At Sea Surveys of Seabirds and Marine Mammals

Aerial at-sea and coastal surveys were conducted to examine the distribution and abundance of seabirds and marine mammals off Southern California, from Cambria, California to the Mexican border. From May 1999 to January 2002, nine
complete aerial surveys were flown on 102 days, covering over 54,640 km of transects, of the entire Southern California Bight (Bight) during January, May, and September. A total of 135,545 birds were counted and identified, comprising fifty four species, in 12 families.

This file contains the species observations summarized as densities based on 5 minute blocks of latitude and longitude. Surveys were flown at 60 m (200 ft) above sea level at 160 km/hr (90 knots) ground speed. The surveys were flown in a high-winged, twin engine Partenavia PN 68 Observer aircraft following methods developed for seabirds by Briggs et al. (1987). GPS points were recorded every five seconds to allow adequate spatial coverage of the trackline (225 m is traversed every five seconds at the survey speed of 160 km/hr) and to limit the size of the resulting data files. Data was collected using a laptop computer running the program dLOG (R.G. Ford Consulting, Inc.). Observers sat on both sides of the aircraft and scanned the sea surface through bubble windows. Each of two observers counted and identified seabirds and marine mammals occurring within a 50 meter strip on their side of the aircraft for a total strip width of 100 meters when both observers were surveying simultaneously. At least one observer surveyed at all times, but individual effort was discontinued when glare obscured > 25% of an observer's field of view. To ensure that we maintained a strip width of 50 meters, we estimated sighting angles from the aircraft to the water using clinometers. Observers rechecked sighting angles with a clinometer several times during each survey.

Seabird and marine mammal observations were recorded on audiotape using hand-held tape recorders. Animals were identified to species or nearest taxon and made exact counts for solitary individuals or small groups and estimated numbers for groups > 10 birds. For each observation, time was recorded to the nearest second, along with species, number of birds, behavior (e.g. flying or sitting on the water), and flight direction.
Each observer transcribed data from audiotape onto standardized data forms and entered data into the compute program SIGHT (Micro Computer Solutions, Portland, OR, USA). SIGHT was used because it had preset data entry protocols that helped to ensure entry accuracy. Two people checked data entry for accuracy by printing SIGHT data for comparison with transcribed forms.