HOW IMPORTANT ARE OUR ESTUARIES? VITAL SAYS ECOfishers!

Most of our recreationally targetted species are estuarine dependent.They include Tailor, Snapper, Yellowfin Bream, Mulloway, Luderick and Sand Whiting, etc. All these species (and more,) depend upon a healthy habitat and healthy water, in the nursery areas of our estuaries. Marine species don't spawn there. They grow up there, after they settle out of their planktonic stage. In estuaries, they undergo, a series of metamorphic stages and changes, in a more secure and friendly environment. Here they need protection and food.
Seagrasses provide a secure habitat and feeding site for these juvenile species of fish. Seagrasses include Posedonia australis, Eel Grasses and Zostera tathracornia. These estuarine plants play hosts to myriads of small crustaceans and copepods, which juvenile fish (30mm) feed on.
Mangroves also fringe the boundaries of the estuaries. Their aerial roots (pneumatophores) provide protection and the decomposing leaves form detritus.
Sadly, the recruitment of juvenile fish to our estuaries often fails and fails very badly.Some of the reasons for poor recruitment to our estuaries include:-
* fertility issues from brood stock during lean times.
* accumulation of fish larvae doesn't coincide with suitable planktonic food sources.
* currents sweep food and larvae away from each other, leading to starvation.
* If the right size food item isn't available at the right stage of larval development then we have mass mortality.
* predators are abundaant some years and they take a huge toll. It's a marine jungle out there!
* adverse currents at the mouth of estuaries sweep larvae away, to perish.
* larval fish and prawns, are often found way out to sea, where they can't survive. This causes a large natural wastage etc.
So many of our marine fish species therefore, have a very unique age structure, which reflects the random arrival of juvenile fish in our estuaries in some years and not in others.
So how important are our estuaries? Absolutely vital for a sustainable fishery, says ECOfishers.
As you can already see, survival from fertilized planktonic egg (embryo) to minimum legal length adult, is very much a lottery, with extreme odds. Everything must go perfectly. Perfectly with the spawning, perfectly with the larval development and perfectly with the recruitment. This perhaps explains why fish lay so many eggs. A sexually mature female Snapper for example, can spawn up to 6.3 million eggs, in one spawning season.
When everything does go perfectly, (all too infrequently) fish of a particular age class dominate a population.
Now if we don't have enough healthy habitat, shelter, food and good quality water, to harness these large numbers of juvenile fish, when they are arriving in our estuaries, we are not going to be able to capitalise on these infrequent years, when we have lots and lots of fish!
It also works on a species by species basis. There is ample evidence to show in some years, a particular species is abundant while others aren't. So a good year for Tailor isn't necessarily also a good year for Yellowfin Bream or Mulloway etc.