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Thread: estuary mouths

  1. #1
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    Default estuary mouths

    Hi guys,ive just posted a reply under "western cape in march",where ive made reference to botriver lagoon.I fished there about a month ago and my cousin has been fishing it without much success either.

    My question is what affect that closed river mouth has had on that lagoon.I beleive the Nature conservation/sea fisheries(or whoever) want the mouth to open naturally.I think because this hasnt been done,the salinity(spelling???)has dropped and the place is just looking siff.There is a smell around aswell.

    Obviously there are other factors affecting the lagoon,such as the nets that were put across the channels etc etc.But if i look back at the fish my old man caught there in years gone by,it was truely a great lagoon.

    On a lesser extent one can also look at kleinmond lagoon.Same thing happening there.We cant compare the two fishing wise,i know.But the mouth closes and the water gets stagnant.The sea weed rots and the place also just looks awefull.I think that the town gets busy with alot of tourists from up country and they come down to the coast to be at the sea.Alot of them swim in that lagoon and i dont think that will be happening if the mouth is still closed.

    What do the rest of you think?
    stephen is wishing he was fishing location x right now.......



    Stephen Smith

  2. #2

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    I spoke to an Inspector of Nature Conservation at Buffelbay regarding Swartvlei and Hartenbos lagoons.

    He said that although residents want to open the mouths, that the rotting and discoloration of the water is needed, as it put nutrients back that is needed for growth, of all species. It is part of nature and is needed.

  3. #3
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    An extract from the Cape Nature Website regarding the Bot River Estuary:

    "Breaching of the Bot River Estuary, 30 August 2006


    The Bot River Estuary was artificially breached at Meerensee at approximately 08h20 on Friday 18th August 2006. The process of breaching using the Overstrand Municipalities Cat 428 II ‘bac***tor’ was started at 16h00 on the previous day (Thursday 17th August 2006) when a channel of about 50 metres long, 2 metres wide and 1 metre deep was dug. This process took about 2 ½ hours starting on the estuary side. A sand bar or ‘plug’ was left overnight on either end (both sea and estuary side) of the channel so as to prevent any premature breaching by the incoming tide. The Cat resumed work at 07h00 on Friday morning 1st removing the sand bar on the seaward side and then finally the sand bar on the Estuary side.

    The timing of this breach was carefully planned and the following conditions/criteria were taken into account:

    Salinity: The average salinity of the Estuary was recorded on 18th August 2006 at 5.91 parts per thousand (ppt). This gives an indication of how much fresh water had entered the system over the last months. This was approaching the critical level for many estuarine organisms, which are well adapted to tolerate a wide range of salinities (Sea water is 35 ppt).
    Water level: The water level had been monitored on a daily basis for the past 2 weeks and was recorded at 2.65 m above mean sea level (MSL) at the Meerensee footbridge. Water level was a crucial factor in determining when to breach and had been monitored together with the predicted rainfall. The fact that the Kleinmond mouth had, unfortunately, been illegally breached by school children early on the morning of the 5th August meant that the system was losing about 1 cm a day (over its entire area). This resulted in about 13 cm being lost in the buildup to the breach at Meerensee. This together with the predicted rainfall meant that the chances of a natural breach taking place was therefore highly unlikely.
    Season and Period since last breaching: This Estuary was last breached on 26th August 2003, staying open until mid January of 2004. According to the Breaching criteria which were set out at an Indaba held in February 2003 the seasonal timing for a breaching to best imitate/emulate the natural system as regards recruitment of fish stocks, migration of fish species and marine lifecycles dependent on estuaries is between June and August. The fact that the Klein River Estuary between Stanford and Hermanus breached naturally on the morning of the17th August in an extra bonus as these two systems between them are responsible for more than 50% of the recruitment of marine organisms between Cape Point and Cape Augulus. These months are also favoured as it is this period which has the least impact on the bird breeding cycle.
    Place: The Meerensee berm is the obvious choice as to the where an artificial breach should take place as it is here where the berm is at its lowest point and is the point at which a natural breach occurred in the past.
    Timing and Tidal influence: The breaching was timed to ensure that the peak outflow of the estuary coincided with daylight. In a past breaching some 300 Red knobbed Coots died, as they were unable to orientate themselves in the night and were washed out to sea. For this reason the last two artificial breaches have taken place during the day. The ideal is to have maximum outflow during a receding /outgoing tide. This enables the forces of nature to work together, as opposed to an incoming tide pushing against the maximum outflow, resulting in the synergy necessary to flush out the sediment deposited over the last three years and scouring the base of the estuary. This enables the estuary to function efficiently and allows the tidal influence to push its way up deep into the system. For the same reason Weather and Sea conditions were also generally taken into account and a small swell is preferable.

