Major Fish Stocks Research Articles

Population connectivity and dynamics in early-life stages of Atlantic fish communities

IntroductionMany hypotheses have been suggested to explain recruitment variability in fish populations. These can generally be divided into three groups, either related to: larval food limitation, predation, or transport. Transport mechanisms are central for reproduction in pelagic species and three physical processes, concentration, enrichment, and retention are commonly referred as the fundamental “ocean triads” sustaining larval survival and thus success of reproductive effort. The aim of this study is to investigate linkages between primary production and transport processes of eggs and larvae for the most important commercial fish species in the Atlantic Ocean.MethodsWe simulated eggs and larvae dispersion using an individualbased model and integrating information on the fish ecology of the major fish stocks. Our work included a review on spawning ground locations, spawning time, eggs and larvae duration. Simulations were performed over a 10-year time period for 113 stocks (17 species) in order to assess variability in dispersion and common trends and factors affecting transport.ResultsThe level of primary production from initial to final position, i.e. from spawning to larval settlement, increased for some stocks (n=31), for others it declined (n=64), and for a smaller group (n=18) there was no substantial changes in level of primary production.DiscussionThis result implies that larval transport will not necessarily introduce larvae into areas of enhanced food availability expressed by the primary production at the site. These findings thus suggest marked differences in how physical and biological processes interact in the early life of major fish groups in the Atlantic Ocean. The results provide a further insight into fish larval drift and the potential role of primary production in emergence of spawning strategies.

Stock discrimination of mackerel scad Decapterus macarellus (Cuvier, 1833) in the eastern Indonesia based on metazoan fish parasite composition

Mackerel scad Decapterus macarellus (Cuvier, 1833), a small pelagic species, is the major catch in Asia, particularly in Indonesia. Despite a high catch volume, its utilization status is relatively unknown since stock assessment is mostly conducted for the entire small pelagic group without separating the species. Studies on population biology and stock distribution of mackerel scad in Indonesia so far involved catch-based production models, growth parameter analyses, otoliths, and fish genetics. We herewith discriminate eastern Indonesian fish stocks of D. macarellus by comparing the respective metazoan parasite community. We collected 105 specimens of mackerel scad from three closely connected fishing grounds representing two Indonesian fisheries management areas. Recorded metazoan parasites belonged to the Monogenea (4 species), Digenea (8 species), Acanthocephala (1 species), and Crustacea (2 species), with the two Monogenea Allopseudodiclidophora opelu (Yamaguti, 1965) and Pseudodiclidophora decapteri (Yamaguti, 1965) being the most prevalent. A multidimensional scaling analysis revealed the clustering pattern of the hosts based on the parasites, identifying two major fish stocks, the North Sulawesi group and the North Maluku group. The strength and weaknesses of the so far applied stock assessment methodologies for this small pelagic fish in Indonesia are discussed.

A novel probabilistic survey method for at sea sampling in pelagic fisheries – the Norwegian catch sampling lottery

Reliable information on the age- and size-structure of the annual harvest of major commercial fish stocks is crucial input to analytical stock assessments. Such information is usually obtained from landing data (census of biomass) combined with biological sampling of selected landings. In this paper we describe a novel catch sampling method that we have developed and implemented for the major Norwegian pelagic fisheries that have annual landings around 1 million tonnes in recent years. The new sampling regime gradually implemented from 2018 is based on three pillars; probabilistic sampling of hauls, use of electronic logbook, and co-sampling. By a minor modification of the electronic logbook the vessels in the pelagic fishery now report the catch quantity at haul level immediately after each catch operation. This electronic report is automatically submitted to the Institute of Marine Research (IMR), where a random draw by computer in real time determines if a small sample of fish should be taken from that haul by the fishermen and be frozen and transported to IMR for analysis. Nearly 100% of the hauls annually goes through this “lottery”, and compliance (fraction of samples received) is currently around 60% and increasing. The sampling regime has been operationalized in cooperation with the fishing industry.

