Report of a cetacean survey in the Western Approaches of the ...

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METHODOLOGYSurvey designThe 2005 survey was conducted from the MV Esperanza, a 72.3m Expedition/Research vessel whichtraveled at either a ‘fast’ average speed of 8.6 knots or a ‘slow’ average speed of 5.3 knots. Data werecollected mainly in the ‘passing mode’, where the vessel did not deviate from the track-line.The surveys took place between 17 th February and 26 th March 2005 in the Western Approaches of theEnglish Channel. The main Survey Area (an area where survey transects and strata were placed) wasbetween 49°20’N-50°20’N and 3°26’W-6°10’W (see Fig. 1). The western stratum (Stratum W)extended to the west, between 49°26’N and 50°06’N and 006°06’W and 4°42’W and covered4,743km 2 . The eastern stratum (Stratum E) lay between 49°33’ and 50°54’N and 005°02’W and3°36’W and covered 4,129km 2 .Fig. 1. The main survey area (boxed in blue) with transects (thin black lines) and the two survey strata(in red: the western stratum to the west and the eastern stratum to the right).Cetacean sighting methodologyTo facilitate systematic data collection, the data-logging program ‘Logger 2000’ (developed by IFAWto promote benign, non-invasive research) ran continuously throughout the survey on a laptopcomputer which was linked to the ship’s Global Position System (a Furuno GP-80 satellite navigationsystem) through an NMEA (National Marine Electronics Association) interface. This programautomatically recorded the ship’s location every 15 seconds and provided a continuous visual displayof the vessel’s track on a map of the area. Data concerning sightings and the environment weremanually entered.The methodology used in the 2004 survey (see de Boer et al., 2005) was based on the line-transectdistance sampling method (Buckland et al., 2002). In the 2005 survey, the methodology also followedthe Mark Recapture Distance Sampling (Buckland and Turnock, 1992; termed the BT methodhereafter). According to this method, observations are carried out from two platforms. Observers fromthe secondary or ‘tracking’ platform search an area ahead of the ‘primary’ survey area and sufficientlywide to ensure that animals are detected prior to any responsive movement to the ship, and to allow thetracking of animals until they are detected by the primary platform. The primary survey area is widerand possibly has a lower probability of detection. The observers from the primary platform searchindependently of the tracking platform.6
Two important assumptions of line transect distance sampling are that the probability of detection onthe trackline, g(0), is unity and that detected animals do not respond to the presence of the surveyvessel before detection. The BT method does not require these assumptions because adjustments aremade by a correction factor. Further, if sighting distances and angles of secondary detections aremeasured without error, the method is unbiased when sighting distances or angles recorded by theprimary platform are subject to bias or error.Data from the primary platform are used to estimate encounter rate (number of detections per unitdistance), while data from the secondary platform allow the effective width of search from the primaryplatform to be estimated.The primary platformThe primary platform was located on the outer bridge wings with an approximate eye height of 11.3mand was visually and acoustically independent from the secondary (tracking) platform. The twoprimary observers scanned backwards and forwards whilst on watch in a 90 degrees sector (on port andstarboard), forming an approximately 180 degrees combined survey area in front of the ship. Scanningwas done with the naked eye. A third person acted as the data recorder, entering sighting informationand environmental details. The observers were rotated every hour to avoid fatigue.Nikon 7x50 marine binoculars with built-in reticule scales were used to measure the angle from thehorizon to the sighting. When the sighting was close to the ship, an estimate was made using a‘distance stick’. The bearing to the sighted animals and the animal(s) headings were determined byusing ‘angle-boards’ which were fixed to the ship’s railings. These were aligned parallel to the ship’sbow and the alignment checked and corrected throughout the survey.Sightings data recorded from the primary platform included the time (hh:mm:ss), GPS position, bearing,distance, species identification (and degree of certainty ranging from definite-100%, probable-75% topossible-50%), presence of calf and/or juveniles, group size (maximum, minimum and best estimate),animal’s heading, travel mode, group composition and behaviour.The following environmental data were collected every hour, and when conditions changed: ship’sposition, heading and speed; wind speed and direction (using an OBSERMET Wind meter OMC 939);cloud coverage; glare conditions (in degrees); visibility; swell height; and the Beaufort sea state. Thesea surface temperature was measured regularly (every hour whilst on high effort search status) withhelp of a digital thermometer (810-926 ETI-Ltd). Water depths were obtained using a FurunoNavigational Echosounder (FE-700). In addition, a count of animals in the vicinity of the survey vesselwas recorded with the environmental data.Secondary (tracking) platformThe tracking platform was situated in the ship’s crow’s-nest, with an approximate eye height of 19.5m,housing one observer searching an area of 30 degrees on either side of the trackline using Nikon 7X50reticule marine binoculars mounted on a tripod. A digital voice recorder with a built-in digital camera(Olympus W-10) was attached to the binoculars (see Fig. 2.) and used to record the following sightingsdata: reticule count, heading, species ID and group size. The camera faced down when photographingthe angle to the sighting. Reference lines on the photographs were used to calculate the accurate angleto the sighting (Leaper and Gordon, 2001). A laptop with the data-logging program ‘Logger 2000’(developed by IFAW to promote benign, non-invasive research) was used to record the exact time(hh:mm:ss) for each sighting. The tracker concentrated beyond 1,000m ahead of the vessel (prioritisingsightings >1,500m), trying to detect animals before they had responded to the approaching vessel, andrecording re-sightings (tracking) until the animals had passed abeam. These distances were based onfindings from the 2004 survey, where animals sighted at distances ranging from 420-1,700m were stillshowing responsive movement (de Boer et al., 2005).The secondary platform was not in operation throughout the survey as this was dependent on sea state.However, it was used whenever possible and when the ship was going at ‘fast speed mode’ in a straightline and was therefore not dependent to following predetermined transects only.Secondary observations made during fisheries observations were not included in the g(0) analysis asthe 2004 survey data showed that common dolphins were encountered in significantly higher groupsize in areas where trawlers were present compared to areas where trawlers were not present.7
Page 1 and 2: Report of a cetacean survey in theW
Page 3 and 4: EXECUTIVE SUMMARYThe Western Approa
Page 5: INTRODUCTIONLittle is known about t
Page 9 and 10: also to report the presence of dolp
Page 11 and 12: RESULTSPart 1. Cetacean distributio
Page 13 and 14: SpeciesFAST MODENumber of sightings
Page 15 and 16: Initial sighting cuesDuring fast su
Page 17 and 18: Harbour porpoiseThe harbour porpois
Page 19 and 20: Part 2. Fisheries observationsFishi
Page 21 and 22: On the 23 rd of March, at 08:23, a
Page 23 and 24: Fig 7. Frequency distribution of si
Page 25 and 26: The estimates of abundance generate
Page 27 and 28: Proportion of sightings by perpendi
Page 29 and 30: Proportion of sightings by componen
Page 31 and 32: Fig. 18. Histograms of perpendicula
Page 33 and 34: DISCUSSIONThe estimated corrected d
Page 35 and 36: extrapolated total estimated mortal
Page 37 and 38: Tregenza, N.J.C. and Collet, A. 199
Page 39 and 40: Dolphin 2SPECIES: Common dolphin (D
Page 41 and 42: CETACEAN POSTMORTEM REPORTDolphin 7

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