Population Dynamics of the Comb Pen Shell Atrina pectinata (Linnaeus, 1767) (Mollusca, Bivalvia: Pinnidae) Collected by Diving from Shallow Areas of the Southwest Visayan Sea, Northeastern Panay Island, Philippines

Abstract

With the objective of determining the population dynamics of the comb pen shell (Atrina pectinata) (Mollusca, Bivalvia: Pinnidae) collected by divers in the southwest Visayan Sea, length-frequency data recorded between June 2018 and May 2019 were analyzed using the FiSAT software. von Bertalanffy growth parameters for the species were SL = 40.69 cm and K = 0.78 yr–1 the range of values for other fast-growing tropical bivalves. The estimated mean growth rate of 0.15 ± 0.05 cm d–1 likewise supports a fast growth rate and a short lifespan (< 1 yr) of the population. The recruitment pattern shows one major and minor pulse that coincides with the northeast monsoon and just prior to the southwest monsoon, respectively. Using ELEFAN II, total mortality (Z) of 2.79 yr–1 was estimated. From an averaged M/K value from the related bivalve literature (1.51) multiplied by the species’ own K, natural mortality (M) of 1.18 yr–1was estimated, which when subtracted from the Z, gave fishing mortality (F) of 1.61 yr-1 and an exploitation rate E of 0.58, considered overexploited. Recommended management measures for more sustainable utilization of the species include non-collection of individuals smaller than the cited minimum size at sexual maturity [20 cm shell length (SL)], and a ban on the collection at least during the major spawning season deemed to be, based on the growth rate between October and December each year. Marketing of the non-adductor portion of the viscera, normally just discarded, is also recommended to increase the income of the fishers.