The future of food from the sea.

Global food demand is rising, and serious questions remain about whether supply can increase sustainably1. Land-based expansion is possible but may exacerbate climate change and biodiversity loss, and compromise the delivery of other ecosystem services2-6. As food from the sea represents only 17% of the current production of edible meat, we ask how much food we can expect the ocean to sustainably produce by 2050. Here we examine the main food-producing sectors in the ocean-wild fisheries, finfish mariculture and bivalve mariculture-to estimate 'sustainable supply curves' that account for ecological, economic, regulatory and technological constraints. We overlay these supply curves with demand scenarios to estimate future seafood production. We find that under our estimated demand shifts and supply scenarios (which account for policy reform and technology improvements), edible food from the sea could increase by 21-44 million tonnes by 2050, a 36-74% increase compared to current yields. This represents 12-25% of the estimated increase in all meat needed to feed 9.8 billion people by 2050. Increases in all three sectors are likely, but are most pronounced for mariculture. Whether these production potentials are realized sustainably will depend on factors such as policy reforms, technological innovation and the extent of future shifts in demand.

Trawl impacts on the relative status of biotic communities of seabed sedimentary habitats in 24 regions worldwide.

Bottom trawling is widespread globally and impacts seabed habitats. However, risks from trawling remain unquantified at large scales in most regions. We address these issues by synthesizing evidence on the impacts of different trawl-gear types, seabed recovery rates, and spatial distributions of trawling intensity in a quantitative indicator of biotic status (relative amount of pretrawling biota) for sedimentary habitats, where most bottom-trawling occurs, in 24 regions worldwide. Regional average status relative to an untrawled state (=1) was high (>0.9) in 15 regions, but <0.7 in three (European) regions and only 0.25 in the Adriatic Sea. Across all regions, 66% of seabed area was not trawled (status = 1), 1.5% was depleted (status = 0), and 93% had status > 0.8. These assessments are first order, based on parameters estimated with uncertainty from meta-analyses; we recommend regional analyses to refine parameters for local specificity. Nevertheless, our results are sufficiently robust to highlight regions needing more effective management to reduce exploitation and improve stock sustainability and seabed environmental status-while also showing seabed status was high (>0.95) in regions where catches of trawled fish stocks meet accepted benchmarks for sustainable exploitation, demonstrating that environmental benefits accrue from effective fisheries management. Furthermore, regional seabed status was related to the proportional area swept by trawling, enabling preliminary predictions of regional status when only the total amount of trawling is known. This research advances seascape-scale understanding of trawl impacts in regions around the world, enables quantitative assessment of sustainability risks, and facilitates implementation of an ecosystem approach to trawl fisheries management globally.

Effective fisheries management instrumental in improving fish stock status.

Marine fish stocks are an important part of the world food system and are particularly important for many of the poorest people of the world. Most existing analyses suggest overfishing is increasing, and there is widespread concern that fish stocks are decreasing throughout most of the world. We assembled trends in abundance and harvest rate of stocks that are scientifically assessed, constituting half of the reported global marine fish catch. For these stocks, on average, abundance is increasing and is at proposed target levels. Compared with regions that are intensively managed, regions with less-developed fisheries management have, on average, 3-fold greater harvest rates and half the abundance as assessed stocks. Available evidence suggests that the regions without assessments of abundance have little fisheries management, and stocks are in poor shape. Increased application of area-appropriate fisheries science recommendations and management tools are still needed for sustaining fisheries in places where they are lacking.

Bottom trawl fishing footprints on the world's continental shelves.

