Greater Zandvlei Estuary Nature Reserve
The Fish saga & interventions in the Estuary - 30/03/2012....
The latest updates are at the top of the page, earilest at the bottom. updated 19/04/2012.
Then follow some of the
sorry fish saga due to initial lack of City Law Enforcement
mismanagement by the City's Environmental Resource Management.
18/04/2012 - Independent
Online News report - Don’t eat vlei’s dead fish
Residents near the Zandvlei estuary have been warned not to eat or collect fish washing out of the water as this is a health hazard and illegal.
The City of Cape Town has now conducted tests at the estuary following the die-off of thousands of fish in the vlei over the past few weeks. Residents had complained of illegal fishing as well as a lack of response from the City and CapeNature. Brett Herron, Mayoral Committee member for Transport, Roads and Stormwater, said a lack of oxygen in the water was a symptom but not the cause of the problem.
Herron said test results from samples taken at the estuary on Monday showed that golden algae was responsible.
“The latest test results have confirmed that an extensive algal bloom comprising the species Prymnesium parvum, commonly referred to as ‘golden algae’, is responsible for
the (fish dying).”
See these links for mor information on golden algae http://en.wikipedia.org/wiki/Golden_algae also http://www.ucmp.berkeley.edu/chromista/chrysophyta.html
Lionel Adendorf, spokesman for the Department of Agriculture, Forestry and Fisheries said: “The public is reminded that it is illegal to collect any of the species that wash out in the estuary without a permit and if found in possession of any fish, they can be fined up to R500 per fish.”
He said fish were dying because of the algal bloom that had been in the estuary for the last six weeks.
“The density of the algal bloom, caused by the high nutrient load that comes from the various sources in the catchment, ranging from stormwater run-off from both urban and
industrial areas and sewerage overflows, increased dramatically over the last four weeks causing low oxygen levels in the estuary,” he said.
He said conditions in the estuary were expected to remain the same for at least another month and urged residents to avoid the area.
Pierre de Villiers, co-ordinator of CapeNature’s Estuaries Programme said: “The aim of opening the mouth during spring tides is to ensure the inflow of marine water at high tides. If the mouth is kept open for lengthy periods the water level will drop drastically.”
De Villiers said the size of the “natural filter” within the estuary would therefore also decrease.
He said CapeNature, the city and partners were setting up an estuary management forum because they needed to work together to ensure the die-off did not occur again.
18/04/2012 - Thousands of dead fish washed out in the Zandvlei estuary in Cape Town.
People should not collect or consume fish washing out in the Zandvlei estuary in Cape Town, the Agriculture, Forestry and Fisheries Department said on Tuesday.
Spokesman Lionel Adendorf said the fish were not fit for human consumption. They were washing out because of low oxygen levels, caused by an algal bloom.
He said the bloom had been present for the last six weeks and was caused by stormwater runoff from nearby areas as well as sewerage overflow.
“It is estimated that, since the first washout was recorded last month, more than five tons of harders – which is the most abundant species in the system – and other mullet species like kob, white steenbras, garrick (leervis), elf or springers have washed out.”
He warned the public that it was illegal to collect any of these species as garrick and white steenbras were protected and could not be sold, while kob and slingers were biologically vulnerable.
He said anyone caught with fish and no permit could be fined up to R500 per fish. – Sapa.
18/04/2012 - Thousands of dead fish have been found in the Zandvlei
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.
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.
11/04/2012 - Belinda Walker,
Mayoral Committee member: Economic, Environmental & Spatial Planning - Alderman City of Cape Town,
In summary, tests conducted showed that the oxygen levels were low at the time of the initial fish deaths and that this may have been the cause of the fish dying. All of the fish that died were removed and both the water and fish were tested.
The proliferation of fish life that was observed just prior to the opening of the vlei mouth on Wednesday, 28 May demonstrates that the fish life in the Vlei is in fact doing very well despite the die-off reported and the challenges of managing a vlei in an urban environment. The City acknowledges that there are areas where the management of the vlei could be improved but the City is working with stakeholders to better manage the situation.
In more detail to the response above, the laboratory reports confirm low oxygen levels particularly at depth while levels at the surface were much higher. This could be due to the large amount of aquatic weeds and algae that proliferates in the vlei and the Marina da Gama canals. The microscopic algae (phytoplankton) present in the vlei on the sample date was mainly of the genus Chlamydomonas which is a green algae of the family group Chlorophyceae and is not noxious or harmful. Note that the temperature of the water in the Marina canals was exceptionally high at the time of the initial fish die off – warm water contains less dissolved oxygen than cool water. Warm conditions would also contribute to accelerated plant/algae growth and any decomposing algae or plant material would break down much faster under these conditions.
