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Why do sharks go nuts over boat engine legs?

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    Posted: 10 Feb 2020 at 3:31pm
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In my 50y Ive spent about 46 of the years spending time under water. Ive seen various big sharks but have never felt unsafe, Ive had Bronzies charge me and a lot steal my catch, but big Oceanic sharks just seem not interested. Where in Aus bull sharks and tiger sharks tend to be a little more aggressive so Ive seen (not experienced).

But there are so many sharks going nuts on Engine props and legs. This one I saw recently on youtube the flappn bull shark (much more crazy cousin of the B Whaler) is just head butting the engine at speed, quite a few times. Then there was the white pointer recently up at the Cavallis chewing on the prop and not going away. I mean Ive seen this at least 8 times over the years.

I know sharks just feel with their teeth, but this seems more odd than that.

Its almost like their is some sort of electric annoyance going on with the metals etc.

I might ask the Mrs to ask the Marine Bios, but if anyone knows of any studies into this bizarre behaviour I would be interested. Im sure I taste better than a Prop ;-p

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Post Options Post Options   Likes (0) Likes(0)   Quote Mr Moritz Quote  Post ReplyReply Direct Link To This Post Posted: 10 Feb 2020 at 4:51pm
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We had a GW hit the OB stern leg, after he chased some burly up when we retrieved it.
I don't think there was any agro in it. He followed the burly up at a steep angle coming in from astern at speed. Did a tight turn under the boat just below the surface and then hit the leg as he was moving away at speed past the stern. The OB was a write off and it certainly got the heart going at a high rate. The boat was anchored and OB not running in the Kaipara. She was big, estimate 5 metres.   
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Post Options Post Options   Likes (0) Likes(0)   Quote Wanda_Ra Quote  Post ReplyReply Direct Link To This Post Posted: 10 Feb 2020 at 5:44pm
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Because of Electrolysis.  Just a friendly exploratory chew.
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Post Options Post Options   Likes (0) Likes(0)   Quote krow Quote  Post ReplyReply Direct Link To This Post Posted: 11 Feb 2020 at 9:05am
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We tagged a 1.5m Mako a few years ago. After release it sat behind the boat a few meters away for about 30 seconds while it eyed us up and then charged and took a bite of the outboard just above the planing plate. Most fish would have high tailed it after release but not this Mako it had a serios aggression issue. As above though strange to attack the outboard. Had a blue shark up B.O.I. in November come chew on the stern leg a couple times too. Is it the same for fibreglass and alloy boats? 
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Post Options Post Options   Likes (6) Likes(6)   Quote Tonto2 Quote  Post ReplyReply Direct Link To This Post Posted: 11 Feb 2020 at 9:31am
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Pretty sure you'll be safe behind your keyboard
slowly going where everyone else has already been
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Post Options Post Options   Likes (0) Likes(0)   Quote kitno Quote  Post ReplyReply Direct Link To This Post Posted: 11 Feb 2020 at 10:21am
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Possibly because it's the only thing hanging down below the water line that they can get their mouth around.
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There is a school of thought that the relatively recent incidence of shark attacks on o/b motors is due to them being attracted to the stream from residual oil bearing exhaust emissions, particularly with larger HP 2 strokes. 
 
Admittedly any such trail would be very diluted but when it is claimed that sharks can detect & be attracted to a small concentration of blood from several kms away, is it beyond comprehension an oil/exhaust trail might have a similar effect. 
 
To support the supposition believers offer the following rational .....
 
The prop area would appear to scent driven sharks to be the primary source of the attraction therefore explains why the leg is invariably the area that is attacked.
 
The increasing number of hitherto rare incidents can be explained by the fact their are far more boats out there with much larger motors often anchored I sub 15 mtrs of water & generally speaking these are the ones experiencing frenzied attacks to the motors.
 
Believers in such theories ( even some sceptics ) now take the precaution of full tilting the motor whilst at anchor ... bit like having bananas on board ... most of us whilst scoffing at the belief dismissing it as pure superstition would I suspect, are like myself, inasmuch choose to abstain taking them rather than tempt fate.
 
Are any of these theories valid ??????
 
Personally I have know idea but imo until a more logical explanation
comes to light maybe they should not be dismissed.
 
Your opinions appreciated.
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Post Options Post Options   Likes (0) Likes(0)   Quote brmbrm Quote  Post ReplyReply Direct Link To This Post Posted: 11 Feb 2020 at 8:11pm
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Originally posted by Tonto2 Tonto2 wrote:

Pretty sure you'll be safe behind your keyboard

Lol out loud
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Post Options Post Options   Likes (0) Likes(0)   Quote bazza Quote  Post ReplyReply Direct Link To This Post Posted: 11 Feb 2020 at 10:55pm
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John ( aka Cirrus ) the resident expert on such matters maintains he has a perfectly logical reason that explains such behaviour by sharks.
 
It is his considered opinion that the marauding sharks are all randy males after a bit of leg !
 
Or perhaps that should read a bit of bit off leg !!
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Post Options Post Options   Likes (0) Likes(0)   Quote terrafish Quote  Post ReplyReply Direct Link To This Post Posted: 11 Feb 2020 at 11:19pm
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Originally posted by Tonto2 Tonto2 wrote:

Pretty sure you'll be safe behind your keyboard

Unless there's a power cut.
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Post Options Post Options   Likes (0) Likes(0)   Quote FizFisho Quote  Post ReplyReply Direct Link To This Post Posted: 12 Feb 2020 at 1:27pm
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Originally posted by bazza bazza wrote:


Your opinions appreciated.


