The Application of Biological Aspects in the Management of Tuna and Tuna- Like Species in Kenyan Waters

Abstract

Fisheries including tunas play a significant role in contributing to the national economy. The management and development of tunas in Kenya has been challenged by the paucity of information and knowledge on this fishery. The main objective of this study was to interrogate the scientific robustness of the Kenya national fisheries policy and legal framework on tuna management in the country. The study sourced catch data from primary and secondary sources. Fish samples from artisanal catches were collected monthly from August 2015 to December 2016 from five landing sites at the Kenyan coast; Amu (Lamu), Shella (Malindi), Mnarani (Kilifi), Watamu and Old Town (Mombasa). Historical catch data from 24 foreign flagged longline tuna fishing vessels licensed to harvest fish in Kenya Exclusive Economic Zone (EEZ) for the period February 2012 to March 2017 was obtained from Kenya Fisheries Service (KeFS). These data sources were complemented by literature reviews, interviews and field visits. The data and information collected was analyzed and used to assess the temporal and spatial variation in fish catch rates, species composition and distribution, size distribution, growth parameters and mortality rates for some artisanal fishery species. A total of 2686 individuals of tunas weighing 31,672 Kg representing 15 species, 13 genera and three families (Scombridae, Istiophoridae and Xiphiidae) from artisanal fishery were sampled. Results of this study revealed that Thunnus albacares, Xiphias gladius and Scomberomorus spp significantly contributed to the coastal fishery in Kenya accounting for 40%, 27.7% and 8%, respectively, of the total catch of tunas sampled. Fish catch rates varied with sites with Amu recording the highest CPUE of 23.7 KgFisher-1Trip-1, closely followed by Mombasawith 19.16 KgFisher-1Trip-1. Watamu, Shella (Malindi) and Mnarani recorded 11.1 KgFisher-1Trip- 1, 7.5 KgFisher-1Trip-1and 6.2 KgFisher-1Trip-1, respectively. Fish catch rates varied monthly with low catch rates reported from December 2015 to April 2016. The highest CPUE of 21.6 KgFisher- 1Trip-1 was recorded in the month of August 2015 while the lowest, 3.0 KgFisher-1Trip-1, was observed in December of the same year. Most of the tunas were landed during the South East Monsoon (SEM) between May to October. Results of the 24 longline tuna vessels flagged to six countries (China, Taiwan, Oman, Seychelles, Spain and Mauritius) fishing in the Kenya Exclusive Economic Zone (EEZ) indicate that a total of 1833 individuals of tunas weighing 1,519,398 Kg were harvest based on the declared catch. Thunnus albacares, Katsuwonus pelamis and Thunnus obesus dominated the catch accounting for 43%, 29% and 17% of the total catch, respectively. Analysis of Similarities (ANOSIM) of catch composition indicated significant differences been vessels flagged to different states. Vessels flagged to Spain and Seychelles contributed 48% and 27% of the total catch, respectively. Vessels falged to Mauritius recorded the highest CPUE of 42,000 KgVessel-1Trip-1 followed by Spain with 5,392.6 KgVessel-1Trip-1 . Results of the analysis for the size distribution, life history strategies, mortality and exploitation rates indicated that over 90 % of Thunnus albacares and Xiphias gladius sampled in artisanal fishery were juveniles. Exploitation rates were also above the optimal indicating that the two fisheries are experiencing growth overfishing. A review of the Kenya fisheries policy and legislative framework reveals that it is coherent with the regional and international law with focus to scientific aspects. However, the challenge is with effective implementation of tuna fishery management and development measures informed by science, in particular biological aspects namely the Total Allowable Catch (TAC), Total Allowable Effort (TAE) and precautionary approach. Information generated by this study will certainly broaden the scientific knowledge and understanding about tunas in Kenya and inform policy for their effective conservation and management.