Length/ weight

Today I caught a 15 inch Brownie from a river. I used to weigh them, but in the interests of effective catch and release I've stopped doing this, I'm going to get approximate weights from the length, having tippexed little white blobs on my rod from 12 inches from the but, up to 16 inches.

I've looked around on the net, I can't find a listing of typical weights for lengths. Can anyone help at all?

My best guess is that my fish weighed 1.12 to 2lb. Am I close?

Why don't you get one of those landing nets with the scale in the end. I use them for a quick check on the weight of trout that I am going to release. Mine is quite accurate.

Ron, do you know if they do one 'tennis racket' style? It's all river fihing I do you see...

Mine is a New Zealand manufactured net made by Maclean Angling. It folds up and has a belt clip.

I have had trout of nearly 10 pounds in mine with no problem, but I think it's a bit too big for your needs. I think Orvis do a small tennis racket style net with a built-in scale.

I'll have a troll.

Whats wrong with hanging your net off the scales?

Nothing Ian, but Trout are a bit frail after they've given their all in the fight, especially during the height of summer. I like to keep them out of water for as little time as possible, so I'll try to avoid rummaging in my bag for scales etc...

Quite right Ric.

It only takes a few seconds to check the weight of a trout caught in my net. Other than that the fish is unhooked in the water and released.

My hooks have the barbs squeezed down slightly so that they come out easily. Don't like barbless hooks at all, they cause more damage than a hook with a barb.

Ric,get yourself a copy of "Muriel Fosters Fishing Diary", a very old book written and illustrated by a pathfinder for women anglers, (covers her fishing around the 1900s). Her weight for length scale in the book is spot on, I have been using it for years and you can leave your net at home. for example, a 14inch brown trout is 1.25 lbs, and you get a salmon scale too, should you hook a big brother. Copies appear on Ebay and are well worth getting. get a copy and enjoy some old time fishing stories from around Britain. She must have been an amazing lassie, for she enjoyed any fishing in any weather. This book may get you to keep a diary of your own, for other folk to read when we are all pushing up daisies, and the british isles is one huge housing estate.

Ric - you say you used to weigh the trout you caught. Did you keep records of length as well? If you did you could work out your own weight/length chart by interpolating (or extrapolating) from a few known examples. That way you would have a 'condition factor' that related to the trout in your particular water.

If you don't know how to calculate for larger or smaller specimens here's how:

The weight of a fish is proportional to the cube of its length; double the length and the weight increases eight times. In other words, if an 8-inch trout weighs 4 oz in one water; a sixteen inch trout from the same water ought to weigh 2lbs.

To work out a range of lengths and weights from a single known example*, divide the proposed length by the known length (in this case 8") cube the result and multiply this by the known weight. So, for a 6" trout you have 6 divided by 8 which is 0.75; the cube of which is 0.42; multiplying this by the known weight (4oz) gives a weight of approx 1.7oz.

For a proposed length of 19 inches it will be 19/8 = 2.38. Cube this gives 13.4. 13.4 x 4 = 53.6 ounces, or 3lb 5oz.

*To get a better idea of the general condition of 'your' trout it would be prudent to record weight and length of several fish and work out a condition factor for each. Just cube the length and divide by the weight.

Suppose you have two trout of 8 inches, one weighing 4oz and one weighing 5oz; the first one has a factor of (8 x 8 x 8 = 512/4) = 128, whereas the second is (8x.... = 512/5) = 102.4. You can take an average from these of 115.2 and work out a notional trout of eight inches thus: length cubed divided by condition factor equals weight (8 x 8 x 8)/115.2 = 4.4oz.

This principle works for most species - Mona's Scale is based on it, which is a pretty accurate guide for the weights of pike (except when carrying roe, as the large females usually are in the last couple of months of the season). However, it doesn't apply too well to carp as, even in an individual water, their proportions can vary so much. For carp it is better to use George Sharman's system, although this is more complex.

Fred, I have fished a few waters in the past where the condition factor has been tremendous. In fact some rainbows have almost looked like bream in shape with tiny heads and deep thick bodies.

When Grafham first opened in the 60, some of the fish were like that.

In Natal lakes over 6000 ft, the rainbows used to put on weight like the clappers. A two year old fish would weigh 6lbs.

Sorry folks, that should read "14 inch brown trout will weigh 1 and 3/4lbs" not 1 and 1/4lb. Whoops.

Ric,

Like Ron, I use a MacLean net with integral spring balance. Mine is similar to Rons, being folding and also extending.

I fish rivers all the time and have fished densely wooded New Zealand and Canadian rivers using this net.If you hang it on a D ring on your back from the hinge (I use a magnetic release, with a lanyard), it actually sits higher on your back and takes up less room than a "tennis racket" type.

Alex

Today I caught an 18 inch Brownie from the Derbyshire Derwent. Now where's me calculator...

Try this:
http://www.letsflyfish.com/weight.htm

For salmon, but in the same ball park.

Tom

link should now work
http://www.letsflyfish.com/weight.htm