A recent study published in Nature Scientific Reports shows that El Niño and La Niña influence the recruitment capacity of Antarctic toothfish in the Ross Sea, a succulent fish sold at a good price. These results will no doubt be discussed by the Commission for the Conservation of Antarctic Marine Living Resources.
Captain Michael Rhodes and his 20-strong crew have been crossing the Southern Ocean aboard the Janas since 2003, heading for the Ross Sea. The ship is one of three New Zealand vessels, along with the San Aotea II and San Aspiring, that fish near Antarctica. Summer has already begun when they embark on this journey in search of a big, fat and delicious fish: the Antarctic toothfish.
If they’re lucky, the cargo will easily find its way to the American market. This lucrative fishery is regulated by the Commission for the Conservation of Antarctic Marine Living Resources (CCAMLR), which sets a quota each year. In 2022, the quota was 3,495 tonnes. If catches are so limited, it’s because this fishery remains “exploratory” and “precautionary”. The Commission’s scientists monitor the effect of fishing on Antarctic toothfish stocks, which are essential in other respects to the fauna of the polar ocean.
“To manage a fishery, there are two options: adherence to the catch rate—that is, the number of adults taken from the ecosystem—and protecting spawning areas,” explains Erik Behrens, an oceanographer at New Zealand’s National Institute of Water and Atmospheric Research (NIWA). He is the first author of a study published last week in Nature Scientific Reports, showing that a tropical climate phenomenon known for thousands of years is involved in the life cycle of these prized fish.
El Niño and La Niña. The former weakens the winds in the Amundsen Sea, while the latter strengthens them. During its powerful phase, the Amundsen Sea Low energises the Ross Sea gyre, moving ice towards the Antarctic Circumpolar Current. Conversely, when El Niño is active, the Ross Sea gyre weakens and the ice remains in this part of the ocean.
Eggs under the ice
The Antarctic toothfish, known to live for over 50 years, spawns north of the Ross Sea. “This happens between July and October, in winter under the ice. It’s never been observed directly because it’s inaccessible,” the researcher explains. “We know this because large aggregations of adults ready to spawn have been caught near extensive underwater mountain ranges.” The eggs rise to the surface and attach themselves beneath the ice.
By observing fishing data and age classes, i.e. counting fish by age, the researcher realized that there was a large fluctuation in juvenile recruitment over time. Overlaying climatic information, he noted that this variation could be linked to the increasing power of the Ross Sea gyre. Patches of ice leave the Ross Sea during La Niña, carrying enough eggs with them to slow down the population’s renewal.
A small fishery, big stakes
If this niche fishery is to survive, as the Commission wishes, this result should be taken into account to preserve the integrity of the ecosystem. Quotas may have to be readjusted, but in any case, this new result opens up the subject for discussion, bearing in mind that there is still much to be understood about this fish.
Climate change has also had a significant impact on ice cover since 2016. “We don’t know if less ice, which protects the eggs, means more predation, or if this will be compensated by the eggs’ stagnation in the Ross gyre,” the oceanographer tells us, referring to the Ross Sea fishery (CCAMLR sector 88). And what will be the impact on other regions which, during La Niña, may receive ice fragments and the toothfish juveniles that go with them?
The results of the study were published just after the end of the CCAMLR’s annual meeting, where discussions about this fishery have not yet been made public. Fishing in zone 88 has been open since 1997, using bottom longlines. In 2017, a vast marine protected area (MPA), the largest in the world, was established there. This MPA restricts the fishing zone for 35 years, and its legitimacy may be reconsidered in 2052.
Although the fishery has long been considered exploratory, the latest report published by CCAMLR indicates that it has not been considered so since 2017. Is this because an MPA is in place, and fishing ambition has reached a climax, or because the fishery is more “open”? The report does not specify, but quotas have been increasing since 1997. Around twenty longliners are registered to claim their share. Ukrainians, Koreans, New Zealanders, and Australians are competing among eight nations.
Sold for an average of $13 per kilo, toothfish can fetch up to $17 in the United States or Japan. This market is more lucrative than that for cod. The two fish are similar in many ways once prepared. The toothfish is also called “Antarctic cod”, but its rarity makes it an even more exceptional delicacy. According to NZGeographic, in 2006, this fishery in the Ross Sea represented 30 million US dollars.
Camille Lin, Polar Journal AG
Link to the study : Behrens, E., Grüss, A., Pinkerton, M., Parker, S., Rickard, G., Stevens, C., 2024. .
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