Image: The Conversation / FIS

Farming tuna on land heralded as a win for sustainability – but there are serious concerns around animal welfare

The following is an excerpt from an article published by The Conversation:

Atlantic bluefin tuna used to be caught only relatively rarely, mainly by sports fishermen in North America. But this all changed in the 1950s when consumers of sushi, particularly in Japan, developed more of a taste for the species.

An 18-day-old Atlantic bluefin tuna (Thunnus thynnus) bred at the Mazarrón Aquaculture Plant in Spain. Source: Instituto Español de Oceanografía

Historically, Atlantic bluefins have either been caught directly from the ocean or caught while young and fattened in large offshore cages called “ranches”. Both wild fishing and ranching pose sustainability issues since they involve taking fish from the wild. The surge in demand resulted in excessive fishing pressure. By 2006, the International Commission for the Conservation of Atlantic Tunas warned that the Atlantic bluefin stock was close to collapse.

Scientists are now exploring ways to breed Atlantic bluefin tuna in captivity as an alternative to catching young fish from the sea. These approaches involve the manipulation and release of hormones into the water to stimulate egg production in the fish. The resulting eggs and fish larvae are then kept in a series of tanks until they grow to a suitable size, at which point they are relocated to cages at sea.

Source: The Conversation

In a significant breakthrough in July 2023, scientists at the Spanish Institute of Oceanography successfully bred Atlantic bluefin tuna in tanks on land for the first time. This development has been seen as a win for sustainability. By breeding fish in enclosed tanks, fewer Atlantic bluefins will need to be caught from the wild.

But there are concerns surrounding the welfare of farmed tuna and their environmental impact. Atlantic bluefins are not well suited to captivity as ordinarily they migrate over thousands of miles of open ocean. Research also suggests that the methods used to get the tuna to spawn may cause them stress.

Divers catching Atlantic bluefins at a farm in Izmir, Turkey. Source: The Conversation 

Welfare in hatcheries

An astonishing proportion of tuna larvae die in the hatcheries. In the EU’s early Atlantic bluefin domestication project, called Transdott, which started in 2012, only 0.44% of tuna larvae survived 30 days after hatching.

This death rate seems shockingly high. But an extremely high number of tuna larvae die in the wild as well. Hatcheries may also become better at preventing some of these deaths in future, since they will struggle to make a profit if most of their stock dies.

There are, however, causes of death within hatcheries that don’t exist in the wild. Some larvae die by crashing into tank walls and others perish when they are moved between tanks.

Source: Science Direct. Clic on the image to enlarge

It’s difficult to assess the day-to-day experience of tuna in hatcheries. Part of the reason for this is because conditions in hatcheries are often kept private. But undomesticated species of fish generally experience greater stress in captivity and in response to human handling than domesticated species, which have adapted to this over time.

Since we are in the early stages of the domestication process for Atlantic bluefins, we should expect the tuna to be stressed by the large degree of human contact.

There is also some evidence that fish can become distressed by noise and are unaccustomed to vibrations. But noise may be hard to avoid on farms, particularly inland. One study found that guppies exposed to chronic noise exhibited a significantly shorter lifespan compared with those in either acute noise or noise-free conditions. [Continues...]

Author: Wasseem Emam | The Conversation | Read the full article by clicking the link here

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