The Fisher Slough Restoration Project, located in the south fork Skagit River tidal delta near the town of Conway, is intended to help recover the six populations of wild Chinook salmon present within the Skagit River and its natal estuary. We report monitoring results related to Project Element 1 (of 3), which replaced an existing floodgate with a new floodgate. The goal of Project Element 1 was to improve fish passage and tidal inundation to areas upstream of the floodgate and to protect adjacent farmland from flooding. We address monitoring questions related to Project Element 1 for fish with data collected in 2009 (Beamer et al. 2010), in 2010 (Beamer et al. 2011), and in 2011 (this report). The primary question for Project Element 1 and juvenile salmon monitoring is: Does juvenile Chinook salmon use increase in habitat upstream of the floodgate after its replacement occurring between the 2009 and 2010 fish monitoring periods?
The new Fisher Slough floodgate, during the monitoring period covered by this report, was operated according to management periods outlined in its hydraulic permit. Upstream juvenile salmon passage opportunity coincides with non-ebb tidal stage periods when floodgate doors are open and was estimated to occur 46.8% of the time during the 2011 fish monitoring period. This statistic varied little over the three years of monitoring Fisher Slough’s floodgate, ranging between 45% and 47%.
In 2011, twelve different species of fish were found in the study area, including five different salmonids and other freshwater and estuarine species. Average monthly juvenile wild Chinook salmon density was higher downstream of the floodgate than upstream of the floodgate in 2011 (year 2 after replacement), but it is not significant at the 0.05 level. In 2009, before floodgate replacement, there was statistically and visually no difference in juvenile wild Chinook salmon density between sites up- and downstream of the floodgate. However, in 2010, there were higher densities of juvenile wild Chinook salmon downstream of the floodgate than upstream of the floodgate. An analysis of juvenile Chinook salmon density and landscape connectivity suggests juvenile Chinook salmon use of Fisher Slough upstream of the floodgate was lower than the normal pattern observed at all other Skagit sites after the floodgate was replaced.
The statistical tests and graphical trends over three years of monitoring indicate that the new floodgate may not be influencing Chinook salmon densities as was originally hypothesized (i.e., juvenile wild Chinook salmon abundance would increase upstream of the floodgate after its replacement). There are factors that may be influencing juvenile Chinook salmon results at Fisher Slough other than floodgate replacement, and we explored six of these: 1) site variability in the local environment, 2) variability in floodgate operation, 3) chance, 4) an unmonitored mechanism, 5) disturbance from restoration construction occurring in 2011, and 6) variability in Skagit River juvenile Chinook salmon outmigration population size. Of these six potential influences, we feel the one most likely to be influencing juvenile Chinook salmon results is variability in floodgate operation, because 2009 had an extended period of gates being held open while years 2010 and 2011 did not.
Beamer, E., Henderson, R. and Wolf, K., 2013. Juvenile Salmon, Estuarine, and Freshwater Fish Utilization of Habitat Associated with the Fisher Slough Restoration Project in 2011. Skagit River System Cooperative, La Conner, WA. pp. 83.
|
0
File Type:
pdf
File Size:
3 MB
Categories:
Technical Reports