Bottom trawlers land around 19 million tons of fish and invertebrates annually, almost one-quarter of wild marine landings. The extent of bottom trawling footprint (seabed area trawled at least once in a specified region and time period) is often contested but poorly described. We quantify footprints using high-resolution satellite vessel monitoring system (VMS) and logbook data on 24 continental shelves and slopes to 1,000-m depth over at least 2 years. Trawling footprint varied markedly among regions: from <10% of seabed area in Australian and New Zealand waters, the Aleutian Islands, East Bering Sea, South Chile, and Gulf of Alaska to >50% in some European seas. Overall, 14% of the 7.8 million-km2 study area was trawled, and 86% was not trawled. Trawling activity was aggregated; the most intensively trawled areas accounting for 90% of activity comprised 77% of footprint on average. Regional swept area ratio (SAR; ratio of total swept area trawled annually to total area of region, a metric of trawling intensity) and footprint area were related, providing an approach to estimate regional trawling footprints when high-resolution spatial data are unavailable. If SAR was ≤0.1, as in 8 of 24 regions, there was >95% probability that >90% of seabed was not trawled. If SAR was 7.9, equal to the highest SAR recorded, there was >95% probability that >70% of seabed was trawled. Footprints were smaller and SAR was ≤0.25 in regions where fishing rates consistently met international sustainability benchmarks for fish stocks, implying collateral environmental benefits from sustainable fishing.

Patagonian grouper Acanthistius patachonicus (Jenyns, 1840) forms massive spawning aggregations in the Southwest Atlantic.

Here we describe massive spawning aggregations and seasonal changes in the large-scale distribution of the Patagonian grouper Acanthistius patachonicus in the Southwest Atlantic based on three sources of information: (a) data from bottom trawl research surveys covering the distributional range of the species within the Argentine continental shelf; (b) folk ecological knowledge gathered from experienced captains of the Argentine industrial trawl fisheries; and (c) sampling of an artisanal trap fishery targeting the Patagonian grouper in a specific location off the coast of Buenos Aires Province. The trawl surveys showed a general pattern of aggregation of Patagonian grouper towards the coast during the reproductive period (September-December). Captains described massive aggregations of the species at specific near-shore locations, where trawl catches of up to 15 t in a single haul were registered during the reproductive season. At a local scale, the artisanal trap fishery described operates exclusively during the reproductive period, targeting near-shore aggregations with a high proportion of individuals releasing gametes onboard. These three sources of information provide evidence of the existence of massive transient spawning aggregations of Patagonian grouper in the Argentine shelf. This is the first report of a reef fish spawning aggregation in the southern region of the Southwest Atlantic. Anecdotal information gathered in this study points to the depletion of many of the aggregations targeted during the 1980s and 1990s by the industrial fleet. At the same time, the spawning aggregation site off Buenos Aires Province has been productive for the last 34 years, being exploited exclusively by traps. The Patagonian grouper is classified as Data Deficient by the International Union for Conservation of Nature, which highlights the need for further research to determine its stock status. Mapping its current spawning aggregations should be a priority to inform the design of a targeted monitoring program and management plan for this species.

Global analysis of depletion and recovery of seabed biota after bottom trawling disturbance.

Bottom trawling is the most widespread human activity affecting seabed habitats. Here, we collate all available data for experimental and comparative studies of trawling impacts on whole communities of seabed macroinvertebrates on sedimentary habitats and develop widely applicable methods to estimate depletion and recovery rates of biota after trawling. Depletion of biota and trawl penetration into the seabed are highly correlated. Otter trawls caused the least depletion, removing 6% of biota per pass and penetrating the seabed on average down to 2.4 cm, whereas hydraulic dredges caused the most depletion, removing 41% of biota and penetrating the seabed on average 16.1 cm. Median recovery times posttrawling (from 50 to 95% of unimpacted biomass) ranged between 1.9 and 6.4 y. By accounting for the effects of penetration depth, environmental variation, and uncertainty, the models explained much of the variability of depletion and recovery estimates from single studies. Coupled with large-scale, high-resolution maps of trawling frequency and habitat, our estimates of depletion and recovery rates enable the assessment of trawling impacts on unprecedented spatial scales.

Beach strandings of Tehuelche scallop, Aequipecten tehuelchus, in Patagonia: Multi-scale processes and management implications.

