I've just come upon this thread, and would like to offer some Western Australian background on this.
Firstly, for those of you who haven't caught up with me on the Boating sub-forum, where I normally hide, I have an extensive background in commercial fishing. I've left it now, but skippered crayboats for 26 consecutive years, and did a fair bit of wetfish ( scale fish, mostly demersal) . I had a lot of involvement with the research side of things, both actively in the field, and sitting on various government committees as a fisherman representative, including a Research sub-committee of the Rock Lobster Industry Advisory Council.
Firstly, on general principles, you need to raise your size limits. On pretty well everything. They started over here with Tailor , raising the size limit to 300mm, and a bag limit of 8., back in 2003. Still a tiny fish, but it had the immediate effect of stopping people fishing the hell out of them in the estuaries. Oh, the wailing and lamentations. " We'll never have a feed of tailor again" Within 2 years, it was obvious it was a success, the average size of the fish off the beaches shot up. Now, plenty of tailor for everyone.
Snapper were originally 35cm. it was raised to a mix of 40 and 50 cm , depending on where you were. Overall the ocean fishery improved., and quite quickly. But snapper is WA a a genetically diverse bunch, actually often restricted to small areas, with little or no population mixing, it is believed. So, prone to overfishing when they aggregated for spawning, the old story all over the world. The Snapper Guardians thing originally mentioned is for the Cockburn/Warnboro sounds stock, which spawns there, but spreads down from Mandurah all the way up to Lancelin out of season.
Shark Bay probably has the largest snapper stocks in Australia, but with 3 separate breeding stocks. Eastern and Western Gulf fish spend their whole lives in those areas, and get very big. They were being badly overfished, they had to bring in closed seasons, an Upper Size Limit as well , and limit you to 1 fish per day(with a fixed catch, ballot system for tags, no tag, no fish) for some years to bring them back--they are now recovering. You'd been dumbstruck at the ease of catching snapper up to just under 50cm ( legal size) in shallow water in the middle of the day. Bring the bream gear, have a ball. Then get blown away when a big one turns up unexpectedly You are allowed 2 fish now, but the breeding season is still closed, and there in no upper size limit.
The third stock in the bay is the ocean fish. They come all the way from at least off the Abrolhos Islands( off Geraldton) to form vast spawning aggregations in the waters off Carnarvon. These have been mercilessly hammered ( under an over-generous quota system) for many, many years. Quotas have been dropped, catches have kept dropping, and the ocean fishery has rapidly declined. This is undoubtedly the worst example of Fisheries mis-management In WA history. And they still really don't seem to get it, only just this year closing off the area of one of the main spawning aggregations . One of three areas, but I guess it's a start.
So you have a booming amateur/charter snapper fishery around Perth, due to the management of the spawning season, and a pretty ordinary. one up our way, because we rely on the oceanic stock just mentioned.
Do your Fisheries know if you have one stock, or several? Your only likely way out of it is upping the minimum size, and imposing much tighter bag limits. Or you might end up like South Australia, which once had an amazing fishery , and now has a total closure. Your expectations on size had really shrunk over the years--I'm originally a Sydney boy, spent a lot of time fishing the harbour off the ferry wharves, and it was full of 20-25cm fish. Can any of the old boys here remember the old name classifications for snapper?
Cockney bream--up to about 150mm
Red Bream -over 150mm, up to around 5 lb.
Squire--5lb to 10lb
Snapper--over 10lb.
Yes, thats right, that's what you had. None of these 35cm "squire" I see referenced over there nowadays. If you can, find a copy of TC Roughleys' "Fish and Fisheries of Australia". it was a reference bible back in the day--read it and weep , for what you had. And don't blame "the Pros" for it all-we have all been complicit in this, the grinning blokes lifting a Fourex in front of a pile of fish you couldn't climb over, when you just couldn't stop your self because they were biting so well. And the decline was well down the road before the explosion of boat numbers, too.