Fishing Dredge Explained: Types, Uses, and Impacts

A fishing dredge is a towed fishing gear designed to scrape the seabed to harvest bottom-dwelling species like scallops, oysters, and clams. It consists of a heavy steel frame with a mesh bag or chain net that digs into the sediment as a boat tows it along. Dredges are highly efficient for catching shellfish but are also controversial due to their significant impact on marine habitats. This guide explains how dredges work, the different types, their environmental footprint, and how they compare to other fishing methods, helping you understand the role they play in commercial fishing and seafood sustainability.

What Is a Fishing Dredge?

A fishing dredge is a type of bottom-towed fishing gear that is dragged along the seafloor to collect shellfish and other benthic organisms. Unlike trawls, which are cone-shaped nets that target fish, dredges use a rigid frame with teeth or a blade that penetrates the sediment, digging out buried species. The catch is collected in a mesh bag or chain basket attached to the frame. Dredges are used worldwide in commercial fisheries for species like sea scallops, oysters, and clams, and are prized for their efficiency in capturing high volumes of shellfish in a single pass.

Why Fishing Dredges Matter

Fishing dredges are a cornerstone of the global shellfish industry. According to the Food and Agriculture Organization of the United Nations (FAO) report “The State of World Fisheries and Aquaculture 2024,” bottom-towed gear like dredges accounts for roughly 25% of global marine capture fisheries landings. In the United States, the Atlantic sea scallop fishery, which relies on dredges, is one of the most valuable in the country, generating over $500 million in annual revenue, as reported by the National Oceanic and Atmospheric Administration (NOAA) in 2023. However, dredging also raises serious environmental concerns, including habitat destruction and bycatch, making it a key topic in sustainable fishing debates.

Who This Guide Is For

This guide is for anyone curious about commercial fishing methods, including seafood consumers, students, environmental advocates, and industry newcomers. If you want to understand how your seafood is caught, the trade-offs of different fishing technologies, or the sustainability challenges facing our oceans, this guide provides a balanced, factual overview. By the end, you’ll be able to distinguish dredges from other gear, assess their impacts, and engage in informed discussions about seafood choices.

How a Fishing Dredge Works

A fishing dredge operates by being towed behind a fishing vessel, typically at speeds of 4 to 6 knots. The dredge’s frame is equipped with either a series of teeth or a flat blade that digs into the seabed. As the dredge moves forward, it dislodges shellfish from the sediment, and the mesh bag collects them while allowing water and fine sediment to pass through. The depth of penetration varies by design: some dredges dig only a few centimeters, while others can penetrate up to 30 centimeters, according to a 2021 study published in the ICES Journal of Marine Science. The catch is then hauled aboard, sorted, and often processed at sea.

Types of Fishing Dredges

There are two main types of fishing dredges: toothless and toothed. Each is suited to different target species and seabed conditions.

Toothless Dredges

Toothless dredges, also known as “rock hopper” or “smooth” dredges, have a flat, smooth lower edge that does not penetrate deeply. They are used on hard, rocky bottoms to catch species like oysters that lie on the surface. According to the Marine Stewardship Council (MSC) 2022 guidelines, toothless dredges cause less habitat disturbance than toothed models but are less effective on soft sediments where shellfish bury themselves.

Toothed Dredges

Toothed dredges feature a row of metal teeth that rake the seabed, digging out buried species like clams and scallops. The teeth are spaced to allow small individuals to escape, reducing undersized catch. However, the physical disturbance is greater. A 2023 report by the Marine Conservation Society (MCS) notes that toothed dredges can turn over the top 10–30 centimeters of sediment, altering the habitat for many benthic organisms.

Fishing Dredge vs. Trawl: What’s the Difference?

Dredges and trawls are both towed gear, but they differ in design and target. The table below summarizes key differences.

Feature	Fishing Dredge	Bottom Trawl
Primary target	Shellfish (scallops, oysters, clams)	Fish (cod, shrimp, flatfish)
Gear structure	Rigid frame with mesh bag	Cone-shaped net with otter boards
Seabed interaction	Digs into sediment with teeth or blade	Sweeps the seabed with net footrope
Typical depth of penetration	5–30 cm	1–10 cm
Bycatch rate	Moderate to high	High
Habitat impact	High, especially toothed dredges	Moderate to high

Both methods are controversial, but dredges are often singled out for their intense seabed disturbance. According to a 2022 analysis by the World Wildlife Fund (WWF), dredging can reduce biodiversity by up to 50% in affected areas, whereas trawling’s impact varies by depth and substrate.

