Abstract :
The recruitment, exploitation, relative-yield per recruit and mortality of Synodontis schall in River Benue were estimated using the length frequencies collected from January, 2009 to December, 2010. Fishing Mortalities (F) of 2.203, 2.355 and 2.360 in the females, males and combined sexes were found to be higher than natural mortalities (M) of 1.235, 1.227 and 1.045 in the females, males and combined sexes respectively. The total mortalities were 3.438, 3.582 and 3.405 in the females, males and combined sexes respectively. Exploitation ratios of 0.64, 0.66 and 0.69 for the females, males and combined sexes were high and exceeded the 0.5 optimal values for sustainable yield. Using the reference points of Emax, E0.1 and E0.5, current exploitation rates suggest unsustainable stocks for this species in river Benue. Recruitment was continuous with two pulses, the first one at the beginning of the year and the second one in the middle of the year. The current exploitation rates suggest growth overfishing with selective mortality towards smaller fish sizes, therefore, the protection of the immature fish will be the key factor to preserve the spawning stock.
Keyword :
Exploitation; Mortality; Recruitment, Relative-yield per recruit, Synodontis schall.