Print Page | Close Window

Why do sharks go nuts over boat engine legs?

Printed From: The Fishing Website
Category: Saltwater Fishing
Forum Name: The Briny Bar
Forum Description: The place for general chat on saltwater fishing!
URL: https://www.fishing.net.nz/forum/forum_posts.asp?TID=132900
Printed Date: 29 Mar 2024 at 7:27am


Topic: Why do sharks go nuts over boat engine legs?
Posted By: FizFisho
Subject: Why do sharks go nuts over boat engine legs?
Date Posted: 10 Feb 2020 at 3:31pm
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




Replies:
Posted By: Mr Moritz
Date Posted: 10 Feb 2020 at 4:51pm
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.   


Posted By: Wanda_Ra
Date Posted: 10 Feb 2020 at 5:44pm
Because of Electrolysis.  Just a friendly exploratory chew.

-------------
If you think you are too small to make a difference,try sleeping with a mosquito in your tent.


Posted By: krow
Date Posted: 11 Feb 2020 at 9:05am
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? 


Posted By: Tonto2
Date Posted: 11 Feb 2020 at 9:31am
Pretty sure you'll be safe behind your keyboard

-------------
slowly going where everyone else has already been


Posted By: kitno
Date Posted: 11 Feb 2020 at 10:21am
Possibly because it's the only thing hanging down below the water line that they can get their mouth around.

-------------
Top 10 finish
2024 Grunter Hunter.


Posted By: bazza
Date Posted: 11 Feb 2020 at 1:32pm
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.


-------------
When you cry, feel pain or sadness, no one notices your sorrow .... BUT
fart just ONE time !!!!!!!!!!!


Posted By: brmbrm
Date Posted: 11 Feb 2020 at 8:11pm
Originally posted by Tonto2 Tonto2 wrote:

Pretty sure you'll be safe behind your keyboard

Lol out loud


Posted By: bazza
Date Posted: 11 Feb 2020 at 10:55pm
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 !!


-------------
When you cry, feel pain or sadness, no one notices your sorrow .... BUT
fart just ONE time !!!!!!!!!!!


Posted By: terrafish
Date Posted: 11 Feb 2020 at 11:19pm
Originally posted by Tonto2 Tonto2 wrote:

Pretty sure you'll be safe behind your keyboard

Unless there's a power cut.


Posted By: FizFisho
Date Posted: 12 Feb 2020 at 1:27pm
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" rel="nofollow - 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" rel="nofollow - https://www.youtube.com/watch?v=R3dQoUr3Bio


Posted By: FizFisho
Date Posted: 12 Feb 2020 at 1:29pm
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" rel="nofollow - 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.




Posted By: OuttaHere
Date Posted: 12 Feb 2020 at 2:43pm
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.


Posted By: FizFisho
Date Posted: 12 Feb 2020 at 2:55pm
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.


Posted By: smudge
Date Posted: 12 Feb 2020 at 3:31pm
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.


-------------
Best gurnard fisherman in my street


Posted By: Tonto2
Date Posted: 12 Feb 2020 at 3:39pm
Sorry

-------------
slowly going where everyone else has already been


Posted By: smudge
Date Posted: 12 Feb 2020 at 3:41pm
Originally posted by Tonto2 Tonto2 wrote:

Sorry
 
All good Tonto


-------------
Best gurnard fisherman in my street


Posted By: Mr Moritz
Date Posted: 12 Feb 2020 at 3:42pm
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.  


Posted By: Alan L
Date Posted: 12 Feb 2020 at 4:35pm
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 


-------------
Legasea Legend member


Posted By: Alan L
Date Posted: 12 Feb 2020 at 4:51pm
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.
Alan


-------------
Legasea Legend member


Posted By: MATTOO
Date Posted: 12 Feb 2020 at 6:43pm
Tonto has the best reply. Good on you.

If your asking this question you have too much time on your hands.

If you don't understand shark behaviour and physiology your either not fishing enough.
Don't read, don't study or have no interest in the environment you have pleasure in.

Stick with Facebook or the Sunday papers if your looking for headlines..

Or if your interested in passing on good info research info and post links.
Rather than catching grazers.


Posted By: FizFisho
Date Posted: 13 Feb 2020 at 12:59am
Originally posted by Alan L Alan L wrote:

I did have a bronzie ...


Was it a stainless prop? Im just wondering if the shimmering does it.

Like hanging kingi attractors off the side of a boat while spearfishing etc.

Just another thought. But I do think the electrolysis sounds logical. It could be 3 things, attraction (shiny prop), electrical annoyance, simply the lowest thing in the water.


Posted By: Alan L
Date Posted: 14 Feb 2020 at 7:24pm
Yes - stainless prop.
Not generally had them aim for the prop. The leg seems more interesting. But it is the lowest bit in the water.
Would be interested to know what happened to my mates 'wired' wetsuits. Was a TV programme on them a while back with some science studies backing them up from memory.
Alan


-------------
Legasea Legend member


Posted By: FizFisho
Date Posted: 17 Feb 2020 at 3:10pm
Originally posted by Alan L Alan L wrote:

Would be interested to know what happened to my mates 'wired' wetsuits...
Sounds like the Shark Shield, which was an aussie invented device you wear around your ankle for divers and surfers. But it didnt take on, at the time, but thats going back nearly 20 years. The technology has been outsourced now, this freedom looks like a much smaller version.

I think some people were of the thought, a White Pointer which typically comes up from the bottom at about 30-35kph is not going to come to a sudden stop when it gets to the Shark Shield, of course nobody can sunstantiate that thought.

But interesting its outsourced tech now and how its utilised.

Will dig up some reviews on it.

Some thoughts on whether it attracts or deters. 

https://www.oceanhunter.co.nz/shop/Brands/Shark+Shield/Shark+Shield+FREEDOM7.html" rel="nofollow - Ocean Hunter

https://ocean-guardian.com/blogs/misc/shark-deterrent-myths-busted" rel="nofollow - Ocean Guardian

In WA which Cottesloe in Perth is notorious for surfers and kayakers being attached by White Pointers, they give a massive grant for you to buy one..... https://www.bbc.com/future/article/20180228-can-technology-save-us-from-shark-attacks" rel="nofollow - link

Sceptical, but this is kind of what bull sharks look like when hitting the back of the boat, NUTS, in this case they all go crazy and get the F out of there fast lol.




Posted By: Mr Moritz
Date Posted: 17 Feb 2020 at 4:23pm
Might be handy to have one of those to keep sharks away from your outboard..


Posted By: Mr Moritz
Date Posted: 17 Feb 2020 at 4:33pm
Why I am careful around GW

https://www.youtube.com/watch?v=DYpGfqEK1A4" rel="nofollow - https://www.youtube.com/watch?v=DYpGfqEK1A4


Posted By: FizFisho
Date Posted: 17 Feb 2020 at 8:27pm
Originally posted by Mr Moritz Mr Moritz wrote:

Might be handy to have one of those to keep sharks away from your outboard..


Well they are meant to go around a Leg baha


Posted By: puff
Date Posted: 18 Feb 2020 at 12:15pm
Some of the replies/trolling on here are pot kettle black which is funny...
The question is quite intriguing really


Posted By: Alan L
Date Posted: 18 Feb 2020 at 3:55pm
The thing I saw - was on a TV prog, was a whole wetsuit - had fine wire mesh in it. NZ invention. I guess if it caught on we would know about it.
Alan


-------------
Legasea Legend member



Print Page | Close Window