Tuna carry evidence of the human causes of global heating

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A group of 22 scientists has discovered that tuna carry inside them clues to how climate heating caused by humans is changing ocean water and types and quantities of plankton – and therefore the tuna we eat.

At the core of their research is one of the elements at the heart of a heating planet: carbon.

By tracing two of the most abundant forms of carbon, the isotopes carbon-12 and carbon-13, they were able to show that a significant amount of global heating is caused by human activities rather than natural processes.

They also found that several other factors also influence the amount of different carbon isotopes in tuna. 

Scientists find evidence of changes in the food chain

One of the most important happens at the start of the food chain, with a group of plankton known as phytoplankton, which use sunlight and carbon to make the energy they need. 

The scientists showed that the abundance of different kinds of phytoplankton has changed in the past 15 years, directly as a result of the burning of fossil fuels. They also showed that the proportion of carbon-12 and carbon-13 available changes the kinds and abundance of phytoplankton. These changes don’t stop here, but alter the kinds and abundance of animals, including tuna, all the way up the food chain.

Numbers of some phytoplankton are shrinking, and this too is affecting the abundance and location of tuna. 

The change in the balance of phytoplankton is made worse by another effect of climate change: ocean stratification. Surface and deep waters of oceans now mix less, and that fewer nutrients are stirred up and made available for plankton to consume. 

The research also showed changes in how quickly phytoplankton grow. 

An example of phytoplankton. Photo US National Oceanic and Atmospheric Administration MESA Project.
Phytoplankton, the foundation of the oceanic food chain. Photo NOAA MESA Project.

The scientists traced two forms of carbon

The research involved scientists from several fields. Among them was Valérie Allain of the Pacific Community (SPC). 

The scientists took 4,500 samples of muscle from albacore, bigeye and yellowfin tuna over 15 years, from 2000 to 2016, from the Pacific, Indian and Atlantic Oceans. They found that changes were most pronounced in the Pacific Ocean.

They traced two forms of carbon, carbon-12 and carbon-13. This is possible because each isotope each has a different weight and also behaves slightly differently. 

Carbon is found naturally in living things, and in the air, land and water. It is also present in coal and oil, and when these burn, carbon-12 is released into the atmosphere. 

More than 90% of atmospheric carbon is absorbed by the oceans. From there, it enters the food chain, being taken up by plankton and passed on to each predator up the chain, until it ends up in tuna, along with other forms of carbon such as carbon-13.

Reporting on their findings in the most recent issue of SPC’s Fisheries Newsletter, Valérie Allain and another researcher, Anne Lorrain, said that the data will be “of inestimable value” in projecting the effects of climate change on the health and quantity of seafood, and in validating modelling. This is because they collected so much data over such a long time and a very large geographical area.

Their research makes much more certain that humans do affect the environments and inhabitants of the open oceans.

Sharks and rays easy to identify in new field guide

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A new field guide should help crew of tuna vessels and observers to correctly identify 44 kinds of sharks and rays that are accidentally caught during tuna fishing in the Western and Central Pacific Ocean (WCPO).

The guide, Shark and ray identification manual, has just been published by the Pacific Community (SPC), and can be downloaded from SPC’s website.

It covers the subtropical and tropical waters of the WCPO, and informs users about the best methods for handling and releasing sharks and rays, recommended by the Western and Central Pacific Fisheries Commission.

Drawings of sharks in pairs from key steps page of shark and ray identification manual. Image Pacific Community.
The key steps pages helps users narrow down the type of shark or ray they are identifying. Image SPC.
Drawing of shark, with information to help confirm which species it is from others. From page of shark and ray identification manual. Image Pacific Community.
The key steps pages lead the user to more detailed information so they can differentiate individual species that may have a similar appearance. Image SPC.

Many shark and ray species in the WCPO (and elsewhere in the world) are in danger of dying out, and accidental catch during fishing is a major cause of deaths in some species. If these species are to be saved, scientists and fisheries managers need accurate figures on how many are being caught. And that means being able to identify them reliably.

SPC says that, as well as helping fishers, it also helps observers, who collect operational data from fishing and report back to fisheries managers, who use the information to manage not just tuna fishing but the care of the marine environments that tuna rely on to remain healthy.

To make identification at sea easier, the illustrations show the most important distinguishing features of each species, and its colour when alive.

Identification will also be made easier by the inclusion of the common name for each animal in six languages: Cantonese, English, French, Japanese, Korean, Mandarin, and Spanish.

The manual is written by Timothy Park, Lindsay Marshall, Aymeric Desurmont, Boris Colas and Neville Smith, and illustrated by shark and ray illustrator Dr Lindsay Gutteridge, who is also a scientist.

The new manual refines an older guide that defines 30 species of sharks and rays.

Shark and ray artist Lindsay Gutteridge sitting at a desk painting a shark. Photo SPC
Shark and ray artist Lindsay Gutteridge at work on an illustration for the manual. Photo SPC.

