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NET BENEFITS FOR FISHERIES ARE ALSO NOT WELL UNDERSTOOD
In theory, MPAs, particularly those that are closed off to all or most fishing, can allow overfished species to mature undisturbed and produce more offspring. The offspring can then swim over the invisible boundaries to adjacent fished areas and provide bigger catches and more money for fishers. Indeed, as mentioned, a good body of research suggests that species targeted by fishers often do respond well to protection. But do more and larger fish inside a protected area really mean higher catches outside its boundaries?
One systematic review published in 2016 found evidence of spillover in 80 percent of its studies. But the researchers added a caveat: “[Twenty] percent of remaining studies that failed to provide any evidence of spillover is likely to be underestimated …because of publication bias in ecology, and specifically in marine protected area science,” where positive results are favoured, they wrote.
But even if there is some spillover, is it enough to compensate for reduced fishing areas with increased fishing pressure and thus provide a net benefit to fishers?
Mongabay’s review captured only one empirical study that looked at this, bearing in mind that their review and search terms were not exhaustive. This study, published in 2001, found that the biomass of five commercially important fish families increased both inside and outside marine reserves in the Caribbean island of St. Lucia within three years of establishment. Moreover, the fish catch increased substantially – by between
46 and 90 percent, depending on the type of traps the fishers used.
The results of this single study cannot be generalised, of course, and experts have noted that while there are some empirical studies looking at how MPAs affect fisheries, most of them are not rigorous and their conclusions are mixed.
For example, a 2013 study found that fishers who worked near the Goukamma MPA in South
Africa saw a nearly steady increase in the catch of commercially important Roman seabream
(Chrysoblephus laticeps) over the 10 years since the park’s establishment in 1990.
By contrast, in a 2000 study from Kenya, researchers found that while the creation of a no-take MPA had led to some spillover, the fish catch was lower than it was before the park’s creation halved the available fishing area. Similar results were found in Australia’s Great Barrier Reef.
Most positive examples come from MPAs that are either very small (so the fishers lose only a small amount of their previous fishing area), or from parks located in areas where fish stocks are severely overexploited, said the University of Washington’s Ray Hilborn.
Halpern agreed that the benefits of MPAs on fisheries are very context-dependent and traditional management techniques, such as seasonal fishing closures or restrictions on certain kinds of fishing equipment, sometimes come out ahead.
“In developed countries and large stocks, traditional fisheries management has been very effective, especially more recently,” he said. “In developing nations and highly diverse fisheries – as is the case with many coral reef fisheries in tropical countries – traditional fisheries management has not been as effective and marine protected areas are often a much more effective and viable strategy. But there are many counterexamples and other issues in play – in other words, context matters.”
“Overall, I am satisfied with the research that is being done to see the ecological effectiveness of marine protected areas. I think it’s useful to keep studying that – how things change with time and protection,” Ban said. “But I do think we need a lot of emphasis on the human element: to what extent marine protected areas affect human well-being for coastal communities that rely on the oceans for their livelihoods.”
Overall, I am satisfied with the research that is being done to see the ecological effectiveness of marine protected areas. I think it’s useful to keep studying that how things – change with time and protection Natalie Ban