Bronze whaler stranding numbers continue to climb

Bronze whaler sharks are continuing to strand in worrying numbers off the Eastern Cape coast — and videos of the big fish swimming in a disorientated way in river mouths and harbours and bashing into sand banks are doing the rounds.

Bayworld marine biologist Dr Greg Hofmeyr said yesterday the situation was unprecedented and it was not yet clear what the problem was.

“More than 40 bronzies have now come ashore dead and alive since February, most of them between East London and Jeffreys Bay, though there have been a couple of outliers in places like Nature’s Valley and Mossel Bay in the Southern Cape.”

He said while a handful of sharks usually stranded on the Eastern Cape coast each year, there was no record approximating the current situation.

“This large number over such a short period is unprecedented. Eyewitnesses have also described peculiar behaviour where the sharks swim in circles and in an unco-ordinated way and return to beach themselves even when attempts are made to push them back out to sea.”

He said the sharks were mostly adults and judging from photographs, many seemed to have empty stomachs.

“One of the stories going around on social media is that it is clear these sharks are discarded sardine fishery by-catch because their stomachs are full of sardines, but that is not our experience.

“We still do not know what is causing this problem but we will continue to collect and analyse data.”

Former Bayworld shark expert Dr Matt Dicken, who is now head of research at the KwaZulu-Natal Sharks Board, said it was possible the mystery stranding epidemic was due to a recent change in the legislation governing the sardine trawl industry.

“It is believed that while the sardine netters used to be able to keep their shark by-catch to sell, they must now take it back to port to hand over to the fisheries inspectors and, because they can’t be bothered to do that, they are just discarding them.

“So it’s possible the bronze whaler washups we are seeing currently are the direct result of this change in legislation.”

He said one photo he had examined showing a shark with its intestine expelled through its cloaca was indicative of net stress.

“Then again, I have not seen the injuries on the sharks one normally associates with net by-catch animals.”

Dicken said another possibility was that the bronzie strandings were the result of the red tide, which was thought to have caused a spate of seal deaths in the Western Cape.

“The theory is that the red tide infects the plankton which the sardines feed on, and biotoxins accumulated in the food chain damage the nervous system of animals feeding on the sardine and kill them.

“I asked both the SA Environmental Observation Network [Saeon] and the department of forestry, fisheries and the environment about recent big red tides off the Eastern Cape coast and there don’t seem to have been any, but Saeon is going to monitor the situation,” he said.

“Once we can retrieve a carcass and conduct an autopsy we will be able to test for this possibility, or perhaps that it is some kind of species-specific disease.” Dicken said reports on Friday of an uptick in gannet and dolphin activity between East London and Kei Mouth indicated that the sardines had begun their annual migration up the coast and if bronze whaler strandings started to manifest in this area, this would arguably support the trawler by-catch theory.

He said the initial hypothesis that the strandings were linked to pregnant females had been discarded because a number of males had since washed up as well.

“That’s the nature of science. Theories are set aside when they are shown to be flawed.

“There are holes in all the remaining hypotheses but that’s not to say any of them are definitely incorrect.

“We do not yet have a definitive answer for what we are seeing.

“But what is definite is this is a real phenomenon.

“I have spoken to a number of Eastern Cape shore anglers and they have never seen anything like this.”

Questions were sent to the department of forestry, fisheries and the environment but no response had been received by the time of going to print.