In Thailand, you can discover a diverse range of marine life and stunning underwater scenery but diving with a whaleshark is definitely a top dream for many divers. In Koh Tao, there are prime spots where whalesharks are seen relatively often. Although sightings aren’t guaranteed, encountering one is a rare and thrilling experience.
Distinguishing Features
The whaleshark (Rhincodon typus) is the largest fish in the world, typically ranging from 4 to 12 meters long, though some can exceed this length. Despite their size, they are gentle giants, feeding primarily on plankton and small fish by filtering them from the water. Their underbelly is white, while the rest of their body is a blend of grey and blue covered in unique patterns of white spots and stripes, much like a fingerprint, making each one distinct! Whalesharks have a flattened head with a blunt snout and short, whisker-like barbels on their nostrils that help them sense food and an immense mouth. Their small eyes are protected by hard, tooth-like scales called dermal denticles, which also reduce drag.
Feeding and Diet
The whaleshark is one of three big filter-feeding sharks, along with the megamouth shark and the basking shark. It mostly feeds near the ocean surface. Its large mouth is perfect for filter feeding and has over 300 rows of tiny, pointed teeth that don’t actually help with feeding. Instead, as it swims with its mouth open, seawater flows in and passes through its gill slits, which act like a sieve to catch plankton and small sea creatures while letting the water flow out. Sometimes, it feeds with its mouth open and its tail down, bobbing up and down to take in water and food. It eats a mix of zooplankton (like shrimp and small crustaceans), phytoplankton (tiny marine plants), and small fish and mollusks (like sardines, squid, and small tuna).
Whalesharks play a vital role in their environment by keeping plankton and algae levels in check. Too much plankton or algae can reduce sunlight and oxygen in the water, upsetting the ecosystem. Additionally, smaller fish benefit from whale sharks by feeding on the parasites on their skin and staying close to avoid predators.
Reproduction
While the reproductive biology of whalesharks is still not fully understood, it is known they are ovoviviparous, meaning the females produce eggs that hatch inside her body and give birth to live young that are already fully formed. The smallest whale sharks observed in the wild are around 55 cm long, which is likely their size at birth. Each litter usually has about 16 young, but some females have been found with up to 300 embryos.
Whale sharks are thought to live between 60 and 100 years, though exact details are still being studied.
We don't know much about whalesharks' lives because they’re challenging to track and study, both alive and after death. Unlike animals with bones, whalesharks have skeletons made of cartilage, similar to human noses, which doesn’t fossilize well. This makes it difficult to learn about their mating rituals, lifespan, or social behavior.
Interactions with humans
A whaleshark, despite being part of the shark family and often mistaken for a whale, is totally chill and poses no danger to humans. These gentle giants might come over and check you out if you're in the water, but they're just curious, not threatening. They’re all about filtering tiny plankton and small fish through their huge mouths, not hunting or causing trouble. Their gentle nature and slow-moving habits make encounters with them a peaceful and awe-inspiring experience.
Predators
Adult whalesharks have no known natural predators, but younger ones can be preyed upon by blue marlin, blue sharks, white sharks, tiger sharks, and orcas. The greatest threat to these endangered giants comes from humans, who hunt them illegally for food and accidentally harm them with large shipping vessels. Whale sharks are listed as endangered on the IUCN Red List, and their populations are decreasing due to threats like boat collisions, bycatch, fishing, finning and climate change.
Where to Find Whalesharks on Koh Tao
Koh Tao, famed for Whaleshark sightings, provides surprises all year round but the prime period, often dubbed "Whaleshark season" by the local diving industry, is from March to June.
Key offshore dive sites are known for these awe-inspiring encounters:
But that's not all! Whalesharks are also spotted at shallower sites like:
