Tortoise Main Menuu

Enemies
Perhaps the most striking observation while diving for tortoises in the rivers of north-eastern New South Wales is the marked scarcity of juveniles. This is generally the case with young reptiles. They are extremely secretive and remain well hidden from their enemies until they attain a size which affords moderate safety.

If diving in an area where the visibility beneath the water can be up to fifteen metres, few tortoises smaller than 4.5cm will be found. But in clear flowing water there is little cover for juveniles to conceal themselves quickly from predators and this may explain their scarcity. The river bed is often rocky and weeds along the banks are generally sparse.

Platypus are often seen, but even if they do eat an occasional hatchling it is doubtful they would cause any significant reduction of the tortoise population. Birds are not prolific along these rivers, preferring the still waters of swamps and lagoons. Undoubtedly one of the foremost predators of juvenile tortoises in these areas is the eel. Large eels, over 1m long and as think as a man's arm, are common in these waters. They lay concealed beneath overhanging banks or logs and strike when a victim swims within range. Tortoises find it impossible to escape the twisting speed of this attacker.

In a short study of a water hole (30m by 15m and 4m deep) which was a tributary of such a river system, 108 tortoises under 7.5cm were caught in approximately fifteen minutes. This water hole differed from others in the area in that the bottom had a deep covering of sediment which could afford protection from predators and might explain the presence of the large number of small tortoises. If pursued the tortoises would be able to drop into the ooze, as in fact many of them did during this study.

A close inspection of the banks of this same water hole revealed four large eels, the largest measuring 1.1m. On dissection it was found to have eaten two small tortoises.

The breeding season is the most critical period for adult tortoises. When a female leaves the water in search of a suitable nesting site, she faces attack from birds of prey from above, and dingoes, foxes, pigs, native rats and goannas on the ground.

On the Murray River crows sometimes chase a tortoise from her nest before she is able to cover the eggs. The birds then break open the eggs and eat the contents. Snakes sometimes attempt to swallow adult tortoises but regurgitate them on reaching the shell, but hatchlings are certainly devoured by snakes. A Mulga Snake (Pseudechis Australis) is recorded as having eaten recently-hatched Krefft's Tortoises (Emydura Kreffti).

In the waterways of northern Australia crocodiles probably keep the tortoise populations in check. They are one of the few predators to feed on adult tortoises. Sharks which travel well into the freshwater reaches of many northern rivers would also include tortoises in their diet. It has been reported that a 5kg catfish has had the remains of a 7.5cm Emydura inside its gut. Is it any wonder small tortoises are scarce and secretive?

Johnston River Crocodile (Crocodylus Johnstoni)
one of the foremost predators of tortoises in northern
Australian rivers.

A Kreft's Tortoise (Emydura Kreffti) collected from the
Fitzroy River shows the apparent result of two snaps
by a pursuing crocodile.

Waterways of Queensland, particularly the lagoons and backwaters, have an abundance of mussels measuring up to 13cm. They bury themselves flush to the earth and the only indication of their presence is the small opening in their shell for feeding. On a recent skin-diving study, a large Krefft's Tortoise was found swimming with a mussel so firmly clamped to its front claws that during the effort to free it one of the claws broke away. A closer inspection showed other claws missing on both rear and front legs. Emydura Kreffti eat a lot of mussels which constitute the main part of their diet.

One of the greatest enemies of the tortoise is man. In the past, indiscriminate bulk sales were made to pet shops and, even today, netting of rivers and lagoons cause many tortoise deaths. On the banks of inland waterways in some areas it is not unusual to find the remains of tortoises that have been killed by fishermen who mistakenly believe that they prey extensively on small fish. Fishermen are also annoyed by their habit of stealing the bait from their hook.

An inexperienced poacher set this gill net in the
Raglan River, Queensland.

Painted tortoises (Emydura Subglobosa) in West Irian.

Extensive draining of swamps and land reclamation has almost eliminated tortoises from areas adjacent to human populations.