Do fish stay in marine sanctuaries?

A simple question, a simple answer – yes! There have been claims that sanctuaries won’t work because fish will just swim out of them.  This is as ludicrous as saying that National Parks won’t work because animals can walk or fly out of them.

Two things.  Firstly, sedentary species.  Many many species of fish and other marine life, including species as large as some dolphins, spend their whole life within a few kilometers, or even a few meters.  A decent sized marine sanctuary will protect them happily all their lives.  You wouldn’t expect a blue wren, or a quokka, or a bilby, or a tree, or a numbat to stray out of a National Park.  So why any different for a clown fish, a goby, a prawn, a starfish, a seahorse, or a harlequin fish, or a blue groper.

Secondly, species that migrate or do swim around.  Some species like Tuna and migratory sharks and whales do spend most of their lives migrating.  Evidence from the Great Barrier Reef shows they will tend to stick around in a sanctuary longer (densities of these species are higher in the sanctuaries) – it makes good commonsense if the going is good stay a bit longer.  They will eventually leave, but not before having benefited from a good feed or rest, and the sanctuary having benefited from their contribution to the nutrient cycle.  It isn’t that different from land either, some species like say American Buffalo in the old days, or migratory birds today,  travel, but they also stop over for a rest where there is a decent wetland, or a good feed of grass.  And they also have important areas for feeding and breeding that they can’t do without.

Then there is another class of migratory fish – fish like snapper that are known to locally migrate to breed and feed. These are an even more interesting group. A bit like kangaroos or emus, preliminary evidence from sanctuaries in New Zealand has shown that they might be preferential migrators.  In other words, when times are good they tend to stay put, whereas when they are not, they tend to migrate.  Tracker work at the Poor Knights Islands showed that snapper, which were also thought to be local migrators in New Zealand, tended to stay primarily in the sanctuary, with a few migrating out to surrounding reefs every now and again (with 14 times more large snapper in the sanctuary, and some swimming out from time to time, that is a good scenario for fishing).  It is likely the same could happen with snapper, rock lobsters, and other demersal fish in WA waters. As so often happens when you put in place a marine sanctuary you learn something new.  Fish behavior can be, and is, changed by fishing, and the safer and more productive waters of a marine sanctuary are a pretty good place for a big fish to hang out.

So, to fishos and scientists like Ben Diggles and Bob Kearney who of late seem to be quick to claim that fish just swim around randomly in the ocean so sanctuaries won’t work (at least thats how I’m understanding their comments) – I think a little more thinking and digging is required.  I’m a bit confused by these two, and would love if someone can send me some information on which working marine sanctuaries they have been involved in studying that has informed their view on the matter.

Especially given there are a number of high profile marine science consensus statements, high profile scientists from major universities such as University of WA, SA and Queensland and the Australian Marine Science Authority who all support establishing a network of sanctuaries in Australia’s waters.

It seems to me that the areas of Australia’s waters with the most marine sanctuaries, Ningaloo and the Great Barrier Reef, remain some of the best fishing spots in Australia, alongside world class conservation.  That is what I’d think of as a win-win for fishing, conservation, and Australia in general.

And so,  yes, fish do stay in marine sanctuaries. At least enough to make them by far the most effective conservation tool, and in many circumstances an excellent fishing management tool too.

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