Sustainable fisheries: Towards operationalization of decision making accounting for biodiversity

Overexploitation of biotic resources constitutes a major threat on marine biodiversity while demand for seafood will rise in the next decades. Application of Life Cycle Assessment to marine ecosystems needs further focus. This study applies two existing methods (Langlois et al., 2014 and Emanuelsson et al., 2014) of fishing impact assessment on biodiversity to 125 common fish stocks fished in the 14 marine areas drawn by FAO and proposes operational guidelines for sustainable production and efficient conservation policies. We show that unsustainable fishing is responsible for a loss of up to 30 times the potential yield of major fish stocks such as Atlantic cod, red snapper and bluefin tuna. We identify depleted fish stocks for which biomass is up to 15 times lower than it should be (yellownose skate fished in South America) and stocks facing fishing mortality up to 1.9 × 107 times higher than required to allow sustainable recovery (Pacific Ocean perch fished on the US West Coast). Regarding intrinsic biodiversity, our study shows that we are not able to understand the consequences of overfishing through a cause-effect chain due to lack of science knowledge. However, we display how to limit the impacts on biodiversity by using complementary indicators at species and ecosystem level. The complexity of marine ecosystems and the remaining limits of studied methods are discussed, showing the compelling need for further data collection and analysis, and opening ways for targeted research.

Feeding strategy and diet overlap in major fish stocks of Ayima and Gelegu Rivers, northwestern Ethiopia

AbstractRiverine ecosystems contribute considerable fisheries production. However, in Ethiopia, there is a lack of comprehensive biological studies on such ecosystems. This study assessed the feeding habits of commercially important fishes of the Ayima and Gelegu Rivers. Fishes' guts were sampled seasonally from April 2017 to November 2018 using gill nets, cast nets and electrofishing. Four hundred and forty‐nine stomachs were analysed. Niche breadth and overlap indices were estimated using Levin and Schoener indices, respectively. The data indicated that Clarias gariepinus (Burchell, 1822), Bagrus docmak (Forsskål, 1775) and Hydrocynus forskahlii (Cuvier, 1819) mostly preyed on fish, whereas Heterotis niloticus (Cuvier, 1829) and Labeobarbus bynni (Forsskål, 1775) consumed detritus and macrophytes. H. niloticus, L. bynni and H. forskahlii were generalist feeders. There was a slight ontogenetic dietary shift observed in some predator fishes. In smaller sized L. bynni (6–20 cm, TL), insects and ostracods were important preys and their contribution differed significantly (p < 0.05). In H. forskahlii, the volumetric contribution of bivalves and detritus differed significantly amongst the different size classes. Generally, resource availability had little effect on the feeding behaviour of most fishes. This implies that fishes in floodplain rivers can forage any available prey without preference and accustom to a general feeding strategy to form biologically insignificant dietary overlap.

Integrated ecosystem impacts of climate change and eutrophication on main Baltic fishery resources

The Baltic Sea is a heavily impacted ecosystem with multiple pressures acting simultaneously. In order to quantify ecosystem impacts of integrated climate change and eutrophication pressures under constant high fishing pressure, and to support decision-making and policies in generating environmental and economic sustainable systems, the Baltic Atlantis holistic and mechanistic ecosystem model was applied. The overall aim was to run scenarios of separate and integrated impacts of climate and riverine nutrient load changes, taking into account the interactions of the full food web in the entire Baltic Sea. This was done to identify which of those two pressures will likely dominate the future of the Baltic Sea ecosystem, and to test effects of different riverine nutrient forcing sources as well as the Baltic Atlantis functions in relation to hydrographic spawning thresholds. By integrating the hydrography, the biology covering all trophic levels of the food web, and multiple pressures, i.e. eutrophication, climate change and fishery, we were able to evaluate relative impacts of 3 climate scenarios and 3 nutrient load scenarios, using two sources of nutrient forcing and predict likely trends in ecosystem effects. With focus on major fish stocks, our model, with its assumptions, indicated that nutrient loads are the main driver of the changes in the ecosystem as long as the hydrographic thresholds for spawning are not reached. If the thresholds are reached for the Baltic cod, climate change impact will become most important. Furthermore, higher nutrient loads resulted in cod decrease, and increase in sprat and herring. This effect is amplified by stronger climate change. Overall, it is of crucial importance for the future of the Baltic Sea fisheries and stocks that potential impacts are considered both separate and integrated in a dynamic ecosystem-based management approach.

