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The Cold Green Tongue And The Twang Of Death

Text and photography by Doug Perrine

 

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Common Dolphins Preying on Sardines
Long-beaked Common Dolphins, Delphinus capensis, preying on a baitball of Sardines, Sardinops sagax, South Africa, Indian Ocean
Image #: 008791

Transmitted through the dense medium of seawater, the syncopated percussion is both deafening and terrifying, like a bombardment of artillery. It penetrates the body and seems to come from all directions at once. The noise is exactly the sound that I imagine would be produced by plucking a very taut metal bass guitar string as long and as thick as a telephone pole – the loudest, deepest twang you have ever heard. For the rapidly diminishing number of small silvery fish in front of me, it is the twang of death.

The sound is generated by the impact of missiles striking the water at various angles, revealing their trajectories with “vapor trails” of small bubbles as they streak through the swirling shoal of fish. The projectiles contact the water at upwards of 100 km/ hr if published estimates can be believed. Only when they start to rise more slowly back toward the surface do they reveal themselves as Cape gannets, seabirds of the family Sulidae, or “boobies.” Their handsome yellow-capped heads carry the same bemused expression that may have prompted Portuguese sailors to label their tropical cousins as “bobos” or clowns.

When a shoal of fish is spotted, however, the goofy-looking birds take on a more menacing demeanor, circling above their prey like an angry swarm of bees. Suddenly the cloud bursts and gannets begin to rain into the water. Their elegant black-tipped white wings are swept back into a W shape, like a supersonic fighter plane. Only in the last fraction of a second are the wings folded flat against the body, transforming the plane into a guided missile. The gannets’ necks and brain cases are cushioned against the impact by special air sacs. We found one floating dead with a broken neck, perhaps the result of an unfortunate collision with another bird in the mayhem.

Some of the gannets strike the water at a straight downward angle, plunging to depths of 10m or more, while others switch to a more oblique approach just before entry, sometimes attaining a nearly horizontal underwater trajectory, after gaining maximum entry velocity from a vertical fall. Underwater videos reveal that the gannets do not strike their targets directly upon entry, but rather pursue them at high speed, using the momentum gained from their aerial free-fall, but changing course as necessary, and sometimes seizing the prey with a sudden sideways snap. On occasion they grab a fish on the way back up from a dive.

As long as the fish remain within the upper 10m of the water column, the bombardment continues. Why do the fish not merely descend below the effective range of the torpedoes falling from the sky? The answer is telegraphed by a sudden explosion of the shoal outwards and upwards, flashing sunlight in all directions as a pod of long-beaked common dolphins plows through at warp speed. Some of the fish actually fly a few cm into the air, vainly attempting to escape the sea surface barrier that the dolphins have trapped them against. It is the dolphins that have forced the fish up to the surface in the first place, separating them from a larger shoal by blowing a ring of air bubbles around them, and using this curtain of fear to herd them upwards where they can be feasted on more effectively.

Death comes from all sides as other players move in to take advantage of the dolphins’ effective cooperative foraging strategy. Copper sharks (also known as bronze whalers) patrol the lower and outer boundaries, making occasional forays through the center of the bait ball. They are sometimes joined by other species: dusky, Zambezi (bull), ragged tooth (sand tiger), and blacktip sharks; and more rarely a great white, great hammerhead, smooth hammerhead, or tiger shark.

Above the shoal, an African fur seal lazes on the surface, making an occasional downward foray through the school of fish. Each fish instinctively realizes that its only chance of survival is to lose its individual identity and become a seamless part of a super-organism. The school morphs constantly, opening up internal passageways to allow the transit of a shark or seal, continuously rearranging components, and reflecting light in dazzling patterns, like a mirror ball in a 1980’s discotheque. Each fish’s chances of survival are directly proportionate to the size of the school, and this school is shrinking rapidly as the little fish continue their dance of death with the packs of predators that surround them on all sides.

