Population dynamics of Donax trunculus on the sandy beach of Taghazout (southern Morocco)

Abstract The study of the structure and the dynamics of populations exposed to environmental pollutants can be a useful investigative tool for finding the connections between different levels of biological organization Population dynamics on wedge clam, Donax trunculus is still unknown in Morocco. FiSAT software (FAO-ICLARM Stock Assessment Tools) was used for calculating population parameters of this species. The specimens of D. trunculus (Linnaeus, 1758) were collected monthly in the Agadir Marine Bay (South of Morocco) for two years (January 2016–December 2017) from three stations (S1, S2 and S3), which are directly exposed to eventual pollutants owing to the developing tourism resort Taghazout Bay. The study of the population dynamics of D. trunculus shows that the annual mean of density, biomass and condition index, presents significant seasonal variations depending on the physico-chemical parameters and the animal’s life cycle. The monitoring of age-class frequency distributions of D. trunculus individuals revealed a slighter difference at the three study stations. Asymptotic length (L ∞ ) was 37.96 mm and growth coefficient (K) was estimated at 1.93 year −1. Total mortality (Z) for D. trunculus was 3.30 year −1. Natural mortality (M) and fishing mortality (F) were 1.73 year−1 and 1.57 year − 1 respectively. Exploitation level (E) was computed as 0.48, indicating an optimum level of exploitation of D. trunculus in the coastal waters of Taghazout. It is well demonstrated that bimodal recruitment takes place twice a year; one in late summer–early autumn and the other in spring. The results of this study provide information on the health status of this ecosystem receiving Taghazout Bay project.