Fouling is often recorded with one simple number:
“30% fouling.”
That sounds useful, but it can hide important structural differences.
Two fish cage nets may both have 30% fouling, while one has light growth spread evenly across the whole cage and the other has heavy buildup concentrated on one side.
These are not the same condition.
The key principle is:
Fouling percentage describes how much growth is present. Zone-based recording shows where that growth is changing load, drag, and net behavior.
Consider two cages.
30% light fouling distributed fairly evenly.
30% total fouling concentrated mainly on the downstream lower side.
The total percentage is the same.
But Cage B may experience much greater local drag and weight imbalance.
This is why one percentage cannot describe the full structural condition.
A useful inspection can divide the net into areas such as:
Upper side panel
Middle side panel
Lower side panel
Bottom panel
Corners
Borders
Upstream side
Downstream side
The exact zoning can be adapted to cage geometry.
The important point is to use the same zones during repeat inspections.
Instead of:
Overall fouling: 40%
record something like:
Upper panel: light
Middle panel: moderate
Lower downstream panel: heavy
Bottom: moderate
Corners: heavy
This makes the maintenance record much more useful.
Under persistent current, some cage geometries can accumulate more fouling or experience greater drag on particular sides.
If heavier growth develops downstream, it may increase local:
Drag
Panel deformation
Border tension
Hardware contact
Do not assume this pattern occurs in every cage, but record it when observed.
Bottom-panel fouling can add:
Weight
Drag
Sediment retention
It may also interact with:
Sinker systems
Bottom borders
Lower seams
So bottom fouling should not simply be combined with side-panel fouling into one percentage.
Fouling around:
Corners
Border ropes
Seams
Attachment loops
can affect load transfer differently from fouling in the open center mesh.
A relatively small fouled area may still be important if it is located at a high-load structural transition.
Different growth can affect the net differently.
Examples may include:
Soft algae
Slime
Mussels
Barnacles
Mixed marine growth
Hard or thick fouling can add more local weight and stiffness than light surface growth.
Therefore, useful records should include both:
Coverage + Type
Two zones can have similar surface coverage but different fouling thickness.
For example:
80% thin algae
80% heavy shell growth
They should not automatically be treated as equivalent.
Where practical, note relative thickness or severity.
Heavy local fouling can reduce effective water passage through the mesh.
Look for:
Partially blocked openings
Asymmetric flow area
Local net deformation
This helps connect fouling condition with actual cage performance.
Zone-based records are most valuable when repeated.
For example:
| Zone | Inspection 1 | Inspection 2 | Inspection 3 |
|---|---|---|---|
| Upper Side | Light | Light | Moderate |
| Lower Downstream | Moderate | Heavy | Heavy |
| Bottom | Light | Moderate | Heavy |
This shows where fouling is developing fastest.
A single whole-cage percentage cannot show that trend clearly.
For each zone, record:
Coverage
Fouling type
Relative thickness
Mesh blockage
Local deformation
Nearby hardware contact
Previous cleaning history
Useful zones may include:
Upper panel
Middle panel
Lower panel
Bottom
Corners
Borders
Upstream side
Downstream side
If fouling is uniform, full cleaning may be logical.
If fouling is concentrated in one structural area, targeted cleaning may be considered.
However, partial cleaning can temporarily change drag distribution.
That means cleaning plans should consider not only where fouling exists, but also how removing it will change the balance between cleaned and uncleaned zones.
Uneven fouling can influence:
Water flow
Drag
Cage shape
Bottom depth
Sinker load
Attachment tension
Hardware clearance
Its structural importance depends heavily on location.
This makes location-based records much more useful than one whole-cage percentage.
Writing:
“40% fouling”
does not answer the most important question:
Where is that fouling concentrated?
The key principle is:
Record Fouling by Zone, Severity, Type, and Trend—not only by total percentage.
A stronger inspection record combines:
Coverage + Location + Thickness + Fouling Type + Mesh Blockage + Structural Effect + Change Over Time
At PL Fishery, we manufacture PE fish cage nets, aquaculture netting, side and bottom panels, reinforced borders, attachment loops, custom seams, replacement mesh, repair twine, marine ropes, and customized net products.
To purchase or customize fish cage netting, send PL Fishery your cage dimensions, mesh size and measurement method, twine specification, water depth, current conditions, fouling environment, panel design, quantity, and maintenance requirements so our factory can prepare a more suitable commercial net specification.https://plfishery.com/
