Wyprawa badawcza 2015

The Waters in the North at Darwin: Crocodile-free or not, that is the Question

Our last days in Australia took us to the Litchfield and Kakadu National Park, in the very north of the Northern Territories. Both national parks are renowned for their abundance of animals and especially for their high numbers of crocodiles. Of these only the saltwater crocodiles are really dangerous. The freshwater crocodiles are not really seen as dangerous and in clear water encounters with them are no problem. In a clash between humans and salties, as the saltwater crocodiles are called, the humans always draw the short straw and every year there are fatal accidents. Once you are in the water and face-to-face with the thick-skinned reptiles, you really have to be cool to distinguish the dangerous salties from their more peaceable, freshwater counterparts. The freshwater crocs don’t grow particularly large – but how can you know that it is not simply a saltie which has not yet reached maturity? Have a look at its dentition – hope this helps, ha ha!

But even in North Australia there are clear freshwaters where no saltwater crocodiles have been sighted for a long time. There are still warning signs at almost each water, but they seem to have been put up as a matter of pure precaution. If there’s really any danger there is another sign in English, German and Chinese mentioning current sightings of salties. Then you really have to be careful. Again in the clear waters we were able to find rainbow fish, barramundis, gobies, archerfish, one perch species (Amniataba percoides) and a species particular to Australia Glossamia aprion (a genus of the family Apogonidae), mouth breeders, which live here in pure freshwater but which we usually know as saltwater dwellers. Glossamia occupy the ecological niche of lurking predators, like the Amazon leaf-fish (Monocirrhus polyacanthus). They are quite well camouflaged and remain motionless between branches in the water to capture their victims. The fact that the purely freshwater variant of archerfish (Toxotes chatareus) is here, also indicates that a lot of freshwaters in Australia must have run into the sea a long time ago. Archerfish are normally to be found in brackish water. A bony tongue also lives in Australia and we were lucky enough to be able to observe these animals (which are about 80 cm in size) together with garfish at Maguk. Their flight behaviour was interesting. Although Scleropages jardinii is a surface predator he can dive to greater depths of up to 8 m at a snorkeler’s approach, but never deeper than that. You’ll have trouble googling freshwater garfish. The species we observed was more than 30 cm long and you will read about freshwater fish species with a maximum length of 8 cm. Although Australia doesn’t have much freshwater species diversity, the few species it does have are really interesting and unusual.