The disco balls of the sea, bait balls (or baitballs), are densely packed groups of small fish formed either voluntarily or as a means of survival. South Africa's annual Sardine Run - often featured in Attenborough-narrated nature documentaries - is perhaps the planet's most famous bait ball, but with big fish preying on small fish worldwide, you never know when one will form. These shimmering orbs offer a unique chance to see the cat-and-mouse interactions between predator and prey, as well as the different attack strategies employed by various raiders. Here's our round-up of the top ten bait ball facts for the next time you happen upon one twinkling out in the blue...

Bait ball with dolphins

1. Bait Balls vs. Dolphins & Killer Whales

Often touted as being the most intelligent of marine creatures, dolphins have also been observed employing different tactics to attack bait balls. Many species of dolphin have been seen corralling bait balls into shallower water to force them closer together. Some dolphin species also use bubbles to either force the mass of fish closer together or to separate individuals from the rest of the school.

Killer whales (or orcas), members of the dolphin family, also use bubbles to push the group of baitfish closer together. Once the bait ball is dense enough, the killer whales will then slap the ball with their large, powerful fluke to stun the small fish, a tactic known as carousel feeding.

2. Bait Balls vs. Silver Flashes

In general, more colourful reef fish - angelfish, butterflyfish and surgeonfish - stick close to the nooks and crannies of a reef, while a glance into the blue often reveals larger, silvery fish, like barracuda, jacks and tuna. It's a fish-eat-fish world, and true to form, the silvery fish are always on the lookout for an unsuspecting fish to stray from the reef's protection.

On the occasions when a bait ball forms a little way off the reef, the silvery fish are the first to attack. Look towards the bait ball and you will see flashes of silver streaking into the densely packed ball of fish, plucking off the stragglers from the pack.

Bait ball and shark

3. Bait Balls vs. Sharks

Sharks also have a penchant for a bait ball buffet, and different species of sharks will employ different tactics to ensure they get their fill. A trip to the Visayas in the Philippines is one of the best ways to maximise your chances of seeing a bait ball under attack.

Specifically, Moalboal, on the western edge of Cebu, sees annual sardine aggregations where lucky divers can see thresher sharks coming into feed. The thresher shark uses its long, scythe-like tail to stun the sardines by swimming towards the bait ball and then seemingly slamming on the brakes, launching its tail over its head into the mass of sardines. Some sardines are struck and stunned while others are stunned by the pressure waves from the tail's motion. Trust us, it's an epic sight!

Silky sharks are also known to enjoy a bait ball feast and are often seen working together to herd the school into a tighter ball. By driving the ball towards the surface, the fish are forced to get closer and closer, making it easier for the sharks to feed.

4. Bait Balls vs. Swordfish

In some locations, swordfish use their impressive speed (over 60 miles per hour!) to attack bait balls is a smash-and-grab method of hunting. These speed merchants will swim straight into the bait ball, often swinging their bill to stun prey as they pass through. Once clear, the swordfish will do a sharp 180-degree turn and return to pick off the stunned baitfish.

Bait ball and whale

5. Bait Balls vs. Whales

If you're lucky enough to see a bait ball under attack by whales, you may be able to discern a couple of different attack strategies: lunge feeding and bubble-net feeding. Lunge feeding is employed by some baleen whales, including the blue whale. This technique involves the whale swimming upwards from below the bait ball, opening its massive jaws as it nears its target. The sudden opening of the mouth leads to a delicious soup of water and fish pouring into the whale's mouth.

Bubble-net feeding has been seen in groups of humpback whales working together. A few whales will swim below the bait ball in ever-decreasing circles, blowing bubbles as they do so. As the bubbles rise, they create a bubble wall that pushes the fish closer and closer together, and once the bait ball is tight enough, the humpbacks start to lunge feed until the ball is no more.

6. How Do Bait Balls Form?

A school of unsuspecting fish hanging out in the blue is like a red rag to a bull for a hungry marine predator. Away from the protection of the reef, the school becomes vulnerable to attack, and if a peckish predator starts lurking with intent, the school will begin to close ranks. While the ever-tightening ball affords some protection to the individuals, it also becomes more inviting for an attack. And invariably, an attack will come, with different predators opting for different strategies...

Birds diving on bait ball

7. Bait Balls vs. Birds

For the small fish in the bait ball, there's little respite. They're attacked from below, the flanks and even above, with various seabirds dive bombing from the sky to take advantage of the buffet-style meal opportunity.

Gannets and shearwaters are among the aerial assailants, often plummeting from 100 feet above in streamlined form to penetrate the surface and grab unsuspecting baitfish from the ball. Gannets have been seen to dive at speeds of around 50 miles per hour and reaching depths as impressive as 30 metres!

8. Where to Witness Bait Balls: Ulong Channel, Palau

Many people venture to Palau, a tropical island archipelago in the Pacific Ocean, to dive the legendary Blue Corner dive site. As exhilarating and impressive as Blue Corner is, many journeys home are spent remembering the epic dives at Ulong Channel. The dive starts at the opening to the channel, where grey reef sharks and manta rays can be seen surfing the current. After admiring the show, divers then drift down the channel past resting white tip reef sharks and healthy coral formations. At the end of the channel, the dive site opens into a big sand bowl, where divers are often rewarded with a bait ball being attacked by hungry jacks, black tips and grey reefs, the grand finale to an epic drift dive!

Diver with bait ball

9. Where to Witness Bait Balls: Moalboal, The Philippines

One of the problems with bait balls is their unpredictability. You never know when one will form, but Moalboal in the Philippines is one of the more predictable places to try your luck. While South Africa's Sardine Run only occurs for a few weeks between May and July, when conditions are just right, Moalboal's sardines are present all year round. And with Malapascua, the world's best thresher shark diving location, just around the corner, there's no shortage of predators on hand either...

10. How to Dive a Bait Ball

Being underwater in the presence of a frenzied attack on a bait ball can be as overwhelming as it can be impressive. With large predatory fish charging in and out at high speed, the best tactic is to simply hang back, relax, and observe. Most of the time, bait balls occur away from visual references in the open blue. This means it's important to keep a close eye on your depth and air consumption. If you feel the need to equalise, check your depth! Also, keep a close eye on your buddy and don't get too close, that way you can ensure you enjoy the epic show safely.

Feeling inspired to dive by these bait ball facts? Get in touch with our diving experts to plan your next diving adventure...

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