First Report of Fishkill Incidence in Bonny-Andoni Coastal Area, Nigeria

Abstract A fish kill is characterised by the death of a large number of fish in a given area within a short period of time. This is an indicator that water quality and ecosystem conditions in general have deteriorated. Remote sensing data from the MODIS instrument on the Aqua and Merra-2 satellites were accessed from 18 to 22 March 2020, a period that spans before and after the fish kill was reported. Analysis of the remote sensing data shows that the fish kill was preceded by strong winds, i.e. major and sustained wind events. The maps of sea surface temperatures prior to the fish kill show that high-temperature water masses flowed from the equator toward the Bonny-Andoni coast. The dates of occurrence of the high-temperature surface water masses and high wind events around the Bonny-Andoni coastal area were consistent with the location and timing of the fish kill, as indicated by community reports. We hypothesise that the low-oxygen, high-temperature surface water masses passing from the equator on the windward side of the coast may have encountered migrating croakers and trapped an entire school of this benthopelagic fish species, causing acute respiratory distress. The results and hypothesis confirm local reports of gasping fish about 2 nautical miles off the Bonny-Andoni coast. This study confirms the relationship between wind patterns, temperature, and fish kills, providing the first empirical account of probable causes. Because fish kills occur episodically and often leave no trace, this report and future analyses of remote sensing data may be the best way to elucidate this event.