California has now largely completed a process for establishing marine protected areas (MPAs) that may be considered a model for other jurisdictions seeking to meet obligations under the Convention on Biological Diversity. In the Californian process, a team of scientists established guidelines on the size and spacing of MPAs, as well as requirements for habitat representation and replication. The final outcomes, in terms of proportion of the coast encompassed by MPAs and the distribution and sizes of MPAs, were largely a result of decisions taken by the advisory scientists, rather than by the designated decision makers. Future legislation must recognize the uncertainties associated with benefits of MPAs and specifically allow for adaptive management including explicit experimental tests of uncertainties. The science team should define at the outset the major uncertainties about impacts, and deliberate experimentation and adaptive management should be essential parts of each design. Future legislation should be much more specific about the objectives of the MPAs and specify the percentage of the area that should be set aside as MPAs. Finally, quantitative models rather than guidelines should be used to evaluate the consequences of alternative designs.

The scientific literature (including some of the most high-profile papers) on the ecological and fisheries effects of permanent no-take marine reserves is dominated by examples from hard tropical and warm temperate ecosystems. It appears to have been tacitly assumed that inference from these studies can directly inform expectations of marine reserve effects in cooler temperate and cold temperate waters. Trends in peer-reviewed studies indicate that the empirical basis for this assumption is tenuous because of a relative lack of research effort in cooler seas, and differences between tropical and temperate regions in ecology, seasonality, the nature of fisheries and prevailing governance regimes.

Seamounts throughout the world's oceans can support diverse and abundant fish communities. Many have been subject to commercial deep-sea bottom trawl fisheries and have exhibited ‘boom and bust’ characteristics. There is growing concern about the effect of fishing on fragile and vulnerable benthic invertebrate species. This review examines why deep-sea fisheries have generally failed, and recommends measures that are necessary to improve their sustainability. Much is based on lessons learned in the south-west Pacific that may be more generally applicable to global deep-sea fisheries. Sustainable fisheries require highly precautionary feature-based catch limits, and credible and timely stock assessment advice. Management also needs to consider fishing impacts on the benthic habitat, and while reducing and spreading fishing effort on seamounts is beneficial for fish stocks, it can have a negative effect on the benthos. To balance exploitation and conservation, elements of spatial management are required, whereby some seamounts are protected before any fishing has occurred. Protected areas should include entire seamounts, and multiple seamounts in a network. A management regime should incorporate closed seamounts, open seamounts for fishing, and management of adjacent slope areas where these are important for the productivity of fish and invertebrate populations.

Studies of marine reserves typically focus upon differences in the size and abundance of target organisms inside versus outside reserve borders, but they seldom provide spatially explicit measurements of how reserves influence mortality rates. This study investigated mortality rates for female California spiny lobster (Panulirus interruptus) at multiple sites inside and outside of three marine reserves at the Santa Barbara Channel Islands, California, USA. Mean total mortality (Z) of female lobsters was lower at sites inside reserves (Z = 0.22 [± 0.05 SE]) than at sites outside reserves (Z = 0.59 [± 0.02 SE]). Mean mortality at all sites inside reserves, and among sites near reserve centres (where Z = 0.17 [± 0.05 SE]), was similar to estimates of natural mortality for other temperate spiny lobster species. Among sites inside reserves, there was a positive relationship between mortality and proximity to reserve borders, but this relationship was absent among sites outside reserves. Mortality estimates were much more variable among sites inside reserves than at sites in fished areas. This variation is probably due to differential emigration rates from the three reserves, as well as site-specific ecological factors that influence population structure, demonstrating the importance of spatially explicit reserve sampling and understanding how ecological heterogeneity influences fisheries models.

