Reef manta ray, Mobula alfredi. Photo credit: Amelia J. Armstrong and colleagues
The study uses satellites and photos to fill important gaps in migration patterns for one of the world’s largest types of radiation.
Marine animals are notoriously difficult to track, resulting in large gaps in scientists’ understanding of their behavior and migration patterns – vital insights into the conservation of critical habitats. Researchers in Australia published an article in. Using satellite tags and a decade-old photographic satellite database Limits of marine science this suggests that a migratory species like the reef manta ray is more of a homebody.
The study found that a population of Mobula alfredi, one of the largest species of rays in the world, lives and travels long-term between two UNESCO World Heritage sites along the west coast of Australia. Nearly 10 percent of the 1,100+ reef manta rays identified by photos have been visiting Ningaloo Marine Park for more than a decade, with the longest lasting about 15 years.
Amelia J. Armstrong attaching a satellite tag to a reef manta ray, Mobula alfredi. Photo credit: Amelia J. Armstrong and colleagues
“This is a great find for the reef manta rays on this coast as these sanctuaries provide the legal framework necessary for further management action,” said Amelia J. Armstrong, lead author of the new paper and a PhD student in biomedical sciences at the University of Queensland.
Reef Mantas are a long-lived species with a relatively slow reproductive life cycle and are listed as “Endangered” on the IUCN Red List of Threatened Species. International trade in manta ray body parts, particularly gill plates used in traditional Chinese medicine, is driving the population decline, according to Armstrong.
Co-author Frazer McGregor demonstrates the satellite day. Photo credit: Amelia J. Armstrong and colleagues
“Unfortunately for manta rays, a slow rate of growth and few offspring means it can take a long time for populations to recover from disorders,” she said.
The researchers tagged 20 reef manta rays in 2016 and two more in 2019 in and around Ningaloo Reef, one of the world’s longest fringing reefs, where deep-sea headwaters and local currents form a hotspot for feeding activities. The satellite tags cannot use GPS while the animals are underwater. The devices therefore record depth, temperature and light values. Models then extrapolate the location based on this information.
The oldest photo in the photo database used in the study is from the early 2000s. Reef manta rays from birth share the same unique speckle patterns that scientists use to recognize individuals over time. The photos, including images collected from photos from local tourism companies and citizen scientists via social media, helped the Australian team identify more than 1,100 individual animals from approximately 5,000 sightings.
The two methods show different, complementary types of information.
“Satellite tags give us a glimpse into the secret life of these animals to understand where they often hang out outside of major tourist spots, and photographic identification helps us track visits over long periods of time,” said Armstrong.
The study notes that understanding the key areas where migratory species like the reef manta ray tend to congregate is critical to their future conservation. While the World Heritage Sites of Ningaloo and Shark Bay are protected, nearby coastal development and tourism create population pressures of their own, including animals injured by boat propellers and fishing gear.
“Further study of population size and evolution is an urgent research priority to ensure this manta ray population is resilient and resilient to future changes,” said Armstrong.
Reference: September 2, 2020, Limits of marine science.
DOI: 10.3389 / fmars.2020.00725
