DOI: 10.5061/dryad.v9s4mw6xv
title: Harbour porpoise hydrophone array data recorded on a gill net

description: Entanglement in net fisheries (static and drift) is the largest known
 cause of direct anthropogenic mortality to many small cetacean species,
 including harbour porpoise (Phocoena phocoena), in UK waters. Despite
 this, little is known about the behaviour of small cetaceans in proximity
 to nets. We have developed a passive acoustic monitoring (PAM) system for
 tracking the fine scale three-dimensional (3D) movements of echolocating
 cetaceans around actively fishing nets by localising their acoustic
 clicks. The system consists of two compact four-channel acoustic recorders
 with sample-synchronised sensor packages that use 3D motion tracking
 technology to accurately log orientation, depth, water temperature and
 ambient light level. Two recorders were used in tandem, with each one
 attached to and floating above the net float-line. The system can be
 deployed during normal fishing operations by a trained researcher or
 experienced fisheries observer. Recordings were analysed in PAMGuard
 software and the 3D positions of echolocating animals in the vicinity of
 the system were calculated using an acoustic particle filter-based
 localisation method. We present findings from four deployments in UK
 waters (each 1-2 days in duration) in which 12 distinct harbour porpoise
 encounters yielded a sufficient number of detected clicks to track their
 movements around the net. The tracks show a variety of behaviours,
 including multiple instances of animals actively foraging in close
 proximity to the fishing net. We show that a relatively inexpensive PAM
 system, which is practical to deploy from active fishing vessels, is
 capable of providing highly detailed data on harbour porpoise behaviour
 around nets. As harbour porpoises are the one of the most difficult
 species to localise, this methodology is likely to be suitable for
 elucidating the behaviour of many other toothed whale species in a variety
 of situations.
description: These data are processed acoustic recordings from two acoustic
 devices recording on an actively fishing gill net. The aim of the study
 was to try and acquire detailed 3D behavioural information on harbour
 porpoises around gill nets via acoustic localisation.
 Each recorder contained a micro-aperture 4 element hydrophone
 array and accurate depth and orientation sensors. The 4-channel array
 within each device allowed for a relative 3D vector to a received harbour
 porpoise echolocation click to be calculated. Depth and orientation sensor
 then allowed the vector to be geo-referenced (i.e., relative to north).
 The two recorders were separated by 15- 40m along the headline of the gill
 net – if two devices detected the same click then the location of the
 harbour porpoise was the point at which the two resulting vectors crossed.
 As porpoises (and dolphins) echolocate regularly, localising successive
 clicks allowed a 3D track of an animal to be constructed over time,
 providing detailed information on animal movements around the gill
 net. Each deployment results in terabytes of raw
 acoustic data- the dataset here are acoustic recordings which has been
 processed in PAMGuard; PAMGuard was configured to detect any transient
 sounds in the 80-150kHz frequency band. Most of these sounds are false
 positive detections but a subset will be the echolocation clicks of
 dolphins and harbour porpoises. An automated classifier was then used to
 detect which transients likely correspond to harbour porpoises. There are
 two datasets, one for each recording device. Each consists of a .sqlite
 database and folder of PAMGaurd binary files. To open the dataset simply
 download PAMGuard (www.pamguard.org),
 start PAMGuard viewer mode and select the database and binary file folder
 in the file browsers which appear. Data can also be imported into MATLAB
 or R (see http://www.pamguard.org/48_MATLABRcode.html).
 The dataset also contains GPS logs of the fishing vessel used to
 deploy the nets. Note that these have been altered to comply with GDPR so
 that the relative co-ordinates are correct but they are not in the
 original location. The GPS data is used to determine the location of the
 devices on the seabed – details are available in the paper that
 accompanies this dataset.
description: Coding libraries can be found at https://github.com/macster110/soundnet/.