No-take marine reserves directly promote the recovery of predatory species, which can have negative indirect effects on prey populations in reserves. When harvesting also occurs on prey species there is potential conflict between the direct and indirect effects of protection, and reserves may not have conservation benefits for prey species. For example, sea urchins are fished in many regions, but may decline in reserves due to increased predation rates. To investigate this potential conflict, this paper compares density, size, biomass and reproductive potential of both a harvested and an unharvested urchin species between a long-term reserve and unprotected sites in California. Consistent with density-mediated indirect interactions, densities of the unharvested species were 3.4-times higher at unprotected sites compared to reserve sites. However, for the harvested species, densities were comparable between reserve and unprotected sites. Both species were consistently larger at reserve sites, and the biomass and reproductive potential of the harvested species was 4.8- and 7.0-times higher, respectively, than at unprotected sites. This is likely due to differences in size-selectivity between harvesting and predators, and potential compensatory effects of predators. While the generality of these effects needs to be tested, these results suggest mechanisms whereby reserves can benefit both predator and prey species.

MPAs are being established worldwide at an increasing rate, however empirical evidence for benefits to mobile species of small areas closed to fishing in temperate regions are little known. Using two North Sea prohibited trawling areas (PTAs) established > 80 years ago, social (fishers’ perceptions), management (fishing effort and compliance) and ecological (fish abundance and size) data were combined to assess the PTAs against their primary societal (conflict resolution) and secondary ecological (stock protection) objectives. Fishers perceived that the PTAs resolved conflicts between static and mobile gear sectors, despite evidence of non-compliance. However, few fishers perceived that they personally benefited from the PTAs. Fish abundance and size data from baited traps (BT) and video (BV) provided no evidence of PTA effects, but trawling effort was a significant predictor of BT fish abundance data and improved the model of BV fish abundance data. The absence of PTA effects on fish is attributable to non-compliance, the high mobility of the fish involved and their continued exploitation within the PTAs using static gear. This points to the need for greater understanding of the behaviour of fishers in relation to closures. The study also highlights the challenges of quantifying possible fishery benefits of small temperate closed areas and questions whether widely advocated fishery benefits may have enhanced initial support, but failure to deliver them may erode faith in such closures as a fisheries management tool.

This review outlines the policy frameworks for marine conservation zones (MCZs) and marine special areas of conservation (SACs), which are the main components of the emerging UK marine protected area (MPA) network. If current recommendations are implemented, the coverage of MPAs in English seas could rise to 27%. The governance challenges that this will raise are explored through case studies of MPA initiatives in south-west England. Whilst the initial processes by which MCZ recommendations have been developed provided for stakeholder participation (bottom-up), the main steer has been from central government (top-down). The subsequent designation and implementation of MCZs is likely to be more top-down. Marine SAC processes have, by contrast, been top-down from the outset. The fishing industry fears that more MPAs will lead to increasing restrictions, whilst conservationists fear that MPAs will not be sufficiently protected, potentially becoming paper MPAs. Both argue that the burden of proof should be placed on the other party. Such combinations of top-down (central government-led) and bottom-up (community and user-led) approaches and the related conflicts are typical of government-led MPAs in temperate countries that have higher governance capacities. Top-down approaches tend to dominate, but this does not mean that they cannot be combined with bottom-up approaches.

National and international policies have encouraged the establishment of a representative network of marine protected areas (MPAs) in South Africa, with the aim of protecting marine biodiversity. The extent to which these marine and estuarine protected areas (EPAs) represent marine fish species and communities was assessed by comparing their species compositions with those of exploited areas, as sampled using four fishing techniques. Seven hundred fish species were sampled, representing one-third of South Africa's marine fishes. MPAs in coastal habitats scored c. 40% on the Bray-Curtis measure of similarity for species representativeness, but this score declined markedly for offshore ‘trawlable’ fishing grounds. The combined effects of sampling error, temporal variation and the effects of fishing on relative abundance suggest that 80% similarity would be the maximum achieveable. Forty-nine per cent of all fish species that were recorded were found in the 14 MPAs sampled. Redundancy in the MPA network was low, with fish species most commonly being represented in only one MPA or absent. There was greater redundancy in the 33 EPAs, with 40% of species being found in two or more EPAs, but many of these estuaries were adjacent to each other and embedded in large MPAs. Deep water fish communities (>80 m deep) and communities located on the west and south-east coasts of South Africa were most poorly represented by MPAs. Routine fishery surveys provide a robust and repeatable opportunity to assess species representativeness in MPAs, and the method used could form the basis of an operational definition of ‘representative’. In contrast to an assessment based on presence-absence data, this analysis of quantitative data presents a more pessimistic assessment of protection.

