Marlin relative weight in water

[Adrian_Graham]

Anyone know what percentage of its weight in air a marlin weighs in the water? This is probably a complex question, because presumably it will depend on the fish's bouyancy, based on what it has in its swimbladder, and how deep it is (based on compression of the gas in the swim bladder), but does anyone know of a typical ratio? I've heard something in the region 6 - 10%.

[Warren_Brantley]

OK (peeked my interest on this one) so I researched it online. Mass is a measure of inertia and WEIGHT is a measure of gravitational pull. It is unchanged by water. Thus a 500# marlin exerts the same gravitational pull whether it is in water or not. Thus the problem faced by anyone with a deceased marlin (been there done that) at the end of the line. The variables addressed regarding air bladder, contents, etc. would involve the weight and mass dynamics of physics, movment, water resistance or friction and many others; but would not effect the more basic concept of the actual weight of the fish.

You don't want a huge one to die on you because 80 - 130# line cannot lift that much weight unless you effectively apply planing concepts (reduction of resistance plus the additive factor of any forward momentum) instead of lifting dead weight. Anyone find any research that is different?

The example they gave was: if you throw a 5# fish in a 21# bucket of water what would it weigh? The answer is 26#.

Hey, too much thinking......let's go billfishing. WGB

[Adrian_Graham]

Not convinced! If you were to get a 200# empty gas cylinder, fill it with liquid or compressed helium until it weight 700# (so you have 500# of helium), then you get a balloon (let's forget how much it weighs); you release the 500# of helium into the balloon --- the balloon don't weigh 500#! All to do with relative bouyancy, I think. Also, try getting into the water and supporting the weight of a big fish (with your feet on the bottom). Now try the same thing on land. Now go to your chiropractor!

Adrian

[Capt._Warren_Brantley]

I agree. Cannot find the formula online. The online site was referring to the "weight" concept only and did not address the other variables.

Linwood......any ideas? I'm normally worrying about running out of line on an 80 wide as one screams for the distance. Have not hopped in the water to support one yet. WGB

[Linwood]

No. If you are getting 80Ws stripped,you need a faster boat.

[Nick_Fuegi]

[Nick_Fuegi]

[Nick_Fuegi]

What you need to know and want to know is the *density* of a "standard" marlin. lol.

http://en.wikipedia.org/wiki/Buoyancy

Let's look at an example. Imagine an oversimplified 1500Kg marlin (it's a real monster (over 3000lbs) to make things exciting;)

Let's assume for the sake of argument that it's also cylindrical. It's 5m long and has an average girth of 2m. The volume of this hypothetical marlin is calculated thus...

Average circumference of 1.8m gives radius of 28.65cm. This gives area of X-section of cylinder of 2578.3cm. For volume, multiply area of x-section by length of cylinder = 1289150cc marlin! That's 1289litres which weighs the same in Kilos. So the fish *displaces* 1289kg, but weighs 1500kg. So, the fishes dead weight in water is the difference. 211Kg. You couldn't haul it straight up. Buy you might be able to get it moving forward and that might generate enough lift to cover the difference. This assumes that the water-resistance at the speed required to generate the lift did not over-load the line.

Of course this is only a hypothetical marlin for the sake of showing the calculation. In short you need to know the volume of the fish and its weight (at STP of course;) to work out the density. Then, from the density and displacement you can work out the buoyancy. I have not included several other factors like the fact marlin swim in salt-water and not distilled (so doesn't weigh exactly 1kg/litre).

Also, I doubt many people have measured the density of a marlin! The next one that comes up dead, you should do it. Google for how - it's simple (on a small scale)!

