Strategies

High Pressure Washing

Much like jet washers for cars, infrastructure can be cleaned by jets of water to blast off fouling (a cleaning process). Pressure washers can come in hand held or industrial sizes.

Applicable to:

Shellfish
- Stock and infrastructure.

Finfish
- Infrastructure (nets, moorings etc).

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Methodology

Shellfish
- A simple pressure washer can be used from on board a support vessel to clean infrastructure at the site.

Finfish
- Disk washers can be deployed from the surface or used by divers within the cage.

Key Factors Positive

- An effective technique for removing all types of fouling.

Key Factors Negative

- It can be quite labour intensive.

Shellfish
- Is limited to use as part of the pre-sale processing for delicate species (e.g. scallop). For hardier species (e.g. mussels and oysters) it can be used periodically during the growing season.

Finfish
- Not always possible to clean the entire cage without the use of divers, which involves another set of costs.
- Dislodged fouling is not necessarily killed and can resettle on local cages.
- Dislodged fouling passing through the cage can cause stress to stock animals.

Cost Benefit

Shellfish
- None of the CRAB partners use this strategy at present so no cost benefit analysis was possible.

Finfish
- The use of disk washing slightly reduces the cleaning cost per sq. metre of netting per annum in combination with machine washing and as a combined strategy with machine washing and net drying (see Best Practice Guidelines for more details).

Conclusions/ Discussion

Shellfish
- A rotating jet of water was 100% effective (? 2000 psi for 2 seconds) in the removal of the kelp seaweed Undaria; a standard high pressure jet was less effective, removing only 60 to 90% of fouling depending on pressure and duration.
- High pressure water jets can be used to enhance mechanical cleaning and have successfully been used with oysters in this way.
- As stock pass through a rotating drum high pressure water jets help fouling and sediment removal as part of the processing system.

Finfish
- Use of disk cleaners can increase the duration between net changes for cleaning purposes. They will have no effect on the timing of net changes to a different mesh size as stock gets larger though.

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