In collaboration with NOAA's Northwest Fisheries Science Center and the Washington Department of Fish and Wildlife (WDFW), PSI is leading a study investigating the possible links between eelgrass and other submerged vegetation and algae abundance and herring populations in Puget Sound. Eelgrass is a key substrate used by Pacific herring for spawning in the nearshore habitats of Puget Sound. Because eelgrass is declining in some areas of Puget Sound, it has been hypothesized that recovery of Puget Sound herring, which have declined in recent decades, is linked to increasing eelgrass abundance. We are testing this hypothesis by measuring herring use of eelgrass and other substrates around Puget Sound and measuring egg mortality rates on each substrate type to determine whether eelgrass provides the highest quality spawning substrate for herring.

Our first year’s results demonstrated that herring show no preference for eelgrass as a spawning substrate, and that egg survival is no greater on eelgrass than on other spawning substrates. Rather, we found that there is greater variation in egg mortality across spawning sites, versus across spawning substrates within a site. Those results can be found in the paper: Habitat limitation and spatial variation in Pacific herring egg survival

The next step in this project is to identify what is driving this variation in egg survival across spawning sites. One possibility is predation: variation in the distribution of herring egg predators may result in different egg mortality rates across sites. To address this hypothesis, researchers excluded large egg predators from some egg deposits, using sablefish traps, while allowing predation on others. Those results are presently being analyzed.

Last, the team is collaborating with WDFW to analyze 40+ years of historical habitat data from herring spawning sites. Using this historical time series, we will be assessing changes in potential and actual herring spawning habitat around Puget Sound over time. These data will provide critical information about potential stressors on eelgrass, and the correlations between spawning habitat and herring population trends.

This field research and data analysis is part of a larger research effort to understand the status and health of forage fish populations in Puget Sound.

More information, and posts from the field season, can be found here:

Contact: Tessa Francis, tessa@uw.edu