Mechanical Cleaning

The fouling is removed by mechanical machines. Disk washers and net washing machines are good examples of mechanical cleaning applied to nets involved with fin-fish aquaculture and mechanised brushing machines in shellfish processing.

Applicable to:

Shellfish
- Stock and infrastructure.

Finfish
- Infrastructure (nets, moorings etc).

Methodology

Shellfish
- Drum washers or mechanised brushes.

Finfish
- Machine washing.

Key Factors Positive

Shellfish
- Drum washers are cheap and can be home-made.
- User friendly.
- Machines last from 5 -15 years.

Finfish
- Services can be contracted out to cleaning stations on a region scale, so the cost for cleaning infra-structure does not have be taken on by every small to medium sized operation.

Key Factors Negative

Shellfish
- Damage or mortality of stock can occur (up to 20% of total stock).
- Long line mussels have thin shells which may be prone to breakage during this process.
- Labour costs can be high (5 - 30% of total costs).

Finfish
- Cleaning procedure involves transfer of stock to clean nets, which can involve stress and mortality.

Cost Benefit

Shellfish
- 5 to 40% of total person hours.
- 5 to 30% of total costs.
- 2 to 20% of the stock can be lost.

Finfish
- This can be a relatively expensive strategy if carried out many times in a year. Combining with other strategies such as air drying and disk washing brings the frequency of cleaning down and can result in savings of up to 50% of the cost per sq. metre of netting, from case studies of the farms involved in the CRAB Project (see more details in the Best Practice Guidelines).

Conclusions/ Discussion

Shellfish
- Procedure needs to be repeated every 8 weeks during the fouling season or just before selling.
- Effectiveness is variable with good success rates with algae and hydroids but not with barnacles and tubeworms.

Finfish
- If nets are left to dry for around 2 weeks prior to cleaning, machine washing removes all fouling effectively.