Aspects of biology, ecology and fishery of the bigfin squid sepioteuthis lessoniana (lesson, 1830) in Kenya

Sepioteuthis lessoniana (Lesson, 1830) occurs along the coast of Kenya from Vanga ordering Tanzania to Kiunga bordering Somalia and supports small scale fishery. Sea surface emperature, chlorophyll-a, wind velocity, rainfall and salinity were related to fishing records from 2001-2010. Fishery data were obtained from Fisheries Department and artisanal fishermen. Physico-chemical data were from satellite data (“oceancolor.gsfc.nasa.gov/cgi/l3”website), Kenya meteorological department and in-situ measurements. Shimoni recorded the highest average landing of 119.6±78.6mt and Lamu recording the lowest of 8.2±5.0mt. Average catch per unit effort (CPUE) was 6.7±4.1kg/man/hr with the highest in Kilifi recording 11.3±9.8kg/man/hr and the lowest at Lamu at 3.7±2.6kg/man/hr. Rainfall and sea surface temperature had significant positive correlation with squid catches while wind velocity had significant positive correlation with catch per unit effort (CPUE). Annual average value for harvested squid was Ksh 12,315,389±5,608,761 with the highest of Ksh 21,587,548 recorded in 2007 and the lowest of Ksh 5,826,216 in 2002. Length/weight relationship for males was: Log10W = 0.336+2.233Log10L; for females was Log10W = 0.565 + 2.412Log10L. Dorsal mantle length had a linear relationship with age (DML=0.093(Age) + 0.667) and a polynomial relationship with weight (Weight =0.002 (Age) 2.28. Asymptotic length (L∞) was 34.1cm, population growth coefficient (K) 0.82/yr, growth performance index (Ø) 2.98/yr, (t0) -0.18913, which were consistent with other regions. Total mortality (Z) was 2.49/yr, natural mortality (M) 2.01/yr, fishing mortality (F) 0.48/yr and exploitation rate (E) of 0.42/yr differed from other regions. Sex at maturity L50 was 20-21.9cm for both sexes while fecundity was 20-1160 eggs and spawning from July to January and recruitment from February to June. Gears and methods that minimize recruitment overfishing should be encouraged in the south coast whereas gears and methods that minimize growth overfishing should be encouraged in the north coast. Correlation between environmental data with catches and CPUE relates well with fishermen’s oceanographic knowledge, accentuating the potential of incorporating such knowledge into evaluations of the squid fishery management.