Occurrence and species diversity of delphinids off-Lagos shore, Nigeria

Abstract

Little has been documented about delphinid communities in the Nigerian coastal waters. This paper gives baseline information about the delphinid community sighted off-shore Lagos, Nigeria. A dedicated survey of the living resources of Nigerian coastal waters (6°08’N and 2°42’W to 6° 13’N and 3° 27’W ) took place from the Nigeria/Benin boarder along Badagry area to the western part of Ondo State between 17th march and 6th June 2009 and included systematic visual searching of marine mammals. A total effective effort of 264 hours was logged. The boat moved along designated transect lines at a cruising speed of 9.2 km/h. Sighting rate for delphinids was obtained by processing visual data obtained at Beaufort wind scale of 2.5 to 4 nautical miles in visibility, using Distance 2.2 software. Species were identified through Photo-identification method. Fifteen (15) schools of 746 individual’s sightings were made. Four (4) schools of 25 individuals representing 3% of total sightings were classified as “Unidentified”, while 11 schools of 721 individuals (97%) were identified and classified into five (5) species. The pantropical spotted dolphin (Stenella attenuate) with two (2) schools of 150 individuals, (Stenella frontalis) with one (1) school of 54 individuals, bottlenose dolphin (Tursiops trucantus) with one (1) school of 32 individuals, Common dolphin (Delphinus delphis ) with four (4) schools of 452 individuals and (3) schools of Atlantic hump-backed dolphin (Sousa teuszii) of 32 individuals. Sighting rate of 5.7 x 10^-2 school/hr was estimated for schools while the sighting rate for individuals was estimated at 2.83 individual/hr. The results suggested that the Lagos coast is rich in delphinid biodiversity, which needs to be quantified more accurately during further research.

Keywords: Sightings, Oceanic dolphins, abundance, species richness, behaviour, Nigeria.