Trawl Ropes and Nets:  Innovations in Optical Ropes and Nets for Fisheries

A Brief History of Bottom Trawling

Bottom trawling is a fishing method that involves dragging heavy nets along the seafloor behind boats. This practice has been used commercially since the late 19th century and involves deploying massive nets, sometimes over a mile wide, that are towed along the ocean bottom. Ropes connect the nets to heavy discs, or "tickler chains," that are dragged along the seafloor to stir up fish and crustaceans from their hiding places so they can be caught in the nets.

Unseen Damage to Seafloor Habitats

While trawling efficiently catches target species like cod and shrimp, the heavy gear also damages fragile seafloor ecosystems in the process. Coral reefs, sponges, and other structures that provide shelter and habitats for many ocean species are vulnerable to being crushed or uprooted by tickler chains and nets. Habitat destruction harms biodiversity by reducing suitable living spaces for plants and animals. Ghost fishing also occurs when trawl ropes and nets continue to ensnare creatures long after a trawl.

Bycatch and Discard Impacts on Wildlife

In addition to altering benthic habitats, trawl fishing has substantial bycatch where non-target species are also caught in nets. Dolphins, sea turtles, sharks, seabirds and other at-risk animals may drown or become injured after being hauled aboard trawlers. Regions with high ecosystem protection recognize the threats to endangered wildlife and have enacted regulations on net and rope materials, tow times, and exclusion devices to allow escapes of protected species. However, large quantities of bycatch are still discarded at sea, dead or dying, as a result of bottom trawling globally each year.

Gear Contamination of Seafloors

derelict fishing gear, which gets lost or intentionally discarded during fishing operations, can continue impacting ocean habitats. Ghost fishing refers to when trawl ropes or nets still lined with nets and weights form "traps" on the seafloor, ensnaring marine life long after active trawling ends. Derelict gear containing synthetic materials like polypropylene or nylon ropes may persist in the ocean for hundreds of years without breaking down. As they degrade, they release microplastics that are ingested by marine life and transfer toxins up the food chain. Rope material is now a recognized form of marine debris polluting coastal and ocean environments.

Alternatives to Traditional Bottom Trawling

While bottom trawling efficiently harvests commercial quantities of fish and shellfish, methods are being tested and adopted by some fisheries to reduce impacts to vulnerable marine ecosystems and protected species. Midwater trawling utilizes nets that are held higher in the water column and off the seabed to target schooling fish without interacting with benthic habitats. Developments in gear technology now allow for rope-free and ropeless catching methods, eliminating ghost fishing risks from lost or cut lines and ropes. Fishery management organizations also implement area closures where bottom trawling is prohibited to protect sensitive reefs, nursery grounds, and spawning aggregations. With sustainably managed catch limits and improved practices that avoid seafloor contact, fishing communities and governments aim to balance food production needs with environmental stewardship of ocean resources.

Risks Posed by Microfiber Pollution

As synthetic rope wears down over time in the ocean environment, it sheds microscopic plastic fibers into surrounding waters. These shed microfibers, often less than 5mm in size, are then easily ingested by plankton, fish and other marine life. Research now shows microplastics are being found in the stomachs of creatures from the smallest plankton up through larger fish, turtles, seabirds and marine mammals. The tiny particles absorb pollutants in seawater yet are not digested, allowing toxins to accumulate up food chains. Concerns are growing over potential effects on animal and human health from chemical exposures and microplastic pollution of seafood. Rope debris represents a growing but overlooked source of microplastic contamination threatening ocean ecosystems globally.

Addressing Concerns Through Best Practices

Responsible fishing practices and gear innovations aim to address valid sustainability concerns over bottom trawling. Fishery certifications promote standards for minimizing habitat impacts, restricting trawl times over vulnerable seafloor areas, and mitigating risks of bycatch and pollution. Biodegradable rope alternatives made from natural fibers are being developed and tested in trials. Fisher cooperative programs collect derelict nets to prevent ghost fishing and microplastic shedding. Some governments have implemented “ropeless” fishing requirements where buoys and ropes are removed during hauls to avoid potential loss and pollution risk from gear. Continued research on trawl gear technologies and fishery management improvements offers promise for achieving both ecological protection and food security into the future.

In Summary, trawl ropes and nets play a critical role in commercial fishing operations, but their impact on marine life extends far beyond their intended use. These fishing gears, when lost or discarded, become hazards known as "ghost gear," posing significant threats to marine ecosystems and wildlife. Entanglement in abandoned trawl ropes and nets is a common fate for marine animals, leading to injury, suffocation, and death. Species such as whales, dolphins, sea turtles, and seabirds are particularly vulnerable to entanglement, with devastating consequences for their populations.