However, someone has measured the density of a "fish carcass". http://www-personal.umich.edu/~pwebb/NRE422-BIO440/lec12.html

So, if we assume marlin to be standard fish carcasses, it is said that they would weigh 1025kg/m3 in sea water and 1075kg/m3 in air. If true, you can say that every 1000Kg of dead marlin exerts 50kg strain on the line in water. Obviously this does not take into account inertia, water resistance, skill/smoothness of angler, where the fish is hooked, whether the fish is hung up on the bottom, whether its swim bladder has been crushed (depth of fish will change its density - deeper will be denser) and so on. However it shows that if one is careful and the seas are not too rough, it should be possible to 'plane up' even very large marlin on 130 gear. The deeper the fish, the bigger the problem. The further forward it's hooked the easier it'll be to plane up (more leverage to get the head up). The stories tend to go with this too.

Hope that helps! ;)
Can't believe you made me think about that! It's going in the book as the saddest moment of my sorry life. rofl!

Nick

[Nick_Fuegi]

Just to really top this crazy thread off. Some people believe that a marlin is neutrally buoyant in water as it uses its swim bladder so it doesn't sink. However this is not true. In fact it is not even necessarily true. Fish generate a lot of hydrostatic lift as they swim, so they need not use the swim bladder much unless they are stationary. Much like an aircraft does not need to be lighter than air to fly, and it doesn't fly unless it's moving. Consequently they don't need fill any planes with helium, or tie them down at the airport.

Marlin are always swimming and generating as much lift as their speed/attitude in the water and posture (of pectoral fins etc) cause.

Also, if a fish goes deep the water, pressure will crush the swim-bladder rendering the fish negatively buoyant. If the fish is big, deep and dead, it could be heavy. This phenomenon is well known to divers. Below surprisingly shallow depths (like 10m) the pressure crushes their lungs until they no longer cause the body to float. You have to swim upwards until the body becomes positively buoyant again.

Anglers use the hydrostatic lift principle to lift heavy dead fish from depth. We have clearly established why it would always be best to plane a fish up as much as possible and also that if the fish make it to the bottom, the hardest part will be getting it moving (pecs/tail dragging through mud/rocks).

So, next time your fish goes deep and you have an idea it might have died, might be an idea to move the boat away to shallow the angle of the line and lock up the drag to plane it up before it reaches bottom. This won't necessarily work because if the fish is tail-wrapped, and/or hooked funny, or gets rigormortis with its pecs pointing down, you won't be able to plane it up. It seems to be pretty standard practice to move the boat away from deep fish anyway. Obviously if the fish didn't plane-up and makes bottom, you've only got one option. Try to haul it up like a sack of potatoes or lose it. I suppose a resourceful crew might slide a gaff/anchor down the line and snag the fish on a strong rope!

I've also heard that mono line is better at resisting a slow steady pull than braids of the same strength. This and the elastic properties might make it better for planing fish up. Can't say I've tried it tho.

Nick

[Nick_Fuegi]

They don't have to fill planes with helium *to make them fly* - or have to tie them down at the airport to stop them floating away.

Divers lungs are crushed *enough* at about 10m to render them negatively buoyant. - Obviously they and/or their lungs are not completely crushed! ;)

Thought I'd get there before someone asked!

Nick

[Nick_Fuegi]

I've been referring to hydrodynamic lift as hydrostatic lift.

In above coms read hydrodynamic wherever you see hydrostatic.

Hydrodynamic relates to moving throught the water. The swim bladder, bod fat etc provide hydrostatic lift.

Nick

[Adrian_Graham]

Nick,

Answer sounds plausible, thanks.

Adrian

[Nick_Fuegi]

All this made me realise something which many capts will probably already know. The most important thing in planing up dead fish (that's too heavy for the line class to pull straight up), is the angle of the line at the start of the process. Too steep an angle and you increase the chance of a break-off. So, the best chance is theoretically... Before starting the pull, let out line and get far enough away from the fish horizontally so the line is at an angle of less than 45degrees (you want more horizontal pull than vertical).

