Scientists find largest whale shark group
Scientists at the Smithsonian Institution say whale sharks can be found in large numbers and amass in groups of hundreds to feed in coastal waters.
The new study which involved both surface and aerial surveys has revealed the “Afuera” aggregation, the largest aggregation of whale sharks ever reported with up to 420 individuals off the coast of Mexico’s Yucatan Peninsula.
“Whale sharks are the largest species of fish in the world, yet they mostly feed on the smallest organisms in the ocean, such as zooplankton,” Artdaily quoted head of the Department of Nutrition Sciences and biologist at the Smithsonian Conservation Biology Institute Mike Maslanka as saying.
“Our research revealed that in this case, the hundreds of whale sharks had gathered to feed on dense patches of fish eggs,” he added.
Although whale sharks can be found in all tropical and sub-tropical regions of the ocean around the world, food sources determine much of their movement and location.
Researchers used fine nets to collect food samples inside and immediately outside the school of feeding whale sharks. They followed by conducting DNA barcoding analysis to examine the collected fish eggs and determine the species.
According to the study published in the scientific journal PLoS ONE, the eggs were found to be from little tunny (Euthynnus alletteratus), which belongs to the mackerel family.
“Having DNA barcoding is an incredibly valuable resource for this research,” said head of the Laboratories of Analytical Biology at the Smithsonian’s National Museum of Natural History Lee Weigt. “It not only allowed us to know what exactly this huge aggregation of whale sharks were feeding on, not readily done from only physical observations of eggs, but it also revealed a previously unknown spawning ground for little tunny.”
The team also examined a nearby, less dense aggregation, known as the Cabo Catoche, off the northern tip of the Yucatan Peninsula.
Their studies revealed that this group mainly fed on copepods (small crustaceans) and shrimp. Increased sightings at Afuera and decreased sightings at Cabo Catoche, which both had the same sex ratio, implies that the same animals were involved in both aggregations.
“With two significant whale shark aggregation areas and at the very least one active spawning ground for little tunny, the northeastern Yucatan marine region is a critical habitat that deserves more concerted conservation effort,” said Maslanka.
The International Union for Conservation of Nature and Natural Resources has listed the whale shark as “vulnerable”.
Source: presstv.ir
