Oceanic whitetip shark: Marine fish conservation

The oceanic whitetip shark is a large highly migratory species that is most abundant in tropical regions of the world's oceans.

This species is reported to reach 3.9 m in total length, although specimens more than 3 m in length are exceptional. One of the characteristics of oceanic whitetip sharks is their large, very broad and rounded first dorsal and pectoral fin.

There has been a substantial decline in abundance of oceanic whitetip sharks linked to overfishing. The species is protected within the Territorial Sea and New Zealand Fisheries waters.

Facts

The oceanic whitetip shark (Carcharhinus longimanus) has a circumglobal distribution in tropical to warm-temperate oceanic waters. Although it may be encountered over continental and insular shelves, it is most abundant well away from land.

Oceanic whitetip sharks are infrequently recorded from northern New Zealand, and have been recently protected within the Territorial Sea and New Zealand Fisheries waters.

Range and habitat

Oceanic whitetip sharks are one of the most widespread sharks. They occur in all tropical to warm-temperate waters but are most abundant in oceanic waters between about 30° N and 35° S.

In New Zealand waters, they have been recorded at and near the Kermadec Islands, off the northeast coast of North Island south to about Mahia Peninsula, and a pregnant female recently washed ashore at Muriwai on the west coast North Island. They have been recorded from the surface to 150 m depth but are likely to occur deeper.

Population

This species was once considered to be among the most abundant sharks in the oceans, being recorded almost everywhere in waters greater than 180 m depth and warmer than 20° C.

However, there has been a substantial decline in abundance linked to overfishing, and these sharks are now only occasionally sighted and recorded. The IUCN classifies the oceanic whitetip as "Vulnerable" in the Red List of Threatened species. The species status in New Zealand waters is unclear due to a lack of scientific observations. Fisheries catch data suggest that it is rare but levels of non-reporting and misidentification are unknown.

Diet and foraging

Oceanic whitetips feed mainly on bony fishes (including swordfish, tuna, marlin, barracuda, lancetfish, dolphinfish, oarfish and threadfish) and cephalopods (octopuses and squids). They are also known to eat seabirds, marine mammals, stingrays, and flotsam, including garbage.

Life history

Like most sharks the oceanic whitetip gives birth to live young. These are estimated to be 60 to 65cm long at birth. They mature around 4 to 5 years of age between 170 - 196 cm in total length for males, and 170 - 190 cm for females.

Characteristics

Oceanic whitetips are characterised by their large, very broad and rounded first dorsal and pectoral fins; a prominent ridge of thickened skin between the dorsal fins; a conspicuous pre-caudal pit at the origin of the upper lobe of the tail; and upper lobe of the tail much longer than lower lobe. The upper teeth are serrated and broadly triangular.

Oceanic whitetip sharks are bronze-grey above, and pale below. They are born with prominent black tips to the second dorsal, pectoral, pelvic, anal and lower lobe of the caudal fin. These become white when they about 130 cm long.

The maximum reported size is 3.9 m in total length but individuals more than 3 m in length are considered exceptional. The maximum length reported from the Southern Hemisphere is about 2.7 m.

Threats

About 50 years ago, these sharks occurred in such large numbers that they were considered a threat to the sustainability of commercial longline fisheries. More recently they are barely mentioned in scientific papers and fishing reports.

This spectacular decline in abundance has been due to both directed and incidental catch in commercial fisheries. Commercial landing of this species has grown rapidly due to the demand for their fins. Their broad fins are highly valued for use in shark fin soup.

Catch rates of oceanic whitetip sharks in tropical waters were recently estimated to have declined by 17% (Confidence Interval 14% to 20%) per year from 1995 to 2010. This decline has also been associated with a significant decrease in average size.

DOC's work

Protection

Oceanic whitetip shark have been fully protected in our waters under the Wildlife Act 1978 (Wildlife (Oceanic Whitetip Shark) Order 2012) since 3 January 2013.

Prohibitions on retention, transshipment, and landing of oceanic whitetip sharks have also been adopted by the following regional fisheries management organisations (RFMOs):

International Commission for the Conservation of Atlantic Tunas (ICCAT);
Inter-American Tropical Tuna Commission (IATTC);
Western and Central Pacific Fisheries Commission (WCPFC).

Fishers

Fishers are reminded that for this and all other protected species:

Accidental capture is not illegal but must be reported
Accidental captures during commercial fishing must be reported on the Non-fish/Protected Species Catch Return
Animals can not be retained
Live caught animals should be released immediately with care taken to maximise the chance of survival
De-hooking and line cutting gear should be used to free animals from fishing gear, preferably with all gear removed, or at least with minimal length of snood or net attached.

You can help

Protect sharks when fishing

Carefully release any unwanted sharks and rays. Oceanic whitetip sharks are protected and must be released alive and unharmed.
Consider using circle hooks when targeting sharks as these tend to hook sharks in the corner of the mouth making successful live release more likely.
Follow the Ministry for Primary Industries set net Code of Practice and avoid leaving nets set unattended or over night.

Don't discard rubbish at sea

Do not discard plastics, nylon fishing line and other types of rubbish at sea.
Like whales, large filter-feeding sharks and rays can accidentally ingest these, and all species suffer from entanglement in marine debris.

Identifying sharks

Great white sharks, whale sharks, basking sharks, and manta rays can often be individually identified from photographs showing distinctive markings and scars.
Please report details of sightings or captures of these species to marine@doc.govt.nz or to 0800 DOCHOT line (0800 362 468).
Retain or photograph unusual specimens of sharks and rays and contact DOC marine@doc.govt.nz or Museum of New Zealand Te Papa Tongarewa for identification.