Climate Change Affects the Sardine Run

South Africa's sardine run along its Indian Ocean coast occurs increasingly later in the year and sometimes not at all. This can be disappointing for divers who have made the journey to enjoy what should be a spectacular blue water experience. (Undercurrent September 2016)

It's what scientists call a phenological event -- something that's meant to happen at the same time every year. But as ocean temperatures increase the timing of the sardine run becomes more unreliable.

Exploring how the dates have changed over the last 65 years has proved difficult because there are few records for South Africa, but researchers have sought to determine changes in the pattern of the sardine run. They discovered sardines arriving off the coast of Durban have been increasingly late -- so that the date has eventually moved from mid-June to mid-July.

Sardines can tolerate a maximum surface temperature of 70°F, but this is no longer consistently being reached, and this has caused problems for those promising sightings of shark and dolphins feeding on the sardines. There has also been an increase in mid-latitude cyclones in the east coast region of Africa, adding yet more unpredictability.

In fact, this unpredictability causes a species mismatch between predator and prey, increasingly observed as a result of climate change on these phenological shifts world-wide. This is because each species has its own unique trigger for a particular activity, so although the sardines might eventually show up, the sharks and dolphins might not.