This cruise report provides an overview of the fifth survey in a series of seabirds at sea surveys that will be carried out in 2010 and 2011 over the Dutch Continental Shelf (DCS) of the North Sea and adjoining waters. This fifth survey in the series was carried out in August 2010. Two seabird observers joined a cruise that was aimed at surveying plankton, by taking plankton samples at more or less hourly intervals. In between the plankton stations, the ship steamed full speed (speed ranging from 10-12 knots) and seabirds were surveyed during all daylight hours while the ship was steaming. The sailed route was more or less the same as the two previous surveys. Due to repairs on the ship the survey started later and the route had to be adjusted in order to get ashore on time. Furthermore, the use of a slower ship resulted in different windows of daylight for the seabird observers and hence, the coverage between this survey and the previous ones differs. Weather conditions were generally moderate to poor. During the week, a total of 590 counting bouts of on average almost 5 minutes each were conducted. These stretched over a total of 971.1 km and covered, at a strip width of 300 m, a total survey area of 291.3 km2 (Table 1) A total of 3722 birds, 6 marine mammals (all Harbour Porpoises), 22 balloons and 1 set-net flag were recorded (Table 3). Weather conditions were moderate to poor and had an negative impact on the probability to detect seabirds and porpoises in particular.
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