Sepik River Piranha

The people of the Sepik
Are hungry and need fish
Let's introduce the Pacu
That's a tasty dish

It may be a piranha
But it doesn't feed on meat
It mostly crushes nuts
With its large and fearsome teeth

Now the ball-cutter piranha
Feeds on other nuts
As it lurks in shallow water
Close to peoples huts

No one likes to see hungry people but the decision to introduce piranha into Papua New Guinea's Sepik River as a food source beggers belief. Yes, they may be vegetarian in their native Amazon but they are still piranha and nobody should have been surprised when they became carnivorous when their natural diet of nuts and river vegeation became scarce. Referred to a "The Mutilator" in Jeremy Wade's River Monster programme they appear to be responsible for at least two deaths in the Sepik when they bit off the genitals of men wading in the shallows. It is unsurprisingly now referred to as the "ball-cutter" throughout PNG and it is greatly feared. It is a large and hardy species that has spread throughout theSepik River system since fingerlings were introduced into the river by the misguided "FishAid" Project in 1994 and then into the Ramu in 1997. They will undoubtably infest all PNG rivers in the longer term.

The ecological and social cost of active introductions of invasive exotic fish species into Papua New Guinea's river systems has been enormous and yet the introduction programmes continue with the latest menace being the genetically modified GIFT Tilapia. Crocodile populations have plummeted as the river vegetation that they need for nesting is consumed by introduced tilapia and carp. Freshwater prawns are also vanishing and so are iconic game fish species such as the Black Bass and the Sepik Grunter. It is a tragedy unfolding.

We seem incapable of learning and keep making the same mistakes again and again with the same predictable consequences. The long term answer lies in education but by then it will be far too late for many river catchments and their unique species of fish.

Mangroves

The rhythm of the sea
Pulses through the trees
While the leafy canopy
Rustles in the breeze

The fish and crabs are feeding
Among the mangrove roots
While birds and bats are breeding
In their leafy roosts

But now the trees are dying

In a smelly stagnant pond
Because their roots need drying
And they’ve lost their tidal bond

 Mangroves are marvellous! A productive tidal forest adapted to the rhythm of the sea. But to conquer this niche they had to first overcome the challenges of salt and waterlogging. Salt is excluded at the roots but also accumulates in the leaves which shed and in turn support a detritus food chain feeding crabs, prawns and fish. The tidal pulses on the other hand provide regular respite from waterlogging.

Marvellously adapted they may be but like many organisms living on the edge they are close to their upper tolerance limits. They are hence vulnerable to both waterlogging and hyper-salinity should the tidal flushing be inhibited. Great care is therefore necessary in the construction of causeways and other tidal barriers to ensure adequate flushing and complete drainage which in turn will prevent the death of mangroves and the loss of fish, crabs and prawns. It is very sad to see a marvel of nature transformed into a stagnant, foul smelling and mosquito infested swamp dotted with dead skeleton trees.