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Thread: Sharks and groupers and divers

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    RBW Member Anthony Appleyard is an unknown quantity at this point Anthony Appleyard's Avatar
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    Sharks and groupers and divers

    https://en.wikipedia.org/wiki/Giant_grouper

    It seems from some marine biology television programs that sharks are a major factor in stopping groupers from growing too big to fit into available shelter. There have been occasional unconfirmed reports of giant groupers big enough to swallow a man :: for example Arthur C. Clarke wrote that he saw one in a sunken "floating dock" off Sri Lanka. If sharks are made rare by e.g. the shark fin trade, how much risk is there of giant groupers that big or bigger becoming much more common and a serious risk to unequipped bathers, or to divers?

    An item in a USA scuba divers' magazine I once read, said that in an incident at sea a big grouper sucked a scuba diver into its mouth head first so far that even his fins went inside; luckily its prey-crushing heavy pharyngeal teeth closed only on his scuba cylinder and dented it right in, and it spat him out alive and uninjured.
    Last edited by Anthony Appleyard; 14th October 2018 at 15:27. Reason: ed

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    Re: Sharks and groupers and divers

    Quote Originally Posted by Anthony Appleyard  View Original Post
    https://en.wikipedia.org/wiki/Giant_grouper

    It seems from some marine biology television programs that sharks are a major factor in stopping groupers from growing too big to fit into available shelter. There have been occasional unconfirmed reports of giant groupers big enough to swallow a man :: for example Arthur C. Clarke wrote that he saw one in a sunken "floating dock" off Sri Lanka. If sharks are made rare by e.g. the shark fin trade, how much risk is there of giant groupers that big or bigger becoming much more common and a serious risk to unequipped bathers, or to divers?

    An item in a USA scuba divers' magazine I once read, said that in an incident at sea a big grouper sucked a scuba diver into its mouth head first so far that even his fins went inside; luckily its prey-crushing heavy pharyngeal teeth closed only on his scuba cylinder and dented it right in, and it spat him out alive and uninjured.

    Hello Anthony, interesting idea you have posited.

    The grouper story sounds apocryphal, the only giant grouper I have encountered was a Queensland on wreck in PNG. It was definitely bigger than me by weight, it’s eye was big as saucer and upon seeing me come around the large funnel, it slapped its tail and displaced enough water to knock me backwards end over end. My point being, here was a predator bigger than me, yet it took off like a rocket after glimpsing my alien form.

    The same thing happened most of the times I encountered very big sharks. I was surprised, they were surprised and off they went. I think most big marine animals who have never or rarely encountered divers, are shocked by CCR divers. On rare occasions I have been subjected to territorial displays, bumping and once, in the case of a very large bull shark, aggressive staring. Which was way worse than it sounds..

    My point is that aside from deeply triggered instinctive behavior, apex marine predators usually treat me the way I would treat a visitor from one of Neptune’s moons who had a weird body shape almost as big as mine. Which is to put some distance between us.

    In my experience, there seem to be more groupers in the inshore tropical waters than sharks, so my guess is that their habits will not be significantly altered by less sharks in their territory. I think sharks have a greater range than groupers and other inshore reef fish. I looked for comparative population data, but couldn’t find any. I’m no scientist, just another fish lover..
    Last edited by silent running; 16th October 2018 at 05:19.

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    Re: Sharks and groupers and divers

    One thing to remember about groupers is that they are also prized food fish. Taking that into account, most of the larger grouper spieces numbers are “kept in check” more by human intervention that anything else. A recent case in point would be the proposal in Florida to reopen Goliath Groupers to sport fishermen, based on the argument that their increased numbers (barely back from nearly complete anihilation) are causing a lack of smaller fish for the sport fishermen to catch... 🤦*♂️

    Unfortunately, it seems, that we humans are reluctant to acknowledge that we don’t fully appreciate how marine ecosystems work and how our actions impact them...

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    RBW Member Anthony Appleyard is an unknown quantity at this point Anthony Appleyard's Avatar
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    Re: Sharks and groupers and divers

    The risk of them growing big enough to be dangerous, does not apply to groupers in general, but only to the big species Epinephelus lanceolatus.


    https://en.wikipedia.org/wiki/Epinephelus_lanceolatus

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    Re: Sharks and groupers and divers

    Here in Florida, particularly in Palm Beach County, we have a sizeable population of Goliath groupers (Epinephelus itajara), which grow to the same size as the Queensland Cod (Epinephelus lanceolatus) in the Indo-Pacific and Western Pacific.

