They are the largest fish species in the ocean, but the majestic gliding motion of the whale shark is, scientists argue, an astonishing feat of mathematics and energy conservation.
Sharks are known to "dive" frequently through the water column and many functions have been attributed to the behaviour, such as thermoregulation, search and reduction of the COT. Few studies, however, have been able to frame these in conjunction with theoretical optima and test predictions for differing movement structures.
For most animals, movement is crucial for survival, both for finding food and for evading predators. However, movement costs substantial amounts of energy and while this is true of land-based animals it is even more complex for birds and marine animals which travel in three dimensions. Unsurprisingly, this has a profound impact on their movement patterns.
In new research published today in the British Ecological Society's journal Functional Ecology, marine scientists reveal how these massive sharks use geometry to enhance their natural negative buoyancy and stay afloat.
"The key factor for animal movement is travel speed, which governs how much energy an animal uses, the distance it will travel and how often resources are encountered," said lead author Adrian Gleiss from Swansea University. "However, oceanic animals not only have to consider their travel speed but also how vertical movement will affect their energy expenditure, which changes the whole perspective."
The team's data revealed that whale sharks are able to glide without investing energy into movement when descending, but they had to beat their tails when they ascended. This occurs because sharks, unlike many fish, have negative buoyancy.
Also, the steeper the sharks ascended, the harder they had to beat their tail and the more energy they had to invest. The whale sharks displayed two broad movement modes, one consisting of shallow ascent angles, which minimize the energetic cost of moving in the horizontal while the second characteristic of steeper ascent angles, optimized the energetic cost of vertical movement.