Tuna

Scope

This record documents how tuna are exploited within globally standard animal-use systems. It describes dominant, routine practices across industrial wild-capture fisheries and tuna ranching operations, independent of country-specific regulation or market branding.

Differences in scale, enforcement, and legal framing are documented in country records. System-specific mechanisms are documented within industry records.

Species context

Photo by James Thornton

Tuna are large, fast-swimming pelagic fish belonging primarily to the genera Thunnus, Katsuwonus, and Euthynnus. They are adapted for long-distance, high-speed oceanic movement and are capable of crossing entire ocean basins.

Tuna possess advanced sensory systems, including acute vision and lateral line detection of water movement. Many species are partially endothermic, enabling sustained swimming in varying temperatures. They form dynamic schools and undertake extensive migratory routes linked to feeding and spawning cycles.

Under natural conditions, tuna move continuously through open ocean environments, maintaining high levels of muscular activity and interacting within large pelagic ecosystems.

These characteristics establish tuna as wide-ranging, endurance-adapted animals whose biological and behavioural needs are incompatible with confinement and industrial extraction.

Natural versus exploited lifespan

Natural lifespan

In the absence of exploitation, tuna lifespans vary by species:

Smaller species (e.g., skipjack): approximately 8–12 years
Larger species (e.g., bluefin): up to 30–40 years

Some species reach sexual maturity only after several years of growth.

Lifespan under exploitation

Within exploitation systems, tuna are typically killed far earlier:

Industrial wild-capture fisheries: often killed as juveniles or sub-adults before full reproductive contribution
Ranching operations: captured young and fattened for months before slaughter

The divergence between natural lifespan and exploited lifespan is driven by market demand, fleet capacity, and quota allocation rather than ecological maturity.

Systems of exploitation

Tuna are exploited primarily through:

Industrial wild-capture fisheries
Tuna are captured in open ocean using purse seine nets, longlines, pole-and-line methods, and drifting fish aggregating devices (FADs).
Fish aggregating device (FAD) fisheries
Artificial floating structures are deployed to attract tuna and other species, enabling mass capture.
Longline fisheries
Thousands of baited hooks are set across tens of kilometres of ocean to target tuna.
Tuna ranching (capture-based aquaculture)
Juvenile tuna are captured alive and towed to sea pens, where they are fattened before slaughter.
Byproducts and processing industries
Tuna bodies are processed into canned products, loins, sashimi-grade cuts, fishmeal, and oil.

These systems rely on large industrial fleets, refrigeration vessels, aerial spotting, satellite tracking, and global processing networks.

Living conditions across system types

Wild capture

In purse seine fisheries, entire schools are encircled by massive nets and drawn together, resulting in extreme crowding, compression, oxygen depletion, and panic behaviour. Fish may be trapped for hours before hauling.

In longline systems, tuna are hooked through the mouth or body and may struggle for extended periods before retrieval, resulting in exhaustion, injury, and suffocation.

Tuna ranching

In ranching systems, captured tuna are towed—sometimes over long distances—into large sea pens. Confinement restricts natural migratory behaviour. Tuna are fed large quantities of smaller fish to accelerate fattening.

The confined environment contrasts sharply with their natural requirement for continuous, high-speed movement across open ocean.

Standardised lifecycle under exploitation

While methods vary, tuna typically move through a broadly standardised exploitation lifecycle:

Oceanic existence
Tuna migrate and feed across large pelagic ecosystems.
Detection and aggregation
Fleets use sonar, spotter planes, and FADs to locate or attract schools.
Encirclement or hooking
Tuna are captured in nets or hooked on longlines.
Immediate death or transfer
In wild-capture systems, tuna are killed onboard. In ranching systems, selected fish are transferred alive to pens.
Slaughter and processing
Tuna are killed through gill cutting, brain spiking (ikejime in some contexts), or exsanguination, then processed for market.

Chemical and medical interventions

In wild-capture systems, chemical interventions are absent; mortality results directly from mechanical capture and suffocation.

In ranching systems, tuna may be subjected to:

Antibiotics to manage disease in confinement
Chemical treatments for parasites
Feed manipulation to enhance fat content

However, compared to fully farmed species, ranching involves shorter confinement periods before slaughter.

Slaughter processes

Tuna slaughter methods vary:

Onboard wild-capture vessels, tuna are often clubbed, gill-cut, and bled.
Large individuals may be stabbed in the brain or left to suffocate.
In purse seine operations, fish may die from crushing and oxygen depletion before handling.

In ranching systems, tuna are crowded within pens and killed individually by shooting, brain spiking, or gill cutting.

Death may not be immediate, particularly in mass-haul operations. Large body size and strength can complicate stunning consistency.

Slaughterhouse labour impact

Tuna exploitation involves:

Handling extremely large animals under hazardous conditions
Repetitive processing in cold-storage and canning facilities
High injury risk from heavy equipment and sharp tools

Labour conditions vary widely across industrial fleets and processing hubs, with some operations occurring in remote or poorly regulated maritime contexts.

Scale and prevalence

Tuna are among the most commercially valuable fish globally. Millions of tonnes are captured annually across all major ocean basins.

Industrial fleets operate continuously, targeting multiple tuna species. High-value species such as bluefin are subject to intense pressure due to premium markets.

Tuna exploitation also drives bycatch mortality of sharks, seabirds, turtles, and non-target fish species.

Ecological impact

Tuna exploitation contributes to extensive ecological disruption:

Depletion of top pelagic predator populations
Disruption of marine food webs
Bycatch mortality linked to longlines and purse seines
Ghost fishing from lost gear
Capture of juvenile tuna before reproductive maturity

FAD use alters natural movement patterns and increases bycatch rates.

Ranching systems require large quantities of wild fish as feed, compounding extraction pressures.

Language and abstraction

Tuna are commonly referred to as “stocks,” “quota units,” “tonnage,” or “catch.” Market categories such as “canned,” “sashimi-grade,” or “premium bluefin” fragment the animal into commodity classifications.

Terms such as “harvest” and “resource management” frame industrial extraction as neutral or sustainable activity.

Editorial correction notice

Tuna are frequently framed as renewable marine resources within fisheries management systems. This record documents tuna as large, migratory predators systematically targeted, confined, and killed across industrial oceanic operations, independent of sustainability narratives or market value.