Nearly 17,000 tuna tagged in latest research cruise

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More than 16,600 tuna were tagged in a recent scientific tagging expedition in ocean generally north of Papua New Guinea.

The voyage targeted skipjack tuna, which makes up 70% of the volume of tuna caught in the Western and Central Pacific Ocean (WCPO).

Tuna tagging helps the Western and Central Pacific Fisheries Commission (WCPFC) and national fisheries managers assess numbers of tuna. The assessments are used to set catch limits.

This voyage was conducted largely in the exclusive economic zones (EEZs) of Papua New Guinea, Solomon Islands, Palau, and Federated States of Micronesia, with a little time spent also in two pockets of high seas.

In its most recent fisheries newsletter, SPC reported that fisheries authorities in PNG, Palau and FSM provided research permits and gave support to the research being done in their EEZs.

An average of almost 450 tuna were tagged and released each fishing day. Most – 93% – were skipjack, the rest being yellowfin (6%) and bigeye (1%). Most came from free-swimming schools (i.e. the tuna were not caught near fish-aggregating devices, or FADs).

Some fish were implanted with what is known as an archival tag, a physical device which must be inserted using small surgery and a very fast turnaround – no more than 30 seconds – so that the tuna doesn’t become too stressed and lacking in oxygen.

Two tuna lie in a cradle on a fishing vessel at sea. They are being tagged for scientific research by two men. Photo Pacific Community.
Tagging tuna on a pole-and-line vessel during an earlier research voyage in the WCPO. Photo Pacific Community (SPC).

SPC reported that it expected some of the tuna tagged in this way would be recovered and would provide good data on the behaviour and movement of the fish.

The agency also reported that some tuna were injected with strontium chloride, a slightly radioactive salt that becomes incorporated into a part of the tuna’s skeleton known as the otolith (or ‘ear stone’). As the fish grows, scientists can use the mark left by the strontium chloride in the otolith to estimate how old the fish is. (Otoliths help fish to balance and to understand how fast they are swimming.)

To conduct the tagging cruise, SPC chartered a pole-and-line vessel from Noro, in Solomon Islands. 

This was the fifth western Pacific tagging cruise, and it lasted from July to September 2019.

Tuna tagging has been carried out regularly since the Pacific Tuna Tagging Programme ran its first voyage in 2006.

This trip came under a new tagging experiment introduced by the Pacific Community (SPC) to implement a recommendation of the 12th meeting of the Scientific Committee of the Western and Central Pacific Fisheries Commission (WCPFC). 

Dongwon wins South Korea’s first MSC certification for western Pacific tuna fishery

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Republished from Undercurrent News, 25 October 2019

South Korea’s Dongwon Industries has achieved Marine Stewardship Council (MSC) status for its tropical yellowfin and skipjack tuna fishery in the Western and Central Pacific Ocean (WCPO). 

It is the first fishery owned by a South Korean company to be certified to the sustainability standard. The free-school purse-seine fishery, which produced 162,000 metric tons of tuna in 2017, was certified by assessment body Control Union.

“I would like to offer my congratulations to Dongwon for this historic certification,” said Rupert Howes, the CEO of MSC.

“We hope this achievement will lead to other South Korean fisheries entering into the MSC assessment process to demonstrate their commitment to ocean sustainability and the stewardship of our precious ocean resources.”

The certification applies to free-school yellowfin and skipjack tuna caught by 12 purse-seine freezer vessels owned by Dongwon. Control Union determined it fulfilled the 28 principles for sustainable fishing set out in the MSC fisheries standard.

This includes strong management and governance, including 100% observer coverage and real-time monitoring via a remote Fisheries Monitoring Centre in Busan, South Korea. 

Impact on other species is minimal, with 99% the catch made up of skipjack and yellowfin. The fishery is also required to further demonstrate that it is not having a detrimental impact on manta and mobula rays.

“It’s a great honor to achieve the first MSC fishery certification in Korea. By achieving the most prestigious certification, we are now able to give even further confidence to our customers that our operations are duly carried out in accordance with international regulations and international best practices,” said Myoung Woo Lee, the president and CEO of Dongwon. 

Before tuna from the fishery can be sold with the blue MSC label, Dongwon will need to complete a traceability assessment to earn certification to the MSC’s chain-of-custody standard.

Also, like all other tuna fisheries operating in the WCPO, in order to ensure that the fishery can respond to future changes in the health of these tuna stocks, certification is conditional on the adoption of harvest strategies ,including harvest control rules, by all member states of the Western Central Pacific Fisheries Commission by 2021. 

Tuna caught by the fishery is landed in Busan, Masan, and Mokpo in South Korea, Bangkok (Thailand), General Santos City (Philippines), Ho Chi Minh City and Cam Rahn (Vietnam), Manta (Ecuador), and Mazatlan and Manzanillo (Mexico).