Fisheries Minister Phil Heatley has rejected calls for an easing of blue cod fishing rules in the Marlborough Sounds.
The cod fishery was re-opened in April after a three-year closure.
However recreational groups say a new rule that fishers can only take blue cod of 30cm to 35cm length is causing a lot of fish to be thrown back, resulting in a high mortality rate.
Fishers can only take or possess two such blue cod per person per day.
Mr Heatley says the size limit is to protect larger breeding fish, and he has no plans to change the rules.
He says he has asked for a report on the Sounds cod fishery and may reconsider any new evidence then.
