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Thread: Conservation- some notes and updates

  1. #1
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    Default Conservation- some notes and updates

    Now a big fish like that would have ensured the next year's little ones.... they're not even that good to eat at that size.

    As for leeries stuck in estuaries- they don't spawn there. All leeries are spawned at sea, after which they recruit into estuaries when really little. They are bright yellow with black stripes, don't know if you guys have seen any. You wouldn't think that it was a leerie.
    They feed voraciously and are relatively safe from predators. they also have a high tolerance for salinity changes. If the mouth doesn't open for a long time, well they don't mind. Just stick around and eat more mullet (which also need an open mouth to recruit as youngsters). They've got all the time in the world to wait for the mouth to open...
    Estuaries need to be taken care of as many of our fish are entirely dependent on estuaries as juveniles. Our estuaries are becoming more and more disturbed. All our estuarine fish (kob, grunter, leeries, white steenbras) are decreasing- coincidence???
    The fish getting foul hooked is quite likely just a result of their chaotic strikes and swimming around the fly. They wouldn't use their fin spines to impale prey.
    Cheers all, and hope the next leerie season turns out well...
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  2. #2
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    I have copied my comment from the leerie thread. I have an interest in the state of our fish stocks, and will occasionaly post facts that I come across, things I hear from researchers and fisheries scientists etc. I'm not referencing anything because a lot of this is simply from discussions and debates. Any literature that I find i'll try get links up.
    Oh yes, please keep posting your unidentified fish in the 'Identifying your catch' thread.
    Regards, Carl

  3. #3
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    From leRoy

    Carl, I have seen the juvy leeries you speak of. I mentioned earlier that I think we have only scratched the surface in terms of targetting leeries consistantly. I should have included the science of leerfish biology there. I also mentioned that the world and its climate is changing, and it's creatures are changing with it. Now I know that you base what you said here on scientific "fact", but how does one then explain the sudden population burst I personally experienced in an estuary last year, that has been closed for years, or the fact that there's a self-sustaining population of them in a brackish lake, which is part of the same system, but never accesible from the sea due to a big weir in the feeder stream? If the leeries didn't spawn in there they'd be extinct long ago, due to the catch-and-keep live-baiting boater moegoes that plunder it regularly?
    In the more "normal" estuary I mentioned first (does open periodically, but not naturally, only when there's a serious risk of the houses built on its banks flooding, Parksboard ever so politely opens it up. You mentioned this earlier in the thread, but I confirmed this months ago with one of Parksboard's Big Sticks..anyway..) do the babies stay tiny and yellow until one day one of them gets an epiphany to the tune of, "Hey guys, it's August already! The mouth is opening in December, we'd better go murder some mullet so we can get big enough to tackle the ocean by then!"?

    Now, I am not a scientist, conspiracy theorist or even an expert, and I know that the written word on leerfish biology is not all based on guesswork, but I have more than just these reasons to think it's lacking. Just because leerfish spawning has been witnessed and proven in the sea, and spawning in estuaries has not been witnessed, does not mean it can't happen. I'm not trying to prove YOU wrong here, though, Carl, so please excuse this post!

    An example of active evolution: Less than ten years ago, cape weaver birds had a little problem - they kept being parasitised by Diederick cuckoos that entered their nests, kicked out their eggs, and laid their own in there for the weavers to raise. Today the weavers don't have this problem anymore, because the Diedericks no longer fit through the entrance holes to Cape weaver nests. In the last ten years, weavers have become fractionally smaller, and so did their nests. Just enough to keep the pesky cuckoos out. Interresting, hey? You could say that I'm comparing lemons with litchis here, but I would not be surprised if similar phenomena take place in the rest of the Animal Kingdom as the changing planet dictates.

    Sorry for jacking the thread with my verbal diarrhea, but I said earlier that I can talk about leeries for days.

  4. #4
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    Interesting observations you guys have made, i'll ask some of our lecturers what they think...