Lurking below, unseen in the darkness of the depths, the Great Death listens and watches for its opportunity. It picks its moment, and ten meters and 40 tons of hungry hot-blooded predator comes hurtling upwards through the silvery shoal. Its mouth and throat expand to many times their normal size, engulfing hundreds of fish as nearly one sixth of the shoal vanishes down its gullet in a single pass. The hapless sardines are forced up against a bristly wall of baleen as hundreds of liters of sea water are expelled from the mouth of the Bryde’s (rhymes with “Buddha’s”) whale, then pushed down into its stomach to be digested alive.

Some of the sardines escape the whale’s charge by hurtling themselves into the air, but their reprieve is short-lived. Once the giant has passed through, the smaller predators return to their task, picking off the survivors one at a time. As the ball of fish becomes ever smaller, the position of each of its members becomes more precarious. With fewer members, the ability of the troupe to dazzle and confuse its tormentors is continually diminished. As the numbers of comrades surrounding it falls, the survival prospects of each individual drop geometrically.

About an hour after it was first forced to the surface, the baitball is inexorably reduced to the last fish. The dolphins, sharks, seals, whales, and gannets rush off to attack another target, leaving only a slow rain of sparkling fish scales drifting into the deep, like handfuls of glitter thrown at a confetti parade, where only moments before an entire miniature ecosystem had been in the throes of the struggle between life and death. On the surface, an oily sheen, shimmering with ephemeral colors, and a faint but pungent odor wafting away on the wind provide the only evidence of the massacre that has just concluded.

Forty fathoms down, however, a might black river flows along the bottom. The baitballs brought to the surface by the enterprising dolphins, and devoured by them and their eager allies, are but small bites taken out of the great army that moves tenaciously forward at an average speed of ---two to five kph. The sardines, or “pilchards” as they are also known, are confined by a narrow tolerance of seawater temperature, being found almost exclusively in water between 14 to 20 degrees C, with 17 degrees as the preferred temperature. During the southern summer, this keeps them in the cooler waters around the southern tip of the African continent. The cold Benguela current, flowing northward up the west coast of South Africa, allows sardines to thrive as far north as Namibia.

On the east coast, however, the opposite situation prevails. A river within the sea, the Mozambique, or Agulhas, Current sweeps warm, clear, blue water from the tropical regions of the Indian Ocean southward along the African coast at an average speed of over 1m per second (3.6 km/ hr or about 2 knots) at its core. This mighty river, up to 100 km wide, meanders along the continental slope, bringing water temperatures of 20 degrees and above well into the temperate zone, and making these waters inhospitable for sardines.

As winter approaches, the underlying waters begin to cool, allowing the sardines to expand their range northward along the east coast from the Cape region into the Transkei and Kwazulu-Natal provinces during May-July. An intermittent counter-current often pushes a tongue of cold, green water northward along the coast at this time, inshore of the warm blue waters of the Mozambique. This cold tongue allows the sardines to travel in shallow water, where plankton concentrations are higher, and to access pockets of upwelling, where current eddies have brought up nutrient-rich water from the depths, stimulating blooms of the tiny plants and animals upon which the filter-feeding sardines depend. Sardines feed upon a variety of plankton, fish eggs, and larvae, each of which typically contains a tiny droplet of low density lipid. It is the sardine’s vocation to harvest thousands upon thousands of these minute droplets and aggregate them into a few ounces of fish oil – the most concentrated and healthiest food source on the planet.

