Assessment of Jellyfish Bloom Frequency and Its Impact on Artisanal Net Fishing in Lagos Coastal Waters

Jellyfish blooms have been increasingly reported in Nigerian coastal waters, where they clog fishing nets, contaminate catches, and inflict painful stings on fishers, yet quantitative documentation of bloom frequency and fisheries impact in Lagos coastal waters is limited. This study assesses the temporal and spatial occurrence of jellyfish blooms and their reported impacts on artisanal net fishing operations along the Lagos coastline and in the Lagos Lagoon system over a 12-month monitoring period. Bloom occurrence data were collected through biweekly vessel-based observations along three transects, complemented by structured reporting from 90 artisanal fishers maintaining standardised fishing diaries. Jellyfish species were identified from representative specimens, and biomass per haul was estimated from net samples. Results recorded 23 distinct bloom events during the monitoring year, concentrated between April and July, corresponding to warm sea surface temperature anomalies and post-rainfall surface stratification periods. Bloom biomass in affected hauls averaged 38 kg per net set, equivalent to 41% of total haul weight, displacing equivalent volumes of target fish catch. Fishers reported abandoning fishing for an average of 4.2 days per bloom event. The dominant species recorded were Aurelia aurita and Chrysaora africana. The study provides the first quantified dataset on jellyfish bloom impacts on the Lagos coastal fishery and recommends the development of an early warning system for bloom events to allow fishers to temporarily relocate fishing effort.

Keywords: jellyfish bloom, artisanal fisheries, Lagos coastline, net fouling, coastal monitoring