Population Dynamics of the Cockle Cerastoderma glaucum : A Comparison Between Lake Qarun and Lake Timsah, Egypt

The cockle Cerastoderma glaucum represents one of the most common marine mollusc species present in Egyptian waters. This study aims to investigate the population structure, growth, mortality, and exploitation status of this cockle along Lake Qarun and Lake Timsah in order to make a comparison study. Cockles were collected from Lake Qarun at monthly intervals between February 2008 and May 2009 and collected from Lake Timsah at four seasons only. Length frequency data were analyzed using FiSAT software for estimation of population parameters to evaluate the stock. Asymptotic length (L infinity) was smaller in Lake Qarun (28.35 mm) compared to that in Lake Timsah (33.60 mm). Growth coefficient (K) was higher in Lake Qarun (0.450 yr(-1)) than in Lake Timsah (0.280 yr(-1)). Growth performance index (Phi) values were similar (2.56) in both cockle stocks. The theoretical maximum age (T-max) was higher in Lake Timsah (12.6 yr(-1)) than in Lake Qarun (7.4 yr(-1)). Total mortality (Z) was estimated by length-converted catch curve at 1.02 and 0.24 yr(-1), fishing mortality (F) at -0.04 and 0.47 yr(-1) and natural mortality (M) at 1.06 and 0.71 yr(-1) for Lake Qarun and Lake Timsah, respectively. Recruitment was continuous and showed two major pulses in the two lakes.