Obviously this still won't work if you are pulling towards the fish's tail. You need to be pulling from the head end. When the fish sinks, it will sink with its head towards the boat (pulled that way by the line). This will be modified somewhat by any current. The head head will be pointing into current somewhere between the direction the boat was pulling from and the direction of the current. You need to remember which way the boat was facing/travelling when the fish sank, take into account any current and start your pull in the original direction of travel and slightly into the current. This would (theoretically) give the best chance of planing up the fish assuming it wasn't hung up etc etc.

I gather that when planing fish up, the boat pulls then backs down to gain a bit of line, then pulls etc. It's important not to back down too much (and increase the angle too much). Each time the boat moves ahead again, it needs to come tight gently. I guess the point at which you'd back down would be when the fish was no longer rising in the water, and you'd start forward again just before the line reached the original angle (that you know works for raising the fish). It would pay to know what the max speed each line class can drag a big marlin through the water at. This could be tested if when an marlin dies and you have it at the boat, rope it off with a long rope coiled in the boat. Tow the fish on the rod line with the drag locked down(Imaging it's the worlds largest bait) and the rod-tip in the water (so the fish isn't skipping). See at what speed the line breaks. Recover the fish with the rope. Have a good laugh at what you jus did and then be ashamed the marlin died. Doubt you'll find many fishermen taking a few minutes out of their day to do it though! :)

If you did it really scientifically, you could calculate the hydrodynamic efficiency of a marlin.

I wonder if this will ever be of any use to anyone?! If it is, remember to post here! ;)

Nick

[Nick_Fuegi]

Just read about your trip to the Azores last year Adrian.

Nice! Good story too.

Stumbled upon the write-up of your 6h battle when I was researching/dreaming about Azores billfishing. Congrats on the release.

Sorry to hear about the fish that died. On reflection, it's for the best that the other fish is still around. Whilst there is a lot of skill in finding, hooking and fighting the fish, there's a lot of luck when it turns out to be one of the biggest ever. Therefore, you can say that all world records in fishing are at least as much luck as judgement. Maybe if I got one, I'd think differently! However, I'd be deluding myself - as fishermen love to do.

That fish was one in a million and could produce millions more marlin. Killing it would be a shame.

Who needs a record like that anyway?

Satellite tagging it. That would have been priceless.

Nick

[Adrian_Graham]

Nick,

You're right. The good thing was not to get the record, but to run into fish of that size, something very few anglers will ever do in their lives - even dedicated marlin anglers.

Guess where I've booked up to go next year, at about the same time...

Adrian

[Nick_Fuegi]

I'm not surprised! Good luck Adrian.

The Azores needs a more powerful presence around here imho.

Atlantic SST's are looking warm. If the stream doesn't miss, there could be a bumper crop this year.

Can't wait for reports of your trip. I've always wanted to fish there. Big marlin; chance at Bigeye and/or BFT. For someone relatively inexperienced (like me), the Azores seemed risky. If I had the cash/fishing buddies to go after really big fish without having to 'worry' about 'ordinary' (HA!) pelagics as trip insurance, the Azores would be about top of my list.

Have you tried for swords in the Azores? Any luck?

Nick

[Adrian_Graham]

Nick,

Don't think there are any swordfish in the Azores - think the local fishermen have done for them. Florida seems to be a good place to get them now - large numbers but not large fish. Never caught any tuna in the Azores. Bluefins are ocassionally caught and there are yellowfins (see the Blue Planet!), but I have never hooked any big ones. If you want tuna, go to Ascension. Yellowfins galore - you can see them off the end of the pier and catch as many as you want from a mooring - don't even have to troll. When I was there, I caught a 160lb big eye, a 150lb yellowfin, a couple of 100's (double header) and lost count of the smaller fish (smallest about 30-40lbs). One night, the captain was using sabikis to hook goggleeyes. As soon as he got one, it was put on my hook and dropped the other side of the boat, where they were taken as soon as they dropped past the keel - tuna after tuna after tuna, all 50 - 80lb, until I could take no more. Marlin seems a little more hit and miss there (I didn't get any on my trip, and this year past was pretty slow generally), but there are big marlin there.

Adrian