AbstractsBiology & Animal Science

The marbled murrelet (Brachyramphus marmoratus) is listed as threatened in both Canada and the United States due to logging of old-growth forest stands, their primary nesting habitat. Existing research is primarily focused on this terrestrial aspect of the species’ ecology. Our understanding of their at-sea foraging ecology, however, is limited to broad-scale studies of population abundance and dynamics. In order to further understand the spatial and temporal variations of marbled murrelet at-sea foraging behaviour and habitat use, bi-weekly surveys of marbled murrelets were conducted in Clayoquot Sound, BC, between May 1 and September 1, 2007 and 2008. Data were first analysed using a Getis-Ord Gi* spatial analysis to identify high-use foraging areas. Total marbled murrelet presence was consistent between years, but spatial distribution varied significantly in both years. A subsequent analysis of oceanic environmental variables found that temperature, salinity and phytoplankton densities (measured as chl a) were spatially ubiquitous, with no significant variation in measures across the study area. Chl a levels showed significant temporal variation, though similar trends in marbled murrelet abundance over time in both seasons suggest that phytoplankton levels do not directly affect murrelet presence. Marbled murrelets were also observed foraging within several metres of gray whales (Eschrictius robustus) feeding on epibenthic zooplankton in 2006 and 2008, a previously undocumented relationship. Join count statistics identified significant clustering of murrelets up to 300m from 39 feeding gray whales in 2006, and no association with 5 gray whales in 2008, marking a foraging association conditional on the abundance of both gray whales and their prey, but potentially significant to marbled murrelet survival and fecundity.