In order to better understand community-level effects of fishing on temperate reefs at continental scales, changes in densities of common species in five Australian marine protected areas (MPAs) were estimated from prior to establishment to three years after enforcement of fishing prohibitions. A before-after-control-impact survey design was used, with 5–14 replicated sites distributed within both sanctuary and fishing zones associated with each MPA. On the basis of published meta-analyses, exploited species were generally expected to show increased densities. By contrast, only two of the 11 exploited fish species (the red morwong Cheilodactylus fuscus and latrid trumpeter Latridopsis forsteri), and none of seven exploited invertebrate species, showed significant signs of population recovery within sanctuary zones. Four fish species increased in biomass between survey periods. When variation in abundance data was partitioned by PERMANOVA independently for the five MPAs, the ‘zone × year’ interaction component consistently contributed only c. 4% of total variation, compared to site (c. 35%), zone (c. 8%), year (c. 8%) and residual error (c. 45%) components. Given that longer-term Australian studies show clear community-wide responses following MPA protection, the discrepancy between weak observed recovery and a priori expectations is probably due, at least in part, to the three-year period studied being insufficient to generate clear trends, to relatively low fishing pressure on some temperate Australian reefs, and to meta-analyses overestimating the likelihood of significant short-term population responses.

Effective spatial management of marine species requires informed planning, as well as ongoing assessment. For mobile species such as fish, knowledge of the scale and variation in movement is central to key planning decisions, such as the size and shape of marine reserves and the interpretation of the response of protected populations. For example, populations of species that require large areas of habitat may not show increases in abundance inside small reserves, but calculating optimal reserve size is complicated by individual variations in behaviour. Fish movements can be used to quantitatively inform marine reserve planning and assessment. An individual based numerical simulation model including acoustic telemetry and census data was used to simulate changes in populations of snapper Pagrus auratus in north-eastern New Zealand. Four behavioural categories and offshore migration were used to represent the observed variability in movement. Age-structures of modelled fish populations in fully exploited areas, marine reserves and virgin populations differed substantially. However, the population structure within reserves resembled a fully fished population more closely than an unfished population. Due to the range of movement types shown by snapper, fish were not ‘locked up’ by reserves, and fish with centres of activity based in reserves were predicted to have a relatively high chance of being caught outside these reserves. Furthermore, the model showed that the response of fish populations within marine reserves was dependent on levels of exploitation in fished areas. For snapper in coastal reef areas, reserves c. 40 km2 or more may be required to achieve abundances > 50% of the unfished stock. On balance, while marine reserves with sizes similar to Leigh and Tawharanui (c. 5 km2) can achieve significant levels of protection for snapper, they are too small to fully protect resident reserve snapper populations.

Monitoring species’ response in marine protected areas is important for informing both the management of those areas and the establishment of additional protected areas. Populations of spiny lobsters Jasus edwardsii were monitored in eight New Zealand marine reserves for up to 34 years. The populations displayed highly variable responses to protection. While a few showed rapid (within 1–2 years of protection) increases in abundance, others showed little response even after a decade of protection. Some reserves displayed little initial recovery, then a sudden increase following several years of protection, while others displayed significant declines in abundance following initial recovery. Marine reserves located in areas with initially high densities of juveniles tended to have rapid recovery, but aspects of reserve design had no significant influence on the recovery rate. Variability among recovery trajectories also suggests that supply-side dynamics may be a key driver of lobster recovery. Densities of legal-sized lobsters were positively correlated with reserve age, but the abundance of juvenile lobsters increased in all but one reserve, indicating enhanced recruitment, survival and/or movement of juvenile lobsters into reserves. It is important to consider the placement of reserves, with respect to potential levels of larval supply, when establishing marine reserves for either conservation or fisheries management purposes and for evaluating their effectiveness.