The Impacts of Climate Change on the World’s Largest Population of Oceanic Manta Rays
November 2023
Researching a migratory species certainly has its challenges…oceanic manta rays, as their name suggests, spend a huge portion of their lives in a deep, oceanic abyss. Manta ray researchers must therefore rely on the promise of the appearance of these mysterious creatures at seasonal aggregation sites.
Between 2005 and 2018 Proyecto Mantas Ecuador and The Manta Trust identified more than 2,800 individual rays and estimated a total population of more than 22,000 in mainland Ecuador, making this the largest known oceanic manta ray population in the World. Sightings at Isla de La Plata, a small island off the coast of Puerto Lopez, are reliable and peak between August and September, often boasting numbers of 50+ oceanic manta rays on a dive (hard to comprehend right!)
The Ecuador Manta Expedition Research Team. © Jasmine Corbett
After the release of our collaborative publication ‘Demographics and dynamics of the world’s largest known population of oceanic manta rays Mobula birostris in coastal Ecuador’ in 2022, this year thanks to the generous funding from Carl F. Bucherer, we were able to bring together a team of manta scientists, educators, and media experts to study this distinct population, learning more about their population ecology, habitat use and migration behaviour.
Prior to departure, our research team planned the expedition meticulously; we sourced satellite and acoustic tags to deploy on the mantas, sent in highly advanced technological equipment such an underwater ultrasound scanner to study the reproductive behaviour of the females, and ensured that a diverse range of manta experts were available for the trip. However, as the expedition drew closer, news of a pending El Niño event emerged, raising concerns amongst our team about whether the predicted mass abundance of oceanic manta rays would in fact appear.
Proyecto Mantas Ecuador founder Michel Guerrero with acoustic tag and acoustic receiver. © Guy Stevens
So what exactly is an El Niño event, you ask?
The El Niño is a complex meteorological phenomenon characterized by the warming of equatorial Pacific waters, impacting global weather patterns. It occurs irregularly every few years and can result in varying intensities. With increasing global temperatures, the regularity and intensity of these events are only growing.
El Niño events have been linked to the alteration of oceanic current patterns, which can disrupt the distribution of planktonic food sources, such as krill and copepods, essential for the manta ray's diet. With oceanic warming and changes in upwelling patterns, the nutrient supply to the marine ecosystem is affected, leading to a decrease in the abundance of planktonic organisms. Consequently, these food shortages influence the migratory patterns of oceanic manta rays, as they need to follow their food sources for survival.
Isla de La Plata from the air. © Jasmine Corbett
Upon arrival to Ecuador, our team heard news that a few oceanic manta rays had shown up in the area but were dismayed to not encounter any individuals on the first research boat day. As the days passed, the lack of mantas became a consistent theme, and despite the delightful abundance of whale sharks due to the warmer water, the team couldn’t help but feel saddened by witnessing the first-hand effects of climate change in the region and to not be able to achieve their research goals.
The whale sharks showed up in big numbers due to the warmer water. © Guy Stevens
However, no data is still data! The low sightings offered us an unprecedented opportunity to examine the impact of this event on the population of manta rays here. This will help us to better understand the environmental conditions that bring manta rays to Isla de la Plata and to assess the potential impact of a warmer climate on this population.
We are certain that the mantas were playing games with us, because on the day that the majority of the team departed, the mantas showed up in full force! Luckily a few members had stayed behind to continue the research, so they were able to able to identify 30 oceanic manta rays, deploy 4 acoustic tags, and collect ultrasound scans making the trip very much worthwhile!
A research team member using a Stereo-Video-Photogrammetry device to measure manta wing spans. © Guy Stevens
Despite the El Nino event, we had the opportunity to give presentations to the local community, including park rangers, naturalist guides and school students, to raise awareness on the importance of their home as a site for these species. This expedition also allowed us to bring together, for the first time, members our network of affiliate projects from Mexico, Peru, Ecuador and Costa Rica, to share learnings and promote collaboration on manta and devil rays in the Eastern Tropical Pacific region.
To view the expedition video series on YouTube click here.
JASMINE CORBETT
Manta Trust Media and Communications Manager