How knock-on effect of increasingly later sardine run affects whole ecosystem

Data spanning 66 years shows timing of cold-water fish's winter migration is shifting due to climate change.

The sardine run is awaited with much excitement every year along the KwaZulu-Natal coastline.

It's of economic importance not only thanks to the fishing opportunities it provides, but because, along with locals out for their share of the bounty, it also attracts tourists as the waters erupt in a feeding frenzy by ocean predators.

RELATED: [WATCH]: Long-awaited sardines netted on KZN shore

But a study analysing data from a 66-year period indicates that this annual sardine winter migration is happening later and later.

John Maytham speaks to Dr Jennifer Fitchett, senior Lecturer in Physical Geography at the University of the Witwatersrand (Wits).

We found, across the world, whether it's plants or animals, whether marine or terrestrial, all of these events are changing in their timing as a result of recent climate change.

Dr Jennifer Fitchett, Senior lecturer in Physical Geography - Wits University

Each of these responses are very specific to the species and to the location.

Dr Jennifer Fitchett, Senior lecturer in Physical Geography - Wits University

When it comes to the sardine run, the cold-water fish are now arriving on the KwaZulu-Natal coast at a rate of 1.3 days later, per decade.

It's progressively moving from dates that are very common in mid-June to dates now in mid-July and stretching through into August.

Dr Jennifer Fitchett, Senior lecturer in Physical Geography - Wits University

That has been related to a pole-ward movement in the annual sea surface temperature levels, because sardines cannot really survive in temperatures much warmer than 21°C.

Dr Jennifer Fitchett, Senior lecturer in Physical Geography - Wits University

As the ocean's warming up it means the sardines have to wait later in the year until it's cool enough for them to migrate north. It's also being affected by the mid-latitude cyclones that come through, because they have quite a significant impact on temperatures, as well as pressure and rainfall patterns.

Dr Jennifer Fitchett, Senior lecturer in Physical Geography - Wits University

Dr Fitchett says this development is important not only because it affects fishing and tourism, but in fact affects a whole ecosystem.

Predators are going to start to suffer and we are going to see knock-on effects lower down on the ecosystem, where we're going to have blooms in species as well and that's what we call a species mismatch.

Dr Jennifer Fitchett, Senior lecturer in Physical Geography - Wits University

For more of this important conversation, listen here: