Decimation of a population of the endangered species Scutellastra mexicana (Broderip and Sowerby, 1829) (Mollusca, Gastropoda) in the Marías Island (Eastern Ocean Pacific) Biosphere Reserve

Abstract

Scutellastra mexicana is the largest known patellid limpet species and probably is one of the most endangered marine invertebrates. The species was once distributed along the American Pacific coast from Mexico to Peru, but their large size (up to 35 cm long) and easy accessibility (shallow sublittoral), made it very vulnerable to human collection and now is extinct on most of the mainland Mexican coast. In August 2017, a large population of this species was found on María Cleofas island, off the coast of west‐central Mexico (Marías Archipelago, Pacific Ocean). This constitutes the only report of a population of this species since 1988. A total of 808 adult individuals of up to 26 cm in length and 20 cm in width were estimated, together with the presence of juveniles, suggesting that it is a self‐sustaining population. The population was monitored in August 2017 and August 2018. Although the species is under the category ‘Special Protection’ in the General Mexican Wild Law, and that María Cleofas island is a Biosphere Reserve, fishermen that operate with impunity in the area decimated the limpet population within a year of its discovery. Abundance in the shallowest area decreased significantly from 120 individuals per transect (65 m long and 2.75 m wide) in August 2017 to 48 individuals in August 2018, and the estimated adult population decreased from 808 to 304 limpets. Neither passive national conservation policies nor local practices have reduced current threats to biodiversity and resource depletion in Marías Archipelago. Protected areas like this are ‘paper parks’—parks in name only—because there is no active conservation strategy or protection of marine species.

Methodologies for Patellid Limpets’ Aquaculture: From Broodstock Management to Juveniles

“…Currently, the exploitation of limpets continues for either ornamental, food, or fishing bait collection purposes (Espinosa and Rivera-Ingraham, 2017;Firth, 2021). The exploited taxa include the genera Cellana (Lasiak, 1993;Harada et al, 1997;McCoy, 2008), Cymbula (Branch and Odendaal, 2003), Lottia (Pombo and Escofet, 1996;Sagarin et al, 2007), Patella (Guerra-Garcıá et al, 2004;Guallart et al, 2013c;Henriques et al, 2017;Sousa et al, 2019a;Sousa et al, 2020a), and Scutellastra (Carballo et al, 2020;Valdez-Cibriań et al, 2021). Overfishing has led to a detrimental impact on several populations of limpets worldwide, resulting in smaller specimens and population sizes, a reduced female:male ratio, and an overall plummet of biomass and reproductive/recruitment output (Branch, 1975;Branch and Odendaal, 2003;Guerra-Garcıá et al, 2004;Espinosa et al, 2006;Espinosa et al, 2009a;Sousa et al, 2019b;Sousa et al, 2020b).…”

Population status of the endangered giant Mexican limpet Scutellastra mexicana in the central Mexican Pacific

“…In this study, the size of the limpets ranged from 5.0 to 23.3 cm in length compared to the maximum size for Scutellastra mexicana of 35.0 cm (Powell, 1973). Carballo et al (2020) reported a maximum size of 26.0 cm for limpets in the Islas Marias. Whilst the maximum length recorded in this study was lower than those mentioned above it was considerably greater than that reported by Ávalos‐Vizcaino & Méndez‐Reyes (1992) in Michoacan (14.6 cm for females and 15.6 cm for males) after years of intense exploitation of the species.…”

“…Recently, Carballo et al (2020) determined a density of 0.7 limpets/m 2 on a site in the Islas Marias archipelago. This is a remote place and a natural protected area, so it is likely to be an unexploited site as well as the last relict for this species.…”

“…Area‐based conservation measures should be applied swiftly. Marine protected areas have successfully been used as a way to rapidly enhance the abundance and size of exploited stocks (Martins et al, 2010); however, as Carballo et al (2020) highlighted, they have not worked for the giant Mexican limpets in Marias Island National Park. Another approach could be through using locally managed marine areas.…”

“…Data on this species are scarce and consist of records on its presence throughout the Mexican Pacific Coast and on taxonomic lists from the coasts of Jalisco, Colima, Michoacan, and Oaxaca (Esqueda‐González et al, 2000; Ríos‐Jara et al, 2001; Fuentes Farías, Villarroel Melo & Solís‐Marín, 2005; Holguín‐Quiñones, 2006; Ríos‐Jara et al, 2006; Bastida‐Zavala et al, 2013; Landa‐Jaime et al, 2013; Carballo et al, 2020). On the islands of the Mexican Pacific, the National Commission of Natural Protected Areas (CONANP) also reported the presence of S. mexicana in the Islas Marietas National Park (CONANP, 2007a) and in the Islas Marías Biosphere Reserve (CONANP, 2007b) (Figure 2b).…”