Many herring stocks have under gone critical declines, and there is concern that pinniped predation may have increased the natural mortality rate of herring in some areas (Musick et al., 2000), although it is acknowledged that there are likely many factors that contributed to the decline of herring (Stoutet al., 2001). Spawner biomass of herring for the northern Puget Sound, an index of population abundance, remained low through the study period, yet herring has been identified as one of the top prey species of harbor seals in a San Juan Islands diet study since 2005 (Lance et al., 2012).

Like herring populations, salmonid populations have undergone serious declines, and there is also concern that pinnipeds may affect salmonid recovery (NMFS, 1997; Wright et al., 2007).