Central South Island Fish and Game officer Mark Webb said while there had not been any reported issues with people fishing for kahawai alongside those fishing for salmon or trout, inquiries were ''identifying that there may be a developing problem''.
He said salmon fishermen needed to pay for a sports fish licence, but standing next to them were people using the same gear to catch kahawai free.
That meant there was ''potential for some aggravation'', and it would be timely to remind both groups of their responsibilities, he said.
Mr Webb said even though a fishing licence was not needed to catch native fish, there were still ''obligations'' that people targeting native species needed to be aware of, especially if they were using equipment that could also catch salmon or trout.
''Problems can arise when they fish in areas where sports fish are present and with gear capable of catching sports fish. The mouth of the Waitaki River is such an area.
''Fish and Game New Zealand, Central South Island Region undertook successful prosecution of an angler using salmon tackle and claiming to be a kahawai angler, as a test case some years ago.
''The judge's decision clarified the responsibilities of anglers if they intend to fish in trout and salmon waters for non-sports fish species.
''The decision was that if an angler is fishing in waters where trout and salmon are present with gear capable of catching trout and salmon it is up to the angler to prove he or she did not intend to fish for sports fish and also that he or she took reasonable steps to ensure sports fish were not caught.
''In other words, the angler will need to prove their intent to catch kahawai/flounder and not to catch sports fish.''
However, to prove intent without evidence was not easy and he advised anglers to clearly use gear unlikely to catch sports fish, or if they used gear which was permitted for sports fishing, then they should hold a current sports fish licence if they fished during the sports fishing season in a Fish and Game region.
''Fish and Game's advice to its rangers will always be that if they believe gear being used is likely to catch trout or salmon if they are present, and if the angler is not the holder of a current sports fish licence, and the angler cannot provide any immediate evidence in support of their intent or activities, then an infringement notice should be issued.''
