If sailing north of perth watch out rigging in the dunes between scrub...
In cervantes i found a 2 ft tiger slither out from under my sail when i picked it up
To walk to the water..watch out for these ones they can sting a bit..

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There are a couple of other critters that are very capable of stopping your heart and removing limbs and torsos and the like that you should be aware of.
In the swan river and other estuarys you wil find bull sharks..but these are not that scary as you wont see them...but their there..
Watch out for white pointers anywhere off the coast up to shark bay (and beyond)
When you get there your main concern would probably be tiger sharks and hammer heads.
Keep going north you will find other critters that look like giant lizards and make great wallets and hand bags and the like if you can catch one and skin it..
You will prob also come across a little jelly fish called irukandji..make sure you have a bottle of vinegar handy and perhaps a chopper to ferry you to hospital would also be good to have as well in case one swims into you...
These are a choice selection of creatures that are available for viewing here on the west coast.
I wouldnt worry too much as there are far more dangerous creatures to encounetr while sailing..
I am not sure of the proper species name for them but i prefer to call them ....teabaggers..
These are to be avoided at all costs..they have been responcible for more injurys and grief to sailboarders than any other critter that i can think of!
Unlike the other creatures that i have listed above tnese are not a native species!