Basking sharks have surprised researchers by leaving the cold waters of the north Atlantic during fall and head down to Bahamas and the Caribbean.

“While commonly sighted in surface waters during summer and autumn months, the disappearance of basking sharks during winter has been a great source of debate ever since an article in 1954 suggested that they hibernate on the ocean floor during this time,” said Gregory Skomal of Massachusetts Marine Fisheries. “Some 50 years later, we have helped to solve the mystery while completely re-defining the known distribution of this species.”

Basking Shark

Basking sharks are notoriously difficult to study for several reasons. They feed exclusively on plankton which means you can’t catch them using traditional rod-and-reel methods and they disappear down to deep waters for extended periods of time. During the part of the year when they do stay close to the surface, they are only found in cool waters teaming with plankton where the underwater visibility is close to zilch.

This situation has led to a lot of speculation about their life style and where they actually spend the winters. Despite being the second largest fish in the world, the basking shark is remarkably elusive and mysterious.

What finally solved the puzzle was the aid of new satellite-based tagging technology and a novel geolocation system which made it possible to track the basking whales as they commenced their annual migration. Data sent out from the tags unveiled that basking sharks migrates to warm tropical waters in fall. Their migrations have been able to go undetected until know since the sharks travel at depths of 200 to 1,000 meters and sometimes remain at those depths for weeks or even months at a time.

Skomal said he and his fellow researchers were absolutely surprised when they first received a signal from the tagged sharks coming from the tropical waters of the western Atlantic, since virtually everyone assumed basking sharks to be cool-water dwellers found in temperate regions only.

This new breakthrough show just how little we still know about even the largest marine animals inhabiting the world’s oceans. The basking shark can reach a length of 10 metres and weigh up to seven metric tons, yet it has managed to spend every summer in the Caribbean without anyone noticing it.

You can find more information in the report published on May 7 in Current Biology.

A new species of giant clam has been encountered by researchers in the Red Sea and given the name Tridacna costata. The new species is fairly similar to two other well-known species of Red Sea clams and it was therefore first suspect to be a hybrid, but genetic analysis has now deemed it a separate species. Further research carried out in the Red Sea also supports this; there are significant differences in behaviour between the two other species and the newly discovered clam. The two previously known clams spawn during a long period in summer while the new clam spawns during a short period in spring.

Fossil evidence uncovered by researchers has now unveiled something even more interesting; Tridacna costata might be one of the earliest examples of marine overexploitation by humans. Fossil records suggest that the Red Sea Tridacna costata population began do decline rapidly roughly 125,000 years ago. This is the part of our early history when scientists believe modern humans to have first begun to migrate out of Africa. Before this point in history, Tridacna costata accounted for over 80 percent of giant clams in the Red Sea – at least according to current fossil studies. Tridacna costata is a two feet long clam and it is not unreasonable to suspect that it would have been a splendid catch for early humans in search of food. Today, the species is believed to constitute less than one percent of giant clams, but this figure can of course change as the Red Sea becomes even more thoroughly explored.

Tridacna costata is the first new living species of giant clam found in two decades and was accidently discovered by scientists engaged in a Tridacna maxima breeding project. Tridacna maxima, another giant clam, is a much sought after clam in the aquarium trade.

If you want to find out more, the researchers behind the finding have posted their article online in the journal Current Biology on August 28.