Current and Emerging Bycatch Reduction Solutions

General Overview of Bycatch Reduction Solutions

• Categories of Bycatch Mitigation Strategies:

  • Spatial and Temporal Management: Implementation of time-area closures to restrict fishing in high-density non-target species habitats or during peak migration/breeding seasons.

  • Bycatch Limits, Caps, and Monitoring: Establishing species-specific bycatch quotas or hard caps paired with intensive monitoring programs (such as $100\%$ observer coverage or electronic monitoring).

  • Fishing Gear Modifications:

    • Turtle Excluder Devices (TEDs): Mechanical grid inserts inside trawl nets designed to exclude large marine organisms while retaining target catch.

    • Acoustic Deterrent Devices (ADDs): Acoustic emitters ("pingers") used to alert marine mammals to gear presence.

    • Hook Modifications: Altering shape, size, or offset (e.g., circle hooks vs. traditional J-hooks) to reduce ingestion or deep hooking.

    • Bait Modifications: Changing bait species, consistency, or color to reduce attraction to non-target species.

    • Line Modifications: Adding weights, changing leader materials, or altering leader breaking strength.

  • Fishing Technique Modifications:

    • Night Setting and Side Setting: Altering the timing or location on the vessel where longline gear is deployed.

    • Offal Management: Strategic disposal of fish processing waste to distract or deter foraging non-target animals.

  • Effort Reduction: Overall reductions in fishing duration, total hook counts, or tow times.

Seabird Bycatch Reduction Solutions

• Global Impact and Regulations:

  • Mortality Scale: Historically, an estimated $160,000\text{--}320,000$ seabirds were killed annually worldwide in longline fisheries (Anderson et al. 2011). Current global totals remain uncertain.

  • Regulatory Frameworks: Managed through national government policies, Regional Fisheries Management Organizations (RFMOs), and international treaties such as the Agreement on the Conservation of Albatrosses and Petrels (ACAP).

• Tori Lines (Streamer Lines):

  • Mechanism: Brightly colored streamer lines towed behind the vessel during longline setting to create a visual barrier and deter seabirds from diving onto baited hooks.

  • Limitations: Highly effective for surface-attracted birds, but does not fully mitigate bycatch of deep-diving seabird species.

  • Design and Performance Standards:

    • Davit/Mast Height: Attached at an elevation of approximately $20\text{ feet}$ above sea level.

    • Streamer Spacing: Streamers made of UV-protected orange tubing ($0.25\text{ inch}$ thickness) spaced $16\text{ feet}$ apart.

    • Line Specifications: Total streamer line length of $50\text{ fathoms}$ constructed from $5/16\text{ inch}$ blue steel 3-strand polypropylene line, anchored by a buoy or drogue at the terminal end with swivel breakaways.

    • Protection Area: Covers the "Bird Zone" ($30\text{ fathoms}$ behind the boat), where the vast majority of bird attacks occur before the main longline sinks below $1\text{ fathom}$.

• Weighted Longlines:

  • Function: Primary method to mitigate bycatch of deep-diving seabirds by accelerating line and hook sink rates through the surface water column.

  • Application: Frequently deployed in tandem with tori lines.

  • Weight Configurations:

    • $\le 1\,\text{m}$ from hook with a $45\,\text{g}$ weight.

    • $\le 3.5\,\text{m}$ from hook with a $60\,\text{g}$ weight.

    • $\le 4\,\text{m}$ from hook with a $98\,\text{g}$ weight.

    • Standard weight placement ranges between $45\text{--}98\,\text{g}$ per branch line.

• Dyed and Thawed Bait:

  • Blue Dye Application: Mackerel and squid bait are dyed dark blue to diminish visual contrast against ocean water, rendering the bait less visible to searching seabirds.

  • Thawing: Bait must be fully thawed prior to setting to ensure trapped air inside frozen bait escapes, increasing the sink rate.

• Strategic Offal Discards:

  • Discards Strategy: Discarding fish offal (such as heads and livers) on the side of the vessel opposite to where longlines are being set.

  • Effect: Distracts seabirds away from the active gear setting zone.

• Operational Setting Modifications:

  • Night Setting: Setting lines strictly in darkness prevents visual detection of baited hooks. Example: Hawaiʻi shallow-set longline regulations prohibit setting earlier than $1\text{ hour}$ after sunset and require retrieval completion by $1\text{ hour}$ before sunrise.

