112 research outputs found
Passive acoustic methods for fine-scale tracking of harbour porpoises in tidal rapids
The growing interest in generating electrical power from tidal currents using tidal turbine generators raises a number of environmental concerns, including the risk that marine mammals might be injured or killed through collision with rotating turbine blades. To understand this risk, information on how marine mammals use tidal rapid habitats and in particular, their underwater movements and dive behaviour is required. Porpoises, which are the most abundant small cetacean at most European tidal sites, are difficult animals to tag, and the limited size of tidal habitats means that any telemetered animal would be likely to spend only a small proportion of time within them. Here, an alternative approach is explored, whereby passive acoustic monitoring (PAM) is used to obtain fine scale geo-referenced tracks of harbour porpoises in tidal rapid areas. Large aperture hydrophone arrays are required to obtain accurate locations of animals from PAM data and automated algorithms are necessary to process the large quantities of acoustic data collected on such systems during a typical survey. Methods to automate localisation, including a method to match porpoise detections on different hydrophones and separate different vocalising animals, and an assessment of the localisation accuracy of the large aperture hydrophone array are presented.Publisher PDFPeer reviewe
Identification of high-risk areas for harbour porpoise Phocoena phocoena bycatch using remote electronic monitoring and satellite telemetry data
ABSTRACT: The bycatch of harbour porpoise Phocoena phocoena is an issue of major concern for fisheries management and for porpoise conservation. We used high-resolution spatial and temporal data on porpoise abundance and fishing effort from the Danish Skagerrak Sea to identify areas with potentially higher and lower risk of porpoise bycatch. From May 2010 to April 2011, 4 commercial gillnet vessels were equipped with remote electronic monitoring (REM) systems. The REM system recorded time, GPS position and closed-circuit television (CCTV) footage of all gillnet hauls. REM data were used to identify fishing grounds, quantify fishing effort and document harbour porpoise bycatch. Movement data from 66 harbour porpoises equipped with satellite transmitters from 1997 to 2012 were used to model population density. A simple model was constructed to investigate the relationship between the response (number of individuals caught) and porpoise density and fishing effort described by net soak time, net string length and target species. Results showed that a model including both porpoise density and fishing effort data predicted bycatch better than models containing only one factor. We therefore conclude that porpoise telemetry or REM data allow for identification of areas of potential high and low bycatch risk, and better predictions are obtained when combining the 2 sources of data. The final model can thus be used as a tool to identify areas of bycatch risk.Publisher PDFPeer reviewe
An overview of the state of bycatch monitoring and mitigation measures being implemented in European Fisheries
Fisheries interactions
Fisheries are extremely important in the context of marine mammal ecology, conservation, and behavior. Fisheries have changed the structure and dynamics of many fish and other prey populations. Competition between marine mammals and fisheries would seem inevitable, but the complexities of marine food webs mean that impacts of one on the other may be substantially dampened and have proved very difficult to demonstrate. Operational interactions, whereby marine mammals use fishing gear to improve their foraging efficiency are widespread. Marine mammals have learned to exploit numerous gear types, sometimes without causing any loss to the fishery, occasionally by cooperating with fisheries, but most often by taking catch from gear and often also damaging the fishing gear, both considerable problems. Various measures have been developed to minimize bycatch and damage, most frequently involving either acoustic deterrence or changes to the gear or mode of operation.</p
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