Tuna are awesome. We don’t get to say that enough, so since
it’s World Tuna Day, I want to make amends. These fish are majestic ocean
wanderers, who have earned their place in history, but today they are sadly the
icons of global overfishing& dodgy fishing methods, and a globally-traded commodity.
There are 8 recognised species of ‘true’ tuna (Atlantic
bluefin, Pacific bluefin, southern bluefin, bigeye, yellowfin, albacore,
longtail & blacktail) and a further 8 species in the extended family that
are normally called ‘tuna’.
Skipjack, the most commonly-eaten tuna is not biologically a
proper tuna, it’s more of a distant cousin.
Big tuna are super-predators. They eat fish that eat fish,
so they are a few steps up the food chain. That makes them comparable with
tigers, or wolves on land. Being high up the food chain has its disadvantages –
it also means that the bigger species like bigeye and bluefin also accumulate more
toxic chemicals, most notably mercury.
Bluefin tuna are also called ‘red tuna’ because of the
colour of their flesh. It’s red because it’s oxygen-rich. These fish are
effectively warm-blooded, and regulate their temperatures.
Being warm blooded means that bluefin can live in cooler
waters - being big also helps deal with cooler climates. Although there are a lot less of them around
these days, bluefin tuna have been found as far north as Norway, and used to be
a popular fish for anglers to catch in the North Sea.
Bluefin are fast. They can accelerate quicker than a sports
car, which is a force to be reckoned with when a fully-grown bluefin can be
3 metres long or more.
The front fins on a tuna 'fold down', tucking into handy grooves and making them more
hydronamic - perfect when the tuna feel the need for speed.
The propulsion in a tuna comes from the stiff crescent-shaped
tail. All the muscles in the body effectively drive the tail which in turn
drives the tuna.
Yellowfin tuna are the ones most likely to be seen doing
acrobatics out of the water - perhaps to show off their go-faster long curved
(yellow) fins.
Albacore meanwhile are blessed with a fine set of pectoral
fins. Perhaps they are heading for an evolutionary leap out of the ocean, after
picking up some tips from flying fish.
Albacore are sometimes known as ‘white tuna’ because of
their pale flesh. That has also earned them the dubious nickname of ‘Chicken of
the sea’.
Yellowfin tuna hang around with dolphins. Whilst it’s hard
to tell if either group is a bad influence, this led to a horrific practice of
targeting and killing schools of dolphin to catch the yellowfin. This caused international
outrage, and led to changes in the fishing techniques and the widely (over) used
‘Dolphin Friendly’ logo that is attached to almost all tuna sold today.
Female tuna are capable of producing up to 30 million eggs.
They are mass spawners, which can be a very, er, messy way of procreating, and
usually means they are very fickle about getting the water temperature just
right before making baby tuna.
Apparently some yellowfin like to breed while
they feed, which is even messier, and probably not worth dwelling on…
Bluefin have been fished in the Mediterranean since at least
2000 BC, and it is said that their shoals sustained Roman legions. But it has
been the impact of the relatively-recent industrialisation of fishing that has
plunged Atlantic bluefin to the brink of extinction.
The decline of bluefin has led to crazy demand for prize
specimens – in 2013 over £1 million ($1.8 million) was spent on a single fish in
Japan.
So tuna are undoubtedly awesome. Given half a chance, they
should be able to survive in our oceans, but as we already know, we humans are
having a pretty huge impact on tuna and their ocean home.
Here are a few ways you can help tuna on World Tuna Day:
1)
Support Greenpeace’s oceans campaign. We’re
tackling overfishing, destructive fishing and climate change, as well as trying
to build support for ocean sanctuaries, and transform tuna markets. But we need
your help.
2)
Eat tuna better. If you do eat fish, only choose
responsibly-caught tuna, which means more than just looking for the ‘dolphin
friendly’ logo!
3) Don’t eat tuna. Skip the skipjack for a day (at
least). They deserve a break.
4)
Share this, and tell a friend why you think tuna
are awesome.