Whale Shark Secret Deep Water Strategies

Whale Shark and Diver Australian Institute of Marine Science AIMS 

A new study revealed the secrets of Whale Sharks as they take to the depths. The study focused on strategies which Whale Sharks take to reach the lower layers and revealed how they withstand colder temperatures and stay warm. The study assured that through these strategies Whale Sharks save up to 30% of energy.  From a conservation perspective understanding the dynamics of Whale Sharks -specie listed as Vulnerable serves in the drafting of marine policies of conservation. Protected marine parks must englobe the entire dynamic area of the specie is aims to protect. 

The new study of researchers of the Australian Institute of Marine Science AIMS assures to have broken into the secrets of the depths of Whales Sharks. 

The study found that Whale Sharks spend almost 60% of their time at the surface and the rest in the depths filter feeding. The remaining 40% of the time Whale Sharks take to deep waters set as much as 500 meters where temperatures are registered to be 20 Degrees colder than surface waters. 

Australian researchers found that Whale Sharks spent part of the time (16–41%) within 5 meters of the sea surface. The rest of the time they performed “dives” to up to 500 meters. The sharks tended to swim away from the reef during the morning and afternoon and toward the reef in the evening.

The Paper titled "Swimming strategy and body plan of the world's largest fish: implications for foraging efficiency and thermoregulation" was published at the Journal of Frontiers of Marine Science on September 15. 

Still today Whale Sharks conceal many secrets. Numerous aspects of the life of these illustrious ocean giants are hidden and concealed from mankind. Whale Sharks are known by expert divers as one of the most elusive creatures. Even in locations which are known to be their home they are sometimes hard to find. This “shy” behaviour can be considered an evolutive adaptation intentionally taken on to avoid risks. 

Amazingly there is no human record at all of any Whale Shark mating nor mating or pupping. The capture of a female in July 1996 that was pregnant with 300 pups indicated Whale Sharks are ovoviviparous. 

Today Whale Sharks are listed by the IUCN as “Vulnerable” but even up to 1996 the IUCN recognized to not have enough data to conduct a specie listing estimation. “There is currently no robust estimate of the global whale shark population,” IUCN still today recognizes. 

The largest populations are registered in Yucatan Mexico and Australia as well as Caribbean Islands, South Africa, Galapagos, Seychelles, Malaysia, Asia, India and several other countries. 

Whales Sharks -like other Cetaceans have followed the convergent road of evolution which reaches filter feeding adaptations. Fossils show that filter feeding evolution draws back to toothed prey hunters. Ancient marine animals which used to hunt for prey slowly but steadily adapted to filter feed to capture more energy by taking in larger amounts of smaller prey.  

"Using a combination of biologging and satellite tagging, we show that whale sharks use four strategies to save energy and improve foraging (feeding) efficiency: 1 fixed, low power swimming,  2 constant low speed swimming, 3 gliding, and 4 asymmetrical diving. These strategies increase foraging efficiency by 22–32% relative to swimming horizontally and resolve the energy-budget paradox of whale sharks," Australian Researchers stated. Similar energy-conservation tactic have been documented in marine mammals and birds 

To answer how Whale Sharks cope with cold deep ocean waters researchers signaled to a self-regulating heat system which is directly linked to the size of the animal. 

Texas A&M Today interviewed Dr. Randall Davis Marine Biologist at Texas A&M of Galveston University who collaborated and worked side by side with Australian researchers of AIMS. With over 38 years of experience in marine life Dr. Davis worked with Dr. Mark Meekan of the Australian Institute of Marine Science AIMS and Dr. Lee Fuiman of the University of Texas Marine Science Institute Dr. Davis stated that the new study helps in the understanding of “how Whale Sharks feed and how they interact with the environment”. Dr. Davis added that the information could also aid in the awareness of the specie and the design of environmental strategies of conservation and management of the “Vulnerable” marine species. 

“Dr. Davis and the Team attached small video and data recorders to two whale sharks near the Ningaloo Reef off the Western Australia coast, the second largest coral reef in the world behind only the Great Barrier Reef,” Texas A&M reported. When drafting policies of conservation experts require understanding of the environment, movement and dynamics of the specie. Conservation plans need to protect the entire area of movement of a specie, if they go deep or go horizontal or vertical -protected waters boundaries must adapt to the dynamic.

  

The paper assures that depths registered for Whale Sharks immersion range from 250 to 600 meters during the day time. Experts call for more studies to verify peak depths of the specie. Water temperature at these depths registered a drop of 20 Degrees Celsius compared to surface temperature. Whale Sharks using the negative buoyancy anatomy take on long, slow and gliding descents. 

One would assume that taking this drop, making use of energy required for the deep swim down plunge and reaching colder waters would result in a dramatic loss of body temperature affecting the normal functioning of the anatomy of Whale Sharks, but the new study says Whale Sharks are naturally adapted to respond to this scenario. 

“We suggest that Whale Sharks may overcome this problem through their large size and a specialized body plan that isolates highly vascularized red muscle on the dorsal surface, allowing heat to be retained near the center of the body within a massive core of white muscle. This could allow a warm-adapted species to maintain enhanced function of organs and sensory systems while exploiting food resources in deep, cool water," researchers stated. 

Dr Mark Meekan, Principal Research Scientist at the Australian Institute of Marine Science AIMS, lead author of the study explained findings to the media.

“Whale sharks are negatively buoyant meaning they naturally sink. When feeding, they allow themselves to glide gently down to the krill in deep water, which means they don’t expend much energy in swimming".

“We estimate that this behaviour, followed by a steep return to the warmer surface waters, allows them to conserve up to 30% of the energy they would use if just swimming horizontally".

“These ocean giants have another trick up their sleeve”, says Dr Meekan. “Their critical organs are surrounded by huge blocks of white muscle that appear to insulate the whale shark, so that it stays warmer for longer, even during these long descents to much cooler depths”.

Dr. Davis of Texas A&M could not avoid linking the status of the specie, the way it filter feeds on key elements of oceanic food webs and unsustainable coastal fisheries impact. 

“The species is considered vulnerable by the International Union for the Conservation of Nature IUCN, but fishermen in some countries, especially around Southeast Asia and Indonesia, continue to hunt them,” Dr. Davis told reporters back home.

“Our research and that of other scientists may provide new information on their natural history that will assist with their conservation and draw public attention to protect these fascinating sharks from fishing,” Dr. Davis ended it.