Scientists left guessing over sardines

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iol news pic Sardine run INLSA File image - The annual sardine run is one of the highlights of the year for KwaZulu-Natal residents.

Durban - This year’s sardine run has been declared over before it even happened.

“Not one sardine has been netted on the KwaZulu-Natal coast,” Debbie Hargreaves, for the KwaZulu-Natal Sharks Board said last night.

“There has been a total no-show, but they might decide to play games and still come sometime before the end of October, but we have shut down our sardine hotline. It has never been as bad as this.”

Bruce Mann, a senior scientist at the Oceanographic Research Institute, said “very speculatively” that this may be due to a reduced biomass of sardines in the ocean around South Africa.

“There has been an overall shift in the sardine biomass with the bulk of the fish having moved onto the Eastern Agulhas Bank for the past few years.”

Adult sardines are normally found in greatest abundance on the Western Agulhas Bank where the bulk of spawning takes place. This is enhanced by the nutrient-rich upwelling which takes place in this region. The eastward shift of sardines would likely have resulted in less successful spawning due to the reduced nutrients levels.

“Scientists think that it is temperature related and there hasn’t been good spawning and recruitment (survival of eggs and larvae) for a couple of years now.”

This had resulted in a decrease in the overall sardine biomass in the Indian and Atlantic Oceans around South Africa.

Along the KZN coast water temperatures appear to have been slightly higher than average this year, Mann added.

“Sardines prefer temperatures of around 18 degrees Celsius. “We haven’t had these cooler temperatures inshore on the KZN south coast this year.”

It has also been a poor shad season. Fishermen think it could be linked to the poor sardine run and climate change.

Mann backs up their assumptions, adding that last year’s spawning season could also have been poor.

“Surveys show a general decline in shad catches over the years. Indications are that all is not well,” he said yesterday, adding that shad stocks were likely to be suffering from both overfishing and the effects of pollution.

This is in spite of the fact that fewer people go shore fishing compared with around 20 years ago, owing to their not feeling safe alone at isolated fishing spots and because of the impact of the ban on driving vehicles on the beach.

He also said that shad numbers varied every year, depending on the availability of nutrients and the water temperature.

Shoals of shad are also sometimes found further out to sea and this is where spawning is believed to take place.

That hasn’t been the case for Brenton Sharp, from Ballito.

“It hasn’t been a great year for shad even out at sea” he said.

Sugen Naidoo, from Tongaat, felt that sand banks that had been in existence offshore for the past few months had been blocking shad from coming close to the shore. He questioned whether global warming wasn’t playing a part.

Independent on Saturday



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