Striped marlin

Scientific name: Kajikia audax (formerly Tetrapturus audax)

Family: Istiophoridae

Other names: Pacific striped marlin, stripey, beaky, beak, billfish

Description: Striped marlin have elongated bodies with a long thin pointed bill. They have dark blue or black backs, with 12‑16 blue vertical bars on the lower sides. When the fish is excited, the colour of these bars rapidly changes from blue to lavender via the contraction or expansion of chromatophores (special pigmented cells). The first dorsal fin is dark blue, with the other fins being dark brown and sometimes tinged with blue.

Size (length and weight): Up to about 4 metres in length and 260 kg. Commonly found at 1.6‑2.5 metres and 30‑120 kg.

Life span: Up to about 10 years.

Habitat: Striped marlin occur in tropical to temperate waters of the Pacific and Indian Oceans. Striped marlin are a highly migratory pelagic species that can be found to depths of 289 metres. They are rarely seen in coastal waters, except where sharp drop-offs into deeper water occur. Striped marlin are mostly solitary but form small schools by size during the spawning season. They hunt prey in surface waters at night.

Prey: Fish such as sardines, trevally and small tunas, cephalopods and crustaceans.

Predators: Large sharks and toothed whales.

Reproduction: Striped marlin reach reproductive maturity at about 2-3 years of age. Males mature earlier than females. Spawning occurs in summer. Striped marlin are multiple batch spawners with females releasing eggs every few days, with 4‑41 spawning events occurring over the spawning season. Females can produce up to about 120 million eggs per spawning season.

Other notes: Unlike other marlin species striped marlin slash their prey with their bill rather than impaling it. Striped marlin is classified as Near Threatened by the IUCN Red List of Threatened Species.

The Commonwealth catch of striped marlin is managed by quota. This means the catch of this fish by commercial fishers is restricted by weight. AFMA also restricts the type of gear that can be used to fish for striped marlin.

Commercial fishermen are required to fill in records of their catches, during each fishing trip and when they land their catch in a port. This helps us keep records of how much is being caught.

AFMA decide on the amount that can be caught each year from expert advice and recommendations from fisheries managers, industry members, scientist and researchers.

As striped marlin is caught by many other countries in the western and central Pacific Ocean and the Indian Ocean, the Western and Central Pacific Fisheries Commission and the Indian Ocean Tuna Commission are the international bodies responsible for managing the world’s tropical tuna and billfish catch in the Western Pacific Ocean and the Indian Ocean. Australia is a participating member of both commissions, along with several other major fishing nations and small island countries.

The Commissions meets every year to review the latest available scientific information and set global catch limits for key tuna and billfish species such as striped marlin. They also specify what each member country must do to manage their catch of the tropical tuna and billfish species, such as carrying observers, sharing fishing information and tracking fishing vessels by satellite. AFMA has to follow the decisions made by both the Commissions when managing the Australian catch of striped marlin.

AFMA also sets requirements for having scientific observers, supplying fishing data, satellite tracking of fishing vessel and fishing gear requirements to minimise impacts on wildlife.

Striped marlin is an oceanic species caught worldwide throughout tropical, temperate and occasionally cold waters. They are found commonly in eastern Australian waters, but they are also found in the waters of other countries within the Pacific and Indian Oceans.

In Australia, striped marlin are caught anywhere along both the east and west coasts and is a targeted species by fishers in both the Eastern Tuna and Billfish Fishery and the Western Tuna and Billfish Fishery. Striped marlin is a species and prefers tropical, temperate and occasionally cold waters.

Striped marlin are also sometimes caught recreationally off Queensland, New South Wales and Victoria. These recreational catches are managed by the state governments.

There are generally low levels of bycatch, or other species, caught in the Eastern Tuna and Billfish Fishery, but some sharks, seabirds and other species may be caught when fishing for striped marlin using longline gear.

Pelagic longline fishing has minimal impact on the marine environment as they hang in the water column not touching the seafloor. Sometimes seabirds, turtles and sharks are caught accidentally. The capture of these species is monitored by on-board AFMA observers and any interactions with these species must be reported to AFMA and the Department of the Environment. In recent years, AFMA in conjunction with the Department of the Environment and the fishing industry have worked hard to reduce seabird interactions with longline gear.

Ecological risk assessments are done for the Eastern Tuna and Billfish Fishery and all other fisheries to find out if the fishing of striped marlin is harming other species. The most recent assessment was done in 2009 and the risk to other species was assessed as low.

Gear

• Pelalgic longline