Fish and Game had to seek regulatory change from the government to put in place a season bag limit - something that hasn't been done here before.
Grubb said, without knowing what's causing the drop in numbers, reducing the catch limit is the best option.
"We don't know what's happening to them when they go out to sea, it seems reasonable to expect there are changes occurring at sea, which is affecting the salmons ability to continue back to spawn."
He said the degradation of rivers in Canterbury is definitely having an impact on numbers.
"A lot more work needs to be done to protect spawning grounds. Habitat deterioration is a massive problem for Fish and Game across the South Island through intensive agriculture and irrigation."
He said Environment Canterbury (ECAN) needed to stand up and do more to protect salmon habitats.
"They're not doing enough and haven't been doing enough for years which has led to this situation."
Fish and Game estimated the new limit will reduce angler catch by about 35 per cent which should help increase the number of fish that can spawn.
Grubb said they're not sure how long the two a season bag limit will be in place for.
The council will monitor stocks in coming seasons to see if things improve - and if they do the limit will be reviewed.
He accepted there could be a decrease in the number of anglers buying a license due to the new limit.
"If that's the case then so be it, but we need to do something to help the stock recover."
- RNZ
