Mike Anderson-Reade scans the ocean through the window of a six-seat light aircraft, looking for signs "the greatest shoal on Earth" is making its way up the east coast.Dark patches are clearly visible in the water. Fish. Lots of them. For about 20km there's an uninterrupted dark stretch of water - from north of Port St Johns to the Mbashe River mouth - and it's a hive of fish activity.But even as he flies closer, he cannot tell if these are pockets of sardines, which would indicate the start of the annual "sardine run".Every year, usually between June and August, billions of sardines make their way from the cold west coast waters up the eastern shores. This migration triggers a feeding frenzy for sharks, dolphins and birds - and also attracts thousands of fishermen, who try to net the fish as they come close to shore. Anderson-Reade, head of operations at the KwaZulu-Natal Sharks Board, said: "There is none of the associated species with them. There are no gannets, no bottlenose dolphins and no sharks. It's difficult to say if they are sardines. " he said.Gannets feed almost exclusively on sardines, Anderson-Reade said, and large flocks diving to feed on a shoal are the clearest indication that the fish are sardines. Pods of dolphin, which can be 3000-strong at the height of the run, are also a good indication. But on Wednesday, even though the 20km stretch of activity looked promising, Sharks Board operations manager Greg Thompson said it was made up mainly of bait fish.There were pods of dolphin, the largest of which was made up of 500 animals, but they did not seem to be feeding on sardines. And the only flock of gannets, no more than a dozen birds, were sitting on the surface and not feeding.Anderson-Reade, who has been tracking sardine activity for 39 years, said: "It was probably a mixture of bait fish. I'm sure there were sardines among them, but it was not a solid shoal." Apart from the sardines, Thompson noted other species, such as more than 40 turtles, manta rays, bottlenose and common dolphins, humpback whales and sharks.Anderson-Reade said it was important to know when the sardines were coming so that shark nets along the coast can be removed to ensure animals do not get trapped.He and Thompson will fly the same route next week - and then we might know when to expect the arrival of the greatest shoal on Earth...