LENGTH–WEIGHT RELATIONSHIP, GROWTH, MORTALITY AND EXPLOITATION STATUS OF SEPIA HIERREDDA (RANG, 1835) IN IVORIAN WATERS, GULF OF GUINEA

Abstract

Population parameters of the giant African cuttlefish Sepia hierredda were estimated from length-frequency data collected in Ivorian waters. A total of 962 individuals were measured. The asymptotic length (L∞) was 32.03 cm and the growth coefficient (K) was 0.69 year-1, giving a growth performance (φ’) of 2.85. The length–weight relationship was W=0.20614LD2.73634, (R² = 0.9023), and the exponent b was significantly lower than 3 (p<0.001), indicating negative allometric growth. Total mortality (Z) for S. hierredda was 2.52 year−1, with natural mortality (M) and fishing mortality (F) were 1.31 and 1.22 year-1, respectively. The exploitation rate (E) was 0.48, slightly higher than the E50 reference point (0.466), whereas E10 and Emax were both 1.00. Recruitment pattern was continuous throughout the year, with two major pulses in March-April and August-September; the latter was the stronger pulse and represented 18.78% of reconstructed recruitment. Virtual population analysis showed a progressive decline in population numbers with increasing length and an increase in fishing mortality toward larger length groups. The results indicate that the stock is subject to substantial fishing pressure, although the exploitation rate remains close to the conventional reference level of E= 0.5 rather than clearly indicating severe overexploitation.