The Trawl Blind Spot: How Bycatch Reduction Gear Fixes the Net Mistake Most Fisheries Make

Every trawl net has a blind spot. It is not a physical gap in the mesh, but a design flaw: the net catches everything in its path, including species that were never the target. This indiscriminate capture—bycatch—wastes resources, harms ecosystems, and increasingly triggers regulatory penalties. The mistake most fisheries make is treating bycatch as an unavoidable cost of doing business, rather than a solvable engineering problem. Bycatch reduction gear (BRG) offers a fix, but only when fisheries understand where the blind spot lies and how to address it.

This guide is for fleet managers, net technicians, and fishery regulators who want to move beyond compliance checklists. We will explain why bycatch happens, how BRG works, and—most importantly—how to avoid the common errors that render BRG ineffective. You will leave with a clear framework for selecting, installing, and maintaining gear that reduces bycatch without sacrificing target catch.

The Hidden Cost of the Trawl Blind Spot

When a trawl net sweeps through the water, it creates a cone of capture. Fish, turtles, and other marine life that cannot outswim the net are funneled into the codend. The blind spot is the assumption that all captured animals are equally vulnerable or that bycatch is simply a numbers game. In reality, bycatch includes juvenile fish of target species, endangered sea turtles, marine mammals, and non-commercial fish that die before they can be released. The economic cost includes lost future catch (when juveniles are killed), reduced quota availability, and potential fines under fisheries management plans.

Many fisheries operate under the belief that bycatch is proportional to effort—that catching more fish inevitably means catching more non-target species. This is not accurate. The blind spot is a net design issue, not a volume issue. Studies from regulatory bodies and independent observers consistently show that simple modifications to net geometry and mesh orientation can dramatically reduce bycatch rates. The mistake is ignoring these modifications because they seem counterintuitive: adding an escape opening might seem like it would let target fish escape too.

Why Traditional Nets Create a Bycatch Trap

A standard trawl net has a uniform mesh that narrows toward the codend. As the net fills, water flow slows, and animals that could have escaped through the mesh earlier become trapped. The key insight is that many species respond differently to net geometry. Sea turtles, for example, tend to swim upward when stressed and can be guided out through a top-opening chute. Fish often swim forward and downward, making bottom escape panels more effective. Without understanding these behavioral differences, a net is just a wall—and the blind spot remains.

The economic impact is not trivial. One composite scenario: a midwater trawl fishery targeting pollock reported that juvenile halibut bycatch consumed 15% of their allowable catch quota, forcing early season closures. After installing a simple sorting grid, the bycatch of halibut dropped by 70%, allowing the fishery to operate longer and land more target fish. The initial investment in BRG was recovered within one season through reduced downtime and higher quota utilization.

How Bycatch Reduction Gear Works: Core Mechanisms

Bycatch reduction gear functions by exploiting differences in behavior, size, or swimming ability between target and non-target species. The three primary mechanisms are mechanical exclusion, behavioral guidance, and size sorting. Understanding these mechanisms helps fisheries choose the right BRG for their specific catch profile.

Mechanical Exclusion: TEDs and Sorting Grids

Turtle Excluder Devices (TEDs) are rigid metal grids installed in the neck of the trawl. The grid bars are spaced to allow shrimp and small fish to pass through while deflecting larger animals like sea turtles and sharks toward an escape opening. The key design parameter is bar spacing: too narrow, and target catch is blocked; too wide, and non-target animals pass through. Most shrimp fisheries use a bar spacing of 2–4 inches, depending on local regulations. Sorting grids function similarly for fish: a grid with vertical bars separates fish by body depth. For example, a grid with 50 mm spacing allows haddock to pass but excludes larger cod or flatfish.

Behavioral Guidance: Fisheyes and Square-Mesh Panels

Fisheyes are cone-shaped openings sewn into the top or sides of the net. They exploit the tendency of fish to swim upward when encountering an obstruction. The funnel shape guides fish toward the opening, and the water flow helps push them out. Square-mesh panels are sections of netting where the mesh is oriented at 90 degrees to the standard diamond mesh. Diamond mesh closes under tension, trapping fish; square mesh stays open, allowing smaller fish to escape. Placing a square-mesh panel in the top panel of the codend can reduce juvenile bycatch by 30–50% in some demersal trawl fisheries.

