Since the end of the 20th century, the maximum sustainable yield (MSY) has been at the core of debates in the fisheries sector from a biological, economic, and geopolitical perspective. In theory, MSY aims to maximize fishery yields while preventing harmful declines in stock biomasses. However, MSY is primarily derived from monospecific population dynamics and does not necessarily achieve a suitable balance between exploitation, socioeconomic objectives, and foodweb and ecosystem functioning. Since the reform of the European Common Fisheries Policy (CFP) in 2013, FMSY has been the management target for European fisheries. Given the high prevalence of overexploited stocks at the time, fisheries theory suggests that, for those stocks, a reduction in fishing mortality should lead to an increase in biomass, which in turn should result in an increase in fishing opportunities. While some of the indicators calculated to monitor the effectiveness of the CFP show encouraging signs regarding stock status, the fishing industry, which in the meantime has also been affected by a series of crises, does not seem to perceive the expected benefits. Using a meta-analysis of 92 stocks assessed by ICES in the Northeast Atlantic, we examined how scientists' advice on fishing opportunities has evolved and whether it has responded to changes in F and SSB since the last CFP reform. While the analyses show that fishing opportunities have increased mainly in cases where fishing mortality and spawning stock biomass have changed the most, they also appear to be evolving more slowly, and the picture remains rather mixed. This may also reflect adverse signals of global change and the impact this may have on future fishing opportunities.

Monthly sampling of cephalopod at Port-en-Bessin fish market (Normandy, France) over a 30-year period, combined with commercial fishery statistics, provides essential insight into the exploitation patterns, composition and size frequencies of these resources. Port-en-Bessin cephalopod landings are shown to decrease which is consistent with the decline observed in the entire French fleet operating in the English Channel. Cuttlefish landings exhibit a bimodal length distribution which is expected for this 2-year life cycle (and two-cohort) population. Juveniles of the year are recruited from October (from 8 cm). By the end of their second year of life, cuttlefish reach their maximum size (on average about 22 cm in April–May) prior to dying following spawning. Cuttlefish average size of the second cohorts has decreased from 20 to 17 cm over the period 1996–2022. This seems to be a reduction in size rather than a change in the timing of catches. Squids are not segregated in commercial landings, and the protocol was developed to inform on the prevalence of Loligo forbesii and L. vulgaris in the catch. Both species have a 1-year life cycle with a 3-month offset (recruitment of L. forbesii occurs in June and L. vulgaris in September). Over the 30 years of data, an increase in L. vulgaris landings is observed, while L. forbesii landings have decreased. These findings, in line with climate change, consider biases such as fishermen behaviour determining landings geographical origin.

Inshore waters off the south coast of Ireland are an important foraging area for a range of cetacean species. Some of the main prey species of these cetaceans are herring and sprat, two economically valuable fish species in the region. The Celtic Sea herring stock suffered a marked decline in 2013. The present study aimed to investigate potential changes in the ecosystem associated to the herring decline and to determine the potential impacts on predators. Here we analyzed sightings information of common dolphins, fin, minke, humpback and unidentified whale species, acoustic data of herring and sprat, and a range of environmental variables mainly derived from satellites. Firstly, we characterized spatio-temporal patterns in the relative abundance of predator and prey species, and environmental variables, and compared periods before and since the herring decline. Since the 2013 herring decline, (i) the herring stock has mainly concentrated in south-eastern coastal waters and southern offshore Irish waters, (ii) sprat density has increased, (iii) chlorophyll concentration has decreased, (iv) sea surface temperature has risen, and (v) the euphotic layer has extended deeper. Secondly, we modelled the effects of prey density and environmental conditions on the relative abundance and distribution of cetaceans, as well as the effects of environmental conditions on prey density, between 2005-2018 by applying Hurdle Generalized Additive Models. The models for herring and sprat support the idea that these species have different environmental relationships, for example herring tended to be found in shallower waters than was the case for sprat. The presence and relative abundance of common dolphins were significantly affected by both environmental conditions and herring density, whereas whale species presence and relative abundance were found to be correlated with sea surface temperature and prey density. The model results suggest differences in prey choice among whale species. Understanding the dynamic relationships between predators, prey and the environment is important to inform an ecosystem-based approach to fisheries management.

