RARE SEA LIFE WASHING UP ALONG EASTERN CAPE BEACHES AFTER DROP IN SEA TEMPERATURES
Communities and fishermen along the East and South Coast of the Eastern Cape have witnessed a tragedy as rare fish species have been washing up ashore.
According to experts, the fish were killed by a temperature shock. This occurred when South Africa's sea temperatures suddenly dropped from 24 degrees Celsius to 12 degrees Celsius. East London Museum scientist, Kevin Cole, has been busy attending to the species which has washed up. Some of these include two giant oceanic manta rays, one pregnant, a 3.1m Dusky shark, a 2.1m Carcharhinus and a host of other unknown species.
The sharks washed up in Gulu and Kidd's beach over the weekend, and several rays washed up at Morgan Bay and Haga Haga beaches last week.
Both familiar and unknown species have also been seen washed up on the popular and unspoiled wild coast in the former Transkei.
The first report of washed-up sea life came from the Morgan Bay community on Wednesday. A giant pregnant oceanic manta ray, pregnant with a 60kg pup, washed up on a rocky shore.
According to Cole's report, the manta measured up to 5.17 metres from wingtip to wingtip, while its unborn baby was 2-metres wide. He also estimated the animal to be 15-years-old.
Another slightly smaller ray washed up at Haga Haga beach. It was reported that the specimen measured 4.53m wingtip to wingtip.
The South African Association for Marine Biological Research [SAAMBR] also confirmed that the fish washing up ashore was due to sea temperatures dropping from 26 to 14 degrees Celsius.
Cole explained that "The most likely cause of death is a dramatic change in sea temperature these past days – very warm to cold (upwelling event). This would have affected the physiology of the warm water species, and it could not cope with the rapid change in water temperature."
Disturbing reports suggests that these incidents have created a feeding frenzy in rural communities as locals are fetching the dead fish. This was confirmed by the Provincial Department of Environment, Forestry and Fisheries. The Provincial environment, forestry and fisheries spokesperson, Ncedo Lisani, confirmed that coastal communities quickly took advantage of this bonanza. Many were seen picking up fish and shellfish lying on the beach and in rock-pools.
According to Lisani, many of these fish were familiar catches. However, the majority were those seldom seen or caught. The Provincial Department of Environment, Forestry and Fisheries has issued a warning to the communities to stop eating washed-up fish as they could be harmful.
"There is concern around the health aspects of consuming these washed out fish. Many may have been dead longer than thought, while some of the unfamiliar ones may be toxic. We do not yet know whether the anomaly also resulted in 'red tides' or Harmful Algal Blooms (HABS).
Consequently, coastal communities need to be made aware of the potential risks around collecting and eating these washed-up fish and shellfish," said Lisani.
Lisani also confirmed that the issue is connected to climate change, saying: "The broad answer is yes. Wind regimes and the Agulhas Current have been predicted to become more turbulent under the influence of climate change. Which would imply that such meanders and associated 'marine heatwaves' and cold upwelling events could increase in frequency in the future."
The event was monitored and tracked by the National Oceans and Coastal Information Management System (OCIMS).
SAAMBR released a statement on their Facebook page that explained how a temperature shock happens.
The statement read:
"During summer along the east coast of South Africa, a strong thermocline (a steep temperature gradient between two bodies of water, with warmer water above and cooler water below) is normally established above the continental shelf.
"With a south-westerly wind, Coriolis forces (caused by the spinning of the Earth) cause surface waters to be deflected to the left (in the southern hemisphere), and this brings warm, clean water from the Agulhas Current inshore and forces the thermocline down into deeper water (a process known as downwelling).
"With north-easterly winds, the surface waters are deflected offshore, and the thermocline moves shallower (a process known as upwelling). In cases of prolonged strong north-easterly winds (as was experienced last week), the thermocline comes to the surface, causing a sudden drop in surface water temperature. In severe cases, it can stun and even kill fish and other marine life that cannot escape the sharp drop in water temperature.
"During winter, the occurrence of strong south-westerly winds and large swells associated with passing cold fronts tend to break down the thermocline and result in the mixing of the water on the continental shelf. "Obviously, this is a fairly simplistic explanation of water movements off the east coast.
"They are, in fact, very complex and, in addition to the large, south-westerly flowing Agulhas Current, there are numerous eddies and gyres associated with this current. While the current generally follows the continental shelf drop-off, which occurs at a depth of about 200m, it does meander. Furthermore, the coastline is generally not straight and the numerous headlands and bays cause further changes in in-shore water movement patterns. Nevertheless, this description does help to provide a broad explanation of why the water gets cold after strong north-easterly winds."