    As a South Florida resident, I spend a lot of time diving (on CCR of course) with these magnificent reef fish, and have as many as 60 plus around during their spawning season, which runs August through September.
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    Re: Sharks and groupers and divers

    Quote Originally Posted by Anthony Appleyard  View Original Post
    The risk of them growing big enough to be dangerous, does not apply to groupers in general, but only to the big species Epinephelus lanceolatus.


    https://en.wikipedia.org/wiki/Epinephelus_lanceolatus

    Understood, but as I said above, all groupers are inshore species with a smaller range than most sharks, and my guess is they are not much affected by shark populations one way or another. Nor do I think sharks try to eat them unless they are old, sick or injured. I have seen a shark fight a Queensland grouper over a hooked fish and lose...

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    RBW Member Anthony Appleyard is an unknown quantity at this point Anthony Appleyard's Avatar
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    Re: Sharks and groupers and divers

    Quote Originally Posted by silent running  View Original Post
    ... all groupers are inshore species with a smaller range than most sharks, and my guess is they are not much affected by shark populations one way or another. Nor do I think sharks try to eat them unless they are old, sick or injured. I have seen a shark fight a Queensland grouper over a hooked fish and lose...
    Quote Originally Posted by Anthony Appleyard  View Original Post
    https://en.wikipedia.org/wiki/Giant_grouper
    It seems from some marine biology television programs that sharks are a major factor in stopping groupers from growing too big to fit into available shelter. There have been occasional unconfirmed reports of giant groupers big enough to swallow a man :: for example Arthur C. Clarke wrote that he saw one in a sunken "floating dock" off Sri Lanka. If sharks are made rare by e.g. the shark fin trade, how much risk is there of giant ...
    Likely Arthur C. Clarke's supergiant grouper got that big because it had a big-enough enclosed-enough wreck to shelter in. Someone told me that after the sunken floating dock was salvaged and taken away, the supergiant grouper was seen no more. On a TV sea biology program I once saw sharks attacking and demolishing a large grouper that they had caught in the open. I still suspect that when the sharks are gone, there will be much less control (except cold water) on where Epinephelus lanceolatus operate and how big they grow. In the incident described in the item in the USA scuba divers' magazine, his scuba cylinder saved him; if he was snorkeling with no scuba, he would likely have been swallowed.
    Last edited by Anthony Appleyard; 16th October 2018 at 16:48.

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    Re: Sharks and groupers and divers

    Quote Originally Posted by Anthony Appleyard  View Original Post
    Likely Arthur C. Clarke's supergiant grouper got that big because it had a big-enough enclosed-enough wreck to shelter in. Someone told me that after the sunken floating dock was salvaged and taken away, the supergiant grouper was seen no more. On a TV sea biology program I once saw sharks attacking and demolishing a large grouper that they had caught in the open. I still suspect that when the sharks are gone, there will be much less control (except cold water) on where Epinephelus lanceolatus operate and how big they grow. In the incident described in the item in the USA scuba divers' magazine, his scuba cylinder saved him; if he was snorkeling with no scuba, he would likely have been swallowed.
    Your post describes several factors which illustrate my points about range and habitat: a giant grouper who has grown too big to leave a confined space, has a very big advantage in terms of the energy it must expend to eat any prey unlucky enough to enter the cage, basically none. And, it is also protected from other large competitors entering its confined space. Conversely, a giant grouper is at huge disadvantage in the open ocean because sharks are faster, more agile and more numerous especially pelagic sharks like oceanic white tips. On the reef or a shipwreck, the grouper has the advantage of cover and a more local knowledge of its surroundings. If shark numbers dwindle in a particular area, it’s hard to imagine giant groupers significantly expanding their ranges without running into other giant groupers who will challenge them at risk of injury for both. Nor could I imagine groupers flourishing in a pelagic environment where their camouflage and physical characteristics keep them at a disadvantage over other large pelagic predators like tuna.

    Still find the giant grouper swallowing the diver story suspect. Every predator makes calculations about their prey’s ability to fight back. I can’t imagine any animal looking at a flailing, 4 limbed creature like an adult human and think it’s going to be easy to swallow them whole without a fight. Never mind the size of the mouth cavity and jaw required to do so...

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    RBW Member Anthony Appleyard is an unknown quantity at this point Anthony Appleyard's Avatar
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    Re: Sharks and groupers and divers

    Quote Originally Posted by silent running  View Original Post
    ...Still find the giant grouper swallowing the diver story suspect. Every predator makes calculations about their prey’s ability to fight back. I can’t imagine any animal looking at a flailing, 4 limbed creature like an adult human and think it’s going to be easy to swallow them whole without a fight. Never mind the size of the mouth cavity and jaw required to do so...

    Ordinary-sized groupers routinely swallow crabs and lobsters and octopuses despite their projecting struggling legs.
    Last edited by Anthony Appleyard; 20th October 2018 at 09:20.

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