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.

According to University of Washington geologist and tsunami expert Jody Bourgeois, the idea that chevrons – a type of large U- or V-shaped formations found along certain coasts – were caused by mega-tsunamis is pure nonsense.

The term chevron refers a special type of vast dunes shaped a bit like the stripes on soldier’s uniform. They can be anything from hundreds of meters to a kilometre in length and can be seen in places such as Egypt, the Bahamas, Madagascar, and Australia.

Some scientists have suggested that a possible explanation for these mysterious stripes is mega-tsunamis caused by asteroid or comet impact. According to this school of thought, the chevrons may be deposits left by gigantic tsunamis 4,800 to 5,000 years ago, tsunamis that might have been up to 10 times larger than the earthquake-caused Indian Ocean tsunami of December 2005. Due to the location of known chevrons, the Indian Ocean has been suggested as ground zero for the comet or asteroid impact.

Bourgeois, a professor of Earth and space sciences who has studied earthquakes and tsunamis in various parts of the world, does not agree. According her, the chevrons are not lined up the way you would expect from deposits caused by gigantic waves. Many of the chevrons on Madagascar are for instance parallel to the coastline, instead of perpendicular to the shore.

Models created by Bourgeois’ colleague Robert Weiss, assistant professor of geology at

Texas A&M University, show that deposits formed by gigantic tsunamis would point in the same direction as the waves were travelling when the reached land, which is mostly perpendicular to the shore.

“And if it really was from an impact, you should find evidence on the coast of Africa too, since it is so near,” Bourgeois explains.

The computer model generated actual conditions for a tsunami which made it possible to use the model to explore the effects of an asteroid or comet hitting the part of the Indian Ocean suggested by mega-tsunami chevron proponents. According to the model, the gigantic waves would approach land at a 90-degree orientation to the chevron deposits.

“The model shows such a tsunami could not have created these chevrons, unless you have some unimaginable process at work,” Bourgeois says.

Bourgeois and Weiss have used satellite images from Google Earth to get close-up looks at chevrons in different locations. Chevron are most common in coastal regions but you can find quite a lot of them in semiarid inland areas as well.

Bourgeois and Weiss wrap up their paper, which can be found in the May issue of the journal Geology, by stating that “the extraordinary claim of ‘chevron’ genesis by megatsunamis cannot withstand simple but rigorous testing. […] There are the same forms in the Palouse in eastern Washington state, and those are clearly not from a tsunami.”