Are you saying the oil aggravates possibly?

Ive not heard that one before, but it certainly would be detectable surely to an animal that smells 1/1mill blood to water. Interestingly human blood though doesnt seem to interest them where as pigs blood did. I will have to dig that science experiment up, was quite good.

Normally a shark will bite and know straight away if something isnt food, even humans when bitten usually are fatal due to loss of blood not due to being eaten alive as such.

So it is weird they are seemingly angry when these incidents occur. Thanks to cellphones more are being posted but there is bound to be a lot more that arent being reported.

I was going with the electrolysis type theory given. You also have different metals one being sacraficial to rust (annodes)

This is the one with the bull shark going nuts at the boat. It is a little bit OTT on the dramatics, but none the less is a bit different to the grab and go bites which Ive seen on the sides of boat by big white pointers (one on a big RIB totally moored up, an expensive pontoon fix bahaha)

https://www.youtube.com/watch?v=9xYiL1-y9Wo

This one the bull shark bites the leg while the prop is going lol, and people still swim in the Gold Coast canals.

https://www.youtube.com/watch?v=R3dQoUr3Bio
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Post Options Post Options   Likes (0) Likes(0)   Quote FizFisho Quote  Post ReplyReply Direct Link To This Post Posted: 12 Feb 2020 at 1:29pm
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Originally posted by bazza bazza wrote:

It is his considered opinion that the marauding sharks are all randy males after a bit of leg !
 
Or perhaps that should read a bit of bit off leg !!


Bahaha thats a cracka Cirrus. Did he come up with that one himself?

Edit: Just found this one in SAFA on another RIB this time with people in it. Even all 3-5 pontoons down most RIBs would stay afloat but would still have given the German tourists a bit of a fright lol, or great pics.

https://www.youtube.com/watch?v=523KJ8pp8DU

I can understand sharks biting the sides of boats etc, letting go once they realise its nothing to eat.

Its more this specific phenomena thats going on with them not liking boat legs.

I asked one of our marine biologist mates the Mrs dd her PHD with but she studied Molluscs so no answer, she is also a spearo and also was curious if it was some kind of electrical annoyance.

Strangely Ive only seen white pointers and bull sharks do it. Tiger sharks are just about as nutty as bull sharks but not heard of them doing it.

Either way oil, electric, just crazy sharks seeing something flashing in the water, it would spoil your day losing your prop.


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Post Options Post Options   Likes (0) Likes(0)   Quote Rozboon Quote  Post ReplyReply Direct Link To This Post Posted: 12 Feb 2020 at 2:43pm
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I always thought it was because of the sacrificial anodes creating a small electrical field. I've had a couple of them come up and mouth at the leg, never aggressively bite it, as above they just seemed to be trying to work out what was going on.
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Post Options Post Options   Likes (0) Likes(0)   Quote FizFisho Quote  Post ReplyReply Direct Link To This Post Posted: 12 Feb 2020 at 2:55pm
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Originally posted by Rozboon Rozboon wrote:

I always thought it was because of the sacrificial anodes creating a small electrical field.


That is exactly my theory.
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Post Options Post Options   Likes (0) Likes(0)   Quote smudge Quote  Post ReplyReply Direct Link To This Post Posted: 12 Feb 2020 at 3:31pm
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Originally posted by terrafish terrafish wrote:

Originally posted by Tonto2 Tonto2 wrote:

Pretty sure you'll be safe behind your keyboard

Unless there's a power cut.
 
Guys, let's not wind up Fiz,  you may have difficulty accepting some of his posts and if that's the case best not to comment on his posts.


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Post Options Post Options   Likes (0) Likes(0)   Quote Tonto2 Quote  Post ReplyReply Direct Link To This Post Posted: 12 Feb 2020 at 3:39pm
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Sorry
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Post Options Post Options   Likes (0) Likes(0)   Quote smudge Quote  Post ReplyReply Direct Link To This Post Posted: 12 Feb 2020 at 3:41pm
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Originally posted by Tonto2 Tonto2 wrote:

Sorry
 
All good Tonto


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Post Options Post Options   Likes (0) Likes(0)   Quote Mr Moritz Quote  Post ReplyReply Direct Link To This Post Posted: 12 Feb 2020 at 3:42pm
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I have heard about a boat which had an out of balance prop, which made a distinctive noise in the water. This noise attracted king fish to it for some reason.  
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Post Options Post Options   Likes (0) Likes(0)   Quote Alan L Quote  Post ReplyReply Direct Link To This Post Posted: 12 Feb 2020 at 4:35pm
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I could go with the electrolysis thing. Sharks - as well as the smell sensors have extremely good electromagnetic sensing - eg the pulses given by living things - heart beats etc.
I did have a bronzie have an aggressive chomp at the bottom leg a couple of months ago.
Full teeth bared and a head swipe  at the leg. But in its defense it was tied to a rod that was hauling it to the boat. Could be forgiven - but fearsome to watch at close quarters.
I have had blues come up and nudge the back of the boat repeatedly.
Alan 
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Post Options Post Options   Likes (0) Likes(0)   Quote Alan L Quote  Post ReplyReply Direct Link To This Post Posted: 12 Feb 2020 at 4:51pm
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There was a guy (old hang gliding mate) a decade or so ago, promoting shark proof wet suits. These were based on a mesh of wires in them and the magnetic field it produced. Whether it ever proved it s worth, dunno. But do recall him in a shark tank demonstrating when he turned it on/off.
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