Optimizing the Width of Strip Transects for Seabird Surveys from Vessels of Opportunity

Optimizing the width of strip transects for seabird surveys from vessels of opportunity.Marine Ornithology 35: 29-38.We present a study to determine the most appropriate strip width for conducting at-sea surveys of marine bird populations from novel platforms of opportunity.We surveyed seabirds during two seasonal (spring, fall) cruises across the North Pacific in 2002.We used these observations to quantify potential biases associated with varying the survey strip width.More specifically, we compared the proportion of the sighted birds that were identified to species level, and the observed and expected apparent densities (birds•km -2 ) of various taxa from 100-m, 200-m and 400-m strip transects.We also examined the effects of weather (Beaufort sea state, cloud cover) and bird behavior (sitting versus flying) on speciesspecific identification rates and density estimates.Although various taxa showed distinct detection curves, we conducted a community-level analysis to determine the most effective strip transect for surveying the entire avifauna.Based on the results, we determined that a 400-m strip width was most appropriate for our large and high-speed survey platform, the bulk-cargo carrier Skaubryn.We offer some suggestions to select the most suitable strip width for seabird surveys from vessels of opportunity.We urge marine ornithologists using novel survey platforms to test the underlying assumptions of at-sea survey techniques and to determine the methods best suited for their specific survey conditions.