Highly Migratory Species of Fish

Highly migratory species (HMS) are fish that travel long distances – through different countries’ Exclusive Economic Zones (EEZs) and throughout the high seas.

Some examples of HMS include: 

• different kinds of tuna (such as southern bluefin, albacore, and bigeye) 
• sharks (such as blue and mako sharks) 
• billfish (such as marlin and swordfish).

Managing HMS

Ships that fish inside a country’s EEZ must follow that country’s fishing rules. On the high seas, ships must fly the flag of a country they are registered to and stick to the rules of that country.

Different countries have different rules about fishing for HMS and no single country manages the high seas – some countries don’t even have any rules about fishing for particular species of fish. Groups of countries have started joining together as Regional Fisheries Management Organisations (RFMOs) to develop agreements that will protect HMS from over-fishing in certain areas of the high seas.

Life of an HMS

To find out more about HMS, let’s look at the southern bluefin tuna.

There is just one known spawning ground for southern bluefin tuna. It’s in the Indian Ocean south of Java, Indonesia. From here, the tuna generally migrate in two directions. Swimming at an average speed of 2 to 3 kilometres per hour, some head towards South Africa, while others come down the west coast of Australia, into the Tasman Sea towards New Zealand. After travelling for about 8 years, the tuna will return to their spawning ground to breed.

As they travel, they feed on fish like lantern fish, squid, lancet fish and ray’s bream. We know this because, over the last 17 years, observers have opened up the stomachs of more than 20,000 southern bluefin tuna to see what’s inside!

Southern bluefin tuna can grow up to 2 metres long and weigh up to 200 kilograms (that’s heavier than most humans)! But most tuna caught in the New Zealand fishery are around 170 centimetres long and weigh about 100 kilograms. Their main predators include large sharks and, of course, humans.

The main way we catch southern bluefin tuna is long-line fishing. The fishing lines are many kilometres long with up to 3000 hooks.

In Australia, some fishers catch southern bluefin tuna using the purse seining method. Once the tuna have been captured in the net, they are moved to special towing nets, and slowly towed back to Australia. It can take the ships several weeks to reach port, where the fish are shifted to large floating cages that are anchored to the sea floor. They are kept there for several months while they are fattened up, and then they are sold. While they are being shifted around and fattened up, the southern bluefin tuna are guarded by divers known as tuna cowboys, who also remove any sharks that can occasionally break into the nets.

Japan is the biggest market for southern bluefin tuna. The Japanese eat tuna raw as sashimi.
There are now so few southern bluefin tuna that the species has been classified as critically endangered. A RFMO called the Commission for the Conservation of Southern Bluefin Tuna (CCSBT) was established in 1994 to look after the fishery. The CCSBT runs annual science meetings where information on the health of the southern bluefin tuna population and its management are discussed.

The CCSBT has set a yearly Total Allowable Catch (TAC) for the fishery of 11,810 tonnes, which is split among the different countries involved.

Tuna fishing quotas for members

The quotas shown below are fixed to the year 2011 for Japan and to 2009 for the other members.

	Japan	3000 tonnes/year
	Australia	5265 tonnes/year
	Republic of Korea	1140 tonnes/year
	Fishing Entity of Taiwan	1140 tonnes/year
	New Zealand	420 tonnes/year

Tuna fishing quotas for co-operating non-members and observers

Here are the quotas for co-operating non-members and observers for 2007/08.

	Indonesia	750 tonnes
	The Philippines	45 tonnes
	South Africa	40 tonnes
	European Community	10 tonnes

The CCSBT is also working out ways to stop illegal fishing. Illegal fishing can undo all the work the CCSBT has been doing to protect the fishery – if the annual catch limits are exceeded because of illegal fishing, the fishery will continue to decline.