The counter-current can also become a corridor of death for the sardines. Their high oil content means that sardines provide more energy per gram than almost any other fish in the sea. Their bodies are swimming bundles of energy-rich bio-fuel sought after by all the animals at the top of the food web. The clupeid fishes, including sardines and their relatives, the anchovies and herrings, are the most important fishes in the ocean, both in terms of value to fisheries, and significance to marine ecosystems. Sardines are the preferred food of a number of seabirds, including gannets and penguins, mammals, including dolphins, seals, and whales, and various fishes and sharks. About 20,000 long-beaked common dolphins move into the east coast of South Africa during the annual “Sardine Run,” and their diet at his time consists of about 85% sardines. It has been suggested that the dolphins, as well as several species of gamefish, may time their reproductive cycles to the movements of the sardines. Local populations of bottlenose dolphins also feast on the sardines as they pass through, and their numbers are swelled by additional bottlenose dolphins that migrate in for the season. Large numbers of copper sharks also move northward along with the sardines, sometimes showing themselves by breaching above the surface, for reasons unknown. Such large numbers of sharks and dolphins travel up the coast feeding on the sardines that the Sharks Board is forced to pull out its nets that protect swimming beaches each year in anticipation of the event, to avoid having them swamped with hundreds of carcasses.

South African fur seals and Cape gannets both leave their rookeries in the south and follow the sardines hundreds of kilometers up the coast, resting on the sea surface between feeding bouts. Neither will go ashore again until they return to their rookeries in the south to breed. Around 140,000 to 160,000 gannets move north to feed on the sardines each year. Although African penguins mostly stay in the cooler waters of the Cape and west coast, they have been known to pursue the sardines up the east coast as far north as Durban. Sardines are so important to the penguins that several populations of penguins crashed following the collapse of the South African sardine stock in the 1960’s.

With improved management, the sardine population has seen a steady recovery since the 1980s and now supports a fishery that takes over 100,000 tons each year in South Africa. Most of this is taken by purse seiners along the southern and western coasts, and is used for human consumption, both fresh and canned, bait, fish meal, and fish oil. The millions of sardines that move up the east coast are relatively insignificant in terms of the overall fishery, and are not enough to support either large fishing vessels or processing plants. They are sufficient however, to produce a cultural phenomenon.

The Sardine Run has been an important seasonal event in Kwazulu-Natal since before the memories of the oldest residents, and Zulu legends relating to the Run have been passed down for generations. Shifting currents or persistent predators can drive shoals of sardines right onto beaches, sometimes burying the beaches calf-deep in fish, and requiring a bulldozer to clear the beach. They often collect along the shoreline in such concentrations that the water appears black, and may even suffocate themselves by packing so tightly together that they consume all the oxygen in the water.

To bring in a huge haul of sardines, it is merely necessary to hold one end of a beach seine on the shore and use a skiff to carry the other end out around a mass of sardines, and back to the shore. The arrival of the Sardine Run produces a holiday atmosphere which inspires many coastal residents to take off work or school and rush to the beach, where they are often swept up in a sort of madness known locally as “sardine fever.” Staid citizens suddenly lose all their inhibitions and rush fully-clothed into the water, scooping up sardines with any available device, including bare hands, and stuffing fish into pockets, skirts, waistbands, brassieres, or any receptacle that can be found. Tempers sometimes flare as sardines are snatched right out of nets being pulled, and fistfights may break out over a bucket of sardines while thousands more are flopping all over the beach. In general, however, a festive mood prevails, and everyone from small children to octogenarians participates. The sardines are mostly either consumed fresh or frozen for bait. Recreational anglers prize sardines as the best bait available for a variety of gamefish.

Sardines may continue to appear and be netted in Kwazulu-Natal through the end of July and even into August, but then they disappear. For years it was uncertain if they moved offshore, continued north, or if this was a one-way migration to death, with fishermen and predators eventually taking every last sardine. However, plankton surveys by Dr. Allan Connel and others have recovered sardine eggs off Kwazulu-Natal through November, indicating that the sardines descend into deep water (or perhaps most of them never leave the deep water), and remain until water temperatures start to rise again at the onset of summer before embarking on a return trek to the south.

Scientists insist that the mass movement of sardines up and down the east coast of South Africa is not actually a migration but rather a range extension. The distinction is that a migration is generally undertaken by most or all of the members of a population for some essential purpose, such as feeding or reproduction. However, only a relatively small portion of South Africa’s sardine population makes this trek. To be sure, they are feeding and spawning along the way, but so are the sardines that stay at home at the Cape.

