Biodiversity conservation has now become a primary concern of governments, NGOs, and the public. Recently, both terrestrial and marine conservation have relied on protected areas as the primary tool. Many NGOs and national leaders have supported setting aside 30% of land and oceans as protected areas by 2030 in what is known as 30 by 30 (Kubiak, 2020). What most species need is habitat and protection from exploitation. While protected areas in the form of parks on land and marine protected areas (MPAs) in the ocean can achieve this when large enough and enforced (Edgar et al., 2014), the same ends can be achieved in human used areas. If we include areas outside parks with intact habitat and protection from exploitation then 30 by 30 is too modest a goal, and we should aim for much higher levels of protection but may not need 30% in parks. On land, human occupation and crop production has totally transformed landscapes so that many species simply cannot survive there, and parks have proven to be an effective mechanism both to protect habitat and limit exploitation (Dudley & Stolton, 2010). In the oceans, fishing changes ecosystems much less (see Figure 1) and provided that exploitation is regulated, perhaps all species can be maintained outside of no-take areas. In the oceans, target species abundance has been reduced by 60–70% (Christensen et al., 2014) and nontarget species, particularly marine birds, mammals, and reptiles have often been greatly impacted. But no harvested marine fish and only 15 marine birds, mammals and fish have gone extinct, and none in the last 50 years despite major increases in fishing pressure. Major declines in targeted species have been associated with expanding industrial fisheries from 1950 to 1995. These declines have now been largely reversed and stocks are increasing where fisheries management is effective (Hilborn et al., 2020). The major biodiversity concerns in the ocean are now non-target species and vulnerable ecosystems such as coral reefs that are subject to a wide range of stresses including terrestrial run off, a warming and acidifying ocean, and, in places, overfishing. Marine protected areas are particularly effective in protecting ecosystems that have easily defined boundaries such as coral reefs and estuaries. They preserve sedentary or fragile species, ecosystems, and breeding areas for marine mammals and birds. However, the major effect of marine protected areas is to relocate fishing pressure to areas that remain open to fishing and where the great majority of marine biota occur. Given that many species of most concern such as sharks, albatross, and turtles are very wide ranging, even very large MPAs may not protect them. MPAs also do not remove human impacts such as pollution, warming and ocean acidification, and exotic species invasions. At a local scale, effectively enforced MPAs have been shown to increase abundance inside of reserves but there have been almost no evaluations of whether overall abundance of fish increases when areas outside MPAs are included (Ovando et al., in press). Theory suggests that allocating 10–30% of areas to MPAs will cause total abundance to increase only when stocks were heavily overfished prior to implementation (Hilborn et al., 2006; Ovando et al., in press) but most MPAs are in countries where overfishing is uncommon. Effective fisheries management promises to protect 100% of the area from overfishing and fishing practices that destroy habitats. Protection of endangered nontarget species has typically been accomplished by modifying the fishing gear and how and when it is deployed (Hall & Mainprize, 2005) benefiting albatrosses, turtles, and dolphins. These methods have been effective, but many fishing fleets have not adopted them and thus there is a great potential for increasing biodiversity by universal use of these tools. Much human use on land is largely transformative and dramatically reduces biodiversity. Agriculture and pastoralism cover an estimated half of the earth's surface. Crop production has the greatest impact on biodiversity, with near total loss of native vegetation and most other biota in some areas (Figure 1). Terrestrial protected areas, where consumptive exploitation is kept to a minimum, have been the primary tool for land-based conservation, and have been largely successful where enforced (Wuerthner et al., 2015). Maintenance of intact habitat and protection from exploitation are essential for the conservation of large carnivores, and mega-herbivores, and they also must be large enough to maintain sustainable populations and migrations within them (Wright & Mattson, 1996). However where at least some components of native terrestrial habitat, such as refuge habitat and some of the prey base, has been maintained and exploitation controlled, even wide ranging top predators such as wolves, bears and cougars have been able to recover and be maintained outside of parks (Chapron et al., 2014). Preservation of representative native ecosystems as reference baselines requires strict protected areas. However, with 14.7% of the terrestrial surface currently protected (see https://www.protectedplanet.net), these areas can only cover some of the biota, so the remaining species that would have occurred outside the protected area before human use must be conserved there. Theoretically, parks could be placed strategically to minimize species left outside parks (gap analysis) (Margules & Pressey, 2000), but in practice most parks are situated for other reasons. However, this approach would be suitable for identifying optimal human-use areas for restoration in future (Pressey et al., 1997). There is a vital need to expand research into conservation of biota in transformed landscapes while simultaneously improving food production, particularly where areas with the original native biota have been completely extirpated or are likely to be in the future, as in Africa (Kremen & Merenlender, 2018). The major difference between terrestrial and marine systems is that in the former many types of human use, particularly crops and habitation, completely distort the food chain, altering all trophic levels. In contrast, marine ecosystems generally retain most of their food chain structure at least at low trophic levels when subject to managed fishing. Figure 1b illustrates there is relatively little change except at higher levels as a result of human harvesting. In contrast, biodiversity loss in even low-intensity agriculture outside a terrestrial protected area such as the Serengeti National Park in Tanzania is considerable and ranges from 80% to 90% (Figure 1b). To counteract threats from human exploitation in terrestrial environments, conservation has depended primarily on protected areas. However, biota within them is declining (Craigie et al., 2010) and static boundaries cannot accommodate a dynamic environment (Sinclair et al., 2015). Human-use areas on land are, therefore, necessary for conservation but they are currently constrained by excessive exploitation and invasion of nonnative species. In marine systems, protected areas may be necessary as undisturbed reference sites. In addition, in places where exploitation rates cannot be effectively controlled outside parks, but can within them, then parks are clearly the most effective form of biodiversity protection. Nevertheless, MPAs are insufficient to protect the bulk of marine biodiversity, which lie outside the MPA. Enforcement within MPAs will become more difficult as human pressures increase, so protection must come primarily from improved fisheries regulation outside. Climate change is a major threat to both terrestrial and marine biodiversity because its effect is to shift the geographical location of suitable environments. Hence, static protected areas may not protect the biota they were designed for. Similarly, we already see poleward shifts in marine species, which threatens international fisheries agreements. Thus, although protected areas are essential for biodiversity conservation in both marine and terrestrial ecosystems, there are limits on what they can protect and we see that the best way to increase biodiversity protection is by a focus on human-used areas especially those where the ecosystem structure can be maintained largely intact. If human used areas were more intensively managed to enhance biodiversity presumably, this might reduce the urgency to increase protected areas, especially where such land is unavailable. If the benefit of protected areas is reduction of exploitation, then reduction of exploitation in human used areas can supplement benefits from protected areas. This is true for almost all of the oceans and those areas of the terrestrial world not converted to crops or human occupation. Even in modified ecosystems there remains great potential to increase biodiversity. The focus for the future in both areas must be on learning how to merge enhanced human food security with long-term persistence of biota needed for stability of ecosystems. Ray Hilborn and Anthony R.E. Sinclair contributed equally to conceptualization and writing of the paper. The work in this paper has not been submitted elsewhere, and no animals or human subjects were used in preparation of the paper. RH receives research funding from many groups that have interests in fisheries outcomes including environmental NGOs, foundations, governments, and fishing industry groups. ARES declares no conflicts of interest. No new data were collected for this paper and all data in the figure was taken from published sources described in the text or Supporting Information. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

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