# Marlin — Facts, Threats & Conservation

*Makaira nigricans (Lacepède, 1802)*

> The blue marlin (Makaira nigricans) is a Vulnerable billfish of tropical oceans, declining from longline bycatch and overfishing; white and striped marlin face similar pressures.

**IUCN status:** Vulnerable  ·  **WARN range:** Tropical and subtropical oceans worldwide — Atlantic, Pacific and Indian

## Quick facts
| Fact | Value |
| --- | --- |
| Weight | Up to 450 kg (blue marlin females) |
| Length | Up to 5 m including bill |
| Speed | Bursts exceeding 110 km/h |
| IUCN status | Vulnerable — decreasing |
| Main threat | Longline bycatch on tuna fisheries |
| CITES | Appendix II (blue marlin) |

## Scientific classification
- **Kingdom:** Animalia
- **Phylum:** Chordata
- **Class:** Actinopterygii
- **Order:** Istiophoriformes
- **Family:** Istiophoridae
- **Genus:** Makaira
- **Species:** Makaira nigricans (Lacepède, 1802)

## Conservation status
- **Status:** Vulnerable (IUCN, 2019). Decreasing population from longline bycatch and overfishing.
- **Population:** No reliable global count; declining across major ocean basins
- **Trend:** Decreasing
- **Assessed:** 2019
- **CITES:** Appendix II (blue marlin)

## Key facts: Marlin
- Blue marlin are Vulnerable — declining from longline bycatch and directed fishing.
- Marlin are caught incidentally on tuna and swordfish longlines worldwide.
- Sport fishing targets marlin — catch-and-release reduces but does not eliminate mortality.
- Marlin are slow-growing — maturity at 2–4 years; recovery from overfishing takes decades.
- White marlin is Near Threatened; striped marlin is Data Deficient.
- Circle hooks and fishery closures reduce marlin bycatch on longlines.

## Giants of the billfish family
Marlin belong to family Istiophoridae alongside sailfish and spearfish. The blue marlin — Makaira nigricans in the Atlantic and Indo-Pacific — is the largest, with females exceeding 450 kg and 5 metres including bill. Metallic blue-black upper body, silver flanks and a rigid, sail-like dorsal fin define the species.

Marlin use their bills to stun tuna, mackerel, squid and dorado — slashing through schools or striking individual prey. They are among the fastest fish, capable of bursts exceeding 110 km/h. Endothermy maintains muscle and eye temperature for high-performance hunting in cool deep water.

White marlin (Kajikia albida) and striped marlin (Kajikia audax) are smaller relatives. Black marlin (Istiompax indica) of the Indo-Pacific is the heaviest bony fish recorded — over 700 kg.

## Longline bycatch crisis
The primary threat to marlin is incidental capture on pelagic longlines set for tuna and swordfish. Hundreds of thousands of hooks deployed daily across tropical oceans catch marlin alongside target species. Most marlin are dead when lines are retrieved — discarded or landed as low-value byproduct.

ICCAT and other regional fisheries bodies require some bycatch mitigation — circle hooks, dehooking tools, release protocols — but compliance and observer coverage remain insufficient. Estimated blue marlin bycatch in the Atlantic alone exceeds thousands of tonnes annually.

Directed marlin fisheries — commercial harpoon and gillnet — add mortality in the Pacific and Indian Oceans. Data reporting is poor; IUU fishing compounds uncertainty.

## Sport fishing and trophy pressure
Marlin are premier sport fish — the centrepiece of tournaments from Kona to Cairns. Billfish tournaments historically killed all catches for weigh-in; modern events increasingly practice tag-and-release. Tagging programmes provide migration data — blue marlin cross entire ocean basins.

Catch-and-release is not mortality-free. Fight duration, hook location and handling stress kill a proportion of released fish — estimates range from 5% to 30% depending on methods. Circle hooks in the jaw reduce deep-hooking mortality compared with J-hooks.

Trophy fishing removes the largest, most fecund females — disproportionately impacting breeding stock. Minimum size limits and slot limits protect spawning-capable individuals.

## Conservation status and management
The IUCN lists blue marlin as Vulnerable with a decreasing population trend. White marlin is Near Threatened. Striped marlin is Data Deficient — insufficient data for assessment despite heavy fisheries pressure. Black marlin is Data Deficient.

CITES Appendix II regulates international trade in blue marlin parts. Regional management through ICCAT, IOTC and WCPFC sets bycatch limits and retention bans in some fisheries. Retention bans — requiring marlin to be released — reduce landings but not necessarily hooking mortality.

Time-area closures around spawning grounds, mandatory observer coverage and gear modification offer the best prospects for reducing mortality while maintaining tuna fisheries.

## Protecting billfish for the future
Marlin are apex predators — indicators of healthy open-ocean ecosystems. Their decline signals unsustainable extraction from pelagic food webs shared with tuna, sharks and turtles.

Consumers can reduce marlin mortality indirectly by choosing pole-and-line tuna, supporting fisheries with bycatch limits and avoiding seafood from IUU sources. Anglers should use circle hooks, minimise fight time and support tournaments with mandatory release.

WARN publishes this marlin guide as free public education about billfish caught in the crossfire of industrial longline fisheries — Vulnerable giants whose recovery depends on bycatch reform across the world's tuna fleets.

## What WARN does
WARN publishes this marlin guide as free public education. Billfish bycatch on tuna longlines is a hidden crisis — reducing it protects marlin, sharks and ocean ecosystem integrity.

If this guide helps you understand wildlife and the pressures it faces, a gift to WARN supports habitat protection and free public education in our partner countries.

## Frequently asked questions: Marlin
### Are marlin endangered?
Blue marlin is Vulnerable (IUCN, 2019) with a decreasing trend. White marlin is Near Threatened. Striped and black marlin are Data Deficient.

### Why are marlin declining?
Incidental capture on tuna and swordfish longlines is the primary cause. Directed fisheries, sport fishing mortality and slow growth compound the decline.

### What is marlin bycatch?
Marlin caught unintentionally on longlines set for tuna and swordfish. Most die on the line. Atlantic blue marlin bycatch alone exceeds thousands of tonnes annually.

### Do sport fishermen kill marlin?
Modern tournaments increasingly use tag-and-release, but fight stress and hook injury kill 5–30% of released fish. Trophy fishing removes large breeding females.

### What is the difference between marlin and swordfish?
Marlin have round bills, rigid dorsal fins and visible pelvic fins. Swordfish have flat bills and belong to a separate family. Marlin are generally more associated with tropical surface waters.

### How can bycatch be reduced?
Circle hooks, night setting, time-area closures, mandatory observers and retention bans reduce marlin mortality on longlines. Pole-and-line tuna fisheries avoid most bycatch.

## Sources
- [IUCN Red List — Makaira nigricans](https://www.iucnredlist.org/species/170314/6483776)
- [ICCAT — billfish bycatch reports](https://www.iccat.int/)
- [Billfish Foundation — conservation](https://www.billfish.org/)

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Full guide: https://worldanimalrescuenetwork.org/wildlife-guides/marlin