Atlantic herring in International Council for Exploration of the Sea (ICES) Divisions 6.a, 7.b–c comprises at least three populations, distinguished by temporal and spatial differences in spawning, which have until recently been managed as two stocks defined by geographical delineators. Outside of spawning the populations form mixed aggregations, which are the subject of acoustic surveys. The inability to distinguish the populations has prevented the development of separate survey indices and separate stock assessments. A panel of 45 single-nucleotide polymorphisms, derived from whole-genome sequencing, were used to genotype 3480 baseline spawning samples (2014–2021). A temporally stable baseline comprising 2316 herring from populations known to inhabit Division 6.a was used to develop a genetic assignment method, with a self-assignment accuracy greater than 90%. The long-term temporal stability of the assignment model was validated by assigning archive (2003–2004) baseline samples (270 individuals) with a high level of accuracy. Assignment of non-baseline samples (1514 individuals) from Divisions 6.a, 7.b–c indicated previously unrecognized levels of mixing of populations outside of the spawning season. The genetic markers and assignment models presented constitute a ‘toolbox’ that can be used for the assignment of herring caught in mixed survey and commercial catches in Division 6.a into their population of origin with a high level of accuracy.

This study evaluates the relationship between both commercial and scientific spatial fisheries data and a new satellite- based estimate of potential fish production (Ocean Productivity available to Fish, OPFish) in the European Seas. To construct OPFish, we used productivity frontal features derived from chlorophyll- a horizontal gradients, which characterize 10%– 20% of the global phytoplankton production that effectively fuels higher trophic levels. OPFish is relatively consistent with the spatial distribution of both pelagic and demersal fish landings and catches per unit of effort (LPUEs and CPUEs, respectively). An index of harvest relative to ocean productivity (H P index) is calculated by dividing these LPUEs or CPUEs with OPFish. The H P index reflects the intensity of fishing by gear type with regard to local fish production. Low H P levels indicate lower LPUEs or CPUEs than expected from oceanic production, suggesting

Sexually produced larvae are used in various fields of coral research. Because the vast majority of scleractinians reproduces only on one or few occasions per year and ex-situ spawning induction is still very hard to achieve, high efforts are required to obtain planula larvae. Brooding corals have been used to harvest planulae, but the larvae oftentimes differ in various traits, e.g. settlement behavior, from most spawning corals. Other cnidarians, such as Aiptasia spp., have been substituting scleractinians in many aspects of coral research. However, organisms such as Aiptasia differ strongly from scleractinians limiting the transferability of obtained results. This study examines the potential of Leptastrea purpurea as a reliable source of larvae for coral research. Larval output throughout the year as well as settlement behavior of planulae was investigated. Our results show that L. purpurea allows permanent access to planula larvae. The settlement behavior of L. purpurea is similar to many spawning species which increases the transferability of conclusions. We discuss the aptitude of L. purpurea for research on scleractinian physiology, ecology and larval settlement and conclude that L. purpurea is a well-suited organism to accelerate progress in many fields of coral research.

DNA methylation is a critical epigenetic regulator of development in mammals and social insects, but its significance in development outside these groups is not understood. Here we investigated the genome-wide dynamics of DNA methylation in a mollusc model, the oyster Crassostrea gigas, from the egg to the completion of organogenesis. Large-scale methylation maps reveal that the oyster genome displays a succession of methylated and non methylated regions, which persist throughout development. Differentially methylated regions (DMRs) are strongly regulated during cleavage and metamorphosis. The distribution and levels of methylated DNA within genomic features (exons, introns, promoters, repeats and transposons) show different developmental lansdscapes marked by a strong increase in the methylation of exons against introns after metamorphosis. Kinetics of methylation in gene-bodies correlate to their transcription regulation and to distinct functional gene clusters, and DMRs at cleavage and metamorphosis bear the genes functionally related to these steps, respectively. This study shows that DNA methylome dynamics underlie development through transcription regulation in the oyster, a lophotrochozoan species. To our knowledge, this is the first demonstration of such epigenetic regulation outside vertebrates and ecdysozoan models, bringing new insights into the evolution and the epigenetic regulation of developmental processes.

Almost all of the world's fisheries overlap spatially and temporally with foraging seabirds, with impacts that range from food supplementation (through scavenging behind vessels), to resource competition and incidental mortality. The nature and extent of interactions between seabirds and fisheries vary, as does the level and efficacy of management and mitigation. Seabird dietary studies provide information on prey diversity and often identify species that are also caught in fisheries, providing evidence of linkages which can be used to improve ecosystem based management of fisheries. However, species identification of fish can be difficult with conventional dietary techniques. The black-browed albatross (Thalassarche melanophris) has a circumpolar distribution and has suffered major population declines due primarily to incidental mortality in fisheries. We use DNA metabarcoding of black-browed albatross scats to investigate their fish prey during the breeding season at six sites across their range, over two seasons. We identify the spatial and temporal diversity of fish in their diets and overlaps with fisheries operating in adjacent waters. Across all sites, 51 fish species from 33 families were identified, with 23 species contributing >10% of the proportion of samples or sequences at any site. There was extensive geographic variation but little inter-annual variability in fish species consumed. Several fish species that are not easily accessible to albatross, but are commercially harvested or by-caught, were detected in the albatross diet during the breeding season. This was particularly evident at the Falkland Islands and Iles Kerguelen where higher fishery catch amounts (or discard amounts where known) corresponded to higher occurrence of these species in diet samples. This study indicates ongoing interactions with fisheries through consumption of fishery discards, increasing the risk of seabird mortality. Breeding success was higher at sites where fisheries discards were detected in the diet, highlighting the need to minimize discarding to reduce impacts on the ecosystem. DNA metabarcoding provides a valuable non-invasive tool for assessing the fish prey of seabirds across broad geographic ranges. This provides an avenue for fishery resource managers to assess compliance of fisheries with discard policies and the level of interaction with scavenging seabirds.

