Natural mortality-at-age estimations for the benthonic commercial pen shell Atrina maura

Abstract

Natural mortality-at-age (Mt) is key for fisheries stock management, especially on sedentary resources such as bivalves under heavy adult and juvenile exploitation. This study aims to calculate Mt for the commercial bivalve Atrina maura from the Gulf of California by applying two approaches: the gnomonic interval model (GIM) and Chen & Watanabe model. The GIM uses biological data to assemble Atrina's life cycle into gnomonic intervals. This study also explores the effect of the variability in embryonic development under short and long-longevity scenarios on Mt. The Chen and Watanabe model uses the growth parameters of the species found in the literature to estimate Mt. Results show that both models described the typical form of Mt with high mortality rates at early ages and a reduction and stabilization of Mt from the age of first maturity to adulthood. The range of M values based on the GIM was 2084 (larval development) to 0.71 yr−1 (adults) for the 6 years longevity scenario and 2084 (larval development) to 0.39 yr−1 (adults) for the 10 years longevity scenario. For the Chen and Watanabe model Mt ranged from 4.6 (juveniles) to 0.73 yr−1 (adults). The Mt vectors at early ages showed higher values in the GIM (8.0 vs. 4.6 yr−1), followed by similar values during the age of sexual maturity (0.59 yr−1 for both models), and slightly high values in the Chen Watanabe model at older ages (0.39 vs. 0.64 yr−1). Furthermore, the estimates of natural mortality based on independent studies for larvae and adults of A. maura showed similar values with the Mt vectors estimated in this study, confirming the validity of their application on bivalve stock assessment by reducing bias and improving bivalve fisheries management.