Why should we leave tuna off the menu?

We want to use World Tuna Day to draw attention to the fact that tuna are worth so much more than a meal. Did you know that fish are unique and have differing personalities? Research has found that fish vary in their response to stimuli and environmental changes - just like us. Some are curious and willing to take risks, while others are more sensitive and stick to a routine. Despite knowing this, when fish are killed for human consumption, they are grouped together and referred to in weight, rather than the number of individuals. When looking at all species of sea creatures, researchers estimate that between 1 and 3 trillion wild fish are caught and killed every year and 51 to 161 billion farmed fish are killed every year. Despite the high number of individuals killed, the loss of lives only makes up 7% of the global protein supply - in comparison to plant foods, which make up 63% of the global protein supply.

With so many alternatives available, we can help end their mass slaughter, and environmental damage, by leaving them off our plates. Let's dive into a few fascinating facts about these incredible animals.

1. Some tuna can reach speeds of 100km per hour!

Tuna have a torpedo-shaped body and their complex muscles, skeletal, and vascular systems allow them to cut through the water with extreme speed. They can expand or retract their dorsal and pectoral fins to reduce drag allowing them to accelerate their swimming speed and maneuver through the water. They can also swim near the surface or dive down over 900m while searching for food. That's not all, they are warm-blooded and retain the heat they generate from swimming. This allows them to regulate their body temperature to be warmer than the water around them. There are 15 species of tuna and while their sizes vary, on average a tuna weighs 250kg and reaches around 2-3 meters in length! The largest tuna recorded was 6.4m long and weighed 725kg (the average weight of a Sumatran rhino!).

2. They camouflage in the water.

The colour of their dorsal (back of their body) is dark blue, allowing them to blend in with the ocean floor when observed from above while their belly is a blend of silver and white to mimic the ocean surface when viewed from below.

3. Some tuna travel over 11,000km!

Migration is key to their survival. Those born in the Gulf of Mexico travel across the entire Atlantic Ocean to feed off the coast of Europe. When they have reached sexual maturity, they swim back to the Gulf to breed. They can complete their journey across the entire Atlantic in just 30 days. Others born in the Sea of Japan, travel across the Pacific Ocean to the California coast, where they spend years feeding and growing before returning to spawn.

4. Not many survive into adulthood.

Tuna reach sexual maturity at 5 years old. On average, tuna lay around 540 million eggs during a spawning season (PDF) (about 15-30 million eggs at a time). Of each 30 million, researches estimate that just two survive into adulthood! The average life span of those who survive is 15 years, however, some believe they can be up to 50 years old. Unfortunately, due to fishing, only a small per cent of tuna manage to survive this long.

5. Tuna play an important role in cycling nutrients and oxygen production keeping the oceans (and ultimately, us humans) healthy.

Just by swimming, diving, eating, excreting, and living, tuna are helping with oxygen production and carbon sequestration. They mix water layers, moving phytoplankton and nutrients around, and allowing for the absorption of carbon. On top of this, Tuna are top predators and also an important food source for other marine life. Tuna eggs and young feed smaller fish, while adults are an important part of shark and orca diets. They help to maintain a balance in the ocean environment and their extinction would have detrimental effects on other sea animals and even us. 

Consumer demand, over-fishing, fish farming, and ocean dead zones are threatening tuna populations

Tuna are caught with longlines, gillnets, and purse seines.

Tuna are caught using longlines, gillnets and purse seines. Longlines are kept near the surface with floats and contain long snoods with baited hooks - they can be almost 1km long. Gillnets are a wall of netting placed below the surface, when fish swim into the net, they become trapped by their gills. Purse Seines is when a vertical net ‘curtain’ is used to surround the school of fish, the bottom of which is then drawn together to enclose the fish, like tightening the cords of a drawstring purse. All three methods cause immense stress and fear in the tuna, and pain. According to the United Nations, more than 7 million tonnes of tuna and tuna-like species are killed every year for human consumption.

Consumer demand is driving over-fishing

In Australia, canned tuna is one of the most popular seafood items, and our appetite is having devastating impacts on these incredible creatures and the oceans. Almost all of Australia's tuna supply comes from the Pacific, which, after only a few decades of industrial fishing, almost all of the commercial tuna species are now exploited at unsustainable long-term levels.

Bluefin and yellowfin tuna populations are in huge decline due to overfishing for consumer demand. A recent report by financial think-tank Planet Tracker warned that Yellowfin tuna populations are heading for a collapse by 2026, with a decline of at least 70% in adult biomass (both biomass landed and biomass in the sea) over ten years. Meanwhile, all types of Bluefin tuna populations are endangered, with the Pacific Bluefin populations at a mere 2.6% of their historic numbers.

