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The loggerhead turtle (Caretta caretta) is a circumglobal species and is listed as vulnerable globally. The North Pacific population nests in Japan and migrates to the Central North Pacific and Pacific coast of North America to feed. In the Mexican Pacific, records of loggerhead presence are largely restricted to the Gulf of Ulloa along the Baja California Peninsula, where very high fisheries by-catch mortality has been reported. Records of loggerhead turtles within the Sea of Cortez also known as the Gulf of California (GC) exist; however, their ecology in this region is poorly understood. We used satellite tracking and an environmental variable analysis (chlorophyll-a(Chl-a) and sea surface temperature (SST)) to determine movements and habitat use of five juvenile loggerhead turtles ranging in straight carapace length from 62.7–68.3 cm (mean: 66.7 ± 2.3 cm). Satellite tracking durations ranged from 73–293 days (mean: 149 ± 62.5 days), transmissions per turtle from 14–1006 (mean: 462 ± 379.5 transmissions) and total travel distance from 1237–5222 km (mean: 3118 ± 1490.7 km). We used travel rate analyses to identify five foraging areas in the GC, which occurred mainly in waters from 10–80 m deep, with mean Chl-aconcentrations ranging from 0.28–13.14 mg m−3and SST ranging from 27.8–34.4°C. This is the first study to describe loggerhead movements in the Gulf of California and our data suggest that loggerhead foraging movements are performed in areas with eutrophic levels of Chl-a.

The Gulf of California Large Marine Ecosystem (LME) is one of the most productive and biologically rich marine ecosystems in the world with a high rate of endemic species. The combination of high biological productivity and biological richness characterizing the region is the result of its unique geology and geography, shaping strong currents and tides that generate the upwelling of cool, nutrient-rich waters. These waters support an extremely high abundance of plankton that in turn is the basis of a complex food web sustaining a diversity of fish, birds, and marine mammals. As Mexico's most important fishery region, the Gulf of California provides seafood to locals and for export to other countries. In addition, manifold coastal lagoons, coastal marine sea-beds, mangrove forests, and 922 islands are important reproductive, nesting and nursing sites for hundreds of resident and migratory bird species. However, even when several oceanographic processes that confer a high productivity to the Gulf of California LME have been documented, there is very little field work to monitor these phenomena, such as coastal upwelling in the southern region, as well as the spatial and temporal variability in nutrient concentrations, the effect of exchange with coastal systems and the role of the Gulf of California as a sink or exporter of carbon dioxide (CO₂), for example, in winter the region of the Grandes Islas , there are a source of CO 2 to the atmosphere (pCO 2 >580 µatm). On this, the records show that in the last 250 years the concentrations of atmospheric CO₂ in the world have increased and it has been reported that the ocean daily fixed 2.2 metric tons of CO₂, this content has changed from 280 µatm before the industrial revolution to 407 µatm in recent times. In the Gulf of California, studies conducted on carbon dioxide (air-ocean flow, dissolved inorganic carbon, total alkalinity) are scarce, and suggest a net flow CO 2 from coastal waters into the atmosphere mainly in the region of the Grandes Islas , caused by the intense vertical mixing. In the absence of time-series data on the processes occurring in the southern part of the Gulf, it is necessary to start continuous records of temperature, salinity, dissolved oxygen, pH vertical structure and the measurements of dissolved inorganic carbon, total alkalinity and nutrients to improve understanding of the biogeochemical structure of the water column and possible exchanges with the coast.