Effect of seismic operations on cetaceans sightings off-shore Akwa Ibom State, south-south, Nigeria

Abstract

The possible behavioral and physical problems involving cetaceans and marine seismic surveys have attracted the interest and concern of several authors. However, studies on cetaceans frequenting Nigerian waters have not been detailed in literature. This research work is appropriately driven by these requirements. Opportunistic data was collected on board six different marine vessels belonging to ExxonMobil. Data collected were analyzed using descriptive statistics, t-test and ANOVA at p=0.05. A total of 8,327 hours 36 minutes observation effort was accomplished during twenty-six months, representing almost 800 km² of coverage. Two hundred and eighty-three (283) sightings were recorded comprising of 189 (66.78%) sightings of whales and 94 (33.22%) sightings of dolphins. Four species of cetaceans were identified, bottlenose dolphins (Tursiops truncatus) were the most abundant followed by pantropical spotted dolphins (Stenella attenuata). These two species occurred throughout the sampling months, while the predominant whales specie were the humpback whale (Megaptera novaeangliae) and killer whales (Orcinus orca) which seem to be present in just a part of the year. Whales were sighted more when the guns were active. Conversely, less of the dolphins were sighted while the guns were active. There were significant differences (P=0.05) regarding the air-gun operational state between the number of whales and dolphins sightings. The result suggests that swimming behavior was dependent of air-gun operational state.

Keywords: Cetaceans, seismic survey, Sightings, Akwa Ibom state, south-south Nigeria.