Ngqura a fish magnet

THE Port of Ngqura has become an extraordinary magnet for marine life, and could point the way to an important new role for harbours, according to Bayworld marine biologist and shark specialist Dr Matt Dicken.


Among the rich con glomerations of fish that have been recorded there, sharks have been a stand-out feature, not least shivers of little-known gully sharks in the shallows right inside the port, hundreds-strong.


Previous studies on Ngqura pinpointed the threat of oil spills, and the huge plume of sediment which hung in the water for months during construction, finally settling but possibly altering in the long term the composition of the seabed and the integrity of the Algoa Bay food chain.


They highlighted the threat of future oil spills, and the danger especially for the African penguin.


But Dicken said if the explosion in fish life could be capitalised on by monitoring and protecting it, this would be a good way of ensuring the general health of the surrounding bay and all its residents.


For a year, he and a  team of specialist tag-and-release anglers targeted the waters of the harbour and recorded their catches. They were “blown away” by their findings.


“We caught more than 4 500 fish representing 47 different species from 5cm long Cape stumpnose and puffer fish to 2.5m raggedtooth sharks.


“In addition to relatively commonly encountered species like kob, elf and garrick, we also caught sub-tropical species of kingfish and queen mackerel rarely recorded in the Eastern Cape.


“Although not caught, great whites and whale sharks and even manta rays were regularly observed in the port.


“To put this into perspective, the abundance of fish recorded was more than 10 times greater than any other estuary or shore location in South Africa.


“The port is one if not the most productive fish environments in South Africa and is functioning as an important nursery area for many species of fish.” 


One of the most surprising and exciting discoveries was the abundance and diversity of sharks from bronze whalers and hammerheads to cat sharks, raggedtooths and great whites, he said.


“Many of the shark species recorded are highly sensitive to over-exploitation and have been decimated in other parts of the world.”


One of the most commonly encountered sharks was the dusky. There are particular concerns about this species as it is not only heavily targeted by anglers, it also has very slow growth rate, is late to mature, produces just a small number of pups and has a long gestation, he said.


“Yet our finding was that there are over 500 duskies using the port as a nursery area and core activity zone. So this is very important in the management and conservation of this species in South Africa.”


Aerial photos showed Ngqura is also home to hundreds of gully sharks, he said.


“These sharks are endemic, they grow to about 1.8m long and they congregate in the shallows…. But apart from these facts and some data about their feeding and reproduction,  there is little information available to guide management of the species.


“These congregations are infrequent and have only been observed before in Western Cape.”


Whether these sharks are breeding, pupping, feeding or aggregating in response to upwelling of cold water in the bay is unclear, he said.


“But whatever the reasons, it is evident Ngqura  is functioning as a key habitat for this potentially vulnerable species.”


Dicken’s finding was that the attraction of Ngqura for the gullies and other shark species is not only the abundance and diversity of fish prey but also the relatively calm and sheltered environment created by the port.


“So, far from destroying valuable fish habitat, the Port of Ngqura has provided a novel habitat and conditions similar to those in estuaries, on an otherwise wave-battered sandy bottom coastline.”


With the excellent present biological status of the port established, any future construction should avoid critical biological activity like the congregating gully sharks, spawning fish and endangered species like whale sharks and dolphins, he said.


“Best practice construction methods should be employed to minimise impacts, including turbidity and movement of sediment on the seabed. Blasting during construction should be avoided if possible as this can cause fish kills.”


Air bubble “curtains” can be used to reduce sound wave energy `when blasting cannot be avoided, and screening systems can be used to prevent fish from moving to dangerous spots  like power station turbine intakes, he said.


“Retention of the nursery function of the port for many juvenile fish and shark species is particularly important considering the continued degradation of estuaries, which are vital in the life histories of so many over-exploited linefish species.


“The diversity and abundance of fish recorded within Ngqura suggests the potential use of ports and other artificial structures for enhancing local fisheries in South Africa.”


 


 

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