Figure 4
From: Seasonal and diel acoustic presence of North Atlantic minke whales in the North Sea
Number of total identified detections of minke whales (ncalls) at the Helmsdale recording site, aggregated by week (y-axis, tick marks indicate start of month) and hour of day (x-axis, tick marks indicate mid-hour), for (a) 2015, (b) 2016, (c) 2017. Black and grey lines indicate dawn/dusk and sunrise/sunset times, respectively. This high latitude recording area experiences all-night nautical twilight from May to August as indicated by the broken black dawn/dusk lines. The ‘sun-methods’ function of the R46 maptools library47 was used to determine times for sunrise, sunset, dawn and dusk based on nautical twilight (defined as sun altitude between 0 and 12°) for each day. Light grey shaded areas indicate periods of missing data. Data for January 2018 were omitted from this graph for ease of presentation and since no detections were made during this month.
