Characterizing gear-based exploitation patterns of artisanal tuna fisheries in the western Indian Ocean: A snapshot from Kenya

Abstract

This study explores gear-based patterns in catch rates and catch composition of landings by artisanal tuna fishers along the Kenya coast based on data collected at eight landing sites from March 2014 to March 2020, representing 1960 fishing trips and 192 mt of fish. Tuna and tuna-like species constituted 55% and 38% respectively of the sampled catch by weight. Troll lines, ringnets and handlines were the most commonly used representing 52%, 18% and 12% of the sampled fishing trips. Ringnets were the most productive catching an average of 547 ± 99.3 kg of tuna per trip, while handlines caught the lowest (12.6 ± 1.4 kg trip -1). Longlines and drift gillnets caught the highest proportion of tuna representing 95% and 89% respectively of landings, while reef seines and monofilament gillnets caught the lowest. The mean catch per unit effort for tuna was 78.5 ± 7.7 (SE) kg trip -1, while that for tuna-like species was 35.2 ± 1.9 (SE) kg trip -1. Kawakawa (Euthynnus affinis), bigeye (Thunnus obesus), and yellowfin (Thunnus albacares) were the most common and most abundant representing 31.5%, 21.2%, and 20% of the tuna landings, respectively; while skipjack (Katsuwonus pelamis) constituted the lowest at 4%. Although tuna was landed year-round, species-specific variations in catch rates and size distribution were observed among the gear types and between seasons. Cluster analysis and non-metric ordination based on combinations of gear type and season defined four groupings with two gear types (ringnets and set gillnets) showing seasonal differentiation in the composition of tuna and tuna-like species. Majority of tuna were above the reported size at first maturity (L50) except for yellowfin and bigeye tuna. Overall, the findings provide new insights on Kenya's artisanal tuna fishery addressing important information gaps on exploitation patterns of artisanal tuna fleets of the western Indian Ocean region