Env Exp Biol (2014) 12: 113–120

Effect of different harvesting practices on the dynamics of Paphia textile (Gmelin 1792) (Bivalvia: Veneridae) populations at two sites in Zamboanga del Norte, Southern Philippines

Abstract

Paphia textile Gmelin is a commercially-important bivalve clam in Zamboanga Del Norte, Philippines. In two municipalities, different fishing methods are practiced by Paphia fishers. Hookah diving is widespread in Manukan while only free-diving is allowed in Roxas. Higher degree of human disturbance was experienced by the P. textile population in Manukan. Some aspects of growth, mortality and recruitment were studied to assess the impacts of the fishing activities. Asymptotic length (L_∞) was higher in Roxas (69.95 mm) compared to that in Manukan (67.90 mm). Growth coefficient (K = 1.00 year^–1) values were similar in both clam beds. Estimated fishing mortality was high in Roxas (F = 2.65 year^–1) but it appeared that the clam bed can still sustain the fishery. Recruitment in Manukan showed two seasonal pulses while one main recruitment pulse was derived in Roxas. Significantly higher (P < 0.05) clam density and more larger-sized individuals were observed in Roxas. The estimated maximum sustainable yield in Roxas was 9.36 times higher than in Manukan. Environmental conditions were similar in both clam beds. Differences in the dynamics of P. textile populations in the clam beds were influenced by density-dependent processes enhanced by the degree of human exploitation.