits the ability to generalize its effects to piers with substantially increased shadow casting and barrier attributes.