Abstract
The study of local cetaceans in Venezuela has a very recent history, and few efforts have been made in the assessment of coastal populations based on field research. The occurrence of whales and dolphins along the northeast coast of Venezuela has been documented through sightings and stranding records. Given the underwater topographical features and the influence of upwelling processes, this area is considered a very productive coastal ecosystem. Our objective was to establish the sighting frequency and relative abundance of bottlenose dolphins in the area. Sighting records were gathered on bottlenose dolphins and other cetacean species occurring along the northeast coast of Margarita Island and Los Frailes Archipelago through direct observation during land-based (6 surveys, 48 hours of observation) and boat-based surveys (24 surveys, 121 hours of observation, 1295 km covered). A sighting frequency was calculated using two methodologies and then compared, considering: 1) a mean effective observation time (4.27 hours), and 2) distance covered with cetacean sightings (1108 kin). A third method is proposed relating a mean effective distance covered with cetacean sightings and expressed as a percentage. The abundance index was calculated using the mean effective observation time. The sighting frequency of Tursiops truncattus in the study area was 3 - 4 sightings per day of 4.27 observation hours, or by 185 kilometers covered. The relative abundance was calculated as 35 dolphins in the study area, so a total population of less than 60 dolphins could inhabit the proposed range. Tursiops truncatus is the dominant species in the northeast coast of Margarita Island and Los Frailes Archipelago with 70% of all the sightings, so this locality could be termed as the distribution range of a possible local population of bottlenose dolphins.
Highlights
The study of local cetaceans in Venezuela has a very recent history and few efforts have been made in the assessment of coastal populations based on field research
Sighting records were gathered on bottlenose dolphins and other cetacean species occurring along the northeast coast of Margarita Island and Los Frailes Archipelago through direct observation during land-based (6 surveys, 48 hours of observation) and boat-based surveys (24 surveys, 121 hours of observation, 1295 kilometers covered)
Three kinds of sighting frequencies were calculated for T. truncatus
Summary
The study of local cetaceans in Venezuela has a very recent history and few efforts have been made in the assessment of coastal populations based on field research. The occurrence of whales and dolphins along the northeast coast of Venezuela has been documented through sightings and stranding records. Tursiops truncatus is a common species in Caribbean waters, widely documented and reported in literature for the north and central region (Mignucci 1998) as well as in the southeast Caribbean (Van Bree 1975, Debrot et al 1998). In Venezuela as in the Caribbean Basin, the records of the specie evidence a common occurrence in the northeast coast of the country (Evans et al 1977, Naveira 1996), with frequent sightings on the central coast (Gonzáles 2000, Acevedo 2001). The spatial distribution of Tursiops on the east coast of Margarita Island and Los Frailes Archipelago suggests the occurrence of a local discrete population with a distribution range defined by topographical boundaries. The objective of this study is to establish the sighting frequency and the relative abundance of bottlenose dolphins in the study area
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