Elevated fish densities extend kilometres from oil and gas platforms.

Thousands of offshore oil and gas platforms have been installed throughout the world's oceans and more structures are being installed as part of the transition to renewable energy. These structures increase the availability of ecological niches by providing hard substrate in midwater and complex 3D habitat on the seafloor. This can lead to 'hotspots' of biodiversity, or increased densities of flora and fauna, which potentially spill over into the local area. However, the distances over which these higher densities extend (the 'range of influence') can be highly variable. Fish aggregate at such structures, but the range of influence and any implications for wider fish populations, are unclear. We investigated the relationship between fish and platform areal densities using high resolution fisheries acoustic data. Data were collected in the waters surrounding the vessel exclusions zones around 16 oil and gas platforms in the North Sea, and throughout the wider area. We estimated densities of schooling fish using echo-integration, and densities of non-schooling fish using echo-counting. At 10 platforms, non-schooling fish densities were elevated near the platform relative to background levels in the equivalent wider area. The range of influence, defined here as the range to which fish densities were elevated above background, varied from 0.8 to 23 km. In areas of high platform density, fish schools were encountered more often, and non-schooling fish densities were higher, when controlling for other sources of environmental variation. This is the first time such long-range effects have been identified; previously, ranges of influence have been reported in the order of just 10s-100s of metres. These findings suggest that the environmental impact of these structures may extend further than previously thought, which may be relevant in the context of upcoming management decisions around the decommissioning of these structures.

Variable trends in the distribution of Atlantic cod (Gadus morhua) in the Celtic seas.

Despite decades of active fisheries management, many stocks of Atlantic cod in its southern range are in a depleted state and mortality estimates remain high. Recovery of these stocks, as defined by management areas, could be confounded by cod distributions shifting outside of these areas. Here, we assess data from internationally coordinated trawl surveys to investigate the distribution of three cod stocks in the Celtic Seas ecoregion, Irish Sea, Celtic Sea, and West of Scotland, from 1985 to 2021. We mapped cod densities, analyzed trends in mean weighted depth and bottom temperature, and calculated the center of gravity and equivalent area of the stocks. The distribution of the West of Scotland stock shifted north and east, spilling into the North Sea, while the Irish Sea and Celtic Sea stocks shifted west. Each stock showed decreasing trends in equivalent area, but there were no clear trends in the average depth occupied by the fish. There was no apparent relationship between temperature and the distribution of cod, as bottom temperature varied little from 1993 to 2021. Although Irish Sea cod showed a shift into warmer water, this was due to changes in survey distribution. The shift in distribution of the West of Scotland cod stock towards the North Sea whilst impairing local recovery provides further justification for the recent definition of its incorporation into a larger stock unit that includes the northwest of the North Sea. The Irish Sea and Celtic Sea cod stocks are neither shifting northwards, nor into deeper waters, but remained within current boundaries. This suggests that recent temperature conditions did not affect their distribution, but this may change as temperatures increase towards the limit for reproduction.

Developing expert scientific consensus on the environmental and societal effects of marine artificial structures prior to decommissioning.

Thousands of artificial ('human-made') structures are present in the marine environment, many at or approaching end-of-life and requiring urgent decisions regarding their decommissioning. No consensus has been reached on which decommissioning option(s) result in optimal environmental and societal outcomes, in part, owing to a paucity of evidence from real-world decommissioning case studies. To address this significant challenge, we asked a worldwide panel of scientists to provide their expert opinion. They were asked to identify and characterise the ecosystem effects of artificial structures in the sea, their causes and consequences, and to identify which, if any, should be retained following decommissioning. Experts considered that most of the pressures driving ecological and societal effects from marine artificial structures (MAS) were of medium severity, occur frequently, and are dependent on spatial scale with local-scale effects of greater magnitude than regional effects. The duration of many effects following decommissioning were considered to be relatively short, in the order of days. Overall, environmental effects of structures were considered marginally undesirable, while societal effects marginally desirable. Experts therefore indicated that any decision to leave MAS in place at end-of-life to be more beneficial to society than the natural environment. However, some individual environmental effects were considered desirable and worthy of retention, especially in certain geographic locations, where structures can support improved trophic linkages, increases in tourism, habitat provision, and population size, and provide stability in population dynamics. The expert analysis consensus that the effects of MAS are both negative and positive for the environment and society, gives no strong support for policy change whether removal or retention is favoured until further empirical evidence is available to justify change to the status quo. The combination of desirable and undesirable effects associated with MAS present a significant challenge for policy- and decision-makers in their justification to implement decommissioning options. Decisions may need to be decided on a case-by-case basis accounting for the trade-off in costs and benefits at a local level.

