ARGOS USER STORIES

Sea turtle aggregation zones and spatial connectivity within the Gulf of Mexico and the Caribbean

Authors/Contributors: Eduardo Cuevas, María de los Ángeles Liceaga-Correa and Abigail Uribe

Affiliations: Laboratory of Remote sensing and GIS, Department of Marine Resources, Research Centre and of Advanced Studies of the National Polytechnic Institute, Unit Merida. Merida, Mexico.

Sea turtles are highly migratory species that are considered endangered by national laws in most of the countries and by international treaties (International Union for Conservation of Nature, Inter American Convention for the Protection and Conservation of Sea Turtles, Convention on International Trade in Endangered Species of Wild Fauna and Flora). Due to their complex life cycle in which they occupy different ecosystems at different life stages, they are highly susceptible to several threats, and together with their position at the food web, sea turtles are recognized as indicator, umbrella and flag species for marine ecosystems.

 

One of the biggest concerns for marine biodiversity at its different levels is the threat of an oil spill, particularly in the Gulf of Mexico where some of the largest oil industries in the world take place. As was learned in 2010 with the accident at the Macondo well, some of the most affected species in such disasters are sea turtles.

 

In this context, as part of the efforts to be prepared for an event of a large oil spill in deep waters of the Gulf of Mexico, the Gulf of Mexico Research Consortium (CIGoM) is executing the project entitled “Implementation of oceanographic observation networks for the evaluation of potential contingencies related to the exploration and production of hydrocarbons in the deep-water region of the Gulf of Mexico”, in which CINVESTAV Merida, leads the “Sea turtle critical habitats” subproject.

 

The objective of this study is to identify migration routes and aggregation areas for post-nesting female sea turtles of four species (Loggerhead, Hawksbill, Kemp's Ridley and Green). In 2016 we deployed 75 satellite transmitters, with ARGOS location system, to equal number of sea turtle individuals. These individuals were captured along the Mexican coast in the Gulf of Mexico and the Caribbean. In 2017 we will deploy 15 more tags to confirm migration and aggregation patterns already identified, as well as to fill gaps for rookeries less studied in this region.

 

Of the deployed tags, 26.67% of them were deployed on Hawksbill females, 46.67% on Green turtle females, 13.33% on Loggerheads and 13.33% on Kemp’s Ridleys. By December 2016 we had already compiled more than 35,000 satellite records, with a maximum of 243 days of transmission, and a minimum of 24 days. Each record in the individual tracks was classified as “Aggregation” or “Migration” depending on the migratory stage in which was acquired. We split the data per stage, and for each one we grouped all the records in hexagons of 25 km of diameter, so we could identify migratory corridors and spatial connectivity (Migration stage), as well as individual and multi species aggregation hotspots (Aggregation stage) (Figure 1).

 

So far, we have identified at least 31 feeding areas for the tracked individuals, 92.25% inside the Gulf, and 30% of those are sites that had not been reported for individuals nesting in Mexican coasts.

The data has confirmed migrating routes along south and north Gulf of Mexico for Kemp’s Ridleys (Lepidochelys kempii), aggregation nearest to the shoreline for Green turtles (Chelonia mydas), movement from Mexican Caribbean towards the Gulf of Mexico and vice versa, and showed that Hawksbills (Eretmochelys imbricata) mostly stay in Mexican waters, but also confirmed long distance and even transoceanic migrations (Figure 2).

This in-water portfolio contains first level outline hotspots for sea turtle biodiversity in the Gulf of Mexico and Mesoamerican Reef, and it is of the highest interest and relevance at national and international levels for conservation and recovery of these species. Also, as the hotspots represent aggregations of multiple sea turtle species, this information brings out new insights about the contribution of sea turtle populations from the Gulf of Mexico to sea turtle biodiversity and connectivity within it, and with the Caribbean, including the identification of areas with high sea turtle species richness (Figure 3).

The identification and delimitation of their critical habitats will serve to define individual and multi specific sea turtle hotspots based on standardized criteria, evaluate connectivity between nesting beaches inside the Gulf of Mexico and feeding grounds inside and outside this large ecosystem, as well as to evaluate their vulnerability to oil spills, incorporating oil spill scenarios derived from ongoing research in our Gulf of Mexico Research Consortium (CIGoM).

 

This information represents a key input for strategic marine biodiversity conservation, contributing with spatially explicit information for decision-making, policy development, spatial planning, and landscape zoning. It is the basis for preparedness in events of major contingencies such as oil spills, as well as for assessing impacts of global threats such as climate change. With this information, we are setting robust basis for an integral ecological observatory system, including a network of critical in-water zones for sea turtles in the Gulf of Mexico and the Caribbean.

 

The collaborative work with local and international institutions and organizations in charge of biological monitoring of sea turtle nesting beaches and tracking individuals of other rookeries, as well as with decision-makers and managers of coastal and marine ecosystems (natural protected areas) is strategic for an inter-sectorial approach for large ecosystems, as in this initiative.

Acknowledgements
This research is funded by the National Council of Science and Technology of Mexico - Secretariat of Energy -Hidrocarbon Trust project 201441. The female sea turtle satellite tagging was done under permit Num. SGPA/DGVS/09583/15 issued by the Secretary of Environment and Natural Resources in Mexico. This is a contribution of the Gulf of Mexico Research Consortium (CIGoM). We want to acknowledge Sandra Gallegos, Alejandra Ortíz, David Espinosa, Betzabeth Palafox, Guadalupe Mexicano and Héctor Hernández Núñez for their essential work in the PTT deployment. Finally, we want to thank all the institutions, NGOs and governmental institutions in charge of sea turtle monitoring at nesting beaches for all the facilities to complete this study.
 

Figure 1. Sea turtle hotspots derived from normalized abundances of aggregation records for four sea turtle species after nesting in Mexican coasts in the Gulf of Mexico and Caribbean.

Figure 2. Migratory corridors representing spatial connectivity by sea turtles in the Gulf of Mexico and Caribbean derived from normalized abundances of migratory records for four species of sea turtles. These corridors show some outlines of spatial connectivity inside the Gulf of Mexico and with the neighboring Caribbean waters.

Figure 3. Sea turtle species richness spots for post-nesting females moving from Mexican coasts in the Gulf of Mexico and Caribbean. Those spots with highest richness are of the highest importance for sea turtle conservation and management, representing multi species aggregation spots susceptible to be considered as Key Biodiversity Areas as defined by IUCN (https://portals.iucn.org/library/sites/library/files/documents/Rep-2016-005.pdf)