1KMFRI, Box 1881, Kisumu, Kenya. E-mail: an_othina@yahoo.com
2HIFI, University of Hull, U.K. E-mail: cowx@biosci.hull.ac.uk

Analyses and modelling of impacts of artisanal gears and climate on the commercial exploitation of Lake Victoria (K) fish resource for management decision options

Sampling was carried out at 22 beaches for 25 years to determine impacts of gears and climate on commercial catches. Schaeffer, Beaverton and Holts, and Box-Jenkins ARIMA models and cohort analysis were used for exploitation and forecasts. Lates niloticus' annual landings reached 122,800 t in 1991 with a catch per unit effort (CPUE) of 163.4 kg boat-1 day-1 and 4,250 boats. MSY was 85,000 t with fMSY of 1,5000,000 boat days that indicated that the fishery is threatened. Co-relations with R. argentea, Tilapiines, Haplochromines and other species were 0.86, 0.83, -0.54 and 0.41 before 1981 but reduced to insignificant levels ten years later. R. argentea has stabilised at 84,000 t (asymptote 89,310 t) with 1,480 boats. Significant differences were between strata means but not between month variations. Annual differences from 1994 to 2001 had P = 0.096. The trend for L. niloticus landings was polynomial of 2nd degree and linear for Tilapiines. For R. argentea it was of the form:

(Yt - (t)) = 106 / (11.20 + 259.80  0.759t-1)

Beach seine boat days had a linear trend but other gears were polynomials of 2nd degree. CPUE trends were exponential decay curves. Mean lengths for R. argentea in the southern part were smaller compared to other waters. L for beach seine was 238.4 cm and 209.5 cm for passive gillnets. The former had E = 0.898 and F = 1.765. There was seasonal fluctuation in all species landings with 4-year cycles for L. niloticus. Recruitment for L. niloticus was over 80% between April and September but R. argentea exhibited a continuous spawning. Kenyan sector is over-exploited hence the need for reduction of effort; L. niloticus boats by 40%, eradication of destructive gears, closing of recruitment months and diversification of economic activities. Further study required on catch/effort and socio-economics on the islands to understand stabilisation of R. argentea and sustainability of L. niloticus catches.