Methods:
Primary Data Collection - Sightings:
The data presented here was collected over four separate field seasons completed off the leeward shore of the Commonwealth of Dominica in an area that covered approximately 2500km2 along the entire west coast of the island, in waters sheltered from trade winds. In the first and last seasons (2005 and 2008), sightings were collected opportunistically from a small (10-12m) auxiliary sailing vessel whose primary goal was to locate and follow groups of sperm whales (see Whitehead and Gordon 1986 for details of methodology). During daylight hours animals were spotted by three to five observers on deck, often from a crow’s nest located at approximately 9 meters above sea level; while overnight there was only one person on deck whose primary goal was to maintain acoustic contact with the sperm whales. In intermediate seasons (2006 and 2007), research was conducted from a small (3m) outboard (88hp) skiff. The small outboard skiff used a similar protocol to that of the larger research sailing vessel, but with a crew of only two and had to return to port before sundown. Maximum hight above sea level was approximately 2.2m when sighting from the skiff.
The date, species, as well as, minimum (maximum number of individuals seen at the surface at the same time), best (estimate of most likely group size) and maximum (highest estimate of likely group size) group size estimates were recorded for each opportunistic encounter with cetaceans. Certainty in species identification was noted using three levels: 1) confirmed, the species was identified with 100% certainty; 2) unconfirmed, the species was identified but could not be confirmed with 100% certainty due in part to distance from animals and/or sea state, but primarily as a result of continuing our dedicated research on sperm whales and not differing from our course of action to confirm the species identification; and 3) unidentified, these were then further classified into “UNID delphinid” when observers were certain it was a dolphin and “UNID cetacean” when completely uncertain of which species was sighted. For all species except for sperm whales, GPS position and time were recorded at the moment of first sighting the animals. In the special case of sperm whales, GPS position and time were recorded either at first sighting or at the moment of first acoustic contact using omnidirectional hydrophones. As a result, all sightings are point data.
It is important to note that all sightings of non-focal species (all other than sperm whales) were collected opportunistically. The research vessels were actively conducting research on sperm whale behaviour and the track of the research vessel was determined by location, speed, and direction of travel of the sperm whale group being worked. This data was not collected under a systematic line transect survey protocol. As a result, the data presented here on the distribution and abundance of sightings will be strongly biased towards the random effort of the research boat, which could not be standardized here.
Primary Data Collection - Cetacean Watching Vessel Trackline Data:
The movements of one vessel from the main operator on the island were tracked at 1 minute intervals using automatic GPS tracklogs from a Garmin GPSMAP76csx (Garmin International Inc., Olathe, KS) for a total of 45 trips during the 2007 and 2008 field seasons. These trips were haphazardly selected based primarily upon the availability of research observers to be on-board. The resulting data was a series of points each representing 1 minute of travel. Trips lasted between 2h47min and 4h05min.
Go to Other Sources of Data