Fishing for tuna results in the death of millions of other species

Bycatch refers to the incidental capture of non-target species. Longline, gillnets, and purse sines are all responsible for killing non-target animals. For every 10kg of tuna caught, 2kg of juvenile tuna (those who are too young to reproduce) are caught. In 2009, 43,000 tonnes of juvenile tuna were caught. Removing young tuna from the oceans reduces the population of fish who reach maturity, and thus the number of eggs laid - dwindling their future population numbers.

Young tuna aren't the only species at risk of being caught. Approximately 40% of all marine life caught, is thrown overboard as "bycatch". Every year, the fishing industry is responsible for killing approximately 50 million sharks, 1.5 million turtles, over 300,000 whales, dolphins, and porpoises, and 400,000 seabirds (penguins, ducks, albatrosses), to name a few.

Farming tuna isn’t sustainable either

Tuna are also farmed. As mentioned earlier, tuna swim thousands of kilometres in their life. Their food sources vary and they maintain balance in the ecosystem. But on farms, they live in floating cages are are forced to swim in circles, unable to exhibit any of their natural behaviours.

The most common method of farming tuna is by catching juveniles in the wild, transferring them to ocean or land cages, and killing them when they reach a profitable weight. This does nothing to reduce pressure on wild populations, as it is removing young tuna from the oceans - who are vital for the species' survival. In South Australia, juvenile Southern Bluefin Tuna are caught in the Southern Ocean and transferred to ocean cages in Port Lincoln, and are killed after just 3-5 months.

Other countries are breeding these powerful animals completely in tanks. They keep adults confined to cages, collecting their eggs, and hatch the eggs in tanks. Once they have reached a juvenile size, they are moved to larger tanks and fattened up. Despite years of research, just 1% of all eggs survive into adulthood.

Aquaculture still linked to over-fishing

Aside from denying the animals all of their natural behaviours, aquaculture still contributes to over-fishing. To gain 1kg of weight, a tuna needs to eat around 16kg of food. Tuna are considered picky eaters, and most farms rely heavily on wild fish (predominately sardines, anchovies, mackerel, red bait, and squid) as a food source. This means that farming tuna not only removes tuna from the ocean, but also removes other important species, contributing to issues of over-fishing, bycatch loss, and disturbing the natural ecosystem.

Some overseas farms also use feed a supplement called MaGro - the ingredients of which have not been released. We do know that in Australia, other farmed fish, such as salmon, are fed the unwanted parts of sea animals and chickens, as well as wheat, soy, and cornmeal (PDF).

Farming fish pollutes the environment and risks wild populations

Aquaculture farms are also polluting the environment. Ocean cages release high amounts of waste (uneaten food, waste products, disease, pathogens) into the area, increasing the nutrients in the water column. The high concentration of fish in the area can also lead to new diseases and parasites, which can spread to wild fish. To combat algae, disease, and parasites, chemicals and herbicides are often used.

Ocean dead zones

An ocean dead zone is an area where there is not enough oxygen in the water to support marine life. The animals either migrate away or die as a result, leaving the areas as biological deserts. Ocean dead zones can occur naturally, however, are becoming more prolific due to human activities. Nutrient pollution from manure, fertiliser, and sewerage, is the primary cause of human-caused ocean dead zones along the coast. The excess nutrients stimulate a growth in algae, which forms a thick layer on top of the surface, suffocating life below it. As the algae decompose in the water, it consumes oxygen and depletes the supply for other marine life.

A 2008 study declared over 400 areas as ocean dead zones. The full impact of ocean dead zones is not known, but it is expected to impact reproduction and affect population numbers. To help protect marine life, scientists are calling for oxygen loss to be tracked globally.

A global increase in temperature, from both human activity and natural warming, is also responsible for ocean dead zones, as warmer water holds less oxygen.

Slaughtering tuna causes immense suffering

The process of catching and killing tuna is very stressful for the individuals. These powerful animals exhaust themselves trying to escape the nets, hooks, harpoons, or hands that are restraining them. Tuna have a high metabolic rate, which causes them to build up lactic acid in their muscles, because of this, fishermen often don’t kill them immediately - prolonging their suffering. The most common method is for fishermen to tie a rope around their tail, re-hook them in their sensitive mouth, and put them back in the water to swim next to the boat to dissipate the lactic acid. After this, the tuna is then dragged out of the water again, and either bashed or stabbed on the head, before being sliced open and left to bleed out.

You can help by leaving fish off your plate

Tuna, like all animals, are sentient beings, worthy of a life worth living. Scientists have shown that if our appetite for seafood continues on this path, the oceans will be empty by 2048 - but we have the chance to change that. By leaving animals like tuna off our plates, we are one step closer to creating a kinder, and more sustainable world, for all. We've put together some of our favourite animal-friendly seafood recipes to help you get started.