|120705-1 April 29, 2010 Table of Contents|
Juvenile Salmon Use in Lake Union in Relation to Floating Home Complexes
During the spring and summer of 2009, Pentec Environmental conducted a juvenile salmon study in Lake Union for the Floating Home Association (FHA).
The principal objective of the study was to conduct site-specific surveys to provide the City of Seattle with improved scientific data with which to develop reasonable guidance and regulations for floating homes; these data were intended to clarify the actual significance, if any, of these structures to outmigrating juvenile salmon.
Observational data were collected around 9 floating home complexes by fisheries biologists at above water and snorkel transect stations using standardized methodologies. To augment findings, the results from recent acoustic tagging studies conducted by the U.S. Fish and Wildlife Service (USFWS) were also included in this report.
Results and conclusions are as follows:
- Based on above water and snorkel observation events, juvenile salmonids do not appear to be associated with the Lake Union nearshore either at floating home communities or at the Gas Works Park reference site. Only 1 of 97 observations events conducted between late-April and early-July revealed the presence of juvenile Chinook salmon proximal to floating homes.
- These findings are consistent with juvenile Chinook salmon acoustic tagging studies conducted during the 2007 and 2008 outmigratory period. These studies showed a pattern of use in Lake Union and throughout the Ship Canal characterized by a general offshore use of aquatic habitats. Juvenile salmonids largely selected against nearshore habitats in South Lake Union and Gas Works Park.
- Above water and snorkel results showed that nearshore habitats in the vicinity of floating home complexes were used by several fish species, most abundant was the small forage species threespine stickleback. Several other warm water resident species were present in low to moderate numbers including smallmouth bass, yellow perch, prickly sculpin and sunfish. Most warm water residents were juveniles that would not pose a predatory risk to juvenile salmon.
- No large adult smallmouth bass, northern pikeminnow, or other predatory fish were observed during observation events near or beneath the structures of floating home complexes.
- The prevalent offshore behavior of juvenile salmon in Lake Union is likely influenced by a number of physical and biotic factors including prey abundance, predator avoidance, and the high level of nearshore development already present in the lake.