Until recently, “sardine fever” pretty much ended at the shoreline. That was before a mercurial diving outfitter named Mark Addison came up with the outrageous notion of going out with scuba tanks and jumping into the middle of a shoal of traveling sardines, along with all the predators feeding on the hapless fish. At first Addison’s clients were professional wildlife filmmakers such as Peter Lamberti and Charles Maxwell. These South African natives had prior experience filming great white sharks and other dangerous animals, but even Lamberti was unnerved when he was rushed by dozens of copper sharks at once. Fortunately he was working with a full film crew, and was able to assign assistants to watch his back while he filmed. Lamberti produced several documentaries featuring the Sardine Run, and both he and Maxwell were able to sell the spectacular footage of predators rounding up baitballs to international production companies. The Sardine Run footage formed one of the most riveting segments on BBC’s “Blue Planet” series and other television programs. The international broadcasts, along with Addison’s contagious enthusiasm, attracted more filmmakers from abroad, along with still photographers, journalists, and thrill-seeking sport divers.

Addison, who discusses marine biological phenomena with the same zest he uses in recounting the winning game of his favorite rugby team, brought in more and more boats to fill the demand, but still found himself turning away customers, even as competitors sprung up all around him. The Sardine Run was an instant marketing success. Addison’s clients were witnessing never-before-seen events, such as a killer whale killing and playing with a common dolphin (captured on videotape during the 2002 Sardine Run). But Addison was uneasy. He was now putting dozens of clients into waters full of dangerous predators in the middle of a feeding frenzy, in a remote location far from any medical facilities. Most of the divers who came for this even were seasoned professionals, but a few had never seen a shark before, and it soon became obvious that some did not have the diving experience that they claimed.

Addison’s worst fears were nearly realized in June 2002 when professional underwater photographer Tony White and his team of British divers swam out toward a baitball 50 m in diameter that was being attacked on all sides by sharks, dolphins and birds. The water was extremely turbid, with visibility no more than three meters. “It was absolutely amazing,” said White. “I had never seen anything like that. Every time I stuck my head underwater I saw a lot of sharks swimming around and could hear dolphins.” Observers on the boat could see a dolphin actually lying on top of the baitball, with most of its body out of the water, and sharks mowing through the school of sardines with their heads half out of the water and mouths open.

When White approached the ball of sardines, the frantic fish swarmed around his body seeking shelter from their tormentors. Suddenly visibility in the water dropped from three meters to zero. “I could feel sardines flapping around under my armpits,” said White. Breathing through a snorkel, rather than scuba gear, White was unable to drop down below the school to escape. He had his head out of the water, looking for a way out of the bait ball when he felt something grab his right arm around the elbow. The shark lifted its head out of the water, with White’s arm still between its teeth, and White got a brief look at it, just as it let go and slid back below the surface. “The sardines were so thick the shark wouldn’t have seen my arm. I think it was just eating through the sardines until it hit my arm,” said White.

As blood filled the water surrounding him, White felt something hit his leg – probably another shark - giving him “a bit of a shock.” In moments the boat was at his side, and White was pulled aboard. A chunk of flesh fell away from his arm, exposing the elbow joint, and revealing a tooth scratch going down the humerus bone into the joint. A Shark Board scientist who just happened to be flying overhead in a small plane, that by incredible good fortune was carrying a paramedic, landed on a nearby airstrip and rushed White to the closest hospital. The scientist estimated from the bite marks on White’s wetsuit that the injury was inflicted by a two to two-and-a-half meter copper shark.

Immediate medical attention and extraordinary luck saved White from bleeding to death, and he regained about 95% of the function of his arm, although retaining a scar impressive enough that he may never have to pay for an ale in a pub again. He returned to South Africa for the 2003 Sardine Run, along with a film crew which produced a documentary on his conquest of his fear to enter the water again and photograph a baitball. Shortly after White’s incident, another diver had a similarly close brush with fate when she jumped off the boat in water over 1000 m deep with an excess of lead weight on her belt and sank so fast that she burst her eardrums and became disoriented. Another diver saw her sinking, chased her down to a depth of 31 meters, and was able to pull her back to the surface.

