Behavior

The Voyages of The Largest Fish in the World

Gallimore, C. G., Walton, C., Nugent, R., Fradkin, M., Poppell, L., Schreiber, C., Coco, C., Grober, M., Carlson, B., Dove, A. D. M., & Black, M. P. (2024). A longitudinal behavioral analysis of aquarium whale sharks (Rhincodon typus): Insights into anticipatory cues, individual variation, and social interaction. Frontiers in Marine Science, 11, 1418002. https://doi.org/10.3389/fmars.2024.1418002

Male whale shark at Georgia Aquarium Image credits: Zac Wolf via Wikimedia Commons 

The Largest Fish in the World

The whale shark, scientific name Rhincodon typus, is the largest living fish species, making it rare to find in aquaria. 

In the wild, the whale shark is vulnerable to a number of human threats, such as boat strikes and fishing, and is therefore classified as endangered on the IUCN Red List.

Whale sharks are filter feeders, meaning they eat by straining food from the water as they pass through it. They also eat vertically, meaning that they turn into a vertical position and attack their prey from below, most commonly capturing crab and fish larvae, mollusks, and other crustaceans. 

Only 10 aquaria in the world have ever hosted whale sharks. The Georgia Aquarium is home to the Ocean Voyager exhibit, which houses multiple whale sharks and offers visitors the opportunity to swim with them. In this study, researchers use the Georgia Aquarium’s 6.3 million gallon whale shark tank to observe the whale sharks’ behavioral patterns, assessing metrics such as depth, swim speed, lead-follow interactions, and diver presence in order to better understand their behavior and social structure and compare their results to wild whale shark behavior.

The Sharks in the Unbelievable Ocean Voyager Exhibit

Researchers conducted examinations of the whale sharks in the Ocean Voyager tank every six months, in which they measured the weight of each animal and the length of various body parts and fins.

Whale sharks were fed twice a day with krill, silverside fish, squid, and vitamin supplements. 

Over a four year period (2008-2012), volunteers and interns logged over thirty thousand observations of metrics such as depth, swimming speed/direction, and lead-follow interaction (social activity in which one whale shark leads or follows another). Simultaneous recordings taken by different observers were compared to ensure that their notes were consistent.

Swimming speed was measured based on the amount of time the shark took to pass a number of four-foot panels. Swimming direction was classified as clockwise or counter-clockwise. Lead-follow interactions were categorized depending on the distance between the two sharks involved, their positioning, and whether they were leading or following.

The Voyages of the Whale Sharks

Each of the four whale sharks exhibited their own unique behavior patterns, with different swimming speed averages. One shark strongly preferred clockwise swimming, two sharks mildly preferred clockwise swimming, and one swam in both directions practically equally. 

All four sharks tended to increase their speed approximately 30 minutes before feeding times. They also all frequented the top depths of the tank far more than the bottom depths. Interestingly, however, each individual differed greatly from the others in their depth frequency. 

In terms of lead-follow interactions, one shark led more than it followed. Three of the sharks showed patterns in their interactions, while one shark’s lead-follow patterns did not differ from random, suggesting that he may not have had significant interactions or relationships with the others. 

Finally, the researchers found that whale shark swimming speeds increased when diving visitors were not in the tank. 

Greater Cleveland Aquarium 01-22-2015 – Shark Tank Diver 5. Image credits: David Ellis via Flickr Creative Commons 

How Does the Ocean Voyager Represent the Real Ocean?

While this study provides novel insights into the behavioral patterns of whale sharks, it’s important to note that an aquarium setting can be very different from the wild. An additional limitation in this study is that observations were only made in the day time. 

Still, the swim speed of the whale sharks in this study was consistent with the global average. Wild whale sharks, like the sharks in this study, are also found to remain near the surface of the water around 50% of the time. 

The increase in swim speeds of whale sharks prior to feeding times is likely a result of classical conditioning (when a stimulus leads to a learned response), since the feeding of other members of the Ocean Voyager exhibit were fed at this time, and the sharks therefore knew to anticipate their food coming. This type of learning behavior, along with a powerful sense of smell, has been observed in a number of shark species, increasing the likelihood of such a connection between swimming speed and feeding times. 

Whale shark encounter off Caribbean coast of Panama. Image credits: NOAA Photo Library via Flickr Creative Commons 

So What?

Better understanding of the whale shark’s behavioral patterns is crucial for informing management decisions for the endangered species. Additionally, the insight into their social interactions provided by this study can guide decisions regarding their humane treatment in aquaria globally. In particular, the conclusion that the presence of divers in the tank only influences swim speed, which is suspected to decrease in an avoidance attempt by the sharks, may cause marine biologists to reconsider the decision to allow divers into the tank at all.

In general, learning more about a species can only help scientists and policymakers make smart conservation decisions and educate the public about how their interactions with wildlife can affect the ecosystem.

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