Size Sorting: Mesh Size and Shape

Simply increasing mesh size is the oldest form of BRG, but it has limitations. Larger mesh lets smaller fish escape, but it also reduces catch of market-sized fish if the mesh is too large. The shape of the mesh matters: diamond mesh stretches and closes, while square mesh maintains a constant opening. A combination of increased mesh size and square-mesh panels is often more effective than either alone. Many fisheries now use a two-stage codend: a forward section with large diamond mesh to allow small fish to escape, and a rear section with smaller mesh to retain marketable catch.

Step-by-Step: Installing and Tuning BRG on Your Vessel

Installing BRG is not a one-size-fits-all process. Each vessel, net, and target species combination requires tuning. The following steps outline a repeatable process that we have seen work across multiple fisheries.

Step 1: Assess Your Bycatch Profile

Before buying any gear, collect data on what you are catching. Review observer reports, logbook data, or conduct a short trial with a separate bycatch monitoring net. Identify the top three non-target species by volume and the top three by conservation concern. This will guide your BRG choice. For example, if sea turtles are the main concern, a TED is mandatory. If juvenile fish are the issue, square-mesh panels or sorting grids are more appropriate.

Step 2: Select the BRG Type and Configuration

Match the BRG to your net size and target species. Use the comparison table below to narrow options. Consider whether you need a single device or a combination (e.g., TED plus square-mesh panel). Consult with net makers who have experience in your fishery; they can recommend specific bar spacings and panel positions.

Step 3: Install and Test

Work with a net maker to sew the BRG into the net at the correct position. For TEDs, the grid must be angled at 45–55 degrees to the net axis. For square-mesh panels, place them in the top panel of the codend, starting about 1–2 meters from the codend tie. Conduct a trial tow with an observer to measure bycatch reduction and target catch loss. Adjust bar spacing or panel position based on results. Expect to make 2–3 iterations before achieving optimal performance.

Step 4: Train the Crew

BRG only works if the crew knows how to maintain it. Train deckhands to check for blockages, torn mesh, and grid damage after each tow. Establish a daily inspection routine. Many BRG failures occur because a grid becomes clogged with debris and the crew does not clear it, rendering the device useless.

Economic Realities: Cost, Payback, and Maintenance

The upfront cost of BRG can be a barrier for small-scale fisheries. A TED grid costs between $200 and $800 depending on size and material. A square-mesh panel adds $100–$300 to a net. Installation by a net maker may cost another $200–$500. For a vessel that fishes year-round, these costs are typically recovered within one season through reduced bycatch penalties, higher quota utilization, and fewer early closures. However, for seasonal or low-volume fisheries, the payback period may be longer.

Hidden Maintenance Costs

BRG requires ongoing attention. Grids can bend or break when hitting the bottom. Square-mesh panels can tear if the net is overloaded. Fisheyes can collapse if the funnel angle is wrong. We recommend budgeting 10–15% of the initial cost annually for repairs and replacements. Some fisheries have found that using heavier-gauge wire for grids and reinforcing panel seams extends life by 2–3 seasons. Another hidden cost is lost fishing time during installation and tuning. Plan for 2–3 days of lost fishing during the initial setup, and 1 day per year for adjustments.

When BRG May Not Pay Off

Not every fishery benefits equally. If your bycatch is already low (e.g., less than 5% of total catch), the cost of BRG may outweigh the benefit. Similarly, if your target species is very large (e.g., tuna), sorting grids may block your catch. In those cases, alternative methods like circle hooks or time-area closures may be more cost-effective. Always run a cost-benefit analysis before investing.

Common Mistakes and How to Avoid Them

Even with the best intentions, fisheries often undermine their own BRG efforts. The following mistakes are the most common we have encountered.

Mistake 1: Installing BRG but Not Monitoring It

Many vessels install a TED or square-mesh panel and assume it works forever. In reality, grids become clogged with seaweed, panels tear, and escape openings get sewn shut by accident. We recommend a daily check: look at the grid after each tow, clear any debris, and inspect the panel for tears. One composite scenario: a shrimp trawler installed a TED but never checked it; after three weeks, the grid was completely blocked by jellyfish, and bycatch rates returned to pre-BRG levels. A 5-minute daily inspection would have prevented this.

