According to the International Union for Conservation of Nature, whale sharks are now an endangered species – having suffered a population decline of more than 50% in the past three generations.
The whale shark is currently only two classifications from being declared official extinct, and while some conservation efforts are in place, there's still a long way to go to protect these gentle underwater giants.
To help their survival, an international team of researchers – led by marine scientists at King Abdullah University for Science and Technology (KAUST) in Saudi Arabia and researchers from Woods Hole Oceanographic Institution (WHOI) in the USA – has carried out an extensive study of whale shark movement and residency using a combination of three scientific techniques: visual census, acoustic monitoring and satellite telemetry.
The report, recently published in the peer-reviewed scientific journal PLOS ONE, tracked long-term whale shark movement patterns near the Shib Habil reef – a known whale shark hotspot in the Red Sea.
The team monitored 84 different sharks over the six years, and say that the results shed light on whale shark behaviours, which could help to inform conservation efforts.
"The study takes years of passive acoustic monitoring data and combines it with previously published visual census and satellite telemetry data from the same individual sharks,” explains Dr. Michael Berumen, director of the Red Sea Research Center and Professor of Marine Science at KAUST.
“The combined dataset is used to characterize the aggregation's seasonality, spatial distribution, and patterns of dispersal.”
The research team found the aggregation to be highly seasonal, with sharks being most abundant in April and May, and that many of the sharks returned to the hot spot regularly year after year.
The study also shows roughly equal numbers of male and female sharks using the site – characteristics that indicate the site may be vital for the wider Indian Ocean population of the species.
"Using the combined dataset, we can show conclusively that the aggregation meets all of the criteria of a shark nursery,” says KAUST graduate Dr. Jesse Cochran, lead author of the study.
“This is particularly relevant given that Shib Habil is the only site in the Indian Ocean to regularly attract large numbers of juvenile females.
“Growing late-stage adolescents of both sexes into full adulthood is critical for sustaining a species, and management of critical habitats like Shib Habil and other aggregations will be vital for future whale shark conservation."
Whale shark numbers have decreased due to a number of factors, including targeted fishing, bycatch, vessel strikes, and marine pollution.
“The new data collected will enable marine scientists to describe in great detail the residency behaviour, seasonal philopatry, and spatial distribution of aggregating sharks, and allow them to investigate the apparent sexual integration found at this particular site,” says Cochran.