  • Side Setting: Setting longlines from the side of the vessel rather than the stern. Seabirds are unable or unwilling to enter the turbulent, close-vessel zone on the side to pursue hooks.

• Emerging Technology - The Hookpod:

  • Mechanism: A pressure-operated mechanical capsule that encloses the barb and point of a baited hook during longline deployment.

  • Operation Step-by-Step:

    1. The baited hook is locked inside the Hookpod using a locking collar and lug.

    2. The line is set into the water with the hook point completely covered.

    3. As the gear sinks, ambient hydrostatic pressure increases.

    4. Upon reaching a target depth of $20\,\text{m}$ (beyond the diving range of most seabirds), the pressure mechanism opens the pod, exposing the hook for target fish.

Sea Turtle Bycatch Reduction Solutions

• Overview and Key Species:

  • Sea turtles—most prominently Loggerheads (Caretta caretta) and Leatherbacks (Dermochelys coriacea)—face severe population threats from incidental capture in longline and trawl gear.

• Hook Modifications (Circle Hooks vs. J-Hooks):

  • Mechanism: Large circle hooks (e.g., $18/0$ circle hooks with a width of $5.7\,\text{cm}$) feature an inward-pointing hook point compared to conventional J-hooks (e.g., $9/0$ J-hooks with a width of $4.1\,\text{cm}$).

  • Effect: Circle hooks reduce the likelihood of a turtle swallowing the hook into its esophagus or stomach, resulting in jaw-hooking rather than deep foul-hooking, which significantly improves post-release survival.

• Bait Modifications:

  • Bait Hardness: Harder fish bait (such as mackerel) is difficult for sea turtles to swallow whole compared to soft squid bait.

  • Regulation Example: In the Hawaiʻi shallow-set swordfish longline fishery, the use of squid bait is strictly prohibited by NOAA, and mackerel-type fish bait is mandated.

• Trawl Fisheries & Turtle Excluder Devices (TEDs):

  • Definition: A TED is a specialized grid insert fitted into a trawl net's extension section, upstream of the codend.

  • Mechanism: A guiding funnel directs water and catch toward a slanted metal bar grid. Target catch (e.g., shrimp) passes through the narrow grid bars into the codend, while larger animals (sea turtles) strike the grid bars and are ejected through a top or bottom escape opening.

  • Efficiency: Properly fitted TEDs achieve up to a $97\%$ reduction in sea turtle trawl mortality (NOAA).

  • Operational Modifications: Implementing shortened tow times prevents trapped turtles from drowning by allowing them to surface and breathe.

Marine Mammal Bycatch Reduction Solutions

• Gillnet Fisheries - Acoustic Deterrent Devices (ADDs / Pingers):

  • Target Species: Cetaceans (dolphins, porpoises) that utilize echolocation and are sensitive to low-frequency sound.

  • Mechanism: Electronic pingers attached along the floatline or leadline emit periodic acoustic signals ("pings") to make the net acoustically detectable and deter animals from approaching.

  • Performance: Efficacy and adoption rates vary across geographic regions and gear types.

• Pot and Trap Fisheries - Ropeless Fishing (On-Call Gear):

  • Problem: Persistent vertical endlines connecting seabed lobster/crab pots to surface marking buoys cause severe, often fatal entanglements in large whales (e.g., North Atlantic Right Whales and Humpback Whales).

  • Technology Framework: Eliminates static vertical lines in the water column while gear is soaking.

  • Operation:

    1. Traps sit on the ocean floor without surface lines.

    2. Vessel operators locate gear using an app paired with acoustic transceiver signals.

    3. When harvesting, an acoustic trigger signal sent from the surface releases a retrieval system packed at the trap.

  • Retrieval Systems:

    • Pop-up Buoys: Acoustic release opens a latch, releasing a buoyant surface marker.

    • Inflatable Lift Bags: An onboard gas cylinder inflates a submerged bag to lift the gear.

    • Buoyant Spools: A submerged spool unrolls line to the surface upon acoustic trigger.

  • Current Implementation Challenges: High equipment costs, inter-vessel gear tracking issues, and variable retrieval reliability in deep water or strong currents.

Shark Bycatch Reduction Solutions

• Leader Material Modifications: Substituting nylon/monofilament branch line leaders for wire leaders allows sharks to bite through the line and free themselves before retrieval.

• Circle Hooks: Prevents deep swallowing and foul-hooking in shark digestive tracts, promoting post-release survival.

