ORCA Plymouth-Santander surveys 2023

A team of up to four trained volunteers including at least one highly experienced observer recorded cetacean sightings using line transect distance sampling methods from a ferry crossing the western English Channel and Bay of Biscay from Plymouth, UK to Santander, Spain. Two observers searched from either side of the ship with a 10 degree overlap on the trackline to satisfy the assumption that all animals on the trackline are detected while one observer recorded data and the other rested. Effort information including location, vessel speed, course of vessel and environmental conditions (sea state, swell, precipitation, glare and visibility) were recorded every 30 minutes when observers rotated or when conditions changed. Glare was not consistently recorded and has been filled in as the position of the glare relative to the ship where it was mentioned in the comments.