Seining is a fishing method that uses a large net, called a seine, to encircle and capture fish. The net hangs vertically in the water with floats along the top edge and weights along the bottom, forming a wall that corrals fish into a concentrated area where they can be hauled in. It’s one of the oldest and most widely used fishing techniques in the world, practiced everywhere from commercial tuna fleets in the open ocean to hobbyists wading along a shoreline.
How a Seine Net Works
A seine net has three basic parts: two long panels called wings, a cone-shaped body in the center, and a bag or pocket at the narrow end where fish collect. The bottom edge, called the groundrope, is weighted with lead rings or lead-core rope so it sinks and stays in contact with the seafloor or hangs at the desired depth. The top edge carries a line of floats that keep the net upright in the water column. Together, these elements create a vertical curtain that fish can’t easily swim over or under.
The principle is simple. You deploy the net in a wide arc around a school of fish, then draw both ends together to close the circle. As the net tightens, fish are funneled toward the center bag. How exactly this plays out depends on the type of seining.
Types of Seining
Beach Seining
Beach seining, also called haul seining, is the most basic form. Two people (or two groups) wade or use small boats to stretch a net parallel to shore, then walk the ends back to the beach while dragging the net through shallow water. It works best in calm, sandy areas and is commonly used in both small-scale commercial fishing and recreational settings. No heavy equipment is needed, just the net and enough hands to pull it in.
Purse Seining
Purse seining is the industrial heavyweight. A large vessel spots a school of fish, deploys the net in a circle around it, then pulls a drawstring-like cable along the bottom edge to cinch the net closed underneath the school, forming a purse shape. This prevents fish from diving to escape. Purse seines can encircle enormous volumes of water and are the dominant method for catching schooling species like tuna, sardines, anchovies, and herring. Sixty-six percent of the global tuna catch comes from purse seining alone, far outpacing longline fishing at 9% and pole-and-line at 7%.
Danish Seining
Danish seining sits between the simplicity of beach seining and the scale of purse seining. A boat anchors one end of a long rope, motors in a wide triangular pattern while paying out rope and net, then returns to the anchor point. The crew then slowly hauls both ropes in simultaneously. As the ropes drag along the bottom, they kick up sediment clouds that herd fish toward the center, where the net waits. It’s considered a relatively low-impact method because the gear is lighter than a trawl and moves slowly.
Fish Aggregating Devices and Modern Efficiency
One of the biggest changes in commercial seining over the past few decades is the widespread use of Fish Aggregating Devices, or FADs. These are floating objects, often equipped with sonar buoys, that exploit the natural tendency of many fish species to gather beneath floating debris. Purse seine vessels deploy FADs across wide stretches of ocean, then return to set their nets around the concentrated schools that form underneath.
By the early 2000s, FAD-associated sets already accounted for an average of 57% of total tuna purse seine catches. Today, FAD fishing is the primary strategy for purse seine vessels in the Atlantic Ocean. The efficiency gains are significant: FAD trips use roughly 456 liters of fuel per ton of catch, compared to 1,810 liters per ton when vessels search for free-swimming schools without FADs. That’s nearly four times more fuel-efficient, with correspondingly higher profitability.
The tradeoff is bycatch. FAD-associated sets pull in more non-target species because many different animals congregate around the floating structures. Bycatch rates in FAD sets can exceed 40%, while sets on free-swimming schools typically stay below 17%. Sharks, rays, sea turtles, and juvenile fish of non-target species are all caught more frequently around FADs. Some regional fishery management organizations now impose seasonal FAD closures to reduce this impact, though these closures come with steep economic costs. During closure periods, vessels targeting free-swimming schools burn roughly five times more fuel per ton of catch.
Environmental Impact
The environmental footprint of seining varies dramatically depending on the type. Purse seining in open water doesn’t contact the seafloor, so it causes no direct habitat damage. Its main ecological concern is bycatch and the potential to remove large volumes of schooling fish from an ecosystem quickly.
Bottom-contact methods are a different story. When heavy nets or ropes drag across the seafloor, they can tear up root systems of underwater plants, crush animal burrows, and resuspend sediment into the water column. That suspended sediment reduces light penetration, which limits photosynthesis in marine plants that form the base of the food web. Areas of soft mud can be scoured down to bare rock, permanently changing which species can live there. Danish seining uses lighter gear than full-scale bottom trawling, so its footprint is smaller, but any method that touches the bottom carries some risk to the habitat beneath it.
Species diversity and habitat complexity tend to decline in areas that experience repeated bottom disturbance. Recovery times vary from months in sandy environments with strong currents to years or decades in deep, low-energy habitats like mud plains or cold-water coral areas.
Recreational and Small-Scale Seining
Seining isn’t just for commercial fleets. Small beach seines are popular with bait fishers, researchers conducting fish surveys, and hobbyists who want to see what lives in their local waterways. A recreational beach seine is typically 4 to 20 feet long, with fine mesh and simple pole handles on each end. Two people stretch it across a shallow area and walk it toward shore.
Regulations for recreational seining vary widely by state and country. In Florida, for example, non-residents using a beach or haul seine even for recreational purposes must hold a commercial saltwater products license. Many states restrict net length, mesh size, and the species you’re allowed to keep. Some waters prohibit seine nets entirely, particularly in protected estuaries or near sensitive habitats like seagrass beds. Checking your local fish and wildlife agency’s rules before buying a net is essential, because the penalties for illegal netting can be steep.
How Seining Compares to Other Methods
- Seining vs. trawling: Both use nets, but a trawl is towed continuously behind a moving boat, often with heavy metal doors to hold the net open. Seining is more of an encirclement or herding technique. Trawling generally causes more seafloor damage and burns more fuel per ton of catch.
- Seining vs. gillnetting: Gillnets are stationary panels that entangle fish by their gills. They’re left in place and checked periodically. Seines actively surround fish and are hauled in during the same operation. Gillnets tend to be less selective for size, catching anything that fits partway through the mesh.
- Seining vs. hook-and-line: Hook-based methods (longline, pole-and-line, rod and reel) catch fish individually. They’re far more selective but also far slower. For species that school in dense groups near the surface, seining is vastly more efficient.
Seining’s core advantage is volume. When target fish are concentrated, whether naturally or with the help of FADs, a single set of a purse seine can capture hundreds of tons in minutes. That efficiency is why it dominates the global catch of schooling pelagic species, while hook-and-line methods remain the standard for more dispersed or deep-dwelling fish.