    The decision to Breach is not taken lightly and only once all the above factors have been taken into account is a decision made by the Breaching Committee of the Bot River Estuary Advisory Committee (BREAC), which is representative of all major role players in and around the Estuary. It is a formally constituted body, which advises both CapeNature and Overstrand Municipality regarding the management of the estuary. Historically this is chaired by CapeNature who ultimately have to make the final decision if consensus is not reached.

    This particular breach started at 08h20 on the Friday and resulted in a drop off of 2 m over the 1st 24-hour period after breaching. By Monday 21st August 2006 the level had dropped by a staggering 2.3 m (from 2.65 to 0.35 m).
    Many people have different theories as to why, how, and if such an artificial breaching should take place. The fact remains that man has had a huge impact on this incredibly diverse system and it therefore remains mans responsibility to manage what has essentially become an artificial system in a responsible way which best imitates the natural processes based on sound ecological criteria.

    The breaching was successfully concluded without serious environmental consequences or loss to wildlife and all concerned are thanked for their support and assistance"


    Fishing in Bot River has been really bad over the past number of years and this is primarily due to the illegal gill netting in the river. There was talk about the Arabella Estate, in conjunction with Cape Nature, starting patrols on the estuary in order to eradicate this problem. I am not aware of what has become of this. You certainly hear a lot less about netting than what was the case about six years back or so. In those days we often heard reports of violent stand-offs between police and poachers.

    Fishing in the estauries in this area is at its best when the river mouths have been closed for a few seasons. The Leeries and Elf gets trapped along with huge shoals of Haarder. It is like being locked in a well stocked pantry and these fish grow to good sizes in a short period of time. The biggest Leeries ever taken on fly from the Hermanus estuary were taken after it was closed for a period of five years. Quite a few fish of over ten kilos came out and the biggest topped fifteen kilos. Awesome fishing when everybody thought that the estuary had become too fresh.

    These estuaries also generally fish much better during February to April, but I think this is also because the small Elf and Lerries are by then slightly bigger and more willing to chase flies.

    Cheers
    MC

  4. #4
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    This was most probably the most informative piece I've read regarding estuary management, I for one not being a salty by any account never even thought that there was so many things to be considered when dealing with estuaries, blind or open.

    Thanx MC

  5. #5

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    Thanks, MCC

    This was a very informative article, much appreciated

  6. #6
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    Thanks for that article MC.I was aware that the mouth had opened.But the lagoon was still siff.Surely the tides should play a factor in pulling all the weed and grass out to sea.

    I am still sceptical about the impact this has had on the fish.All good and well saying the harders get trapped,more food etc etc.But why wasnt a cencus done on what fish species were still in the lagoon,tagging etc etc.

    My cousin stays in kleinmond and has spent a good few hours prospecting the lagoon.The only action he has seen were harders.He said the harders were having a great time,nothing was chasing them.Surely someone spending that amount of time with little to show for it,would prove that there isnt much happening.

    Unless the fish were lined up at the mouth and as soon as the mouth opened,they made a duck.Probly tired of all the fresh water.

    I speak with little knowledge of the lagoon eco-system.I am merely a fisherman with a couple of years of experience and knowledge of the waters.Maybe i am wrong with my argument.
    stephen is wishing he was fishing location x right now.......



    Stephen Smith

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