Aerial survey of upper trophic level predators on PLatts Bank, Gulf of Maine

Observation effort (two observers) was concentrated from both sides of the plane perpendicular to the flight path. To estimate the distances of sightings of mammals and fish from the plane’s flight path, sightings were binned into five groupings corresponding to 15 degrees of arc from 15° (the area directly beneath the plane was not visible) to 90°. When species identification or number of individuals was uncertain, search effort was interrupted while the plane circled to confirm identifications and number of individuals and to obtain a more precise location.

Birds were recorded only within a 170 m strip on each side of the aircraft (15° to 45° of arc) during the survey legs. Sightings of birds continued when the plane circled for closer inspection of mammals and fish, but these data were not used in analyses since this would bias bird sightings towards areas where cetaceans were concentrated. Data were recorded by a dedicated data recorder directly onto a computer using software that recorded the time and location from the GPS navigation system aboard the plane at regular intervals throughout the flight and for each recorded sighting.