1. Despite the disparities in size and volume of marine and freshwater realms, a strikingly similar number of species is found in eachwith 15 150 Actinopterygian fishes in fresh water and 14 740 in the marine realm. Their ecological and societal values are widely recognized yet many marine and freshwater fishes increasingly risk local, regional or global extinction.2. The prevailing threats in aquatic systems are habitat loss and degradation, invasive species, pollution, over-exploitation and climate change. Unpredictable synergies with climate change greatly complicate the impacts of other stressors that threaten many marine and freshwater fishes.3. Isolated and fragmented habitats typically present the most challenging environments for small, specialized freshwater and marine fishes, whereas overfishing is by far the greatest threat to larger marine and freshwater species. Species that migrate within or between freshwater and marine realms may face high catchability in predictable migration bottlenecks, and degradation of breeding habitat, feeding habitat or the intervening migration corridors.4. Conservation reserves are vital to protect species-rich habitats, important radiations, and threatened endemic species. Integration of processes that connect terrestrial, freshwater and marine protected areas promises more effective conservation outcomes than disconnected reserves. Diadromous species in particular require more attention in aquatic restoration and conservation planning across disparate government agencies. 5. Human activities and stressors that increasingly threaten freshwater and marine fishes must be curbed to avoid a wave of extinctions. Freshwater recovery programmes range from plans for individual species to recovery of entire basin faunas. Reducing risks to threatened marine species in coastal habitats also requires conservation actions at multiple scales. Most of the world's larger economically important fisheries are relatively well-monitored and well-managed but there are urgent needs to curb fishing mortality and minimize catch of the most endangered species in both realms.

Baited remote underwater video stations (BRUVS) were used to examine variation in assemblages of reef fishes at scales of 100s of kilometres (between 3 marine parks in New South Wales, Australia) and kilometres (between 4 sites within each park). Temporal variation over 5 yr was also examined in 1 park (Solitary Islands). BRUVS were able to sample the relative abundance and distribution of species from a wide range of trophic groups, and were particularly effective for detecting cryptic predators. Significant variability in the fish assemblages occurred between each park consistent with the latitudinal distribution of the parks. Fish assemblages also varied significantly between sites within each park. Contrary to expectations, total species richness did not follow the expected latitudinal gradient. However, observed geographical patterns in species richness of certain families such as Labridae (greater richness in the most northern park) and Monacanthidae (greater species richness in southern parks) followed expectations. Abundant schooling species, common to all 3 parks, were important contributors to variation between sites. Temporal variation over 5 yr at 1 park was relatively minor compared to the spatial variation among the 3 parks. This suggests largescale spatial separation is more important for structuring fish assemblages than time. A network of marine parks will therefore be required to represent variation in reef fish assemblages over this latitudinal scale.

Addressing social and economic considerations is crucial to the success of Marine Protected Area (MPA) planning and management. Ineffective social assessment can alienate local communities and undermine the success of existing and future MPAs. The success of methods currently used to incorporate social and economic considerations into MPA planning, however, is rarely critiqued. Three Australian MPA planning processes covering three states and incorporating federal and state jurisdictions are reviewed in order to determine how potential social impacts were assessed and considered. These case studies indicate that Social Impact Assessment (SIA) is underdeveloped in Australian MPA planning. Assessments rely heavily on public participation and economic modelling as surrogates for dedicated SIA and are commonly followed by attitudinal surveys to gauge public opinion on the MPA after its establishment. The emergence of issues around public perception of the value of MPAs indicates the failure of some of these proposals to adequately consider social factors in planning and management. This perception may have potential implications for the long term success of individual MPAs. It may also compromise Australia's ability to meet commitments for MPA targets, made under a range of international agreements, to gazette at least 10% of all its marine habitats as MPAs. Indeed, this is demonstrated in two of the three case studies where social and economic arguments against MPAs have been used to delay or block the future expansion of the MPA network.

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The aim of this study was to collect data on population dynamics and life history for White's seahorse Hippocampus whitei, a geographically restricted species that is listed as data deficient under the IUCN Red List. Data from H. whitei populations were collected from two regions, Port Stephens (north) and Sydney Harbour (south) in New South Wales, Australia, covering most of the known range of H. whitei, from 2005 to 2010. Over 1000 individuals were tagged using fluorescent elastomer and on subsequent recaptures were re-measured for growth data that were used in a forced Gulland-Holt plot to develop growth parameters for use in a specialized von Bertalanffy growth-function model. Growth parameters for Port Stephens were: females L(∞) = 149·2 mm and K = 2·034 per year and males L(∞) = 147·9 mm and K = 2·520 per year compared with estimates from Sydney Harbour: females L(∞) = 139·8 mm and K = 1·285 per year and males L(∞) = 141·6 mm and K = 1·223 per year. Whilst there was no significant difference in growth between sexes for each region, H. whitei in Port Stephens grew significantly quicker and larger and matured and reproduced at a younger age than those from Sydney Harbour. The life span of H. whitei is at least 5 years in the wild with six individuals recorded reaching this age. Data collected on breeding pairs found that H. whitei displays life-long monogamy with three pairs observed remaining pair bonded over three consecutive breeding years. Baseline population densities were derived for two Port Stephens' sites (0·035 and 0·110 m(-2)) and for Manly in Sydney Harbour (1·050 m(-2)). Even though the life-history parameters of H. whitei suggest it may be reasonably resilient, precaution should be taken in its future management as a result of its limited geographical distribution and increasing pressures from anthropogenic sources on its habitats.