You won't have a problem bringing the knife in to Australia in your checked in luggage, but you should be aware that Australian knife laws are quite restrictive. Essentially, it is legal to carry a knife if you have a genuine, good reason for having it. The reason must be specific ie. not 'I carry it to cut things', and self defence DOES NOT count as a good reason. So if you're carrying it specifically for marine activities you shouldn't have a problem, but it would be illegal to carry it whilst going out on the town at night. That's not to say that people here don't carry regularly and without a specific reason, but if you were stopped by the cops and they found it you could be charged with an indicable offence (ie. a felony).