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ISRA FACTSHEETS

CENTRAL AND SOUTH AMERICAN PACIFIC REGION

ISRA FACTSHEETS

CENTRAL AND SOUTH AMERICAN PACIFIC REGION

Revillagigedo Archipelago ISRA

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Revillagigedo Archipelago ISRA

Revillagigedo Archipelago

Summary

Revillagigedo Archipelago is located in the Eastern Tropical Pacific, 400 km south of Baja California state, Mexico. This area is part of a Marine Protected Area (National Park Revillagigedo) and is a UNESCO World Heritage Site due to its high biodiversity and species endemism. The archipelago is composed of four islands: Socorro, Clarion, San Benedicto, and Roca Partida and is characterised by rocky habitats and domes near the islands as well as sandy and silt bottoms, and hydrothermal vents. Within this area there are: threatened species (e.g., Silky Shark Carcharhinus falciformis); reproductive areas (e.g., Galápagos Shark Carcharhinus galapagensis); feeding areas (e.g., Silvertip Shark Carcharhinus albimarginatus); resting areas (Whitetip Reef Shark Triaenodon obesus); areas important for movement (e.g., Whale Shark Rhincodon typus); and distinctive attributes (e.g., Tiger Shark Galeocerdo cuvier).

Revillagigedo Archipelago

Revillagigedo Archipelago

DESCRIPTION OF HABITAT

Revillagigedo Archipelago is located in the Exclusive Economic Zone of Mexico, under the jurisdiction of Colima state, 400 km south of Baja California state. This area is part of a Marine Protected Area (National Park Revillagigedo) and is a UNESCO World Heritage Site due to its high biodiversity and species endemism. The archipelago comprises four volcanic islands: Socorro, Clarion, San Benedicto, and Roca Partida. These islands were formed from volcanoes rising from the Clarion Fracture Zone, a submarine fracture zone defined by numerous transform faults that traverse the northern part of the Eastern Pacific Rise. The islands are located on the southern tip of the north-westward moving Pacific plate just west of the junction between the East Pacific Rise, the Middle America Trench, and the Pacific, Rivera, and Cocos plates. It is thought that the islands date from early Pliocene to late Pleistocene (Brattstrom 1990; CONANP 2019).

The oceanography of Revillagigedo Archipelago is influenced by the California Current, the North Equatorial Current, and the Coastal Current of Costa Rica (Brattstrom 1990; CONANP 2019). During the boreal summer, sea surface temperatures average 28–29°C, while the winter temperature decreases to 22–25°C. The area is characterised by rocky habitats and domes near the islands, as well as sandy and silt bottoms and hydrothermal vents. This area overlaps with a protected area, the National Park Revillagigedo, one of the few fully protected marine areas in Mexico (CONANP 2019). In addition, this area includes one Ramsar site, Reserva de la Biósfera Archipiélago de Revillagigedo (Ramsar 2022), and one Key Biodiversity Area, Islas Revillagigedo (KBA 2022).

This Important Shark and Ray Area is delineated from inshore and surface waters (0 m) to a depth of 1,928 m based on the maximum depth reported for Qualifying Species.

CRITERION A

VULNERABILITY

Eight Qualifying Species considered threatened with extinction according to the IUCN Red List of Threatened SpeciesTM regularly occur in this area. Threatened sharks comprise one Critically Endangered species, two Endangered species, and four Vulnerable species; threatened rays comprise one Endangered species (IUCN 2022).

CRITERION C

SUB-CRITERION C1 – REPRODUCTIVE AREAS

Revillagigedo Archipelago is an important reproductive area for three shark species. Acoustic telemetry studies from 2012–2015 have included the tagging of neonate and juvenile (n = 14; 80–200 cm total length [TL]) Silvertip Sharks showing that this species is regularly occurring around San Benedicto Island and Socorro Island (Muntaner 2016; Ketchum et al. 2020). The reported size-at-birth for the species is 63–81 cm TL (Ebert et al. 2021). Tagged individuals utilised shallow inshore waters of both islands, suggesting that these locations serve as nurseries. In addition, acoustic tagging from 2008–2015 revealed that adults are more common around Roca Partida Island, and there are reports of pregnant females moving to San Benedicto and Socorro islands, with larger juveniles moving from San Benedicto Island to the areas where adults regularly occur (Muntaner 2016; Lara-Lizardi 2018).

Females with recent mating scars and pregnant female Silvertip Shark, Silky Shark, and Galápagos Shark have been regularly observed during underwater visual census and during Baited Underwater Remote Video Surveys (BRUVS) around the different islands over multiple years (Lara-Lizardi 2018).

CRITERION C

SUB-CRITERION C2 – FEEDING AREAS

Revillagigedo Archipelago is an important feeding area for three shark species. Based on stable isotope analysis (n = 26), young-of-the-year and juvenile Silvertip Sharks feed in the Revillagigedo Archipelago in benthic and pelagic habitats. Feeding in different habitats is related to ontogenetic movements described in the section above. This species moves between nursery areas around San Benedicto and Socorro islands, where benthic reef fish communities are available, to areas near Roca Partida Island, highly influenced by oceanic waters where there is a higher availability of pelagic fishes (LeCroizier et al. 2020).

