‘Breakthrough’ research suggests protecting a third of a fishery with ‘no-take’ rule leads to huge boost in surrounding fish populations

Long-term study provides data to support calls for 30 per cent of world’s oceans to be protected by 2030, writes Harry Cockburn

No-take marine protected areas increased the growth of fish populations by 42 per cent when fishing was unsustainable in surrounding areas (Erika Piñeros/WCS)

A long-term study hailed as a “breakthrough” by scientists suggests tightening fishing restrictions in one area can rapidly boost fish populations in surrounding areas and simultaneously protect threatened ecosystems.

The “powerful” findings provide clear scientific backing for global calls to conserve 30 per cent of the world’s oceans, the research team said.

The study, carried out in Kenya, recorded fish catches over 24 years across 12 fish landing sites in two different counties.

While one county enforced a “no-take” marine protected area (MPA) which covered 30 per cent of the fishery, the other county focused on gear restrictions and the use of small-mesh nets.

After 24 years the differences between the two fisheries “were stark”, the researchers said.

In the area where the no-take MPA was enforced, fish populations increased by 42 per cent, and fishers’ per-person daily catches rose 25 times faster than in the county where only the gear restrictions were used.

This shows that no-take MPAs were “far more effective at sustaining stocks of fish than restricting destructive gear,” the researchers said.

The study’s lead author Dr Tim McClanahan, a senior coral reef scientist for the Wildlife Conservation Society, said: “The no-take area in Mombasa occupied 30 per cent of the studied fishing grounds. Fortuitously, this is the target for protection being proposed for the oceans, which is rarely tested and based on the results of simulation models.

“The empirical support for the models and the conservation proposal is reassuring along with the unexpected results of increased production of fish populations that compensated for the lost fishing area.”

He added: “This adds to the evidence that no-take protected areas of sufficient coverage may compensate for the lost fishing grounds, particularly when fisheries are not sustainably fished.”

The research team said the study represents the longest-ever continuous detailed fish catch record for coral reefs, and reveals patterns that took nearly 20 years to unfold due to the small annual increments of change.

They also highlighted the size and timescale of the study as being invaluable.

“The time and resources it takes to complete these empirical studies has long been an impediment to testing the effectiveness of no-take MPAs on fisheries, and is also why simulation models were commonly used,” they said.

Previous empirical studies have been shorter-term and have usually focused on the catch per fisher, rather than the catch for an entire area, which is then compared to another area, a process which the researchers said was a critical metric of sustainable yield estimates.

As a result they said there remains “a compelling need to expand long-term studies to better calibrate and test fisheries production models”.

“This study shows that MPAs where no-take rules are followed can compensate for lost fishing grounds and stocks and therefore help people highly dependent on fish for income and nutritional security that is lost when catches are unsustainable.

“While gear restrictions did have positive benefits for short periods of time, they did not maximise fisheries production over the long-term,” the scientists said.

“Some combination of closure and gear restrictions are therefore likely needed to achieve the full benefits to both fishers and ecosystems.”

The research is published in the journal Marine Policy.