The magnitude and causal mechanisms of a massive beach stranding of Tehuelche scallops that occurred in November 2017 in San José Gulf, Argentina, were investigated with the long-term goal of improving the assessment and management of the scallop fishery. The biomass of scallops washed ashore and deposited over a 10-km stretch of coast was estimated by quadrat sampling and compared with the results of a scallop stock assessment survey conducted three months prior to the stranding event. The resulting estimate of total biomass loss was in the order of 200 t, representing 10% of the estimated total scallop biomass in the San José gulf. The stranding coincided with persistent strong southerly winds (13 m/s) blowing for 24 h in San José Gulf, and large-scale windstorms that affected the southern tip of South America. Surface waves predicted under such windstorm conditions could generate strong bottom orbital velocities at shallow waters (<10 m depth), sufficient to drag and transport ashore scallops by Stokes drift (600-2000 m in 24 h). Analysis of local wind data recorded over a 6.8-year period indicated that such windstorm conditions occurred with an average frequency of 7.7 times per year, implying that beach strandings could have a significant impact on the scallop resource and its fishery. The actual impact of windstorms would depend on the location, depth and size composition of scallop beds, shallow beds (<10 m depth) being more susceptible to stranding risks. The use of spatial harvest control rules, instead of the global total allowable catch used at present, could reduce the risks of yield loss by directing the harvest to the more vulnerable scallop beds.

Variability in abundance of temperate reef fishes estimated by visual census.

Identifying sources of sampling variation and quantifying their magnitude is critical to the interpretation of ecological field data. Yet, most monitoring programs of reef fish populations based on underwater visual censuses (UVC) consider only a few of the factors that may influence fish counts, such as the diver or census methodology. Recent studies, however, have drawn attention to a broader range of processes that introduce variability at different temporal scales. This study analyzes the magnitude of different sources of variation in UVCs of temperate reef fishes off Patagonia (Argentina). The variability associated with time-of-day, tidal state, and time elapsed between censuses (minutes, days, weeks and months) was quantified for censuses conducted on the five most conspicuous and common species: Pinguipes brasilianus, Pseudopercis semifasciata, Sebastes oculatus, Acanthistius patachonicus and Nemadactylus bergi. Variance components corresponding to spatial heterogeneity and to the different temporal scales were estimated using nested random models. The levels of variability estimated for the different species were related to their life history attributes and behavior. Neither time-of-day nor tidal state had a significant effect on counts, except for the influence of tide on P. brasilianus. Spatial heterogeneity was the dominant source of variance in all but one species. Among the temporal scales, the intra-annual variation was the highest component for most species due to marked seasonal fluctuations in abundance, followed by the weekly and the instantaneous variation; the daily component was not significant. The variability between censuses conducted at different tidal levels and time-of-day was similar in magnitude to the instantaneous variation, reinforcing the conclusion that stochastic variation at very short time scales is non-negligible and should be taken into account in the design of monitoring programs and experiments. The present study provides baseline information to design and interpret results from visual census programs in temperate reefs.

Rebuilding global fisheries.

After a long history of overexploitation, increasing efforts to restore marine ecosystems and rebuild fisheries are under way. Here, we analyze current trends from a fisheries and conservation perspective. In 5 of 10 well-studied ecosystems, the average exploitation rate has recently declined and is now at or below the rate predicted to achieve maximum sustainable yield for seven systems. Yet 63% of assessed fish stocks worldwide still require rebuilding, and even lower exploitation rates are needed to reverse the collapse of vulnerable species. Combined fisheries and conservation objectives can be achieved by merging diverse management actions, including catch restrictions, gear modification, and closed areas, depending on local context. Impacts of international fleets and the lack of alternatives to fishing complicate prospects for rebuilding fisheries in many poorer regions, highlighting the need for a global perspective on rebuilding marine resources.

Institutions, incentives and the future of fisheries.

Fisheries around the world are managed with a broad range of institutional structures. Some of these have been quite disastrous, whereas others have proven both biologically and economically successful. Unsuccessful systems have generally involved either open access, attempts at top-down control with poor ability to monitor and implement regulations, or reliance on consensus. Successful systems range from local cooperatives to strong governmental control, to various forms of property rights, but usually involve institutional systems that provide incentives to individual operators that lead to behaviour consistent with conservation.