Population status of the world's largest limpet, Scutellastra mexicana (Mollusca: Patellidae), on María Madre Island, Mexico: Possible last bastion of a species facing global extinction

Abstract

Scutellastra mexicana is the largest patellid in the world, with records of up to 35.5 cm in length, and is one of the most endangered marine invertebrates from tropical Pacific rocky shores. The decline of this species occurred during the 20th century, when fishing cooperatives reported the capture of millions of specimens in less than 2 decades (1970–1980). Since then, the species has continued to be captured illegally to the point that it has practically disappeared. This paper reports the population status of S. mexicana in María Madre Island (Mexican Pacific Ocean), which was used as a Federal Prison from 1905 until 2019. A total of 2,381 limpets were recorded in four main populations: Guayacama, Borbollones, Punta Halcones and Papelillos. The density was very low: from 0.05 to 0.3 individuals m−2, with an ageing population structure, and no recent recruitment. The size-frequency distribution of the populations showed that most of the individuals were between 9 and 15 cm. Mean and maximum shell length varied between 10.5 and 19 cm at Papelillos, 13.6 and 20.3 cm at Punta Halcones, 13.7 and 17.6 cm at Borbollones, and 12 and 20 cm at Guayacama. Evidence of illegal extraction was evident in Papelillos since the size of the limpets was significantly the smallest of the four populations studied, and also significantly smaller than those in an adjacent midden. Now that the prison has been closed it is imperative to establish legal measures, to provide extreme protection of María Madre, and to change the current status of S. mexicana in the Official Mexican Standard (NOM-059-ECOL-2010) from threatened species to in danger of extinction. This may be the last hope for the species.