To what extent can decommissioning options for marine artificial structures move us toward environmental targets?

Switching from fossil fuels to renewable energy is key to international energy transition efforts and the move toward net zero. For many nations, this requires decommissioning of hundreds of oil and gas infrastructure in the marine environment. Current international, regional and national legislation largely dictates that structures must be completely removed at end-of-life although, increasingly, alternative decommissioning options are being promoted and implemented. Yet, a paucity of real-world case studies describing the impacts of decommissioning on the environment make decision-making with respect to which option(s) might be optimal for meeting international and regional strategic environmental targets challenging. To address this gap, we draw together international expertise and judgment from marine environmental scientists on marine artificial structures as an alternative source of evidence that explores how different decommissioning options might ameliorate pressures that drive environmental status toward (or away) from environmental objectives. Synthesis reveals that for 37 United Nations and Oslo-Paris Commissions (OSPAR) global and regional environmental targets, experts consider repurposing or abandoning individual structures, or abandoning multiple structures across a region, as the options that would most strongly contribute toward targets. This collective view suggests complete removal may not be best for the environment or society. However, different decommissioning options act in different ways and make variable contributions toward environmental targets, such that policy makers and managers would likely need to prioritise some targets over others considering political, social, economic, and ecological contexts. Current policy may not result in optimal outcomes for the environment or society.

A switch in species dominance of a recovering pelagic ecosystem.

Although many marine ecosystems have been adversely impacted by human activities,1 some are now recovering due to reductions in fishing pressure.2-4 Here, we document the recovery of an ecosystem subjected to intense anthropogenic activity for over 200 years, the Clyde Sea.5 This region once had productive fisheries for herring (Clupea harengus) and other fish, but these disappeared at the turn of the century.6,7 Using acoustic surveys of the pelagic ecosystem, we found that the Clyde Sea supports 100 times as many forage fish as in the late 1980s. However, herring has now been replaced by sprat (Sprattus sprattus), despite virtually no fishing on herring for 20 years. A combination of a warming sea,6 bycatch of herring in the prawn (Nephrops norvegicus) fishery,8,9 and susceptibility of herring to poor recruitment may have contributed to this unexpected recovery. We compare this to similar unexpected "recoveries" involving unforeseen ecosystem effects, such as the return of hake (Merluccius merluccius) to the North Sea;10,11 the recent expansion of the pelagic squat lobster, "munida," (Pleuroncodes monodon) off Peru;12 and the increase in scallop (Placopecten magellanicus) numbers on Georges Bank.13 The lack of a current sprat fishery in the Clyde presents a unique opportunity to develop an alternative industry for its seafaring community: ecotourism. Charismatic megafauna (whales, dolphins, and seabirds) that people will pay to see14 will, in time-if not already15,16-be drawn in by the abundance of forage fish now present, further restoring the biodiversity of the region after centuries of overexploitation.

Less than half of the European dietary recommendations for fish consumption are satisfied by national seafood supplies.

PURPOSE: To review the seafood dietary recommendations of European countries and compare them to national seafood supplies. METHODS: Current seafood dietary recommendations were collated from national health authorities across Europe. Food balance sheets were downloaded from the FAO, and appropriate conversion factors were applied to each seafood commodity. Average net per capita seafood supplies from 2007 to 2017 were derived from data on imports and production for food from both capture fisheries and aquaculture, accounting for exports. RESULTS: Both national dietary recommendations and seafood supplies varied considerably throughout Europe. At a national level, on a per capita basis, only 13 out of the 31 of European dietary recommendations for fish consumption were satisfied by national seafood supplies. Most of the countries with coastal access, as well as those with traditional fish-eating cultures, such as France and countries in Northern Europe, had adequate seafood supplies to meet their recommendations. The landlocked countries of Central and Eastern Europe did not have enough seafood supplies to satisfy their recommendations. CONCLUSIONS: Our findings emphasise the need to not only consider consumer health outcomes when developing and advocating dietary recommendations, but also the sustainability of food production systems. As many foods are not necessarily locally sourced but traded as part of global production and distribution systems, it is important to consider greater consistency between national dietary recommendations to facilitate more sustainable marine food systems.

