Lefty-green's comments are representative of what I think produces the Marine Parks. 'there are thousands...' if you take it at face value you can't help agreeing. I used to.
On our recent rip to the US we were at the coast on the west side of Florida, down to Key West, then up the East Coast from Key West to Boston. The number of recreational boats was mind boggling. There were plenty of fish and plenty of fishermen. There was also a lot of reef.
If you apply LG's logic the number of US fishermen, outnumbering the number of Aussie fishermen by several orders of magnitude, (add more noughts at the end), should have resulted in there being b*gger all fish in the US, but in fact there are still plenty.
If you want to work it out properly you don't count the number of boat trailers parked at the ramp and make a WAG, you measure the the number of fish caught. At a place like Jervis Bay the numbers of fishermen aren't huge, some like me catch b*gger all on some trips, and only go out about a dozen times a year. Others go squidding not fishing. The rock spots hold about three or four people at a time and take an hour to walk to. How many fish can you cart out for an hour of walking that begins with a trip up a twenty foot cliff? despite this most of the JB southern rock spots are now marine park plus large areas of sheer cliff.
It should be possible to work out how many fish recreational fishermen actually take, and I imagine, how many fish there are beforehand, (the bird experts seem to be able to do it).
When I see pictures of trawler loads of fish, including their dead by-catch, I just can't see that fishos like me, multiplied by the number of Aussie boats, could possibly have anything like the same effect on fish numbers. I also find it hard to believe that the closed off areas at JB like Brook's Rock, are breeding grounds for Trevally, Tuna, Flathead, Kingfish etc. etc. I can believe that a few artificial reefs around the place might provide some breeding grounds for young fish. But I'm not an expert, I just wish some expert would give it a go and see what happens instead of closing more and more of the coastline off based on the premise that those 'thousands' of boats must be destroying the fish stocks.
I'll get out of your way now.