• Electrical Field Deterrents: Emerging devices (such as SharkGuard) emit localized electrical fields that disrupt shark electroreceptors (Ampullae of Lorenzini), deterring them from approaching hooks.

• Net Illumination: Attaching LED lights along gillnet floatlines or mesh panels reduces incidental shark interactions.

Detailed Case Studies in Bycatch Reduction

Case Study 1: Hawaiʻi Pelagic Longline Fishery

• Context: A multi-species pelagic longline fishery targeting tuna (deep-set) and swordfish (shallow-set).

• Integrated Suite of Measures:

  • Spatial management via time-area closures.

  • Strict sea turtle bycatch hard caps combined with $100\%$ observer coverage on shallow-set swordfish vessels.

  • Mandatory de-hookers, line cutters, and fisher handling training.

  • Gear regulations: Requirement for large circle hooks ($18/0$ or larger) and fish bait (no squid) on shallow sets.

  • Bird mitigation: Mandatory night setting, side setting, tori lines/bird curtains, strategic offal discards, and line weighting.

• Results: Near-total reduction in sea turtle and seabird interactions following policy implementation in the early 2000s.

Case Study 2: U.S. Gulf Shrimp Trawl & Kemp's Ridley Sea Turtle Recovery

• Historical Decline:

  • In 1947, a single synchronized nesting event (arribada) at Rancho Nuevo, Mexico, contained an estimated $40,000$ nesting Kemp's ridley (Lepidochelys kempii) females.

  • By 1970, the species was listed as critically endangered; by the 1980s, fewer than $300$ nesting females remained globally due to egg harvesting and trawl mortality.

• Intervention Timeline:

  • Late 1960s: The Turtle Excluder Device (TED) was invented by a Georgia fisherman ($97\%$ turtle escape efficacy).

  • 1982: A bi-national recovery plan was established between Mexico and the U.S., involving egg/hatchling relocation to Padre Island National Seashore in Texas.

  • 1987: The U.S. mandated TED usage in federal waters.

  • 1989: Implementation of the U.S. shrimp-turtle import law (Section 609).

• Recovery Metrics:

  • Texas nesting numbers grew from near zero in the 1980s to 449 nests in 2025 and over 650 nests in 2026 (USFWS data).

  • Texas nests represent a small fraction of total species nesting, with the majority occurring in Tamaulipas, Mexico.

  • Despite substantial recovery, the species remains endangered and sensitive to anthropogenic impacts (e.g., the 2010 Deepwater Horizon oil spill).

Case Study 3: Eastern Tropical Pacific Tuna Purse Seine Fishery & Dolphin Conservation

• Ecological Association: Yellowfin tuna consistently swim underneath dolphin pods in the Eastern Tropical Pacific (ETP).

• Fishery Technique: Purse seine fleets spotted dolphins at the surface, encircled the pods with large nets, and trapped both dolphins and underlying tuna.

• Policy and Market Interventions:

  • Public outrage over high dolphin mortality prompted the passage of the U.S. Marine Mammal Protection Act (MMPA) in 1972.

  • Fleet gear/technique modifications: Implementation of the backdown maneuver, installation of fine-mesh Medina panels to prevent porpoise snout/flipper entanglement, and mandatory observer programs.

  • Import bans on nations failing to meet U.S. dolphin mortality standards led to the creation of the "Dolphin-Safe Tuna" eco-labeling program.

• Mortality Trends: Annual observed dolphin mortality plummeted from roughly $132,000$ in 1986 down to $819$ mortalities in 2018 (NOAA).

Key Ingredients for Successful Bycatch Reduction

• Direct Fisher Engagement: Involving fishermen from the onset of research and policy formulation.

• Co-Developed Solutions: Working alongside harvesters to engineer, test, and refine gear modifications under real-world commercial conditions.

• Protection of Livelihoods: Ensuring gear modifications preserve target catch rates and economic viability for fishing communities.

• Industrial Fleet Capacity: High-revenue industrial fisheries possess the capital necessary to absorb costs for new technology (e.g., satellite gear, electronic monitoring, specialty hooks).

• International Cooperation: Multilateral treaties and RFMO regulations ensuring compliance across EEZ boundaries and high-seas international waters.

• Market Forces: Utilizing consumer purchasing power, trade import regulations, and market-driven eco-labeling (such as Dolphin-Safe certified products) to compel global compliance.