Tuna are fish, and they are wild animals. But to many people, they are simply understood as food. It can be a bit confusing when the short hand of ‘tuna’ is used, as it covers a whole family of species, from the relatively-tiddly and widespread skipjack, right up to the majestic but beleaguered bluefins.
So I've pulled together a quick guide to the tuna species you might frequently encounter. This is not intended to encourage you to eat them, you understand, just raise awareness of what it is that is being served up, and what issues you need to think about.
SKIPJACK (Katsuwonas pelamis)
Relatively small, and the most abundant and widely-fished of tuna species. The fish can be up to a metre in length, but is rarely recognisable when served up – as skipjack makes up most of what we eat as canned tuna. Tuna chunks and flakes in brine, or oil – if it’s on a sandwich, baked potato, or pizza, you can pretty much bet it’s skipjack.
This is a pretty abundant species, but there are still issues around how it is fished. Mostly this is because the methods cause damage to other species – which end up as bycatch. Most skipjack is caught using large purse-seine nets, and when these are set around Fish-Aggregation-Devices (so called FADs, floating structures that act like fish magnets) they result in huge amounts of bycatch – of other fish, as well as sharks, rays and even turtles and occasionally whales or dolphins. Using FADs has been shown to increase the amount of bycatch tenfold.
The famous ‘dolphin friendly’ logo on tuna does tell you that it’s not caught in a way that deliberately catches or sets nets around dolphins, but it doesn’t act as a guarantee that other wildlife has not been collateral damage.
Sadly many of the species caught and killed as bycatch are endangered – including several species of open ocean sharks, and sea turtles. And when you factor in the scale of the fishing operation to fill those little cans, that adds up to a whole lot of collateral carnage, including tens of millions of sharks every year.
Luckily – there are better, cleaner, ways to catch skipjack. Look out for pole-and-line caught skipjack, or some that has been caught without using FADs
TOP TIP – only choose pole & line or FAD-free caught skipjack.
YELLOWFIN (Thunnus albacares)
Yellowfin are widespread and magnificently-streamlined fish. And, yes, they have yellow fins, including characteristically sickle-shaped elongated ‘go faster’ ones. They are found around the world, but mostly confined to tropical waters. They can grow to over 2 metres in length.
Yellowfin tuna can be found canned in the UK, usually in tins as ‘tuna steak’. It should tell you on the tin what species it is (if it doesn’t, put the tin back and don’t buy it!). However, yellowfin is probably most recognisable as fresh ‘tuna steaks’ available on the fish counter and in supermarkets. You may also find it in sushi.
Like skipjack, yellowfin are caught with purse seines, and when FADs are used the vast majority are young yellowfin that never get a chance to breed. Another method of catching them is using longlinesm lines of baited hooks that can be many, many kilometres long. This method of fishing can be very indiscriminate and responsible for lots of bycatch – sharks, swordfish, turtles, and seabirds can all fall victim to the baited hooks. Long lining is the main reason that global albatross populations are endangered, and as with purse seining, some of the species caught and killed are endangered sharks and turtles too.
There are ways to make longlining better, which some suppliers are now insisting on, but the safest way to know that your yellowfin hasn’t come at the cost of lots of other animals’ lives, is to go for pole & line caught.
However, there are now real concerns that populations of yellowfin have been totally overfished, and in many places are still plummeting.
TOP TIP – only choose pole & line caught yellowfin, and eat it sparingly.
ALBACORE (Thunnus alalunga)
Albacore is a cooler water tuna, and even ventures into waters around the south of the British Isles. They have an unusually long pectoral fin, and are sometimes referred to as ‘white’ tuna, because of its pale flesh.
Albacore tuna is not very common in UK shops and restaurants, but you can find it in tins, and also jars of tuna fillets. Much of this is independently certified by the Marine Stewardship Council. There are also albacore fisheries bringing a small amount of fresh tuna into the UK market.
Albacore is mainly caught on longlines, but they can be caught with much more ocean-friendly methods such as pole & line and a similar method called ‘trolling’.
However, most populations of albacore have been totally overfished – the only relatively healthy stocks are in the Pacific, but these are in decline.
TOP TIP – choose MSC certified pole & line or 'trolled' albacore, from the Pacific.
BIGEYE (Thunnus obesus)
With a scientific name that labels it as ‘fat tuna’, this is a big, robust fish, found in tropical waters and growing over 2 metres in length. Sadly bigeye tuna are in trouble, with many populations plummeting in recent years due to overfishing. It’s caught in similar ways to the similarly-sized yellowfin, and whilst you might encounter it served up as tuna steaks, it’s much more likely you would only find it served as sushi in the UK.
STOP PRESS: recently we have found a few branded tinned tuna cans containing bigeye. This is a worrying development given the state of stocks, and may actually be because juvenile bigeye are being caught in purse seining nets alongside the smaller skipjack (this also happens with juvenile yellowfin). Catching juvenile tuna, from threatened or overfished stocks is a big problem, because they are caught before they have had chance to breed. We are looking into this development in tinned tuna. But please, do check the species on the tins!
TOP TIP – AVOID BIGEYE
BLUEFIN (Thunnus maccoyii, Thunnus orientalis & Thunnus thynnus)
There are three species of bluefin tuna: Southern, Pacific and Atlantic, and they are spectacular fish. Growing to over 3 metres, and up to a whopping 450kg, they are warm-blooded top predators that can accelerate faster than a sports car, and are also able to tolerate cold water. As well as being found along the coasts of the US, until recently they were regular sights in the balmy North Sea where they were the target of anglers in places like Scarborough.
However in recent years bluefin tuna has been severely overfished. Atlantic and Southern bluefin are already classified as endangered, and Pacific bluefin populations are at only 4% of historic levels. Traditional methods of catching them in traps and on lines have given way to large purse-seining catches targeting them as they come together to spawn. The fashion for sushi has driven this demand, and as they get ever scarcer, and ever more expensive – there are real concerns for the future of bluefin.
You should only find bluefin in relatively expensive sushi. It may be labelled as ‘o-toro’.
TOP TIP – AVOID BLUEFIN