Seasonal variation in marine bird distribution in the northeast Pacific Ocean

Human impacts can directly (e.g., bycatch, over-fishing, pollution), indirectly (e.g., climate forcing), or in concert affect marine systems and the species that rely on them. These effects can alter ecosystem function, productivity, and the abundance, distribution and demography of many marine predators. Marine birds are particularly sensitive to these impacts and given their ease of observation and diverse foraging tactics and habitat uses are outstanding indicators of ecosystem health. Conserving marine birds and their ecosystems requires robust predictions of species distribution and the identification of ‘hotspots’ of richness and abundance to help mitigate human disturbance in areas and at times when large aggregations of diverse species occur. I modeled seasonal variation in marine bird species diversity (defined by the Shannon Weiner Diversity Index) and in marine bird family occurrence to map the intensity and extent of hotspots in relation to season and climate in Canada’s Pacific Exclusive Economic Zone. To do so, I used 20 years of survey data from the North Pacific Pelagic Seabird Database (1997-2017) and remote sensing data describing marine conditions and local geography (sea surface temperature, chlorophyll a, bathymetry, and distance to shore) to illustrate how seasonality within years and the El Niño Southern Oscillation (ENSO) across years influenced spatial patterns in diversity. Hotspots were most persistent in Hecate Strait, off the west coast of Vancouver Island, and surrounding the Scott Islands in most seasons. Hotspots became less intense and/or shifted northwards as sea surface temperatures rose, reflecting the results of many studies on individual species responses to increasing temperatures and demonstrating such effects at the level of marine bird communities. I describe how my results could be applied to potentially mitigate the deleterious effects of humans on the diversity and distribution of marine birds. I also provide cautions which must accompany such predictions given sparse data for some areas and seasons. Overall, the maps I present provide a template for mapping marine species distribution for the purpose of identifying ‘hotspots’ of diversity, and thereby facilitate planning to minimize harmful impacts in highly diverse and dynamic systems.Forestry, Faculty ofGraduat