Have seen many fish with the tip of the tail bitten off so you will probably find its quicker and easier for them to go for the fork .
That's what I usually do so there is no mistake in getting an undersized fish in your bag.

 is that you ensure that the tail is in the "natural position" and measure to the end of the fin. The natural position being how the rail looks when you first pull the fish out of the water and not squashed together to "extend" the length.

As mentioned above, it is safer to measure to the fork, as that way you know the fish is legal.

Many brag mats out there are not accurate at all, so dont rely on them to give a true indication of a fishes length either.

I always measure to the middle of the V I asked the question to a fisheries officer once and he gave me a explaination his partner then argued he was wrong. I left them arguing the point none the wiser, by measuring to the middle of the V your safe.

 For keeping fish the regs are quite clear: to the tip of the fin with the fin in a natural state (ie not stretched). If you do stretch it and fisheries check you how confident are you that they'll do the same?

as for measuring to the fork. The reason researchers do that is that it a better, more accurate measure of a fishes length, as it's fairly fleshy and not that flexible. The tail on the other hand can vary a but fish to fish, so when calculating weight/length/age data it's better to use the fork not the tip of the tail for accuracy. As weight/length is roughly a measure of how fat the fish is, having a slightly longer tail wouldn't have much effect. Also the nipped tail thing. 

 Well the fisheries stickers say to measure from the nose to end of tail. So unless they are just trying to make it harder to get a size fish who knows what they are on about.

 Ive always measured from the "V" as thats the regultions over in NZ, from the tip of the nose to the middle ray or "V" of the tail. i guess if you do that then you cant go wrong unless you cant read a tape measure.

 Fisheries stickers say to the tips in natural position. 

Recreationl fishing guide states

"To check if your catch is of a legal size, measure finfish from the point of the snout to the tip of the tail."

and the shark bay pink snapper rules states.

"Measure fish from nose to tip of tail"

So if you measure to the V you are easily in the clear.

 I'm surprised this question has even been asked, but considering the confusing answers you recieved i can see how you would like some feed back.  W.A has always been to the tip of the tail as far as i know, it is quite clear in the fisheries guide as Lossie65 has pointed out. 

What dosn't surprise me , is that fisheries officers or volunteers don't even know the basic, simple rule of how to measure a fish in W.A waters. I have called fisheries with other questions only to call back and get a completely different answer, then to call again to get a third answer that was still wrong. Makes it hard for fisho's to do the right thing, I always carry a current rules and guide booklet with me now, and have many times pointed out the laws to fisheries who were trying to tell me i was doing the wrong thing.( i;e how to measure a fish ) 

I'm not against fisheries at all, but would realy like to see them and volunteers trained better . 

 Agree wit ya grantartic1 called them twice on the boat the other week for catch limit on kg and in the space of 10 mins had to different answer so went wit the lowest answer to cover my self which proved to be wrong any way but atleast I was with in the limits. Also a few days later me and my dad went into the fisheries won't mention were and had a different answer from them too, then another guy came over and went through it with us goes to show the need more traing too.