Islas Marías Archipelago is at the entrance of the Gulf of California in the Exclusive Economic Zone of Mexico off the coast of Nayarit. Situated within the Pacific Central-American Large Marine Ecosystem, the area is where promontories influence the speed of marine currents coming from the southern Mexican Pacific. Due to the proximity of the islands to the Central Eastern Tropical Pacific region, the area can be described as tropical and oceanic (Palacios-Hernandez et al. 2010). Shallow channels between the four islands range in depth between 10–30 m. To the west, depths are around 200 m, but in the northeast end of San Juanito Island, there is a pronounced change in the slope where the depths vary between 300 and 660 m. To the west, the platform is very narrow descending to 1,000 m a short distance from the islands.

Around the four islands, the seabed is mostly made up of large rocks with steep slopes, cracks, and rocky bottoms. At depths between 15 and 30 m, the bottom is made up of sandy plains. In the southeast part of Isla San Juanito, the smallest island, the bottom is characterised by rocky and sandy patches (CONANP-SEMARNAT 2007, 2022). The main changes in temperature and salinity are between 40 and 100 m in depth (Palacios-Hernández et al. 2002). Below 300 m, the salinity distribution is the same as elsewhere in the tropical Pacific (Lavín et al. 2006). The proximity of the four islands with the coast of Nayarit (~120 km), which in turn has a wide and regular continental shape, creates the conditions to form cyclonic and anticyclonic eddies (Kurczyn et al. 2012). Wind direction changes seasonally. For instance, during the boreal winter months, winds come from the northwest, and during the boreal summer, winds coming from the west to the southwest dominate. The topography, together with the merging of the temperate water California Current and warm water of the Mexican Coastal Current derived from the Costa Rica Coastal Current, as well as the warm high salinity mass water coming out of the Gulf of California creates considerable turbulence and steep sea surface temperature gradients in the area (Zamudio et al. 2007; Kurian et al. 2011).

Due to the high levels of marine and terrestrial biodiversity, and endemism, the archipelago was categorised as a Biosphere Reserve by the Mexican government in 2007 and then as a World Heritage Site by UNESCO. In addition, it has been a protected area in Mexico since 2000 (DOF 2000; Moncayo-Estrada et al. 2006)

This Important Shark and Ray Area is delineated from inshore and surface waters (0 m) to a depth of 1,000 m based on the maximum global depth of the Qualifying Species.