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.