South Africa’s Sardine Run
(Source)
What is the Sardine Run?
The Kwazulu-Natal Sardine Run is honestly one of the craziest and greatest shows that Mother Nature has given us. It starts in early May along the southern coasts of South Africa, and runs through the beginning of July. During that time, billions of sardines (Sardinops sagax) congregrate in the cool waters of the Agulhas Bank, which is the ocean region where the warm Indian Ocean water meets with the cold Atlantic Ocean waters.
Sardines spawn in those waters, and then start migrating northward along the east coast of South Africa (the Kwazulu-Natal region) up to Mozambique. Some scientists have estimated that the sardine run rivals the great wildebeest migration of eastern Africa (in Kenya and Tanzania) in terms of biomass.
(You can see the mixing of hot waters from the Indian Ocean with the colder waters of the Atlantic. This convergence leads to treacherous sailing conditions, but it also fuels the nutrient cycle for marine life, making it one of the best fishing grounds in South Africa. Source)
The sheer number of sardines thus create an incredible feeding frenzy for birds, whales, dolphins, game fish, bronze whalers and many other shark and fish species. Of course, the local fishermen are also trying to catch as many sardines as possible for their own livelihood. The shoals may exceed over 7km long, 1.5km wide, and 30m deep! It is an open buffet for everybody.
Check out the insanity that is the Sardine Run underwater. Sadly this video is not mine, as I was only able to witness this migration event from the shore (the winter sea conditions were a bit too rough for us to go out), but it was already crazy to see from the beach, and I hope to return someday to be able to dive and witness it first hand.
(Whales arrive to the party at around the 12:00 minute mark)
The run is crucial to the local economy, not only for food and the fishing industry, but also for tourism, as many divers and freedivers fly down to South Africa to dive and witness the migration. Needless to say, you need to be pretty comfortable with your diving skills before they let you be in the middle of the bait ball.
Why do sardines ‘run’?
I am sure now you are all wondering why do the sardine brave such dangers and repetitive, intense predation year after year? Like a lot of things within this field of study, well… scientists aren’t quite sure yet!
From an ecological perspective, the whole phenomenon remains a bit misunderstood, and many theories exist, that sometimes contradict one another. The latest theory is that it might be due to a combination of a seasonal reproductive migration of a genetically distinct subpopulation of sardines, along with their preferences for colder waters.
The sardines like water temperatures below 20C (68F). In winter—June and July in the southern hemisphere—the surface water cools along the east coast, allowing the sardines to expand their habitat and move up north.
(Open buffet for everybody; sea birds do not hesitate to dive in for such an abundant meal. Gannets can dive down to 20m! Source)
Sometimes, this phenomenon does not happen. The conditions have to be ideal for the migration to take place, and the water has to be cool enough, preferably below 21C (70F) for the sardines to ‘run.’ Some years, it does not happen at all.
Favorable migration conditions include cooling sea surface temperatures, calm current conditions, light north-westerly land breezes, calm atmospheric conditions and the large presence of predators inshore such as common dolphins, Cape gannet, and an increased number of sharks and game fishes.
(When whales join the feast, it truly become a magnificent event. Source)
The sardine run is one of the oceans events that help thousands of marine life survive. It's truly a miracle of earth! I wish I could see it one day.