Fig. 4
From: Seasonal habitat use and diel vertical migration in female spurdog in Nordic waters
Evidence for normal diel vertical migration (DVM) behaviour during as significant classified DVM. Normal DVM is indicated by (A) deeper depth used during the day compared to night and (B) negative vertical speeds during dawn and positive speeds during dusk. C–E highlight depth, light level and vertical speed across the deployment for the time of day exemplary for shark 15. A Plot is based on 1-min interval median depth data and boxes indicating the median and the lower and upper quartiles, whiskers are 1.5 times the interquartile range. Violine plots indicate the data range. B Plot is based on hourly vertical mean speeds for different daily periods, with boxes showing the mean and outliers shown. Dawn and dusk mark the time between nautical dawn and sunrise as well as dusk and sunset respectively for all sharks. Asterisks denote significance level of Wilcoxon signed rank (A) and one-sided t-test (B) (***—p ≤ 0.001). One minute interval median depth and light level (C,D) and hourly mean vertical speeds (E) of shark 15 in the context of times of sunrise and sunset (solid lines) and nautical dusk and dawn (sun at 12° below horizon; dashed lines) associated with the tagging location. Light levels of 150, 110, and 70 correlate to 10–5, 10–7, and 10−9 W cm−2, respectively (see Supplement Detail S1). In (E) blue colours indicate ascends and red colours descents