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Beware of aquatic hitchhikers

Beware of aquatic hitchhikers

Summer is the time of year when New Zealanders flock to lakes and rivers, but they may be unwittingly transferring invasive weeds and pests from one waterway to another.

Dr John Clayton, science leader of NIWA’s (National Institute of Water and Atmospheric Research) aquatic plants programme, says almost all North Island waterways already have one or more aquatic pest, and unfortunately South Island waterways will suffer the same fate unless the threat of aquatic pests is taken seriously.

“One of the things that makes New Zealand unique is the high quality and beauty of our lakes and rivers, and New Zealanders have great empathy for waterways, but as time goes by they are being degraded.”

The Foundation for Research, Science and Technology has invested over $2.5 million over three years into this research programme, which has focused on a wide range of biodiversity and biosecurity issues facing New Zealand water bodies, including novel approaches to managing invasive species and how plants can be used to rank the condition or health of a water body.

One of the key research questions presently being addressed is how to prioritise water bodies in relation to the risk they face from pest invasion, so as to best allocate resources.

To do this, it has been necessary to build up a picture of the state of all the water bodies around the country, understand what species are pests, the process of degradation, and determine the factors that heighten risk of pest transfer.

“If a lake is already highly pest-ridden, as bad as it’s going to get, there may not be much point trying to protect it, where as there may be a water body close by worth protecting,” says Dr Clayton.

Research is proceeding well and the research group plans to produce guidelines by the end of next year which will advise groups with an interest in waterway quality, such as regional councils, Iwi, hydro-electric power companies, community groups and the Department of Conservation, which strategies they should implement to minimize pest risk.

In the meantime, the public can help protect the country’s waterways by appreciating how easily aquatic pests can be transferred from one water body to another and taking action to prevent this.

Waders, fishing nets and lines are all potential sources of contamination. The recent discovery of the algae (Didymosphenia) in the Waiau River that flows out of Lake Manapouri— probably the first time the algae has been found in the Southern Hemisphere— is thought to have been introduced on a tourist’s fishing waders, as the area is only accessible by foot.

Many of the weeds that are a problem in New Zealand reproduce vegetatively rather than from seeds, which means it only takes one small fragment to infest a whole lake.

One such example is Hornwort (Ceratophyllum demersum). Formerly concentrated about the Waikato region, it has now spread to the tip of Northland and to the the bottom of the North Island. It forms a dense, unsightly weed bed, which makes swimming unpleasant, fishing difficult and boating hazardous.

The first recent record of this weed in the top of South Island was immediately contained but it did demonstrate just how easy it can be spread from the North Island and between ornamental ponds along with pest fish species. Researchers have also found that Hornwort displaces other native water plants, and it can have a negative effect water quality and other aquatic life such as native fish.

Therefore it is really important that the public remove all plant material from their boats, trailers, propellers, anchors, fishing gear and nets and jet skis before leaving a waterway.

Particularly important is the bilge unit and anchor store as the water or dampness in these systems can allow weed to survive for several weeks, says Dr Clayton.

If weed or plant material is found on equipment after leaving a waterway, an easy way to ensure it can not establish elsewhere is to soak it in salt water (marine strength) or 10% bleach for a couple of hours.

Reminding people to remove ‘aquatic hitchhikers’ when leaving waterways is the purpose of the boat ramp campaigns being run this summer by the National Aquatic Pest Awareness Group, a collection of goverenment agencies, industry and interest groups with a stake in New Zealand’s waterways.

The boat ramp symbol is the first of a series of three which will be used nationally to heighten public awareness of how to prevent the spread of aquatic pests.

National campaign spokesperson Anne Brow says one of the key things about the boat ramp symbol is the message is positive.

“We have really concentrated on moving away from a `don’t, don’t, don’t’ message. We want to encourage a ‘stop and help’ attitude amongst the public.”

Another key aspect of the boat ramp campaign’s message is its simplicity. While different regions are under threat from different weeds, Brow says it is a “big ask” to expect people to tell the difference between water weeds, especially as the pest species vary from region to region. The simplest approach is to advise the public to remove all plant material before leaving an area.

The second and third symbols in the campaign, which will be introduced over the coming months, focus on discouraging people from transferring aquatic species between water bodies and dumping contents of household aquariums.

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