Shark movements in the Revillagigedo Archipelago and connectivity with the Eastern Tropical Pacific

Abstract

Long-distance movements of sharks within and between islands pose substantial challenges for resource managers working with highly migratory species. When no-take zones do not cover the critical areas that sharks use as part of their lifecycle, exposure to fishing activities can be significant. Shark movements between the Marine Protected Areas (MPAs) of the Eastern Tropical Pacific (ETP) have been studied for several years, however little is known about the strength of connectivity between these islands. We analyzed the extensive MigraMar ultrasonic telemetry dataset to assess how Galapagos sharks (Carcharhinus galapagensis) and silky sharks (Carcharhinus falciformis) use different islands as stepping-stones during their migrations within the Revillagigedo National Park and other ETP islands. Of the 66 sharks monitored, 63.5% moved within the same island, 25.4% between two islands or more and only 10.1% across different MPAs. A C. falciformis tagged in Roca Partida Island, Revillagigedo, travelled to Clipperton Atoll and another one tagged in Darwin Island travelled to the atoll on two different years. The largest movement of C. galapagensis was accomplished by a shark tagged at Socorro Island, Revillagigedo, later detected at Clipperton and finally recorded in Darwin Island, Galapagos. This last path was in fact, one of the longest movements ever recorded for the species. Although long-distance dispersion was not common, our results highlight the need for co-operation between different countries to ensure adequate protection for sharks in the form of swimways and other conservation tools in the ETP.

Monitoring elasmobranch assemblages in a data-poor country from the Eastern Tropical Pacific using baited remote underwater video stations

“…Few studies have used BRUVS to assess shark assemblages in the ETP region, and those were restricted to remote and isolated islands 52,53 . For example 52 , reported 10 species of sharks from 4 families in the Galapagos archipelago (Ecuador), whereas 53 detected 8 species of sharks from 2 families in Revillagigedo Islands (Mexico). Similar trends in terms of species composition were observed in Cocos Island, in which our BRUVS were able to detect 8 species of sharks from 2 families.…”

A priority nursery area for the conservation of the scalloped hammerhead shark Sphyrna lewini in Mexico

“…Sites like the Galapagos Islands in Ecuador, Cocos Island in Costa Rica and the Revillagigedo Archipelago in Mexico are world‐famous national parks for hammerhead sharks in abundance. These sites are protected due to the great biological diversity found at these locations, their natural history, international relevance, expansion of the national territory of each country and their economic importance for tourism such as scuba diving (Aldana Moreno et al ., 2020; Bessudo et al ., 2011; Estupiñán‐ Montaño et al ., 2021; Ketchum et al ., 2014; Lara‐Lizardi et al ., 2020; Nalesso et al ., 2019; Prus, 2013). On the contrary, the potential nursery areas are close to human settlements on the coastline, where fishing is the main economic activity; therefore, conservation efforts have historically been very complicated and ineffective (Zanella et al ., 2019).…”

Trophic resources and mercury exposure of two silvertip shark populations in the Northeast Pacific Ocean

“…All ST sharks sampled in our study were juveniles (Compagno et al, 2005), it is therefore possible that the analysis of adult sharks may lead to a wider degree of overlap between the populations of Revillagigedo and Clipperton, reflecting a higher dispersion of adult ST sharks. Finally, other shark species such as the Galapagos shark Carcharhinus galapagensis have been recorded to perform long distance movements between MPAs including Revillagigedo and Clipperton, realizing migrations exceeding 3000 km (Lara-Lizardi et al, 2020). In comparison with more resident species such as ST sharks, these migratory predators probably provide trophic connectivity between MPAs in the North Eastern tropical Pacific.…”

“…The silvertip (ST) shark Carcharhinus albimarginatus is one of the most abundant predator species found in both MPAs in the ETP (Allen and Robertson, 1997;Lara-Lizardi, 2018). This is a large slow-growing shark, from 0.63-0.68 m in total length (TL) at birth to a maximum body size of 3 m TL.…”