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Published: 12 September 2011  
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Agriculture & food  |  Environment


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Scientists find tuna and billfish species at risk

Several species of tuna and billfish are in jeopardy, new international research shows. Presented in Policy Forum of the journal Science, this is the first research study to assess the global populations of tuna and billfish, based on the methods outlined by the International Union for Conservation of Nature (IUCN). It is also part of the Global Marine Species Assessment, a broader study that tackles the concerns that existing methods used to assess the status of these creatures are not enough; many worry that the methods are failing to sustainably manage the multi-national fisheries for these highly valued fish, which are very expensive.

Bluefin tuna © Shutterstock
Bluefin tuna
©  Shutterstock

In this latest study, fisheries experts from Barbados, Brazil, Canada, Chile, Peru, Spain, Switzerland, Taiwan and the United States compiled and analysed data from a global database of information, collated from scientific publications and fisheries reports. Afterwards they evaluated the data using criteria of the IUCN Red List.

Experts use the IUCN Red List, what many believe to be the global standard, to assess the status of species. Categories within this list include 'least concern', 'near threatened', 'vulnerable', 'endangered', 'critically endangered', 'extinct in the wild' and 'extinct'.

The researchers say stock assessments for tuna and billfish are usually determined on data collated by Regional Fisheries Management Organizations (RFMOs). Concerns have grown on how data is standardised and shared among RFMOs. This problem has only exacerbated the difficulties that have emerged when trying to understand the overall population status of the fish species, particularly because these fish are distributed all over the world.

Based on their findings, 7 of the 61 species under review (11%) were 'threatened' (i.e. vulnerable, endangered or critically endangered), 4 species (7%) were 'near threatened' and 39 species (64%) were of 'least concern'. Because there was insufficient data to evaluate 11 species (18%), they were classified as 'data deficient'.

The seven species classified as 'threatened' are: southern bluefin tuna, Atlantic bluefin tuna, bigeye tuna, blue marlin, white marlin and two species of Spanish mackerels.

Co-author Professor John Graves of the Virginia Institute of Marine Science in the United States, a member of the research team, says two key components are responsible for triggering this problem: the high dollar value of the tuna results in heavy fishing pressure, and the species do not reach sexual maturity quickly, which only extends the recovery period from overfishing.

The researchers say the proportion of threatened tuna and billfish species is higher compared with the majority of other groups of marine bony fishes. The values are similar to those recorded for other highly prized and slow-producing species like sharks. A past study, headed by Virginia Institute of Marine Science emeritus Professor Jack Musick, discovered that 17% to 33% of shark, skate and ray species are classified as 'threatened'.

Professor Graves and colleagues say banning the harvesting of these fishes until their populations can once again reach normal and healthy levels will be the fastest way to recovery for the most-depleted stocks.

Because this would be difficult from an economic perspective, potentially even increasing illegal fishing, the researchers believe strong preventive measures must be implemented, including controlling international trade through a listing of these species on the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES).

The team says measures that monitor and comply with the recovery of tuna, billfish and mackerel species exist, and are starting to show positive results.

Reviewing the IUCN Red List, which works for many as a global standard for the assessment and comparison of extinction risks among all organisms, the team says the 'one-size-fits-all' approach has its negative points, particularly when it is applied to heavily fished species, including tuna.

While these drawbacks did not significantly impact the results of their study, the IUCN has been notified of the inconsistencies between the Red List methods and the methods generally used to evaluate and manage fishery stocks, the team says.

The researchers note that the quick depletion of a population to its maximum sustainable yield, what experts say is around 40% to 50% of the virgin stocks of tuna, would place it in the 'vulnerable' category on the IUCN Red List. So, say the researchers, this would be the complete opposite of what a fishery manager would say: that it is both a well-managed and sustainable fishery.

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