The toxin results confirm that there is no significant bloom of Blue green algae (Cyanonphyceae) in the vlei – the latter group of algae is typically implicated in the production of microcystin toxin which can be harmful.
Also commonly present in the vlei is an epiphytic filamentous algae which is often found attached to the Pond weed and is not a harmful species. At the height of its growth it is visible to the naked eye as thin greenish strands. Typically towards the end of summer we find that this epiphytic algae starts to die off and at this stage tends to resemble yellow cotton wool. Die-off of algae and other aquatic weeds and subsequent decomposition can result in significant depletion of oxygen levels.
From observations made by staff on site today: the water clarity in the lower end is very good since the mouth was left open for an extended period during the recent rains and spring tide (see photo: Zandvlei mouth 11 April 2012). This helped to introduce saline water from the sea which is essential for estuarine functioning. It also aided movement of the fish (e.g. large leervis) out to sea. The vlei mouth has since been closed.
Higher up in the vlei and particularly in the Marina canals the water has a distinct brown tinge which may be due to a microscopic algae species (see photo: Marina canal 11 April 2012) – it is hoped that the awaited laboratory results from last week’s sampling will shed light on this. This summer has been exceptionally hot and nutrients derived from various catchment sources have resulted in exceptional rates of aquatic plant and algal growth in many wetland systems around the province. During the day these plants photosynthesise and produce oxygen and at night their respiration results in depletion of oxygen to the extent that fish can perish. Oxygen concentrations at the bottom of the vlei are even lower than at the water surface which could explain why fisherman reported their live bait dying after diving down.
The Marina canals, being somewhat separate from the main vlei did not receive the recent extensive saline inflows and flushing from heavy rains. The water is very still, warm and stagnant. It appears that it is mostly small fish that have suffered from the oxygen deficit in the Marina canals.
The microbiological results of 4 April 2012 indicate that the bacterial levels in all areas of the vlei and Marina da Gama are within required limits. The recent heavy rain and open mouth would have assisted with flushing the system.
11/04/2012 - In addition the following was provided by an expert from the Inshore Resources Research Branch (Fisheries Department Agriculture, Forestry & Fisheries), Dr Steve Lamberth, which corroborates much of the preceding discussions regarding the conditions at Zandvlei. (If you would like to quote from him please contact him directly, however the in information provided corroborates the City’s findings)
“On a positive note, based on more than 10 years seasonal fish monitoring (a DAFF Fisheries Research / City collaboration), similar surveys from the early 1990s and some even earlier data, the current fish assemblage of the estuary is the healthiest ever recorded. Much of this can be attributed to existing mouth management that allows intrusion of saline water much further upstream than was the case throughout most of the 1990s. The reappearance of benthic feeders and dwellers such as gobies, pipefish and white steenbras as well as expansion of sandprawn beds indicate well oxygenated bottom water and that anoxic / hypoxic conditions don’t occur throughout the deeper parts of the system as did previously.
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.
Our sampling surveys are long-term and the data indicate long-term recovery whereas the recent events are short-term responses of the estuary and biota to a suite of stressors.”
11/04/2012 - Dr Steve Lamberth, responded to queries by the concerned fishermen at Zandvlei - Our sampling surveys are long-term and the data indicate long-term recovery whereas the recent events are short-term responses of the estuary and biota to a suite of stressors. The responses of the fish in Zandvlei are near identical to that of fish assemblages in other temporarily
open / closed SA estuaries where similar conditions have occurred. The nearby Bot and Klein have both experienced fish kills over the last 2-years all linked to nighttime low oxygen levels.
31/03/2012 - From the
Sealine website Thursday, Mar 29, 2012 at 9:52 PM, Anton Ressel
"As per my post on the Sealine law enforcement arrived around 8.45pm last night and they took charge very well indeed, considering the large crowd etc.
The diver was seen there this morning very early by a fellow sealiner, whom I spoke to. He saw the guy shoot 3 fish and he said he had shot '3 or 4 others'. His registration number is on Sealine website as well, would be good for him to get his just desserts".
One of the City Metro cars in the parking lot. They had been sent by their Director of Security and Law Enforcement, after the public and other City depts put pressure on them to respond to the illegal activities which had been taking place for the last few days and night. The weekend of 09 - 11 March a worse situation unfolded to which the City's Environmental Resource Management Law Enforcement Section did not respond. Nor did Metro Law Enforcement when requested to do so.
Read about this serious issue as it unfolds to date.
*Kyle directing and being helped by bystanders to screen a shoal of cob from being plundered by illegal fishermen. They walked the fish out of the estuary mouth into the sea.
*Kyle October is the student Conservation Officer at Zandvlei Nature Reserve this year.
Thank you and well done from
Zandvlei Trust and its members and I am sure from all the local fishing fraternity as