Fishing (shore-based and boat-based)

This page explains how fishing can spread INNS, how INNS affect fishing activities, the main high-risk species, and best practice guidance to reduce their introduction and spread.

You can find full details and recommended biosecurity actions, in the Fishing Pathway Action Plan for Wales (shore-based fishing) and (boat-based fishing).

About the pathway 

Boat-based fishing 

Biofouling (or biological fouling) is the build-up and growth of organisms (plants, animals, bacteria and detritus), including INNS, on underwater surfaces. Common biofouling organisms include sea squirts, barnacles and sponges.  

INNS can be spread through: 

• Biofouling on, or entanglement in fishing equipment (e.g., pots, rope, nets etc) 

• Biofouling on boat hulls, surfaces and niche areas (e.g., boat propellers, anchors and pipes) 

• Discard of non-native bycatch (e.g., when processing underway)

Biofouling can quickly build-up if a boat is left in the same place in the water for weeks or longer. If the boat is then moved or travels to a different location without first being cleaned, the species that have built-up on the boat can then spread to this new location. Even boats with antifouling paints or coatings are at risk of INNS fouling because some INNS are resistant to the effects of antifouling coatings.

Cleaning fouled boats in the water, or cleaning ashore where debris is washed straight back into the sea, may also allow INNS to survive and establish in the area. Fragments could be transported to new areas with the tides and currents.

Discarding non-native bycatch away from the site it was fished from can spread INNS. For example, processing catch while underway and discarding INNS (e.g. American slipper limpets) overboard that have been brought up attached to target species (e.g. scallops or whelks). Some bycatch INNS may also remain on the boat and be swept overboard into the landing port waters when the boat deck is cleaned. These discarded INNS may be able to establish in the receiving area, or may contain eggs and larvae that survive, grow and eventually establish. 

See the Boat-based Fishing Pathway Action Plan for more information.

Shore-based fishing 

INNS can be spread through: 

• Becoming entangled/attached to equipment and clothing 

• Fishing gear (rod, lines, nets and rakes) and clothing (e.g., waders and boots) can become covered in INNS 

• Absorbent materials such as nets, clothing and personal protective equipment can transfer tiny larvae, eggs and spores which can survive for days/weeks in damp conditions 

• INNS growing on immersed stationary fishing gear 

• The use of live INNS (or dead INNS carrying eggs) as bait 

INNS can be transferred between locations, especially when multiple fishing grounds are visited within the same few days or weeks. If live INNS (e.g. American slipper limpet) are used as fishing bait, there is the risk of their escape/release, or, if bait has only been recently killed, any eggs that it may be carrying could be released. Organisms can also be spread in or on the packing materials transported with bait, for example, INNS can be attached to seaweed or in mud, making them difficult to spot. 

See the Shore-based Fishing Pathway Action Plan for more information.

How do INNS impact fishing operations? 

• Competition for resources:
  INNS can compete for space and food with native fishery species. This can lead to a decrease in the numbers of native fish, shellfish and bait worms and could result in a loss of business for fishing boat companies or owners.

• Entanglement and reduced access:
  INNS can increase levels of bycatch, become entangled in fishing gear and make fishing areas less accessible. Chinese mitten crabs are known to take bait from fishing lines, as well as heavily predating on target catch species.

• Increased drag, obstruction and boat damage:
  On boat hulls, high densities of biofouling can result in increased drag when underway, meaning higher fuel, cleaning and antifouling costs. Some INNS, like the trumpet tubeworm, can cement themselves to hulls and submerged metal boat parts requiring time-consuming and costly removal. Removing hard fouling species can also cause damage to paints, coatings and the surface itself.

• Costs and movement restrictions:
  Increased cleaning and maintenance of marinas and harbours may be required if there is a high density of INNS. This could result in costs being passed from marina management to boats owners (e.g., in enhanced berthing / mooring fees or memberships). Heavily fouled boats may be refused entry; restricting movements.

• Disease:
  INNS can spread disease to native species. For example, the American lobster can carry a bacteria that causes red tail disease (also known as Gaffkaemia). This disease particularly affects the native European lobster and can result in significant mortalities.

• Habitat alterations:
  INNS can alter habitats in ways that make them unsuitable for the survival of native species. For example, the carpet sea squirt can smother gravel beds used by fish species such as Atlantic herring, which may inhibit egg laying and ultimately reduce adult numbers.

Japanese wireweed covering lobster pot – Andy Riches 

Example INNS relevant to fishing

See Policy and Legislation page for information on INNS, pathways and the law. 

Best practice for commercial fishers: 

✅  Avoid using non-native species as bait

✅  Avoid discarding unwanted catch back into the sea away from where it was caught (e.g. cleaning decks while underway). If it is suspected that an INNS is within the unwanted catch – dispose of it appropriately on land

✅  Ensure that nets, broken pots or other debris are not discarded or left in the water as this can facilitate the transport of INNS. Dispose of this equipment appropriately on land

✅  Wash down equipment into the same water body or wash down well away from the water’s edge. For example, if you haul and clean your creels either wash them down in the area they have been hauled from or onshore away from the water’s edge where no residues can return to the sea 

✅  Use either a waste-capture washdown facility when your boat is hauled out or wash your boat as far away from the water’s edge as you can, well above the high-water line, and make sure wastewater and debris does not enter back into the sea

Best practice for anglers: 

✅  Avoid using non-native species as bait

✅  Ensure that all equipment and clothing is cleaned and dried before and after use

✅  If equipment is being used abroad, ensure that it is clean and dry before travelling between locations

See Marine Biosecurity Action Plan for Wales for information on the seven main areas of biosecurity that cover all pathways in Welsh seas. Click here for useful links and resources. 

Fishing off the rocks at Mwnt Beach – Chloe Powell Jennings