The study evaluated some population parameters of Polydactylus quadrifilis within Ebrié lagoon (Potou sector). Samples were obtained using artisanal gillnet fishery from April 2004 to March 2006. A total of 741 individuals of P. quadrifilis ranged from 11 to 70 cm were examined. Population parameters were estimated where asymptotic length (L∞) was found 60 cm, growth rate (K) 0.33 per year, the longevity (T max) 9.09 years, and growth performance index (Φ′) 3.06. The length at first capture (Lc50 = 10.60 cm) was lower than the length at first maturity (Lm50 = 40 cm). Total mortality rate (Z) was calculated as 1.10 per year including natural mortality and fishing mortality. The exploitation rate (E=0.36) was found to be less than the maximum exploitation rate (E max = 0.44) and indicated that P. quadrifilis is not overexploited. The current exploitation rate should be maintained by sustainable fisheries measures including monitoring of fishing effort.

ABSTRACT:The spatial and seasonal variations of Acartia clausi population structure, abundance, biomass and body length variation in relationship to environmental variables were investigated in the Grand-Lahou lagoon at 21 stations from January to December 2004. A. clausi abundance, biomass and body (prosome) length showed considerable seasonal and spatial variation. On average, total population abundance and biomass obtained during the dry season (Mean: 7.11 ind/l and 9.08 µgC/l respectively) were higher than that those which have gotten during the wet season (Mean: 2.98 ind/l and 2.76 µgC/l respectively). The same tendency was registered for prosome length of all development stages, with 275-1000 µm during the dry season versus 225-975 µm during the wet season. A. clausi population (without the nauplii) was dominated by copepodids stages in all seasons. During the dry season, on average, copepodids stages constituted 76.65% of total density and 52.98% of total biomass. During the wet season, copepodids stages represented 92.23% of total density and 72.42% of total biomass. In the adults stages, on average females (F) were more numerous than males (M), with a sex ratio (M/F) of 0.75. However, males were slightly more abundant than females during the dry season (February to April and September) with sex ratio (M/F) range from 1.10 to 1.46. Correlation on data of this study analyses showed that spatio-seasonal variations of A. clausi abundance, Biomass and Body length were mainly linked to water salinity, pH, transparency and dissolved oxygen, phosphates and nitrates concentrations.

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