East Pacific Green Turtle (C. mydas) Population Dynamics in the Context of Climate Change

BAJA WORKING GROUP – CLIMATE SCIENCE ALLIANCE

East Pacific Green Turtle (C. mydas) Population Dynamics in the Context of Climate Change Michelle María Early Capistrán (Universidad Nacional Autónoma de México) Elena Solana Arellano (Centro de Investigación Científica y de Educación Superior de Ensenada) Alberto Abreu-Grobois (Universidad Nacional Autónoma de México)

FISHERMAN WITH AN EXCEPTIONALLY LARGE GREEN TURTLE. DATE UNKNOWN, PROBABLY BETWEEN 1950 AND 1960.

PHOTO CREDIT: UNKNOWN AUTHOR, COURTESY OF THE GALVÁN FAMILY OF BAHÍA DE LOS ÁNGELES

Key Takeaways •

Climate change can affect sea turtles at all life stages, but specific effects are still scarcely understood due to the spatial-temporal complexity of sea turtles’ life history and the lack of longterm data across habitats and demographic groups.

•

Local ecological knowledge can contribute to the understanding of long-term changes in the abundance of long-lived species such as sea turtles and, together with ecological modeling, aid in understanding the differentiated effects of anthropogenic and non-anthropogenic variables on threatened species.

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Addressing the immense challenges of climate change will require collaborations at multiple scales: between scientists and communities, between regions, and between countries.

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What is the focus and area of your research?

In collaboration with the community of Bahía de los Ángeles, in the Gulf of California, we reconstructed the historical catches of the East Pacific green turtle (C. mydas) by integrating local ecological knowledge and mathematical modeling (1). Currently, we are integrating this reconstruction with scientific monitoring data collected over decades by Mexico’s National Commission of Protected Natural Areas (or CONANP), the Grupo Tortuguero de Bahía de los Ángeles, and academic and non-governmental institutions. Globally, this will be the longest available time series (1952-2018) for any sea turtle foraging habitat.

How do you see climate change impacting the focus of your work?

Climatic fluctuations are significant drivers of sea turtle population dynamics, including embryo survival, hatchling traits and viability, sex determination, food quality and availability, and migratory pathways.

Thus, sea turtles can be important indicators of climate change in marine and coastal environments.

However, the specific effects of climate change are still poorly understood, partly due to the spatiotemporal complexity of sea turtle life history and the lack of comparable long-term data between different habitats and demographic groups (2, 3). Long-term sea turtle conservation and management requires strategies that integrate both anthropogenic impacts and the effects of climatic fluctuations. Likewise, it will be increasingly important to consider the effects of climatic phenomena on population dynamics and abundance.

What do you anticipate being the climate change on your focus area?

Impacts

of

climate

change,

such

as

the

intensification of climatic factors (e.g. ENSO, NPO, storms) and increases in sea surface temperature can affect sea turtles at all life stages (2). Effects during the marine life stage could include reduced foraging success, latitudinal changes in distribution, and changes in reproductive periodicity (4).

GREEN TURTLE MONITORING IN BAHÍA DE LOS ÁNGELES IS CARRIED OUT BY LOCAL FISHERS. PHOTO CREDIT: JOSÉ ARCE SMITH

What are you most concerned about?

One of the greatest causes for concern is the absence of reliable information on the impacts of climate change on marine turtles. Climate impacts are more difficult to mitigate than direct and measurable threats such as directed capture or by-catch (5). While measures such as habitat protection and bans of direct capture have helped green sea turtle populations increase after being on the brink of extinction (6), we will increasingly need new strategies and responses to the effects of climate change. Analogous to climatic processes, sea turtles’ lives occur on vast temporal and spatial scales. Thus, conservation challenges in coming decades will require global cooperation, together with effective local actions.

What are the gaps in understanding that need more research?

Globally, sea turtle monitoring is heavily skewed towards nesting beaches where only adult females are counted. There are important knowledge gaps relating to foraging habitats— which host juvenile turtles up to 20 years before reaching maturity—along with adults of both sexes during non-reproductive periods (7). There are also important gaps in basic knowledge such as age of maturity, life stage duration, and demographic and migratory connectivity (8). There are notable gaps in our understanding of demographic connectivity between warm-temperate foraging areas and tropical reproductive habitats (9), as well as the influence of regional climatological factors that can simultaneously affect different population segments.

Approaches to this topic had previously been hindered by the lack of long-term data from foraging habitats.

However, these data are now available thanks to a collaborative process with the community of Bahía de los Ángeles, the local ecological knowledge of the expert fisherfolk, and the years of monitoring effort carried out by local fishers with the support of various institutions.

TRADITIONAL TURTLE HARPOON FROM BAHÍA DE LOS ÁNGELES. THE FISHING GEARS AND TECHNIQUES USED BY SEA TURTLE FISHERS WERE DEVELOPED THROUGH DECADES OF SYSTEMATIC OBSERVATION OF SEA TURTLES’ BEHAVIOR AND INTERACTIONS WITH THE MARINE ENVIRONMENT. LOCAL ECOLOGICAL KNOWLEDGE, ACCUMULATED OVER GENERATIONS LIVING FROM THE SEA, IS INDISPENSABLE FOR UNDERSTANDING THE PAST AND LOOKING TOWARDS THE FUTURE. PHOTO CREDIT: GERARDO GARIBAY MELO

What is your plan moving forward to start to better understand or minimize the impacts from climate change?

Sea turtle conservation and management in the context of climate change will require collaborative efforts at local, regional, basin-wide, and global scales. Facing the immense challenges of climate change will require deepening scientific knowledge to solve the great gaps within collaborative strategies at different scales: between scientists and communities, between regions, and between countries.

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Koch, V., & Saenz-Arroyo, A. (2020). Quantifying local ecological knowledge to model historical abundance

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