Current Wild Population Status of Protected Mother-Of-Pearl Oyster Pinctada mazatlanica in Mexican Pacific Reefs

Abstract

The mother-of-pearl oyster Pinctada mazatlanica (Hanley, 1856) obtained full protection from the Mexican government after the fishery collapse in 1939. P. mazatlanica was listed in 1994 as a threatened species in the “Special Protection” category. However, no quantitative assessment of the state of the population has been done so far. Our study is the most comprehensive summer interannual monitoring program conducted so far in the Eastern Pacific using SCUBA diving censuses conducted in 314 sampling sites located along the Mexican Pacific between 1998 and 2021. We propose the hypothesis that although P. mazatlanica had full protection with the NOM-059, global warming reported in northwest Mexico has caused a decrease in the population abundance along the Pacific coast, which may render the protection effort useless. However, we demonstrate that P. mazatlanica was the numerically dominant macro–mollusk and occupied the 18th ranked abundance place compared with the entire epibenthic macroinvertebrate fauna that included 241 species at rocky reefs of the Mexican Pacific, particularly abundant along the peninsular coast of the Gulf of California. Population frequency size distribution of P. mazatlanica dorsoventral length showed positive population growth and latitudinally similar dorsoventral length range (2–30 cm, mode 14 cm when protandry takes place) along the peninsular coast of the Gulf of California, indicating a stable population in time and space. We observed high abundances in the central Gulf of California (Baja Peninsula), mainly from Loreto to La Paz. We conclude that P. mazatlanica is a stable and healthy population along the rocky reefs of the peninsular coast of the Gulf of California even during prolonged anomalous warm events in 2013–2016. Therefore, the present protection status should be modified accordingly.