Common rock oystersSaccostrea cucullata(Bivalvia) were sampled from intertidal volcanic rocks at five sites around Ascension Island (central-east Atlantic) in austral winter 2012–2014. Their left valves were sectioned to reveal annual growth increments. Their periodicity was validated by the presence of specific growth marks in the increment sequence visible in consecutive years of sampling. No significant differences in shell height-weight relationships were revealed between sites. Marginal analysis of the increment width showed thatS. cucullataaccelerated their growth in cooler winter months and decelerated the growth in warmer summer months. Rock oysters in Ascension Island lived up to 14–16 years with maximum age of 26 years. Young oysters (1–5 years old) had the same growth rates both in shell height and weight in all sites. However, their starting point (size and weight of 1-year-old animals) was different in various sites, with largest animals occurring in the most protected site Northeast Bay with sheltered inlets and smallest animals inhabiting exposed to surf site of Letterbox. Growth in shell height was best described by von Bertalanffy growth function with the largestL∞in animals inhabiting the windward side and smallest animals occurring in the leeward side of the Island. In summary,S. cucullataaround Ascension Island lived longer but had slower growth than those from tropical regions of Southwest Asia probably due to comparatively low productivity observed in the central part of the equatorial tropical Atlantic.

Gelatinous zooplankton are a large component of the animal biomass in all marine environments, but are considered to be uncommon in the diet of most marine top predators. However, the diets of key predator groups like seabirds have conventionally been assessed from stomach content analyses, which cannot detect most gelatinous prey. As marine top predators are used to identify changes in the overall species composition of marine ecosystems, such biases in dietary assessment may impact our detection of important ecosystem regime shifts. We investigated albatross diet using DNA metabarcoding of scats to assess the prevalence of gelatinous zooplankton consumption by two albatross species, one of which is used as an indicator species for ecosystem monitoring. Black-browed and Campbell albatross scats were collected from eight breeding colonies covering the circumpolar range of these birds over two consecutive breeding seasons. Fish was the main dietary item at most sites; however, cnidarian DNA, primarily from scyphozoan jellyfish, was present in 42% of samples overall and up to 80% of samples at some sites. Jellyfish was detected during all breeding stages and consumed by adults and chicks. Trawl fishery catches of jellyfish near the Falkland Islands indicate a similar frequency of jellyfish occurrence in albatross diets in years of high and low jellyfish availability, suggesting jellyfish consumption may be selective rather than opportunistic. Warmer oceans and overfishing of finfish are predicted to favour jellyfish population increases, and we demonstrate here that dietary DNA metabarcoding enables measurements of the contribution of gelatinous zooplankton to the diet of marine predators.

Fuelled by the raising importance of cephalopod fisheries in Europe, there have been demands from scientists and stakeholders for their assessment and management. However, little has been done to improve the data collection in order to analyse cephalopod populations under the EU Data Collection Framework (DCF). While the DCF allows member states to design flexible national sampling programmes, it establishes the minimum data requirements (MDR) each state is obliged to fulfil. In this study, it was investigated whether such MDR currently set by the DCF allow the application of depletion models (DMs) to assess European cephalopod stocks. Squid and cuttlefish fisheries from the western Mediterranean were used as a case study. This exercise sheds doubt on the suitability of the MDR to properly assess and manage cephalopod stocks by means of DMs. Owing to the high plasticity of life-history traits in cephalopod populations, biological parameters should be estimated during the actual depletion period of the fished stocks, in contrast with the triennial sampling established by the DCF. In order to accurately track the depletion event, the rapid growth rates of cephalopods implies that their populations should be monitored at shorter time scales (ideally weekly or biweekly) instead of quarterly as required by the DCF. These measures would not demand additional resources of the ongoing DCF, but a redistribution of sampling efforts during the depletion period. Such changes in the sampling scheme could be designed and undertaken by the member states or directly integrated as requirements.

