Precaudal length, from the tip of the nose to the notch in the tail
In South Africa we use the method of measuring fish and then using a conversion table (, which can be found on the Ocean Research Institute's website http://www.ori.org.za/fishcalc.php) to calculate the weight of the fish according to its length, or disc width for rays. This is the only method of weight calculation in competitive angling in South Africa, therefore enforcing conservation.
This method of calculating a fishes weight is a means to help conservation of our sharks and rays and other big fish, to ensure that they'll be around in the future for our kids to catch and marvel at their beauty and size. It is a more conservation friendly method, as sharks and rays dont have to be killed and taken to a scale to find out its weight, or be weighed on beach which was/is a long painstaking process, which was/is impractical.
Me with a Diamond Ray, disc width/wing span is measured underneath the fish.
There are various ways in which to measure different fish, some fork length, some total length and others precaudal, all of this can be found out on http://www.ori.org.za/ , make sure you know which one is the correct one for your fish. You don't want to measure a fish wrong be telling everyone that you caught a 300kg shark, when in fact it was only 130kg, and end up looking like a fool.
So if you are new or old to the sport of shark angling, and are targeting rays and sharks, even big Kob, make sure you have a tape measure at hand for when you land your fish, so it can be measured, pose for a quick couple of photos (for the none believers) and quickly returned to the ocean to be able to fight another day.