Large feeding events have been observed in different parts of this area during underwater visual census (Lara-Lizardi et al. 2018). Silky Sharks (around 400 individuals) and Galápagos Shark form large feeding aggregations around bait balls formed by small pelagic fishes (Clupeidae). Silky Shark and Galápagos Shark are found year-round in the area, with higher residency in the boreal winter-spring and spring, respectively. From this area, these species move to other locations in the Mexican Pacific and Eastern Tropical Pacific, which indicates the seasonal importance of this area for feeding.

CRITERION C

SUB-CRITERION C3 – RESTING AREAS

Revillagigedo Archipelago is an important resting area for Whitetip Reef Sharks. This species uses the crevices and caves of Roca Partida and San Benedicto islands to rest during the day, before moving away from these habitats at night to feed (Lara-Lizardi 2018).

CRITERION C

SUB-CRITERION C4 – MOVEMENT

Revillagigedo Archipelago is an important movement area for five shark and one ray species. The area has been reported to support connectivity for many migratory species with other areas in the Eastern Tropical Pacific (e.g., Cortés-Fuentes 2018; Aldana-Moreno 2020; Aldana-Moreno et al. 2020; Becerril-García et al. 2020).

Acoustic telemetry revealed that Silky Shark move from Revillagigedo Archipelago to Cabo Pulmo, Baja California Sur, Mexico (Lara-Lizardi et al. 2018). In addition, two Silky Sharks tagged with satellite transmitters showed movements from the archipelago to areas near Clipperton Island and to coastal areas in Sinaloa and Islas Marías, Mexico (Ketchum et al. 2020; Lara-Lizardi et al. 2020).

Galápagos Sharks also move between Revillagigedo Archipelago and Cabo Pulmo, as revealed by acoustic tagging (Lara-Lizardi 2018). This connectivity has been confirmed based on genetic analyses (Pazmiño et al. 2019). In addition, one Galápagos Shark (180 cm TL) tagged with an acoustic transmitter travelled from Revillagigedo to Clipperton Island and to Darwin Island in the Galápagos, travelling ~3,000 km (Ketchum et al. 2020).

One satellite tagged Tiger Shark moved back and forth between Revillagigedo Archipelago to areas in the southern Gulf of California (Cabo Pulmo) during 2013, traveling 1,014 km during the roundtrip, suggesting connectivity for this species between both regions. Tiger sharks have a high residency to the Archipelago between July–November and less residency in the colder months (December–June), when this long-distance movement occurred (Ketchum et al. 2020).

Based on photo-identification, two Oceanic Manta Rays moved between Revillagigedo Archipelago and Isla Cerralvo in the Gulf of California (Kumli & Rubin 2011). In addition, acoustic telemetry revealed that individuals (n = 4) make movements back and forth between Revillagigedo and Bahía Banderas, Nayarit, Mexico (Preciado-González 2021).

A single acoustically tagged Whitenose Shark moved from Cabo Pulmo to Revillagigedo Archipelago, supporting the presence of connectivity between the Gulf of California and Revillagigedo Archipelago for this species. This report extended the known distribution of Whitenose Shark to 400 km off the mainland coast of the Americas (Lara-Lizardi et al. 2017).

Three Whale Sharks tagged with satellite transmitters showed movements from the southern Gulf of California (La Paz) to Revillagigedo Archipelago and from the archipelago to areas near San Blas, Nayarit (Ketchum et al. 2020).

CRITERION D

SUB-CRITERION D1 – DISTINCTIVENESS

Revillagigedo Archipelago is an important area for the distinct behavior of seven shark species. The area encompasses cleaning stations for Silvertip Shark, Silky Shark, Galápagos Shark, Blacktip Shark, Tiger Shark, Scalloped Hammerhead, and Whitetip Reef Shark. These cleaning stations have been confirmed from underwater visual census between 2017–2021 and are considered distinctive since cleaning stations for these sharks have not been documented elsewhere in the Eastern Tropical Pacific.

Silvertip Shark serves as a host for Blacknosed Butterflyfish Johnrandallia nigrirostris, Blackjack Caranx lugubris, Mexican Hogfish Bodianus diplotaenia, and Cortez Rainbow Wrasse Thalassoma lucasanum. Silky Shark has one specific associated cleaner, Mexican Hogfish. Galápagos Shark has three associated cleaners: Blackjack, Blacknosed Butterflyfish, and Mexican Hogfish. Only Blacknosed Butterflyfish interact with Tiger Sharks. Scalloped Hammerhead has Blacknosed Butterflyfish and Blackjack as their cleaners. Whitetip Reef Sharks serves as a host for Blackjack (Nicolás-Chavez 2022).

Revillagigedo Archipelago

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