Flow-on benefits of cutting the carp
Carp can be detrimental to plant life in rivers.
As the leader of the expert team that prepared the Carp Reduction Plan for the ACT region in 2010, allow me to add some content to the debate about whether we should be spending taxpayers' money on its implementation. Before looking at the ecological issues, let me first comment on the matter of releasing carp back into our lakes and streams once caught, as course fishing is under the spotlight at present.
This loophole, referred to in recent days by John Thistleton's reporting in The Canberra Times, was identified in the Carp Reduction Plan as an anomaly, and there was a recommendation that it be addressed. There were also five other ''policy-related'' issues noted with advice given on how the government should proceed to strengthen our response to this pest species. It is to be hoped that with the commitment to see the Carp Reduction Plan implemented by the new government they will also examine these issues.
On the more central issue of should we try to reduce carp numbers, the argument that because we cannot (at present anyway) hope to see them eradicated, we should just accept their presence is non-sensical. If we applied this same logic to foxes, rabbits, feral cats, feral pigs etc, imagine how degraded our terrestrial environments would soon become. Likewise with introduced plants now declared as weeds.
There are very good ecological reasons why we should implement this plan. Carp are basically mud-suckers, ''hoovering'' the underwater environment, stirring up the lake bed and uprooting aquatic plants. Therein lies two very good reasons for why it is important to try to reduce their numbers. In simple terms, lake ecosystems are healthiest when aquatic plant life is abundant.
These plants are vital parts of the food web but also play a role in ''dealing'' with the nutrients that wash into the waterways and promote algal blooms. Seeing carp numbers reduced is part of the incremental process we need to initiate to bring our lakes back to life and reduce lake closures. This is not the silver bullet people dream of, but it is a part of the smorgasbord of actions we need to apply to this problem.
The Carp Reduction Plan recognises that actions need to be taken in a systematic and strategic way across the region's waterways in order to shut down, or at least minimise, breeding ''hot spots'' from which young carp move out to colonise new areas or make lakes, like Burley Griffin, worse.
Some of these hot spots are known, the others we need to find. Well-timed interception of carp (using traps, nets or electro-fishing) as they move into these breeding areas in early spring will have a big and immediate impact on their numbers. If repeated year after year, we should see the gradual re-emergence of the aquatic plant life that carp are destroying.
With this, we will also be providing better habitats for the native fish in our lakes and rivers, and they will start to take the fight up to carp by gobbling up their young - how ironic!
The ideal situation is for the technological tools being worked on at present to remove the carp scourge from our waterways to come to fruition.
Until then, we have enough knowledge of their life cycles to make significant and strategic interventions, at relatively low cost, to see their numbers seriously reduced. Through this investment will come paybacks and potential cost savings as the underwater habitat improves, less resources are needed to help aquatic plant life to return, and maybe we won't need to spend as much on restocking the lakes with young native fish. The funny thing about ecology is that everything's connected and so we shouldn't treat these issues as one dimensional or in isolation.
Dr Bill Phillips is chief executive of RiverSmart Australia Ltd.