The Bluefin Tuna
_On average, bluefin tuna weigh around 350 kilograms, measure
2 – 3 meters long, and live as long as 30 years. These factors place them at a very critical
area of the food chain, where they act as apex predators. They use as much as 5% of their body weight
daily for energy, so they are continually eating small fish, squid, and
crustaceans. Often called “trophy” fish,
their size plays a significant role in why they are so sought after by
fishermen.
Bluefin tuna are warm-blooded; they use a process called counter-current exchange to prevent heat loss to surrounding waters. This makes it so their core muscles can work faster and more efficiently, and allows bluefin tuna to migrate thousands of miles to much colder areas of the world than most fish. For this reason, fishermen have a wider range where they can fish for them. [1]
Bluefin tuna are warm-blooded; they use a process called counter-current exchange to prevent heat loss to surrounding waters. This makes it so their core muscles can work faster and more efficiently, and allows bluefin tuna to migrate thousands of miles to much colder areas of the world than most fish. For this reason, fishermen have a wider range where they can fish for them. [1]
Northern Bluefin (Thunnus thynnus)
Northern bluefin tuna
_Also called the Atlantic or giant bluefin, Northern bluefin are found
across the Atlantic, as well as in the Mediterranean Sea. They are now
extinct from the Black and Caspian Seas. According to SeaChoice,
this species of bluefin is considered critically endangered, due to
overfishing caused primarily by their role in the Japanese raw fish
market. For more general information on this fish, go here.
The International Commission for the Conservation of Atlantic Tuna (ICCAT) approximated in October of 2009 that in the last 40 years, the populations of Atlantic bluefin tuna in the East Atlantic have declined by 72% and those in the West Atlantic have declined by 82%. In response, the Monterey Bay Aquarium has added these fish to their Seafood Watch list. In 2011, the National Oceanic and Atmospheric Administration (NOAA) declared that they do not yet list Atlantic bluefins as an endangered species. They believe that stringent international fishing laws made in 2010 will allow these fish to recover; NOAA will reconsider their decision in 2013. Read more about their decision here. [2]
The International Commission for the Conservation of Atlantic Tuna (ICCAT) approximated in October of 2009 that in the last 40 years, the populations of Atlantic bluefin tuna in the East Atlantic have declined by 72% and those in the West Atlantic have declined by 82%. In response, the Monterey Bay Aquarium has added these fish to their Seafood Watch list. In 2011, the National Oceanic and Atmospheric Administration (NOAA) declared that they do not yet list Atlantic bluefins as an endangered species. They believe that stringent international fishing laws made in 2010 will allow these fish to recover; NOAA will reconsider their decision in 2013. Read more about their decision here. [2]
Southern Bluefin (Thunnus maccoyii)
Southern bluefin tuna
_ Southern bluefin are found throughout southern hemisphere
waters. They have been exploited across
their entire range. Their population has declined by 92% and so these fish are also considered critically endangered.
They are on both the International Union for the Conservation of Nature
(IUCN) and Greenpeace red list of endangered species. For more general information on this fish, go here.
In 1994, the Commission for the Conservation of Southern Bluefin Tuna (CCSBT) imposed a catch quota on fishermen originating from Australia, Japan, New Zealand, South Korea, Taiwan, and Indonesia. The quotas for these countries were reduced by almost 80%. Since it was imposed, Southern bluefin stocks have slowly begun to recover and the value of the fishermen’s catch has increased. [3]
In 1994, the Commission for the Conservation of Southern Bluefin Tuna (CCSBT) imposed a catch quota on fishermen originating from Australia, Japan, New Zealand, South Korea, Taiwan, and Indonesia. The quotas for these countries were reduced by almost 80%. Since it was imposed, Southern bluefin stocks have slowly begun to recover and the value of the fishermen’s catch has increased. [3]
Pacific Bluefin (Thunnus orientalis)
Pacific bluefin tuna
_
Pacific bluefin have a wide distribution across the entirety
of the Pacific. They spawn in the west
Pacific and then migrate over 10,000 km to the East Pacific. They are over-fished throughout their range
and their conservation status is vulnerable. For more general information on this fish, go here. [4]
For some reason, the stocks of this species of fish are not as highly degraded as the Northern or Southern bluefin. One explanation that has been given for this is that fishing mortality of Pacific bluefin is higher than it should be but is below the generally accepted overfishing threshold. This suggests that a moderate level of overfishing is occurring. However, because there is a high removal rate of the young from these stocks, Seawatch consider these fish to have a high conservation concern. [5]
For some reason, the stocks of this species of fish are not as highly degraded as the Northern or Southern bluefin. One explanation that has been given for this is that fishing mortality of Pacific bluefin is higher than it should be but is below the generally accepted overfishing threshold. This suggests that a moderate level of overfishing is occurring. However, because there is a high removal rate of the young from these stocks, Seawatch consider these fish to have a high conservation concern. [5]