larger Mahseer seem to be the most vulnerable
That they are. I fished the river earlier ion the year and was dismayed to see lots of lines on bamboo poles in several sections of the river upstream of the main fishing beat - where "strangely" there are almost no sizable fish.
On reporting this poaching to the controllers of the stretch, I was told "Yes, we allow this. But those lines will not catch a mahseer".
No, they probably don't catch a lot of mahseer, but I bet they kill a fair few.
Even if only one in 10 big mahseer that picks up a bait fails to shed the hook and subsequently dies, the population will very soon be devoid of big old breeding fish.
Worryingly, this process has been observed to affect fish stocks by providing an evolutionary push in favour of genes that lead to smaller maximum size, faster growth rates and early sexual maturity.
If it keeps up, in 40 or 50 years, the maximum size of a mahseer might drop significantly.