Are MPAs effective?

Before we can begin to consider this question, we must define what we mean by MPA and by effectiveness. According to Wikipedia “Marine protected areas (MPAs) are protected areas of seas, oceans, estuaries, or large lakes. MPAs restrict human activity for a conservation purpose”. By this definition almost anywhere in the territorial waters of developed countries could be considered an MPA since most fishing activities there are regulated to some degree, which makes this definition not really useful. Consequently, for my analysis in this article I will define an MPA as a permanent no-take area, where all extractive activity is prohibited. There are obvious successes of MPAs as tourist destinations and, in heavily overfished places (Vandeperre et al., 2011; Kerwath et al., 2013). MPAs in heavily overfished areas also help to demonstrate what kind of abundance would be seen in the absence of fishing and can provide evidence that reduced fishing effort will benefit harvest. In addressing effectiveness, the most frequent objective in MPA literature is “protection”. A press release from the recent IUCN conference states that “Members have also identified the need for internationally binding legislation to preserve the high seas, and have set an ambitious target of 30% of marine areas to be protected by 2030”. Similarly, (Lubchenco and Grorud-Colvert, 2015) was titled “Making waves: the science and politics of ocean protection.” The question is therefore, do no-take MPAs protect the ocean, and more importantly, are they the most effective tool to achieve such protection? The threats to the ocean and its biodiversity are coming from many directions and we may not even know all of them. They include global warming, ocean acidification, oil spills, garbage in all forms, micro-plastics, energy production, invasive species, land based run-off of sediments and agricultural waste and chemicals, marine traffic, and illegal and legal fishing. Of all these threats, MPAs “protect” primarily against legal fishing but most no-take MPAs also protect the area from local oil and mineral extraction. Mineral extraction is quite rare, but as we’ve seen, MPAs do not protect from oil spills from ship traffic like the Exxon Valdez, nor from spill-over of oil from a blowout like the Deepwater Horizon. The key point I want to make is that stopping legal, regulated fishing is the only thing MPAs can really do to protect the ocean. They have no proven effect whatsoever on the rest. Moreover, we have a whole range of ways to regulate fisheries that are much more effective than MPAs. Consequently, for the rest of this discussion I will consider whether no-take areas benefit biodiversity (and related ecosystem services) and human food security as the dual goals of society. MPAs and area closures in general, do not reduce fishing effort, they only move it elsewhere and effort displacement has long been recognized as a result of MPA establishment or closed areas (Halpern et al., 2004; Hiddink et al., 2006; Greenstreet et al., 2009). In Australia, MPA establishment has often been combined with government financed fleet reductions (Sen, 2010), but in the absence of such compensation, closing areas to fishing simply moves fishing pressure. There has been no major analysis of whether MPAs increase the abundance of fish throughout a region and under what circumstances this occurs and the large meta-analysis of impacts within reserves do not include any analysis of effects outside (e.g. Gill et al., 2017). MPAs when effectively enforced generally increase the abundance of fish inside the protected area (Halpern, 2003), but, even if the IUCN target of locking 30% of the oceans into protected areas is achieved, 70% will remain outside no-take areas and we would expect the increased fishing effort, relocated from the MPA to reduce biodiversity outside. All that no-take MPAs do is move legal fishing outside the protected areas, and under what circumstances the abundance outside the reserve ultimately increases due to higher egg production inside the reserve has not been systematically evaluated. Models suggest that MPAs can benefit abundance outside reserves (and the catch) only when fishing pressure is very high and stocks are seriously overexploited (Hilborn et al., 2004; Rassweiler et al., 2014). Empirical evidence for this can be found in a number of papers including (Goñi et al., 2010; Ojeda-Martinez et al., 2011; Kerwath et al., 2013). To achieve these benefits, the size of the reserves must be tuned to the adult and larval movement of the resident species. Make the MPAs too small and there will be no benefit because fish will move in and out of the reserve frequently enough to be caught outside. Make the reserve too big, and there won’t be a spill-over of eggs, larvae or adults (Hastings and Botsford, 1999; Hilborn et al., 2004). Because different species have different movement patterns, no MPA network design will achieve these goals for all species, whereas fisheries regulations can be much more species specific. I argue that the evidence has shown MPAs can increase fish abundance throughout a region and potentially increase or maintain food security only when fishing pressure is excessive and the design of the size of reserves is tuned to the movement of the species. Because of the many differential movements of species it is unlikely that any reserve can be designed to benefit a wide range of species both inside and outside the MPA. However, if MPAs are to be “effective”, they should provide better protection at lower cost to food production than alternatives. If the threat to an area is overfishing, reducing fishing pressure through management is the answer, because MPAs do not reduce, but move fishing pressure. Where the threat is by-catch of nontarget species, whether sharks, birds, mammals or turtles, technical solutions and gear-specific time/area closures have been effective (Hall et al., 2000). Where damage to sensitive habitats is the issue, those areas can be closed specifically to the damaging gear. Fisheries management regulations generally recognize the spatial heterogeneity of fish populations and habitats and can be highly selective as to which areas are open to what kinds of fishing at specific times of year. All of the methods described above are standard practice in good fisheries management, and there is really no need for no-take MPAs provided you can manage fisheries. Fisheries agencies can better protect biodiversity and associated benefits by implementing and enforcing science-based regulations than simply designating no-take areas. As a reminder to readers, any managed area is considered a MPA under some definitions but the recent literature considers only permanent no-take areas as effective protection. So in conclusion, I see a clear role for MPAs as tourist sites and as reference sites for sedentary species. When other forms of fisheries management are not possible but MPAs can be implemented and enforced they can benefit biodiversity and fisheries when serious overfishing is occurring. Certainly many areas of the world lack effective fisheries management and if MPAs could be enforced, networks of MPAs in those areas would be a positive step. In cases of high uncertainty MPAs can be considered a buffer against that uncertainty and variability (Hilborn and Sibert, 1988). However, MPAs only protect the ocean from legal, regulated fishing. Even if a 30% target were achieved, it would not constitute significant protection from the real threats, nor would it bring particularly good protection from fishing. The food produced from the ocean that is lost when large marine areas are closed must inevitably be replaced terrestrially with the associated high environmental costs (Hilborn, 2013; Helvey et al., 2017). Both biodiversity and food security will generally be better served by expanding fisheries management, not by establishing more no-take areas.