Sardine Run by Thomas P. Peschak

June 8, 2011 2:02 PM EDT

Former marine biologist Thomas P. Peschak spends more than 300 days a year pursuing marine conservation photography and ocean reportage. A fellow of the International League of Conservation Photographers, he has photographed and written four books. Peschak writes for LightBox about his efforts documenting the annual mid-June sardine run in South Africa’s seas.

Every winter I contract a severe case of sardine fever; the irrepressible urge to pursue and photograph schools of silvery fish for months across some of the roughest seas in the world.

Sardines are shoaling fish that prefer the cold waters off South Africa’s west and south coast, but during June/July (the austral winter) vast shoals follow a tongue of cold-water northwards along the sub-tropical east coast. In hot pursuit of this silvery bounty are a vast army of predators; sharks, dolphins, whales and seabirds in the tens of thousands. Some call this phenomenon the sardine run or ‘the greatest shoal on earth’, I often curse it as the hardest thing I have ever done — the odds are always against the photographer! Sardine movements are unpredictable, an abundance of rivers often reduce visibility to near zero and in the depths of winter 15-foot seas are not unusual.

Sardines unfortunately do not have the same public appeal as panda bears or humpback whales and most people believe tins cans to be their natural habitat. A lack of conservation sympathies resulted in severe overfishing beginning in the 1960s and stocks have collapsed more than once since.

I first began to document the sardine run in 2003 with the aim of revealing what an essential component of South Africa’s oceans these fish really were. The survival of popular flagship conservation species such as common dolphins, Brydes whales, bronze whaler sharks and Cape gannets is intrinsically linked to the health of sardine stocks. Without the vast silvery shoals pulsing along our shores, the many tens of thousands of predators that occupy the top of the marine food chain would soon begin to disappear from South Africa’s seas.

—Produced by Marie Tobias

The South African sardine is a pelagic shoaling fish that inhabits the cooler waters of the west and southern coasts. Thomas P. Peschak

Every June and July, vast shoals of sardines migrate northwards into subtropical waters, following a tongue of cold water that streams along South Africa’s eastern flank at this time of year. Thomas P. Peschak

Up to 20,000 long-beaked common dolphins leave their offshore hunting grounds for squid off the southern cape and travel northwards in pursuit of the migrating sardines. Thomas P. Peschak

Common dolphins are the only predators that hunt cooperatively and can control the behavior of the sardines. Working together, they carve smaller pieces, so called ‘baitballs’ off kilometer long shoals, which they encircle and trap against the ocean’s surface.Thomas P. Peschak

Brydes whales reach lengths of 15 meters and weigh in at 25 tons. Their speed, streamlined shape and enormous gape allow them to target and engulf small sardine baitballs with a single lunge feed. Thomas P. Peschak

Cape Gannets are the sardines run’s only airborne predator. More than 20,000 birds migrate northwards from their southerly breeding colonies. When the sardines are spotted, they plunge into the water from heights of up to 30m and catch the fish in their beaks. Thomas P. Peschak

Without common dolphins to corral and herd the sardines, the feeding success of sharks appears to be lower.Thomas P. Peschak

Bronze Whaler or Copper sharks are the most abundant shark found during the sardine run. They patrol the margins of baitballs in large numbers and charge into the seething mass of fish to feed. Thomas P. Peschak

Not every feeding attempt ends in success and sometimes sharks are left encircled by a sardine doughnut and a mouthful of water. Thomas P. Peschak

We don’t know if sharks purposefully use their tail fin to stun sardines or if this is an accidental result of quick and violent turns while charging in and out of the baitball. Thomas P. Peschak

Regardless how many sardine baitballs the predators decimate, vast numbers of fish nonetheless complete their journey. Exactly how far north the fish travel depends on oceanography, but in good years, the sardines can be seen massing off Durban’s subtropical beaches. Thomas P. Peschak

More Must-Reads from TIME