Felt Sole Boots Targeted as Major Didymo Risk

7 December 2006

Both Fish & Game New Zealand and the Department of Conservation are calling for anglers not to use felt sole boots when fishing.

Freshwater anglers are advised to leave their felt sole boots behind this summer or risk spreading didymo throughout New Zealand’s top trout fisheries. Fish & Game regional manager Steve Smith said, “while anglers have previously been advised to clean their equipment between different waters it now seems that it is virtually impossible to effectively decontaminate felt soled boots or waders”.

Mr Smith said that the initial results of research showed that felt soles were an ideal environment to keep didymo alive for long periods of time and that under normal conditions cleaning products failed to penetrate the sole and kill the damaging alga. “We are advising anglers to use a rubber alternative to felt soled boots that will dry rapidly and is easily cleaned. It appears that felt soles can only be successfully decontaminated by onerous cleaning requirements such as soaking in hot water of at least 40 degrees for 10 minutes or more. As a consequence we urge anglers to only use these boots if that use can be restricted to one river.”

He acknowledged that some anglers may feel the advice was unduly alarmist. “The threat posed by felt soles is so significant and the implications of didymo so serious that we simply cannot afford to ignore the information that has become available. We ask all anglers to act on this advice now”.

Mr Smith emphasised that while felt soled boots are a significant high risk vector for spreading didymo it is important to recognise that anything that stays wet could carry didymo. “Kayaks, fishing gear, swimming togs or even the pet dog could carry the single celled organism. The major risk though is likely to come from items that stay wet for long periods of time and are difficult to clean with detergent or household disinfectant.”

The upcoming busy summer holiday period is seen as a major threat. “A lot of New Zealanders spend time around water during the summer. It is a vital ingredient of the typical kiwi holiday. It is also a time when they tend to move quickly and over large distances, which increases the risk of further outbreaks. We ask everyone to consider their holiday plans in advance and make specific provision for cleaning any equipment that they may use in freshwater.”

Soaking in a 5% solution of dishwashing liquid or household detergent is recommended for decontaminating equipment or clothing – other than felt soled boots that is! Mr Smith said that a recent inspection of South Island rivers contaminated by didymo had highlighted the risk the alga posed. “It was devastating to see the areas where didymo had bloomed. Unfortunately didymo likes the same type of conditions as trout and is doing best in the top fisheries. The only way its spread will be limited is if members of the public take responsibility for their own actions. Check, clean and dry now or risk of losing further quality rivers”.

He suggested, however that it was not all bad news and there was room for cautious optimism. “In most cases it is easy and cheap to decontaminate equipment. We are also rapidly learning more about didymo. The critical thing is at this stage is to limit the further spread of didymo while advanced detection and control methods are developed by researchers – which makes this summer more important than ever!”

For more information about didymo, please see What Anglers Can Do to Prevent Didymo and Didymo Biosecurity Alert.

Taupo trout fishery mangers are endorsing calls for anglers not to wear felt soled wading boots this summer to reduce the risk of spreading didymo algae into the North Island.

Department of Conservation Taupo Fishery Area Manager, John Gibbs, said recent research has highlighted that it is almost impossible to effectively clean felt soled boots. “While other gear can and must be cleaned with 5% detergent or disinfectant to ensure didymo is not spread, this does not work with these boots”

Walking on didymo pushes the cells into the felt material where cleaning agents are unable to reach. The most effective way to clean these boots is to either freeze them or immerse in hot water of 50 degrees for 10 minutes or more. “Neither of these methods are very practical, especially for travellers” says Mr Gibbs, “so we are encouraging anglers to wear rubber boots or neoprene waders which dry quickly and are easily cleaned. Either that or wear the boots in one river only”.

This is obviously a hindrance for anglers, acknowledges Mr Gibbs. “However if anglers are serious about protecting the waters and fisheries they value, it is essential they leave their felt soled boots at home. This single action will significantly reduce the risk of spreading didymo, but it is also essential that all river users clean their gear after every trip.

The world famous Lake Taupo fishery, including the Tongariro River and other tributaries, could be severely damaged if didymo became established said Mr Gibbs. “What is clear unfortunately, is that the very waters which grow good trout also grow good didymo”

For more information about didymo, please see What Anglers Can Do to Prevent Didymo and Didymo Biosecurity Alert.