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MLS Number: 13848371
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Users browsing this forum: mike offerman and 28 guests Dead fish in Zandvlei South Africa, Dooie visse in Zandvlei Suid-Afrika
Author Topic: Dead fish in Zandvlei South Africa, Dooie visse in Zandvlei Suid-Afrika (Read 1938 times)
« on: April 23, 2012, 12:26:42 AM »
Muizenberg residents say they are still in the dark about what is killing the fish in the Zandvlei estuary, after yet another weekend removing thousands of fish from the vlei.
When the Cape Argus reported on the problem last month Belinda Walker, the mayoral committee member for economic, environmental and spatial planning, said oxygen depletion in the water was probably the cause.
But on Monday, estuary management staff, law enforcement officers and residents were still removing dead fish from the vlei while thousands more appeared to be dying.
Muizenberg resident Pierre Niehaus said they had removed thousands of dead fish, big and small, from the water.
He said he used to let his dogs swim in the water but has stopped because the dogs developed a skin irritation.
Bob Craske, a Marina da Gama resident for the past 10 years, said other residents who had lived in the area longer than he said they last had a problem like this in the 1970s and 1980s.
Craske said the problem would have been worse had it not been for the small Zandvlei estuary staff who had been working with residents to remove the dead fish and take survivors to the sea: “Without them this would have been 10 times worse. It would have been disgusting.”
Garnet Prince, a member of the Cape Piscatorial Society, said some members fished in the vlei but had stopped when the fish started dying.
Poachers had used pitchforks and dived into the water to catch the fish, some of which were endangered, which was not allowed.
Prince said the incident was unfortunate because the vlei was one of the healthiest. “Two months ago we saw steenbras in the vlei – they have not been seen here for the past 10 years.”
They had rescued a lot of fish over the weekend, some weighing 20kg.
Dr Stephen Lamberth of the inshore resources research branch of the Department of Agriculture, Forestry and Fisheries, said that based on more than 10 years of fish monitoring, the current group in the estuary was the healthiest yet recorded and that the vlei was not contaminated or toxic.
Lamberth was responding to an e-mail from resident Chris Fallows on the possible cause of the fish deaths.
“Much of this can be attributed to existing (estuary) mouth management that allows intrusion of saline (salty) water much further upstream than was the case throughout most of the 1990s,” said Lamberth.
The reappearance of fish such as pipefish and white steenbras, as well as expansion of sandprawn beds, showed well oxygenated bottom water.
“The recent event in which fish became concentrated in the lower reaches was most likely due to two separate events happening at the same time.”
First was day and night fluctuations in oxygen levels over the past weeks, which was a natural product of plant (such as algae and pondweed) photosynthesis and respiration.
Low levels of oxygen at night were made worse by algae blooms.
“Second, throughout the winter rainfall zones of SA, fish in rivers and estuaries take the first significant autumnal pressure drop as a cue to begin moving towards the mouth as this usually indicates the onset of rains and time to be flushed out to sea.
“So, fish in Zandvlei began moving towards the mouth but had to contend with low nighttime oxygen levels…”
This was “near identical” to the response of fish in other temporary open or closed estuaries in SA, while sampling surveys indicated long-term recovery of the estuaries.
Muizenberg inwoners sê hulle is steeds in die duister oor wat die doodmaak van die vis in die monding van Zandvlei, na nog 'n naweek die verwydering van duisende van vis uit die vlei.
Wanneer die Cape Argus berig verlede maand op die probleem Belinda Walker, die lid van die burgemeesterskomitee vir ekonomiese, omgewings-en ruimtelike beplanning, het gesê die suurstof uitputting in die water was waarskynlik die oorsaak.
Maar op Maandag, riviermonding bestuur personeel, wetstoepassers en die inwoners is steeds die verwydering van dooie vis uit die vlei, terwyl duisende verskyn word sterf.
Muizenberg inwoner Pierre Niehaus het gesê hulle duisende van die dooie vis, groot en klein het uit die water verwyder.
Hy het gesê hy gebruik om sy honde te laat swem in die water, maar is gestop omdat die honde het 'n vel irritasie ontwikkel.
. Bob Craske, 'n Marina da Gama inwoner vir die afgelope 10 jaar, het gesê die ander inwoners wat in die gebied gewoon het langer as wat hy sê hulle het verlede het 'n probleem soos dit in die 1970's en 1980's.
Craske het gesê die probleem sou erger gewees het as dit nie was vir die klein Zandvlei monding personeel wat gewerk het met inwoners van die dooie vis te verwyder en oorlewendes na die see: "Sonder hulle sou dit 10 keer erger gewees het. Dit sou gewees het disgusting. "
Garnet Prins, 'n lid van die Kaapse hengelaars Society, het gesê dat sommige lede in die vlei gevang, maar het opgehou toe die vis begin doodgaan.
Stropers gebruik het pitchforks en duik die visse, waarvan sommige bedreig, wat nie toegelaat is in die water op te vang.
Prins het gesê die voorval was ongelukkig omdat die vlei was een van die gesondste. "Twee maande gelede het ons gesien die steenbras in die vlei - hulle is nie hier vir die afgelope 10 jaar gesien het."
Hulle het 'n baie vis oor die naweek gered, 'n paar weeg 20kg.
Dr Stephen Lamberth van die kus hulpbronne navorsing tak van die Departement van Landbou, Bosbou en Visserye, het gesê dat, gebaseer op meer as 10 jaar van vis monitering, die huidige groep in die riviermonding was die gesondste nog aangeteken en dat die vlei is nie besmet is of giftig.
Lamberth het gereageer op 'n e-pos van woonagtig Chris aangegee word oor die moontlike oorsaak van die visse dood.
"Baie van hierdie kan toegeskryf word aan bestaande (monding) mond wat toelaat dat die indringing van sout (sout) water veel verder stroomop as wat die geval dwarsdeur die meeste van die 1990's," sê Lamberth.
Die herverskyning van vis soos pipefish en wit steenbras, sowel as die uitbreiding van sandprawn beddens, het suurstofryke onder water.
"Die onlangse geval in watter vis het gekonsentreer in die benedelope was waarskynlik as gevolg van twee afsonderlike gebeurtenisse op dieselfde tyd gebeur."
Eerste dag en nag skommelinge in suurstofvlakke was die afgelope weke, wat 'n natuurlike produk van plant (soos alge en fontein kruiden) fotosintese en respirasie.
Lae vlakke van suurstof in die nag vererger deur die alge blomme.
"Tweedens, dwarsdeur die winter reënval gebiede van SA, die vis in riviere en riviermondings neem die eerste beduidende herfs drukval as 'n leidraad om te begin beweeg na die mond, aangesien dit gewoonlik die aanvang van die reën en uitgespoel word na die see dui.
"So, die vis in Zandvlei begin beweeg na die mond, maar het te kampe met 'n lae nag suurstofvlakke ..."
Dit was "naby identies aan die reaksie van die vis in ander tydelike oop of geslote riviermondings in SA, terwyl monsterneming opnames aangedui langtermyn herstel van die riviermondings.