Commercial tuna fishing relies on four main methods, each with distinct operational characteristics and environmental impacts:
- Purse seine fishing – Uses large nets up to 2,000 meters long to encircle entire tuna schools, capturing approximately 60% of global tuna production with high efficiency but potential for significant bycatch
- Pole-and-line fishing – Targets individual fish using live bait and skilled anglers, offering the most selective and sustainable approach with minimal ecosystem disruption
- Longline fishing – Deploys thousands of baited hooks across vast ocean areas to catch larger, high-value species in deep waters, though with risks to seabirds and marine mammals
- Trolling – Involves dragging artificial lures behind moving vessels to catch surface-swimming tuna, providing moderate selectivity with lower volume catches
These fishing techniques create a complex global tuna industry where method selection directly influences catch volume, target species, environmental impact, and economic viability. Understanding these differences is crucial for informed decisions about tuna sourcing, sustainability practices, and supply chain management in today’s regulated seafood market.
How does purse seine fishing work and why is it so popular?
Purse seine fishing uses large nets up to 2,000 meters long that encircle entire tuna schools before closing like a drawstring purse at the bottom. Fish aggregating devices (FADs)—floating objects that attract marine life—help concentrate tuna schools, making this method highly efficient for large-scale commercial operations.
When spotters locate tuna schools, the fishing vessel deploys a large net in a circle around the school while a smaller boat guides the net’s positioning. FADs are combined with satellite-connected sonar buoys to improve efficiency. Once the school is encircled, the bottom of the net closes, trapping the tuna. Hydraulic systems then haul the net aboard.
This method’s popularity stems from several advantages:
- Volume efficiency – A single purse seine vessel can catch more tuna in one day than pole-and-line boats catch in weeks
- Cost effectiveness – High-volume catches reduce per-unit costs and market prices
- Technological integration – Fish finders, helicopter spotters, and GPS systems optimize success rates
- Geographic flexibility – Works well in tropical Pacific and Atlantic waters where tuna form large, predictable schools
What’s the difference between pole-and-line and longline tuna fishing?
Pole-and-line fishing involves individual anglers catching one tuna at a time with live bait, while longline fishing deploys thousands of baited hooks along lines stretching up to 100 kilometers. These methods represent opposite approaches to commercial tuna fishing:
- Operational scale – Pole-and-line targets individual fish requiring skilled crews, while longline covers vast ocean areas with automated gear
- Target species – Pole-and-line typically catches smaller skipjack and yellowfin (2–20 kg), while longline targets larger bluefin, bigeye, and yellowfin tuna (50–200 kg)
- Selectivity – Pole-and-line allows immediate release of non-target species, while longline may capture various marine life as bycatch
- Value proposition – Pole-and-line produces lower volumes of sustainably caught fish, while longline yields high-value tuna for premium markets
Pole-and-line fishing demands live bait tanks and precise vessel positioning, requiring extensive local knowledge. Longline operations focus on strategic gear placement, with vessels setting equipment and returning hours later to retrieve catches across multiple zones.
Why does the fishing method matter for tuna sustainability?
Different tuna fishing methods create varying impacts on ocean ecosystems through bycatch rates, habitat disruption, and fishing pressure. Selective fishing practices like pole-and-line generate minimal bycatch, while purse seine and longline methods may capture sharks, sea turtles, mantas, and juvenile fish. Dolphins are seldom caught; dolphin-tuna association only occurs in purse seiner yellowfin fisheries off the Mexican Pacific coast.
Key sustainability differences include:
- Bycatch impact – Pole-and-line allows immediate release of non-target species, while purse seine and longline methods may trap marine mammals, seabirds, and endangered species
- Age selectivity – Purse seine around FADs often captures juvenile tuna before reproduction; free-school targeting yields mostly mature fish. Pole-and-line mostly catches small skipjack and juvenile yellowfin, while longliners almost exclusively hook large mature fish
- Ecosystem disruption – Longline gear may hook seabirds and sea turtles, though modern circle hooks and bird deterrents reduce these impacts
- Resource efficiency – Purse seine requires less fuel per ton caught, while pole-and-line demands more fuel per kg but has less impact on the ocean ecosystem
- Population pressure – High-volume methods like purse seine can deplete local tuna populations if unmanaged, while selective small-scale methods maintain more balanced fishing pressure
How SmarTuna helps with tuna fishing traceability
SmarTuna provides digital traceability and verification for tuna from the moment fishing vessels begin their trips, capturing real-time data through satellite VMS and AIS systems. The platform tracks fishing methods used, assigns unique Raw Material IDs to each catch batch, and automatically verifies compliance against regulatory databases including RFMO registries and IUU blacklists.
Key capabilities include:
- Real-time vessel tracking – Shows exact fishing locations and methods with satellite precision for complete operational transparency
- Automated verification – Cross-references against 15+ certification databases, including MSC CoC and ISSF PVR, eliminating manual compliance checking
- Digital documentation – Links fishing techniques to sustainability certifications with tamper-proof blockchain records
- Complete supply chain visibility – Tracks tuna from fishing vessel through processing and distribution with unbroken data continuity
- GDST-compatible data exchange – Ensures consistent traceability standards across global seafood supply chains
This first-mile tracking approach transforms fishing method verification from manual documentation to automated, real-time monitoring—giving companies audit-ready evidence of responsible sourcing, regulatory compliance, and sustainability commitments.
Ready to verify your tuna fishing methods? Contact SmarTuna to learn how real-time vessel tracking and automated verification can strengthen your supply chain transparency and sustainability documentation.
