Population dynamics of Venerupis aurea (Bivalvia: Veneridae) in two different clam's beds in Lake Timsah, Suez Canal, Egypt

Abstract

The clam Venerupis aurea (Gmelin, 1971) is one of the most commercially important bivalves in Lake Timsah, Suez Canal. Population dynamics for this clam was explored from August 2015 to September 2016 at two clam beds; Taawen site and Etap site of different sediment characters, population densities and fishing exploitation in the lake. The average density of the species at the exploited Taawen site (3,930 ind. m-2) was significantly higher (one way ANOVA, P = 5.15) than at unexploited Etap site (1,141 ind. m-2). Length frequency data were analyzed by FiSAT software for estimation of population parameters to evaluate the status of the stock. Asymptotic length (L8) was similar (36.57 mm) in the two beds. Growth coefficient (K) was higher in Etap site (0.36 yr-1) than in Taawen site (0.28 yr-1). The theoretical lifespan (Tmax) was higher in Taawen site (12.4 years) than in Etap site (9.7 years). Total mortality (Z) was estimated by length-converted catch curve at 0.81 and 0.98 yr-1, fishing mortality (F) at 0.11 and 0.22 yr-1 and natural mortality (M) at 0.70 and 0.76 yr-1 for Taawen site and Etap site, respectively. The estimated value of the exploitation rate (E) was higher in Etap site (0.23) than in Taawen site (0.14). The recruitment pattern was continuous with two major peaks in the two beds and was found to be correlated with the spawning pattern in the species. Recruited juvenile relative to the total population all over the study period was higher in Taawen site (34.50%) than in Etap site (20.47%). Overexploitation can only be mitigated by imposing stringent restrictions in terms of the minimum size for exploitation (12 mm shell length) and closed seasons during the spawning peak (September, December and April).