Mistake 2: Using the Wrong Bar Spacing

Bar spacing is critical. Too narrow, and target catch is lost; too wide, and non-target animals pass through. Many fisheries use the spacing recommended by a neighboring fishery without testing. For example, a flatfish fishery using a 50 mm grid designed for haddock found that their target flatfish were blocked because flatfish have a larger body depth. They switched to a 70 mm grid and saw target catch recover while bycatch remained low. Always test spacing with your own catch.

Mistake 3: Placing BRG in the Wrong Location

The position of the BRG in the net affects its performance. A square-mesh panel placed too far forward allows fish to escape before they have been sorted by size; placed too far aft, fish are already packed in the codend and cannot escape. General rule: place the panel 1–2 meters from the codend tie for demersal trawls. For TEDs, the grid must be in the neck of the trawl, before the codend. If the grid is too close to the codend, animals are already trapped and cannot be guided out.

Mistake 4: Ignoring Crew Buy-In

If the crew does not understand why BRG is installed, they may sabotage it—intentionally or not. We have heard of crews sewing escape openings shut because they thought it was losing fish. Invest in training: explain the regulatory and economic reasons, show them data from trials, and involve them in the tuning process. When the crew sees that BRG helps them fish longer, they become advocates.

Decision Checklist: Choosing the Right BRG for Your Fishery

Use the following checklist to match BRG type to your specific situation. Answer each question honestly; there is no universal best option.

Question 1: What is your primary bycatch concern?

• Sea turtles or marine mammals → TED or excluder grid with large escape opening
• Juvenile fish of target species → Square-mesh panel or increased mesh size
• Non-commercial fish (e.g., jellyfish, small sharks) → Sorting grid or fisheye
• Mixed bycatch → Combination of TED and square-mesh panel

Question 2: What is your target species and size?

• Small target (e.g., shrimp, sardines) → TED with narrow bar spacing (2–3 inches) or fine sorting grid
• Medium target (e.g., haddock, pollock) → Square-mesh panel or sorting grid with 50–70 mm spacing
• Large target (e.g., cod, flatfish) → Sorting grid with wide spacing (70–100 mm) or no grid (use square-mesh panel only)

Question 3: What is your net size and towing speed?

Larger nets and faster tows require stronger BRG materials. For nets over 100 feet, use heavy-gauge grids and reinforced panels. For towing speeds above 3 knots, fisheyes may collapse; use a rigid grid instead.

Question 4: What is your budget and maintenance capacity?

• Low budget (<$500) → Square-mesh panel only; DIY installation possible
• Medium budget ($500–$1,500) → TED or sorting grid; professional installation recommended
• High budget (>$1,500) → Combination of multiple BRG types; full crew training and monitoring program

Question 5: Are there regulatory requirements?

Check with your local fisheries management authority. Many regions mandate specific BRG for certain fisheries (e.g., TEDs in U.S. shrimp trawls). Compliance is not optional, but you can often choose among approved designs.

Synthesis: Turning the Blind Spot into a Clear View

The trawl blind spot is not a permanent feature of fishing—it is a design flaw that can be corrected. Bycatch reduction gear works when it is chosen based on the specific bycatch profile, installed correctly, and maintained diligently. The fisheries that succeed are those that treat BRG as a tool for efficiency, not a regulatory burden. They monitor their gear, train their crews, and adjust over time.

Your Next Steps

Start by auditing your bycatch data. If you do not have data, collect it for one week using a separate bycatch net or an observer. Then, use the decision checklist above to identify the most promising BRG type. Contact a net maker who has experience in your fishery and schedule an installation. Plan for a trial period of at least 10 tows, with data collection on both bycatch and target catch. Adjust and repeat. Finally, share your results with other fisheries in your area—the more that adopt effective BRG, the healthier the stocks and the more stable the regulations.

Remember that BRG is not a silver bullet. It is one part of a broader responsible fishing strategy that includes time-area closures, gear restrictions, and quota management. But for most trawl fisheries, fixing the blind spot is the single most impactful change you can make. The net mistake is assuming bycatch is inevitable. The fix is understanding that your net can be smarter.