Predators
Humans
Large lizards (when babies)
Large birds (when babies)
Predatory fish (when babies)
Other salties pretty rarely
Other causes
Habitat loss
Starvation
Accidents
Illegal fishing
Causes of Death
Diseases
Caiman pox
Hepatitis
Mycoplasmosis
Chlamydiosis
Sexual Competition
Male salties are extremely territorial so there can be instances of them fighting and killing each other in hopes of keeping their space and mating with the females inside.
Hunted saltwater crocodile by humans
Extremely starved crocodile
Diseased crocodile
2 males fighting over territory
Competition
There's not a ton of competition either inter-species or intra-species. Inter-species competition doesn't happen as regularly as you might think as when the saltwater crocs do get together they actually will hunt together and share food making sure breedable females get it a decent amount of the kill. Intra-species competition isn't usually something they have to worry about either other than snakes and large birds. When it is inter-species it is more often than not two males fighting over mates or territory. When it is intra-species it is a fight for food as well as saltwater croc eggs and babies up for the taking by some predators.
Carpet Python
Australian Raptor
Invasive Species
The only real invasive species threat to the Australian Saltwater Crocodile is that of cane toads. The poisonous toad will kill any animal that eats it due to its toxicity including Saltwater Crocodiles who will eat just about anything. These toads also affect other food sources for the crocs as they do eat fish and other animals who may also pray on these toads and because of this there will be less food available for the crocodiles. On the flip side, another invasive species in northern Australia is the water buffalo, but this is actually not too harmful to the salties as they can eat these large mammals giving them a complete meal that will fill them up.
Cane Toad
Water Buffalo
IUCN Rating and Population
Australian Saltwater Crocodiles are actually in very good shape and the IUCN has rated them of least concern on the Red List. In Australia there are between 100,000 and 200,000 adults spread across the top of the continent. The range extends from Broome in western Australia, through the entire NT coastline all the way to Rockhampton, Queensland. The population trends of the large reptiles has boomed in the past 50 years with the minimum shooting up from 3,000 to 100,000 and is expected to keep rising as long as humans let it.
Impact on Humans
The saltwater crocodiles are very helpful to us humans as they eat ailing fish that hurt that environment and ecosystem so they can't get too dominant, as well as other possible problematic invasive species like deer and water buffalo that have been introduced to the continent. The Saltwater Crocodile almost went extinct in Australia in the 1970s due to hunting. These animals do not pose any serious or harmful threats on humans as a whole besides them being wild animals that could get you if provoked or if you're not being careful around them, there are about 1,000 crocodilian related deaths each year but that's not only in Australia.
If the crocodile population gets too out of hand and continues to grow extremely rapidly they could become somewhat of an issue to native Australians but it's not likely and it wouldn't happen for a very long time. Crocodiles are an extremely ancient animal that may have first appeared in Australia over 240 million years ago and because humans have been around for about 300,000 years it's a safe bet to say that early humans on the continent ran into them and the modern people there now have been running into them ever since.
Efforts Being Made
Obey all "Crocodile warning" signs
Special permits for crocodile egg taking
Special permit for hunting
Ban on products using their body parts (mainly skin)
Working on lowering global warming and pollution as these do affect the croc population