Could fishermen hold the key to conservation of ocean species?

A lifeline for the world’s seas could lie at the bottom of a fisherman’s net, according to marine biologists.

Scientists say the slush that comes up with the catch holds the key to a new way of estimating fish stocks involving the fishermen themselves.

“Data is notoriously unreliable on which species of fish are landed, which are discarded, and how much fish is caught. It may be easier to just take a sample of the slush,” says Professor Stefano Mariani, a marine biologist at Liverpool John Moores University.

Advances in Environmental DNA (eDNA) sampling now allow conservationists to forensically examine seawater for fish DNA - traces of skin, blood, faeces, eggs etc - and pinpoint the exact species those belong to. Indeed a recent LJMU study found the technique to be more accurate in identifying which species swim in which waters than traditional visual or catch-and-return surveys.

Rich in DNA

In research published today (10 December, 2020) in the journal Ecological Applications, a team of fisheries ecologists based in Rome and Sicily show that slush collected from the bottom of fishing nets is sufficiently DNA rich to provide a reliable source of data on a vessel’s catch.

“This means that fishing boats could feasibly collect data on fish species and numbers which has all sorts of implications both for conservation and for the industry’s prospects,” explained Prof Mariani.

Overfishing threatens fish stocks globally, reduces biodiversity, alters ecosystem functioning and jeopardizes food security and livelihoods.

Checks by the authorities remain largely inaccurate:  many species are discarded at sea and many analyses of the catch are based on time-consuming procedures such as visual sorting, taxonomic classification, counting and measuring.

Results

The scientists extracted DNA from water draining from the net cod-end, just after it was hauled on board and then used DNA metabarcoding to reconstruct the species composition of several hauls across different locations in the Strait of Sicily and compared them to visual sorting results.

“Our results showed that the assemblages identified using DNA in the slush adequately mirror those returned by visual inspection of catch both qualitatively and quantitatively,” explained Professor Tommaso Russo, who led the Italian team.

“Both science and the fishing industry are interested in building up a better picture of what fish are out there,” added Mariani. “So this approach could produce vast amounts of information on marine communities across the oceans, which no scientific programme could ever afford.”

They say the practice would:

• Record the most prevalent species caught by vessels, making it difficult to conceal/misreport the catch
• Help fishing businesses ‘benchmark good practice’ by allowing participants to ‘certify’ their catch

-The research paper All is fish that comes to the net: metabarcoding for rapid fisheries catch assessment is published in Ecological Applications and authored by Tommaso Russo, Giulia Maiello, Lorenzo Talarico, Lorenzo D’Andrea, Simone Franceschini, Stefano Cataudella  (all University of Rome Tor Vergata), Charles Baillie (University of Salford), Giuliano Colosimo (San Diego Zoo), Federico Di Maio (University of Bologna), Fabio Fiorentino, Germana Garofalo, Danilo Scannella (all National Research Council, Italy), Stefano Mariani (Liverpool John Moores University).