The Kwazulu-Natal Sardine Run
Location/ Description / Jurisdiction / Threats / Management status / Geographic scale, integrity and site type/ Other sites in the region / Key References
The Sardine Run occurs off the East Coast of South Africa during the months of May to June. The area just falls outside of the tropical zone of the WIO, however the uniqueness of this phenomenon, occurring on the boundary of the WIO and touching its southern extreme, is of importance and interest.
The Southern African pilchard (Sardinops sagax) spawns in the cool waters of the Agulhas Bank. As the spawning season matures, the shoals move northward along the east coast of South Africa. The run can contains billions of individual sardines, trapped in a cold current of water between the coastline and the Agulhas Current itself (that heads southwards), which can cause the fish to be concentrated into the dense shoals of the ‘sardine run’.
Limited information suggests that the water temperature has to drop below 21oC in order for the migration to take place. More recent observations have noted that cooling temperatures, calm conditions, light northwesterly land breezes and stable atmospheric conditions promote the development of the run. In terms of biomass, researchers have estimated the sardine run could rival East Africa’s great wildebeest migration. The shoals are often more than 7 km long, 1.5 km wide and 30 meters deep, and are clearly visible from spotter planes or from the surface.
The sheer numbers of sardine create a feeding frenzy of higher predators. For instance, up to 18,000 dolphins are estimated to aggregate to feed on the sardines, mostly the common dolphin (Delphinus capensis) but also the bottlenose (Turisops aduncus). They round up the sardines into bait balls, which instinctively group up as a defense mechanism. These bait balls can be 10 – 20 meters in diameter and seldom last longer than 10 minutes as a large number of other predators take advantage including sharks (bronze whaler, dusky, grey nurse, black tip, spinner and zambezi), other fish (billfish, kingfish), birds (gannets, cormorants, terns and gulls), and cape fur seals.
Like the wildebeest migration, the biomass of sardines and central role it plays in the life history of the predators of the region, and the potential for nature-based tourism to view the phenomenon, make it a unique event.
Jurisdiction - South Africa
Threats - Climate change would lead to changing conditions (temperature, phenology and timing of seasonal events, etc) which may have a devastating effect on the Sardine Run and all it effects. The frequency of the run could be altered.
Management status - Observed, monitored, researched and enjoyed.
Geographic scale, integrity and site type - The sardine run is a mobile phenomenon, so presents challenges in ensuring its integrity, as barriers to movement along the shoreline may significantly impact it.
Other sites in the region - There is no other fish shoaling phenomenon of this type in the WIO or elsewhere in the world.
Key References – Fréon et al. (2010); O’Donoghue et al. (2010); van der Lingen et al. (2010). --> References