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 the situation was unprecedented and it was not 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.”
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. Eye-witnesses have also described peculiar behaviour where the sharks swim in circles and in an uncoordinated 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 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.”
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 bycatch animals.”
Dicken said another possibility was that the bronziestrandings 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.
Anyone who finds a stranded shark should call the regional base of the Stranding Hotline at 071-724-2122.