    Estuarine fishes recruit into closed estuaries during events known as 'overtopping'. During very high seas and storms they enter in the few waves that actually go over the sandbars. Not many people stick around in such foul weather to watch, but if you hold a plankton net in these waves, it will be full of postlarval fishes trying to enter the esuary.
    You have to remember that these fish are VERY small at this age, only one or two millimetres long. The tiniest amount of water overtopping is enough to carry the fish in.
    Sea fish spawning is not as simple as freshwater fish. They have various larval stages which they go through, where the morphology (shape) is completely different from that of an adult. Most sea fishes are highly fecund- i.e. they spawn hundreds of thousands of eggs which drift around in offshore currents. Here the little fish hatch and are surrounded by sufficient tiny food organisms in the plankton zones. As they drift towards areas with estuaries, they move inshore, they detect the presence of estuaries (probably by chemical changes in the water), where they hang around awaiting an overtopping event if they cannot enter on a high tide.
    Now i'm sure you can imagine that the chance of fish getting into the estuary is very slim, which explains why the parents invest into making so many eggs.
    Only some make it, but it pays off. Predation in estuaries is much lower for little fish, and food is abundant.
    This combination of events results in fluctuations in juvenile populations from year to year.
    As to where leeries spawn, you all know that the bigger fish leave in winter and go to natal (unless they are stuck in an estuary). They follow the sardines and pick up condition, after which they spawn in spring. Ichthyologists know this because it is only in Natal where mature fish with ripe gonads (eggs and testes) are found. Larvae can also be found in plankton samples along the coast. The sea currrent is ideal as it carries the fish down and disperses them to their nursery areas in the cape.
    So you see it is all rather complicated, but quite well researched and understood in this species!
    Oh yes, I have yet to catch a leerie!!!! I've tried though...

    The other day I went to an interesting talk on the effects of artificial mouth opening and the dangers it poses. Very interesting, i'll summarise it here:

    Natural mouth- closes with sandbar- water builds up in system (floods low lying areas)- force of built- up water breaks through and washes a deep mouth- this mouth stays open for months and is deep enough to be tidal- fishes recruit and leave.

    Artificial opening- houses threatened- channel dug before sufficient water buildup- water leaves, but not enough to erode a deep mouth- only stays open for a few weeks- not deep enough to be tidal- fish can leave but larval recruitment low.

    This is based on a talk by well-known estuarine Ichthyologist Alan Witfield, with particular reference to the swartvlei system.

    A new stat- the kob broodstock is down to 2.5% of what it used to be- based on tag- recapture statistics.

    Also had an interesting discussion in class regarding fishing licences and South African's general disregard of the law. Many fishermen don't have licences because they know they are unlikely to be caught. We South Africans all too often break the law just because we can, and then we complain about crime...
    We need a change in mindset. In australia, there is peer pressure from from other anglers to stick to the regulations. Somebody who messes up the fishing for everyone else is not tolerated.
    The ethics I generally see on this forum give me hope. If we can only convince other fishermen that the government isn't trying to steal their money with licences, its an investment into the future of your sport...
    Stick to the rules, convince other who don't, especially the types who say 'oh, its not us! Its the Japanese longliners wiping out our white musselcracker!!...) and we can all look forward to a future of recovering fish stocks where we can all catch (and release) that fish of a lifetime and have enough small fish around for the pot...
    Regards
    Carl
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  5. #5
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    HI Clarius

    All fish and wildlife are on the danger list, If we dont do something drastic, as a community against all forms of nature abuse I'm sorry It's tickets.

    Dave
    Handle every situation like a dog.- If you cant hump it, piss on it and walk away. --JASPER.

  6. #6
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    Very interesting and relevant post.
    WRT Zandvlei and houses being threatened by high (or low) water levels.

    The natural state of Zandvlei during summer is a dry salt pan. This was all changed by blocking the mouth for sailing regattas. No water no boating. This was the start of major human interference with Zandvlei's natural rythms.
    Last edited by BuzzLiteBeer; 09-05-08 at 08:34 PM.
    So Long, and Thanks for All the Fish.

  7. #7
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    Thanks, interesting point. Was just referring to estuaries in general.

  8. #8
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    Quote Originally Posted by poppernel View Post
    HI Clarius

    All fish and wildlife are on the danger list, If we dont do something drastic, as a community against all forms of nature abuse I'm sorry It's tickets.

    Dave
    PEOPLE, rats and cockroaches are not on any endangered list!!!
    I always wanted to be somebody,but now I realize I should have been more specific.
    Alcohol is the anaesthesia by which we endure the operation of life. GBS

  9. #9
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    Although if people were, rats and cockroaches would be too. But everything else would be better off

  10. #10
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    Quote Originally Posted by clarias View Post
    Thanks, interesting point. Was just referring to estuaries in general.
    Hi Clarias.

    Refering to Zandvlei in particular. The artifical closing of the mouth to create a permanent waterbody has had a major negative impact on the biodiversity of the vlei. Many species have actually disappeared while other invasive species have moved into the gap. The extremes of dry lake in summer and flood conditions in winter meant that the vlei/saltpan could support a richer variety of lifeforms including fish species. Sadly this is no longer true.

    I look forward to more of your posts on this subject. Maybe it will help educate fishermen in general.
    So Long, and Thanks for All the Fish.

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