Data from: Harbour porpoises respond to small boats by speeding up and moving away
Data files
May 07, 2024 version files 1.07 MB
Abstract
Recreational boats are common in many coastal waters, yet their effects on cetaceans and other sensitive marine species remain poorly understood. To address this knowledge gap, we used drone videos to quantify how harbour porpoises (Phocoena phocoena) responded to a small motorboat approaching at different speeds (10 or 20 knots). The experiment was carried out in shallow waters near Funen, Denmark (55.51° N, 10.79° E) between July and September 2022. Porpoises moved further away from the boat path during approaches at both boat speeds. In addition, porpoises swam faster when approached at 20 knots but not when approached at 10 knots, and they had a higher likelihood of moving away from the boat path when approached at 10 knots but not at 20 knots. Importantly, the received sound level did not depend on how fast the boat approached, suggesting that differences in porpoise responses were related to the speed of the boat's approach rather than to sound itself. The porpoises' behaviour during the minute where the boat was closest did not differ from their behaviour before boat exposure, indicating that the direct impact of small vessels on porpoise behaviour was most likely small. Nevertheless, repeated exposure to noise from small vessels could influence porpoises' foraging efforts and cause them to relocate from disturbed areas. The approach used in this study increases our understanding of recreational boats’ impact on harbour porpoises and can be used to inform efficient mitigation measures to help conservation efforts.
README: Data from: Harbour porpoises respond to small boats by speeding up and moving away
https://doi.org/10.5061/dryad.q83bk3jq8
The dataset comprises seven files: two raw data files in CSV format (‘PorpBoatData.csv’ and ‘BoatNoise.csv’), and five R script files (‘1PorpResponseToBoatApproach.R’, ‘2PorpResponseToExpPhases.R’, ‘3PorpResumeBehaviour.R’, ‘4BoatNoiseLevels.R’ and ‘5FuncCalAvoidance.R’) for conducting data analysis and plotting.
Description of the data and file structure
'PorpBoatData.csv' file contains information on porpoise data extracted from drone videos and boat locations recorded by portable GPS during experiments. This dataset is structured with 16 columns, including:
‘Time’: timestamps of each data point,
‘Trial_speed’: boat speed, either 10 or 20 knots,
‘Exp_stage’: specifying the experiment phases, i.e. pre_disturb, disturb, and post_disturb
‘Porp_x’ and ‘Porp_y’: porpoise locations in UTM 32 N coodinate system at each timestamp
‘Porp_speed’, ‘Porp_abs_angle’ and ‘Porp_rel_angle’: representing porpoise speed (m/s), its absolute turning angle and relative turning angle.
‘Porp_state’: porpoise swimming state extracted from drone videos, i.e. Shallow_dive, Deep_dive and Breathe
‘Boat_x’ and ‘Boat_y’: boat locations in UTM 32N coordinate system at each timestamp
‘Boat_speed’: boat speed in m/s
‘Porp_boat_dist’: distance between porpoise and the boat (m)
‘new_ID’: specifying different individuals
‘react_dist’: Porpoise’s avoidance distance from the boat track (m)
‘attitude’: with ‘N’ indicating porpoise was moving away from the boat track, and ‘P’ indicating porpoise was moving towards the boat track.
Missing data code : NA
‘BoatNoise.csv’ contains data of recorded boat noise levels by sound data logger during boat passages at different speeds (either 10 or 20 knots), it has 6 columns:
‘dB_BB’: Boat noise levels (in dB re 1 μPa rms, 1 s average) at full bandwidth (0.1-150 kHz).
‘dB_16k’: boat noise levels (in dB re 1 μPa rms, 1 s average) at the 1/3 octave (TOL) 16 kHz frequency band.
‘trial’: two trials for each boat speeds (10 or 20 knots)
‘trial_general’: either 10 or 20 knots
‘range’: distance between the boat and the data logger (m), negative values indicate the boat was approaching the data logger, positive values indicate the boat has passed the data logger
‘time_tick’: time in seconds during boat approaches to the data logger. Negative values indicate the boat was approaching the data logger, positive values indicate the boat has passed the data logger
‘1PorpResponseToBoatApproach.R’ contains R code to excute GLMM analysis on porpoises’ behavioural responses (speed, absolute turning angle, distance that moved away from the boat track, the likelihood of moving away from the boat track, of deep-dive and of breathing) during boat approaches.
‘2PorpResponseToExpPhases.R’ contains R code to perform GLMM analysis on the differences of porpoise behaviour (speed, absolute turning angle, the likelihood of deep-diving and of breathing) before and during boat disturbance.
‘3PorpResumeBehaviour.R’ contains R code to use GAMs to explore how long porpoises resume their behaviour after boat passages
‘4BoatNoiseLevels.R’ contains R code to plot boat noise levels recorded by sound data logger.
‘5FuncCalAvoidance.R’ is the function created to calculate porpoises’ avoidance behaviour from the boat track.
Code/Software
The .R files require readers to use R software to open and run the scripts. The author was using R 4.3.2 to create these scripts.