Harbour porpoise surveys in the Blasket Islands SAC, 2014

Published by: Department of Housing, Local Government, and Heritage

Licensed under: Creative Commons Attribution 4.0

Category: Environment

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A visual and acoustic survey of harbour porpoises (Phocoena phocoena) in the Blasket Islands SAC was carried out in 2014 in order to derive local density and abundance estimates. Single platform line-transect surveys were carried out according to a standardised design on six days between June and September 2014, and a towed hydrophone array was deployed during all surveys to collect ancillary passive acoustic data. Distance sampling was used to produce a detection function based on the observed distribution of harbour porpoise sightings. Abundance estimates were calculated using (i) day for three of the survey days as not enough sightings were achieved on the remaining days and (ii) using pooled survey effort and sightings information for those three surveys. The effect of seas-state on density estimates was also investigated.

A combined total of 592km of track-line effort was surveyed over the six surveys throughout the survey area. Sightings per survey ranged from 6 to 18 and from 6 to 57 individuals with a total of 68 sightings of 134 individual porpoises overall. Other species recorded included minke whale (43 sightings, 33% of total sightings) and common dolphin (18 sightings, 14% of total sightings). Harbour porpoise density estimates ranged from 0.59 animals per km2 to 2.20 per km2.

Surveys took place on: 17th, 18th, 24th June, 23rd August, and 8th and 9th September.

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Theme	Environment
Date released	2022-07-06
Date updated	2023-11-20
Dataset conforms to these standards	The INSPIRE Directive or INSPIRE lays down a general framework for a Spatial Data Infrastructure (SDI) for the purposes of European Community environmental policies and policies or activities which may have an impact on the environment.
Rights notes	['http://creativecommons.org/licenses/by/4.0/', 'Copyright Government of Ireland. This dataset was created by National Parks and Wildlife Service, Department of Housing, Local Government and Heritage. This copyright material is licensed for re-use under the Creative Commons Attribution 4.0 International licence. http://creativecommons.org/licenses/by/4.0/', 'otherRestrictions']
Update frequency	Other
Language	English
Geographic coverage in GeoJSON format	{"type":"Polygon","coordinates":[[[-10.650444030762, 50.807923689449],[-10.650444030762, 55.993470564449], [-5.289115905762, 55.993470564449], [-5.289115905762, 50.807923689449], [-10.650444030762, 50.807923689449]]]}
Spatial Reference Systems (SRS)	WGS 84 (EPSG:4326)
Vertical Extent	{"verticalDomainName": "EPSG Projection 5731 - Malin Head height", "minVerticalExtent": "0", "maxVerticalExtent": "1014"}
Provenance information	As part of this survey a towed hydrophone array was deployed during visual surveys. This array consisted of a 200m-long cable with two hydrophone elements (HP-03) situated 25cm apart in a fluid-filled tube at the end of the cable. The cable and hydrophone array were connected to the vessel with a bungee cord to avoid excessive tension on the main line. The equipment is designed to be negatively buoyant in order to tow the hydrophone elements under the surface at a depth of 2-5m depending on the speed of the vessel. The cable contains wires that conduct power from the battery attached at the dry end (MAGREC Ltd HP-27st buffer box) to preamplifier's in the fluid-filled tube at the wet end of the array. The buffer box and an attached dedicated soundcard (National Instruments DAQ-6255) were linked into a laptop computer. The soundcard allows for the detection of sounds which lie outside the processing capability of the computer’s own soundcard. Two sound channels were sampled via the hydrophone array at a 250 kHz sampling rate. This allowed the detection and logging of acoustic encounters occurring within a 2-125 kHz frequency range. The open-source software PAMGUARD (ver.1.11.02 Beta) was used for on-board laptop-based data acquisition. PAMGUARD is a fusion of the IFAW suite and Ishmael acoustic detection and analysis software and it contains applications such as click detectors, tonal whistle detectors, a spectrogram viewer, in-built sound filters and the capability to calculate bearings on maps, to record a track log and several other functions.
Period of time covered (begin)	2014-07-01
Period of time covered (end)	2014-09-01