Scientists use lasers to measure live whale sharks
Whale sharks are really, really big -- they are the largest fish in the sea -- this we know, but just how big and at what rate do they grow? Where in the world do they spend their time at each phase of their life? Those questions are harder to answer because of the whale sharks' large size and the many waters they occupy around the world.
A team of researchers has come up with a technology that is helping them to start answering some of those questions, and, yes, it involves lasers.
Simon Pierce and Chris Rohner from the Marine Megafauna Foundation along with other researchers have developed a technique called laser photogrammetry that allows them to project laser markings of a known length on the side of a whale shark when taking photos so that they can have a scale bar by which to measure the shark when they analyze the images.
This process also helps them to identify the sharks. Each whale shark has a distinctive pattern of white spots over their upper surfaces. "By taking photographs of each flank, we can reliably identify individual sharks over time. That means we can count how many sharks we see and track their movements and behaviours," said Rohner to Peer J, the journal where they published the results of this new measuring method.
The laser photogrammetry allows them to both measure and identify sharks at once, so that they can estimate size and track when and where the big sharks move throughout their life. This means identifying crucial feeding areas and how they move between them so that conservation efforts can be made.
The researchers are also adding their photos to the Global Whale Shark Photo-ID Library, which is already comprised of photos of 4,600 individual whale sharks that have been identified from over 45 countries, thanks in large part to citizen scientists who have contributed photos.
Whale sharks are estimated to grow up to 65 feet in length, but this new technique is giving scientists more specific information. For instance, the team has discovered that male whale sharks in the Indian Ocean reach maturity at over 9 meters in length, which is 2 meters longer than those in the Atlantic. That means there could be biological differences between the two populations.
They have also discovered that the growth rate is slower than expected by noticing that the technique wasn't capturing any definite differences in a 1 - 3 year period. The technology will give better results by using longer time frames between measurements and a new technique will need to be developed for tracking smaller changes, which will give scientists the chance to figure out an accurate growth rate.
The scientists are hoping to eventually fill in some big gaps in what we know about whale sharks. Their research has documented a lot of male sharks in the middle ranges of size, but there is still a lot of information missing about females in general, newborn sharks and mature sharks of the largest sizes.