Fishers' knowledge detects ecological decay in the Mediterranean Sea.

The Northern Adriatic Sea (NAS) is one of the most overexploited marine ecosystems in Europe. Given the gaps in scientific knowledge regarding the NAS, this study sought Fishers' Ecological Knowledge (FEK) to determine NAS' historical baselines for conservation. By interviewing 53 fishers in three ports of northern Italy, estimates of the catch rates of four commercial demersal species were generated over a 60-year period, and perceptions of target and non-target species' diversity and benthic diversity were analysed in three groups of fishers (i.e. novices, experienced and veterans). Results showed a significant decline in perceived abundance of sole (Solea solea), common cuttlefish (Sepia officinalis) and mantis shrimp (Squilla mantis), and evidence was found of a Shifting Baseline Syndrome (SBS) among novices. Given FEK's ability to complement scientific knowledge, fishers' participation in marine management policies and intergenerational communication should be enhanced, to improve the status of marine ecosystems and hinder SBS.

Target strengths of two abundant mesopelagic fish species.

Mesopelagic fish of the Myctophidae and Sternoptychidae families dominate the biomass of the oceanic deep scattering layers and, therefore, have important ecological roles within these ecosystems. Interest in the commercial exploitation of these fish is growing, so the development of techniques for estimating their abundance, distribution and, ultimately, sustainable exploitation are essential. The acoustic backscattering characteristics for two size classes of Maurolicus muelleri and Benthosema glaciale are reported here based on swimbladder morphology derived from digitized soft x-ray images, and empirical (in situ) measurements of target strength (TS) derived from an acoustic survey in a Norwegian Sea. A backscattering model based on a gas-filled prolate spheroid was used to predict the theoretical TS for both species across a frequency range between 0 and 250 kHz. Sensitivity analyses of the TS model to the modeling parameters indicate that TS is rather sensitive to the viscosity, swimbladder volume ratio, and tilt, which can result in substantial changes to the TS. Theoretical TS predictions close to the resonance frequency were in good agreement (±2 dB) with mean in situ TS derived from the areas acoustically surveyed that were spatially and temporally consistent with the trawl information for both species.

Reversal of fish stock decline in the Northeast Atlantic.

Analyses of global fish stocks paint a mixed picture of success, with some holding fishery management responsible for the poor status of many stocks [1-3] or predicting widespread collapse [1, 4]. Some suggest a stable [5] or improving situation [6] in certain jurisdictions. The debate is particularly polarized in the European Union, where the Common Fisheries Policy (CFP) has been criticized for failing to protect stocks [2, 7-10], while others argue that a rebuilding process is underway [11, 12]. We show that substantial change in stock trends occurred in the area around the turn of the century: since then, the fishing pressure (as measured by the exploitation rate) has reduced continuously and there have been increases in biomass, demonstrating the potential for stock recovery. In 2011, for the first time, the majority of assessed stocks, where reference points are defined, were fished sustainably. The reductions in fishing pressure were associated with declines in fishing effort. The last reform of the CFP, in 2002, introduced effort control as part of more enforceable management measures, which were also based on longer-term plans. Further reforms to the CFP are currently being developed, so it is important, when correcting its weaknesses, to also acknowledge and build on the success of a major reduction in the fishing pressure on European fish stocks.

Antarctic krill under sea ice: elevated abundance in a narrow band just south of ice edge.

We surveyed Antarctic krill (Euphausia superba) under sea ice using the autonomous underwater vehicle Autosub-2. Krill were concentrated within a band under ice between 1 and 13 kilometers south of the ice edge. Within this band, krill densities were fivefold greater than that of open water. The under-ice environment has long been considered an important habitat for krill, but sampling difficulties have previously prevented direct observations under ice over the scale necessary for robust krill density estimation. Autosub-2 enabled us to make continuous high-resolution measurements of krill density under ice reaching 27 kilometers beyond the ice edge.