Surf Smelt Spawning Habitat Use Along Camano Island, Puget Sound, Washington

Surf smelt Hypomesus pretiosus are obligate intertidal spawners that require a suite of suitable environmental parameters for successful spawning.  Although some parameters, such as riparian shading and sediment grain size distribution, have been identified, interactions among variables are poorly understood.  We sampled 51 sites around Camano Island, Puget Sound, Washington using a stratified random design.  Two transects at each site were surveyed approximately every two weeks for a year.  We counted the number of live and dead eggs in standard samples of sediment at each transect.  We compared spawn presence, an index of abundance of surf smelt spawn, and egg viability for each transect.  Seasonal differences in spawn presence, abundance and viability were compared between transects at each site and among sites.  Environmental parameters at each site included beach slope (measured at two tidal heights), backshore control structure, driftwood zone extent, driftwood volume, view to sky, and several solar radiation indices.  We used a principle components analysis to simplify covarying habitat parameters into compound variables that were compared against spawn abundance and mortality rate using regression.  Spawn occurrence, abundance and viability differed substantially among sites and seasons.  Spawning was detected throughout the year, but abundance was significantly higher in summer than in winter.  Spawning was detected at least once on 45 of the 51 sites, but about 20% of the sites contributed most to egg abundance.  Relative egg mortality rates were highest during summer when occurrence and abundance were highest.  Mortality did not appear to differ substantially among locations where spawning was detected.  Regression analyses suggest that large scale environmental parameters, such as site aspect and fetch, and local parameters, such as solar radiation and temperature, predicted spawn occurrence, abundance, and mortality.  Common anthropogenic alterations of nearshore conditions can affect the suitability of sites for spawning.  Because a relatively small proportion of sites appear to be responsible for a large portion of successful spawning, anthropogenic impacts to these locations might have profound effects on surf smelt production.