After these close calls, Addison began to think that a feeding free-for-all in the ocean was perhaps not the ideal venue for a mass-marketed diving adventure, and decided to go back to working primarily with professional film crews for in-water activities. By then, however, the potential of the Sardine Run as a setting for boat-based dolphin and whale watching had become apparent. During the season, even when sardines are not visible at the surface, pods of hundreds of long-beaked common dolphins can be spotted charging up the Mozambique current, surfing down the swells in “hilarious shoals, which upon the broad seas keep tossing themselves to heaven,” as Herman Melville described what he termed the “huzza porpoise” because it was so “full of fine spirits.” Bottlenose dolphins stay closer to shore, frequently indulging their own “fine spirits” gamboling in the big surf for which South Africa’s eastern coast is famous.

South Africa’s east coast at this time of year also witnesses a parade of humpback whales migrating from their Antarctic feeding grounds to breeding areas in Mozambique and other tropical regions of the Indian Ocean. Melville lauded the humpback as “the most gamesome and light-hearted of all the whales, making more gay foam and white water generally than any other of them.” The humpbacks have been known to interrupt their travel to scoop up a baitball of sardines, but generally keep moving. Other whales, including minke, Bryde’s, and orca may be either migrating through, feeding on the sardines, or, in the case of orcas, feeding on seals and dolphins that are feeding on the sardines. The combination of so many species, with some present in very large numbers, makes South Africa during the Sardine Run one of the most spectacular cetacean-watching arenas on Earth. Mkambati Game Reserve, from which Addison operates, may be the only place on the planet where it is not unusual to see zebras and antelope grazing along seaside cliffs with humpback whales breaching in the background.

Further north, at Port Edward and Durban, helicopters offer seasonal joyrides to view the sardine shoals and their associated predators from the air. When the sardines are forced into shallow water, they form a black carpet over the white beach sand. Flowing like quicksilver, they quickly open up “doughnut holes” around sharks and dolphins that penetrate the school – a dazzling sight from above. The Sardine Run has always drawn South Africans from around the country to the beaches of Kwazulu-Natal, aided in recent years by daily radio reports and a toll-free “sardine hotline” advising which beaches are hosting shoals. Addison and other enthusiasts believe that the Run could also become a major draw for international tourism – rivaling the big game animals at Krueger Park and other wildlife viewing areas. The challenge is how to bring in large numbers of viewers without having some of them become part of a very dynamic food web.

For the sardines themselves, it would seem that participating in the Run is a fatal mistake. The sight of shoals being decimated year after year makes observers wonder how the sardines can keep repeating the same mistake on an annual basis. Early scientific studies indicated that the sardines were neither feeding nor breeding – compounding the mystery. However, more recent studies provide evidence that both feeding and breeding are occurring. Feeding and spawning are what sardines do best. Feeding is nearly continuous, though it may increase in intensity at night when sardines follow their planktonic prey to the surface. Sardines spawn throughout the year in South Africa, but with a peak in August. A single female can release 30,000 eggs every 15 days, with the entire Sardine Run producing millions more swimming energy bars each year to support the vast numbers of predators and fishermen which depend upon them. Most of the sardines participating in the Run are one to three years old. Many are just reaching sexual maturity, and will breed for the first time during the Sardine Run.

The fish being visibly massacred are merely the unlucky few that are forced to the surface by the dolphins, or other factors, making them available to a variety of predators. They are but the tip of an underwater iceberg, moving unseen at greater depth. Deep plankton trawls have revealed seasonal peaks of sardine eggs that suggest some sardines spawn during the run north and that possibly even more spawn during an unseen return migration through deep water later in the year. The great annual spectacle that affords viewers brief glimpses of nature’s majesty and savagery is likely but a small sideshow of a much larger event that, like much of what transpires in the ocean, remains hidden from our eyes.