IWDG publish paper on harbour porpoise surveys

18th Mar 2009 A new IWDG/GMIT paper on abundance estimates and acoustic monitoring has recently been published by the Royal Irish Academy.

The paper describes a survey of harbour porpoise which was carried out between July and October 2007, within the Blasket Islands candidate Special Area of Conservation (cSAC) on behalf of the National Parks and Wildlife Service.

The survey aimed to derive density and abundance estimates and carry out acoustic monitoring. A total of 44 sightings of 102 individual harbour porpoise were recorded on 74 tracks with a total distance of 389km. Density estimates ±SE were determined using DISTANCE software and ranged from 0.71 to 3.39 porpoises per km2. This gave abundance estimates ranging from 162±120 to 768±198 depending on the number of sightings per day. The most robust estimate of 303 ±76 (CV=0.25: 95% Confident Intervals 186-494) was calculated using all the data from each track-line combined. There were indications of a seasonal increase in abundance from July through to September.

Passive acoustic monitoring was carried out through the deployment of self-contained click detectors called T-PODs. One months' acoustic data were acquired from two sites, and data was extracted as Detection Positive Minutes (DPM) per day and per hour for analysis. Detections were logged every day of deployment at both sites.

This survey provides the first information on the spatial distribution of harbour porpoises in the Blaskets Islands cSAC and baseline data from which to monitor abundance and distribution.

The IWDG consider line transect surveys with distance sampling and acoustic monitoring essential for Environmental Impact Surveys which are attempting to assess the impact of a development on harbour porpoises and are happy that an accepted methodology and analysis is now available.

A copy of the paper can be obtained from the latest edition of Biology and Environment at http://www.ria.ie/publications/journals/journaldb/index.asp?select=journal&id=100007.

Simon Berrow

IWDG Co-ordinator

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