Decadal Changes in Seabird Foraging Activity, Forage Fish, and Plankton in Cattle Pass, San Juan Islands, Washington

Abstract

Published and unpublished reports suggest that seabird numbers have decreased markedly in the Salish Sea over the past several decades. I tested the hypothesis that seabird feeding activity in a known foraging location decreased in 2010 and 2011 in comparison to the mid-1990s, and that this decrease was associated with a concomitant decrease in the abundance of small, pelagic fish, and changes in the plankton community. Data collection replicated methods used in the mid-1990s, including land-based surveys of seabird foraging aggregations, acoustic surveys to determine the distribution and abundance of fish, and vertical plankton tows. I found significant decreases in seabird foraging activity between decades, as well as a decrease in area integrated backscatter (a measure of fish abundance), and calanoid copepod abundance. This demonstrates that well-placed assessments can detect differences in three trophic levels of the Salish Sea community in a way that can inform ecosystem-based management.