Within the English Channel, the common cuttlefish Sepia officinalis is a semelparous species for which a 2-year life cycle was exclusively described in the 1980s. In the 1990s, new research indicated that whilst a 2-year life cycle was still evident for females and the large majority of males, a small proportion of males were actually maturing at only 1 year of age. Since 1980, the interest of French and UK fishers for this resource has increased and it is nowadays one of the most important demersal species of the area and is considered to be fully exploited. From the start of the 20th century, fishing effort and sea surface temperatures have increased in the English Channel and have probably impacted the life history traits of S. officinalis. A 2-year sampling programme was undertaken at French landing sites of the English Channel during the reproduction season in 2010 and 2011 to estimate if the proportion of 1-year-old mature animals has changed. Age determination was carried out by coupling polymodal decomposition and lipofuscin measurement. Size-at-maturity for each year and each sex was estimated by fitting a binomial error GLM. Results highlight that a variable percentage of males and females belonging to the first cohort are mature and that size-at-maturity was lower than that observed in the 1990s. Finally, different parameters, such as temperature and fishing pressure are explored to discuss changes in life history traits suggesting that cuttlefish could be an indicator of the temperature regime shift in the English Channel.

Argentine shortfin squid Illex argentinus (Ommastrephidae) is one of the most abundant cephalopods in the Southwest Atlantic, with total annual catch exceeding 1 mln t in some years. During its annual life cycle, I. argentinus perform long distance migrations, from their subtropical spawning grounds in Uruguay and southern Brazil to temperate feeding grounds on the Patagonian Shelf and back. Oceanography and squid distribution were studied during a research survey carried out in the south-eastern part of the Patagonian Shelf to reveal environmental cues that determine pathways of shelf to continental slope pre-spawning migrations. It was found that the outflows of less dense Patagonian Shelf Waters (PSW) over the slope may act as proxies determining the locations of I. argentinus migrations from the shelf to the slope. During maturation I. argentinus did not significantly change their buoyancy with females becoming slightly more buoyant with depth. Subsequent movement of mature I. argentinus to denser Sub-Antarctic Superficial waters (SASW) located at deeper depths (600–700m) enable them to approach near-neutral buoyancy and therefore facilitate the distant pre-spawning migrations.

The English Channel cuttlefish (Sepia officinalis) is the most abundant cephalopod resource in the Northeast Atlantic and one of the three most valuable resources for English Channel fishers. Depletion methods and age-structured models have been used to assess the stock, though they have shown limitations related to the model assumptions and data demand. A two-stage biomass model is, therefore, proposed here using, as input data, four abundance indices derived from survey and commercial trawl data collected by Ifremer and Cefas. The model suggests great interannual variability in abundance during the 17 years of the period considered and a decreasing trend in recent years. Model results suggest that recruitment strength is independent of spawning-stock biomass, but appears to be influenced by environmental conditions such as sea surface temperature at the start of the life cycle. Trends in exploitation rate do not reveal evidence of overexploitation. Reference points are proposed and suggestions for management of the sustainable utilization of cuttlefish in the English Channel are advanced.

Cephalopods are a relatively small class of molluscs (~800 species), but they support some large industrial scale fisheries and numerous small-scale, local, artisanal fisheries. For several decades, landings of cephalopods globally have grown against a background of total finfish landings levelling off and then declining. There is now evidence that in recent years, growth in cephalopod landings has declined. The commercially exploited cephalopod species are fast-growing, short-lived ecological opportunists. Annual variability in abundance is strongly influenced by environmental variability, but the underlying causes of the links between environment and population dynamics are poorly understood. Stock assessment models have recently been developed that incorporate environmental processes that drive variability in recruitment, distribution and migration patterns. These models can be expected to improve as more, and better, data are obtained on environmental effects and as techniques for stock identification improve. A key element of future progress will be improved understanding of trophic dynamics at all phases in the cephalopod life cycle. In the meantime, there is no routine stock assessment in many targeted fisheries or in the numerous by-catch fisheries for cephalopods. There is a particular need for a precautionary approach in these cases. Assessment in many fisheries is complicated because cephalopods are ecological opportunists and stocks appear to have benefited from the reduction of key predator by overexploitation. Because of the complexities involved, ecosystem-based fisheries management integrating social, economic and ecological considerations is desirable for cephalopod fisheries. An ecological approach to management is routine in many fisheries, but to be effective, good scientific understanding of the relationships between the environment, trophic dynamics and population dynamics is essential. Fisheries and the ecosystems they depend on can only be managed by regulating the activities of the fishing industry, and this requires understanding the dynamics of the stocks they exploit.