This is the kingdom of huge predators and immense shoals of their prey; of microscopic plankton and gigantic pelagic filter feeders which feed on this organic “soup”. Sometimes these creatures, through choice or need, approach the islands further from the coast, following their prey or obeying the mysterious instinct of reproduction. With much patience and a little luck, it is possible to see species of great interest along the coast of Malaysia during spring, the courting and reproduction season which coincides with the plankton bloom and the increase in the availability of food.
One of the largest pelagic filter feeders living in this sea is the whale shark Rhincodon typus, the biggest fish in the world, absolutely harmless despite its ten metres of length.
Another is the manta Manta birostris, with its majestic “wing span” which can exceed six metres. These spectacular and extraordinarily elegant creatures, with their graceful and powerful movements will often allow divers to swim by their side if they are not pointlessly harassed. The much shyer but equally beautiful eagle rays Aetobatus narinari, boasting an exquisite white-spotted livery, are sometimes encountered in the open sea or along the coast where they search for food.
Oceanic sharks (and those in some way linked to the open water environment) which may be encountered occasionally when diving in Malaysian waters include the silky shark (Carcharhinus falciformis), the oceanic whitetip shark (Carcharhirius longimanus),; the pelagic thresher shark (Alopias pelagicus), characteristic of deep waters, the silvertip shark (Carcharhinus albimarginatus), generally found in small shoals of females on deep sandbars, the tiger shark (Galeocerdo cuvieri), more common in deep, turbid water, and several other species of requiem shark.
All of these are large and potentially dangerous to man, but it is in fact unusual to encounter them. However, it should be noted that these are solitary predators whose behaviour changes radically during the night, when their habitual daytime caution can give way to surprising aggressiveness. In the waters off Sipadan and Layang Layang the highly gregarious scalloped hammerhead Sphyma lewini can be seen in shoals of some tens to hundreds during spring.
These gatherings appear to be linked to reproduction rituals. Being extremely shy creatures, however, they generally avoid man, apparently scared by the noise of regulators. Along the coast (at the same time of the year, but sometimes year round) gather shoals of hundreds to thousands of smaller predators such as trevally (Caranx sexfasciatus), chevron barracuda (Sphyraena putnamiae), and pickhandle barracuda (Sphyraena jello).
These genera are represented in the seas by numerous species which are all fairly similar, and have a distinct predatory nature.
These gregarious fish can reach extremely high speeds when making their violent surprise attacks. The much larger and impressive dogtooth tuna (Gymnosarda unicolor) reaches a length of up to two metres and lives in shoals with a more open structure. These fish unexpectedly arrive from the open sea to explore the reefs further offshore and decimate the shoals of jacks found there: their lightning-fast raids are among the most impressive sights to be seen in these waters.
While pelagic sharks and rays are generally characterised by countershading or low visibility camouflage (livery with a bluish or dark grey back and a paler, or even white, belly which makes them difficult to see from either above or below), the bony fish of the open sea, which generally live in shoals, usually have a silvery, in some cases even chromium-plated look. The reflections from this livery probably helps to temporarily disorient both the predators and their potential prey.
Finally, many species of cetaceans are found in Malaysian waters, such as dolphins (Stenella and Tursiops), killer whales (Orcynus orca), sperm whales (Physetercatodon) and various species of finwhales. These are, however, very difficult for a diver to approach.