CHARACTERIZATION OF THE SMALL-SCALE TUNA FISHERY IN KENYA

Abstract

una are marine fish that belong to the family Scombridae. Worldwide, they provide major source of income, food and livelihood to the coastal fishing communities. They are widely distributed in tropical waters with vast migration patterns; often trans-oceanic and near-shore waters. Kenya tuna fishery is categorized into two groups: (1) the small-scale tuna fishery operating within the inshore areas and (2) the industrial tuna fishery comprising distant water fishing nations (DWFN) that exploits the Exclusive Economic Zone (EEZ). The small-scale tuna fishery uses traditional fishing crafts and gears which are technologically restricted to the inshore waters. Knowledge on the reproductive biology, catch compositions, gear and vessels used by the small-scale tuna fishers that is important for development of a strategic tuna management remains scanty. This study aimed at characterizing the small-scale tuna fishery in Kenya, focusing on catch and population structure, based on primary data of the landed species, in an effort to provide information that will guide development of a sustainable tuna fisheries management plan. The study therefore, assessed variation in vessels, gears, catches, catch-per-unit-effort (CPUE) species composition and biological aspects of the exploited tuna species. It was conducted at four landing sites; Vanga, Mbuyuni, Amu and Kiwayu. Data collection was done each in month, from August 2014 to July 2015. Sampling took four days for each selected site. The vessel types recorded constituted of dhows (mashua) outriggers (ngalawa) inboard engine boats, outboard engine boats and others using foot to fish and five gear categories (gillnet, handline, longline, ring net and trolling line) were recorded. The vessels either use sail, outboard engine or inboard engine for movement. A total of 1,622 fishers landed a total of 1,590 samples comprising 28 species from 11 families. The total catch landed was 21.1 Mt. Longline fishing at Vanga had the highest CPUE with 28.9±1.8 (kg.fisher-1.day-1, mean±SD) while gillnet fishing at Amu had the lowest vi CPUE, estimated at 2.8±1.6. A three-way factorial ANOVA showed significant differences between season, gears and sites (p<0.05). The abundant tuna species was Euthynnus affinis. Other tuna species were Thunnus albacares, T. obesus, and tuna-like were Acanthocybium solandri and Scomberomorus commerson constituting of 28.6%, 17.4%, 10.8%, 8.9% and 7.4%, respectively. The size at sexual maturity (L50) for E. affinis was 54.4 cm and 52.0 cm fork length for male and female, respectively. The slope of the L-W relationship for the male and female E. affinis was b=2.5737 and b=2.9713, indicating allometric (<3) and isometric growth (~3) respectively. The slope for T. albacares value was b=2.1475 for male and b=2.5011 for female. The slope for T. obesus and A. solandri were 1.8233 and 1.4933, respectively, while S. commerson and C. hippurus were 3.8552 and 3.7406, respectively. This study revealed higher catch of mature E. affinis indicating that present tuna fishery is at sustainable levels. The results will provide a basis for stock assessment and sustainable management of the tuna fishery. There is, however, a need for tuna stocks assessment and priority towards funding a strategic tuna management plan. Keywords: small-scale tuna fishery, length-weight relationship (LWR), size sexual maturity (L50), sustainable management.