Environmental Impact of Fishing Dredges

The environmental impact of dredging is a major concern for marine scientists and conservationists. Dredging physically disturbs the seabed, destroying habitats like seagrass beds and coral reefs that are crucial for many marine species. A 2020 study published in the journal Nature Reviews Earth & Environment found that bottom-towed gear, including dredges, is responsible for a 56% reduction in benthic biomass in frequently trawled areas. Additionally, dredges can cause significant bycatch of non-target species, including juvenile fish and invertebrates, which are often discarded dead.

Habitat Destruction

The physical action of dredging removes or damages bottom-dwelling organisms and alters sediment structure. According to the United Nations Environment Programme (UNEP) 2023 report, repeated dredging can lead to long-term changes in benthic communities, favoring opportunistic species that tolerate disturbance over slower-growing, sensitive species. This can reduce overall biodiversity and ecosystem resilience.

Bycatch and Discards

Dredges are not very selective, capturing a wide range of species in addition to the target shellfish. According to the FAO 2024 report, bycatch rates for dredges can be as high as 30% of total catch, depending on the fishery. Many of these bycatch organisms are discarded, often dead or dying. This not only wastes resources but also disrupts the food web.

Regulations and Management of Dredging

Fishing dredges are subject to various regulations to mitigate their environmental impact. In the United States, the Magnuson-Stevens Act governs federal fisheries, requiring management plans that specify allowable gear types and fishing areas. For example, NOAA 2023 regulations restrict dredging in certain essential fish habitats. In the European Union, the Common Fisheries Policy sets technical measures, including gear restrictions and closed areas, to protect vulnerable habitats. Additionally, some areas have banned dredging entirely, such as the UK’s Marine Protected Areas, where dredging is prohibited to allow habitat recovery, as reported by the Joint Nature Conservation Committee (JNCC) in 2022.

How to Choose Sustainable Seafood

If you’re concerned about the environmental impact of dredging, you can make informed seafood choices. Look for ecolabels like the Marine Stewardship Council (MSC) certification, which indicates that a fishery meets sustainability standards. According to the MSC 2022 annual report, only about 15% of global marine fisheries are MSC-certified, and dredge fisheries are often excluded due to habitat concerns. Alternatively, choose shellfish from aquaculture, which is generally considered more sustainable. According to the FAO 2024 report, aquaculture now provides over 50% of the world’s seafood, reducing pressure on wild stocks.

The Future of Dredging: Innovations and Alternatives

Innovations are emerging to reduce the impact of dredging. Some fishers are adopting lighter gear that penetrates less, while others are using real-time habitat mapping to avoid sensitive areas. According to a 2023 study in the journal Marine Policy, the use of “smart dredges” equipped with sensors can reduce bycatch by up to 20%. Additionally, alternative fishing methods like hand-diving and raking are being promoted for high-value species like scallops, as they have minimal seabed impact. For example, the Nantucket Bay scallop fishery uses hand-dredging and has been certified as sustainable by the MSC, as noted on the MSC website in 2023.

Frequently Asked Questions

Is dredging illegal?

Dredging is not illegal, but it is heavily regulated. Many countries restrict where and when dredging can occur, and some marine protected areas ban it entirely to protect habitats. Regulations are designed to balance commercial fishing with conservation.

How deep does a dredge dig?

The depth of penetration varies by design and seabed type. Toothed dredges can dig up to 30 centimeters, while toothless dredges disturb only the surface. The depth also depends on the weight of the dredge and towing speed.

What is the difference between a dredge and a trawl?

A dredge is a rigid frame with a mesh bag designed for shellfish, while a trawl is a cone-shaped net for fish. Dredges dig into the sediment, while trawls sweep the bottom. Both have environmental impacts, but dredges are often more damaging to the seabed.

Can dredging be sustainable?

In some cases, yes. Dredging can be sustainable if it is managed carefully, with closed areas, gear modifications, and quotas. The MSC certifies some dredge fisheries, like the Nantucket scallop fishery, proving that with proper management, dredging can minimize harm.

Now That You Understand the Basics

Now that you understand the basics of fishing dredges, you can appreciate the trade-offs between efficiency and environmental impact. To learn more about sustainable fishing practices, explore our guides on [other fishing methods] and [seafood sustainability].