looks like you could make a DIY one in minutes,
Yes, and here are a couple of examples of simple DIY release weights posted on Western Australian fishing forums.


The second one is used for larger fish (about 15kg up)
The main point of all these posts is to tell people about the release weight and that they DO work to get fish back down to depths:-
1. where the fish are recompressed to minimise the effects of barotrauma (it's like the bends in divers),
2. so they don't have to fight their way down past the predators - because while they are swimming on their own they are often sending out those "I'm struggling - come and eat me" signals
The posts are not about promoting a commercial product. Here in Western Australia those Release Weights are sold in many tackle shops at just above cost, and come with a free DVD on how to use them and the benefits of using a release weight.

Download and view it from
http://www.recfishwest.org.au/ReleaseWeightDVD.htm Lots of other links in there too.
The free DVD and videos is one of the initiatives of Recfishwest which is an organisation which represents the interests of recreational fishermen in Western Australia.
And one of the interests of recreational fishermen is to make sure that the iconic species don't get overfished and disappear.
So every possible way to increase the survival of any fish which is/has to be returned to the water is VERY important.
Tagging and recapture studies
http://www.recfishwest.org.au/TaggingPr ... aryResults show that release weights DO work better than any other method on some of the vulnerable species on the West Coast of Australia.
See
http://www.recfishwest.org.au/ for lots of info about what Recfishwest does.
TerryF
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Beavering away in the background.......