Abstract
Relative abundances and relative densities of dolphins in Northern Chile (18°30'S-70° 27'W; 25°23'S-72°53'W) between March and December 2000, are informed using 99 fringe transects (length 31.7-162.4 km; mean 95.26 ± 22.14 km). During the study 5841 individuals corresponding to 8 species were sighted.
The relative abundance of species in general, presented a main peak between 23°-23°59´S (0.48 ind/km) and a secondary peak at 19°-19°59´S (0.21 ind/km). The relative density for the total area was 0.13 ind/km2 (standard error 0.03) and the highest relative density was recorded between 23°-23°59´S (0.254 ind/km2; standard error 0.129). The 18°-18°59´S sector showed the lowest relative density (0.04 ind/km2). At the species level, the relative abundances were less than 0.1 ind/km, except Lissodelphis peronii (0.33 ind/km), restricted to the 22°-24°S sector, and Tursiops truncatus (0.12 ind/km) at 22°-23°S.
In the oceanic sector (west of 71°W) T. truncatus was more abundant between 22°-23°9´S (0.085-0.110 ind/km), and in the neritic sector (east of 71°W) it was between 19°-21°59´S (0.140-0.244 ind/km). Globicephala macrorhynchus and Grampus griseus were mainly oceanic, with a main maximum (0.04 ind/km) between 18°-18°59´S and a secondary maximum (0.02 ind/km) at 22°-22° 59´S. In the neritic sector these species were only present between 21°-21°59´S, and with very low representation (0.005 ind/km).
Tursiops truncatus was the most abundant species and the only one with a constant presence throughout the study period (100% of monthly periods) and present in 17.2% of the transects. For the entire study area it presented an estimated mean relative density of ??0.45 ind/km2 (standard error = 0.0157; coefficient of variation = 3.399).
The information is discussed in the context of previous studies in the area, and its importance in the design and implementation of conservation and ecosystem management.
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