February 7, 2011

Whale Sharks Larger Than Thought

A new study has found that whale sharks could be even bigger than previously recorded.

Scientists working in Mozambique have developed a new method of measurement using a camera mounted with lasers.

Previous estimates put the world's largest fish at up to 60 feet in length, but accurate details of the fish have been difficult to obtain in the past.

Researchers believe regular measurements will reveal more about the lifecycles of the whale sharks.

The scientists' findings are published in the Journal of Fish Biology.

"Our paper is the first to publish accurate measurements for whale sharks in the field," PhD candidate Christoph Rohner told BBC.

"Other researchers have previously tried to measure the sharks with a tape measure, or by visually estimating size, which is obviously difficult to do accurately," he explains.

Previous size records were based on the estimates measured from photographs.

Researchers claim they have dramatically improved the precision of this method with the addition of two laser pointers.

By positioning lasers 20 inches apart on either side of the camera, the distance between the projected points provides a fixed scale so photographs can be analyzed with greater accuracy.

"The laser system will allow us to reliably obtain accurate measurements from free-swimming sharks, so we may well find out that the world's largest fish is even larger than presently recorded," Rohner told BBC.

The team said their new method has already seen the recorded size of some individuals increased by up to 20 inches.

Researchers say the photographs could reveal more about the enigmatic species, in addition to recording the length of whale sharks.

"Whale sharks can be individually-identified using the distinctive pattern of spots on their flanks. We project laser spots onto this region, allowing us to obtain both the identity and length of the shark with a single photograph," says Rohner.

"At present we have no clear idea about how long whale sharks live, but it may be for over one hundred years. By repeatedly measuring the same individuals over time, we hope to be able to eventually find out how old a twenty meter shark might be," he adds.

Conservationists are concerned the giant fish are under threat from commercial fishing, including harpoon fisheries and incidental capture.

The scientists say that by understanding whale sharks' lifecycles, they can more accurately predict how populations are impacted by these activities.

Rohner emphasizes the importance of measuring individuals over time to learn more about their development and confirm their growth rate.

"Whale sharks are globally threatened, and this kind of basic but hard to get information is vital for effectively conserving the species," he told BBC.

The team says that 19 percent of the global population of whale sharks has been recorded off the coast of Mozambique.

Satellite tagging experiments have shown the fish migrating extremely long distances of up to 8,000 miles.

Researchers on the team were from the University of Queensland, the Marine Megafauna Foundation and CSIRO Marine and Atmospheric Research


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