A synthesis of the ecosystem responses to the late 20th century cold period in the northern North Atlantic

Following rapid cooling in the 1960s, much of the North Atlantic Ocean was characterized by a cold period during the 1970s and 1980s. This cold period was part of the multidecadal variability in sea surface temperatures known as the Atlantic Multidecadal Oscillation or AMO, which has a period of ∼60–80 years. During this cold period, below average air and sea temperatures predominated, increased ice cover was observed in those northern regions with seasonal sea ice, and evidence was found of reduced Atlantic inflow into the Northeast Atlantic Ocean. The ecological responses included a reduction in primary production and geographic shifts in zooplankton species. Also, there was a general southward expansion of arctic and boreal fish species and a retreat of the temperate species. Major fish stocks such as Atlantic cod off Greenland and Labrador/northern Newfoundland, as well as the Norwegian spring-spawning herring, collapsed commercially. These collapses were partly driven by climate-induced declines in growth rates and recruitment survival, as well as fishing. In contrast, in the more southern range of Atlantic cod, such as the North Sea, the opposite response occurred as the cool conditions led to improved growth rates and higher abundance. Long-term measurements in the English Channel documented the replacement of several warm-water species with more northern cold-water species. Benthic and nearshore species also underwent distributional shifts and changing abundances. Comparisons with the responses to the warm periods suggest that following the cold period of the 1970s and 1980s, the ecosystem in the 1990s and 2000s returned to conditions akin to what they were in the previous warm period of the 1930s–1950s. However, there were some notable exceptions, such as the continued low abundance of Atlantic cod off West Greenland and Labrador/northern Newfoundland.

Assessment of natural mortality coefficients in fish stocks: a review

PDF HTML阅读 XML下载 导出引用 引用提醒 鱼类自然死亡系数评估研究进展 DOI: 作者: 作者单位: 1. 中国水产科学研究院南海水产研究所, 农业部外海渔业开发重点实验室, 广东省渔业生态环境重点实验室, 广东 广州 510300;2. 上海海洋大学 海洋科学学院, 上海 201306 作者简介: 耿平(1993-),男,硕士研究生,从事渔业资源评估研究.E-mail:bsg1030@live.com 通讯作者: 中图分类号: S931 基金项目: 国家自然科学基金项目（31602157）；农业部财政专项“南海北部近海渔业资源调查”项目（2014-2018）；公益性行业（农业）科研专项经费项目（201403008）. Assessment of natural mortality coefficients in fish stocks: a review Author: Affiliation: 1. Key Laboratory of Open-Sea Fishery Development, Ministry of Agriculture;Key Laboratory of Fishery Ecology and Environment, Guangdong Province;South China Sea Fisheries Research Institute, Chinese Academy of Fishery Sciences, Guangzhou 510300, China;2. College of Marine Sciences, Shanghai Ocean University, Shanghai 201306, China Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:自然死亡系数是渔业资源评估中不可或缺的重要参数，其准确度直接决定了资源评估结果的可靠性，进而影响渔业管理策略的制定。本文从生活史参数、标志回捕和年龄结构3个方面列举了国内外自然死亡系数的常用评估方法，讨论了相关方法的优缺点及影响因素，并以犬齿牙鲆（）和中国近海鱼类为例对比分析不同模型的计算结果。在此基础上，着重介绍了Pauly经验公式在中国近海主要经济鱼类自然死亡系数评估中的应用进展及存在问题。根据渔业资源调查和研究数据现状，认为现阶段使用Pauly经验公式评估中国近海经济鱼类自然死亡系数具有积极作用。 Abstract:Natural mortality coefficient () is a key parameter in fisheries stock assessment. Its accuracy directly determines the reliability of assessment results and also influences the establishment of fisheries management. Most mathematical models of fish stock dynamics incorporate , either directly or indirectly. Fishery scientists have explored accurate estimates of for a long time, in order to develop a more precise understanding of fish populations and to establish a more scientific basis for managing fisheries resources and sustainable development. The present study introduces and evaluates the most common models for estimating natural mortality coefficients for fish populations from three aspects, namely life-history parameters, tag-return, and age-structure. The first approach to estimate the instantaneous rate of natural mortality in fish stocks is based on the observation that is strongly correlated with life history parameters, such as maximum observed age, age at reproductive maturity, asymptotic fish length, and growth rate. The Pauly empirical equation, Gislason empirical equation, and Tanaka's maximum observed age's method are among the most commonly used methods for assessing inshore fisheries in China. By classifying tagging data, based on catch per unit effort, size at release, and the probability of tag loss, Chapman, Hampton, and Treble have each constructed their own models, and some scholars have combined these methods to develop a model that is superior to any of the individual models. The assessment results of using tag-return methods would have a high reliability, but the huge costs of investigation, lower credibility of recapture, and prior model assumptions contribute to poor generality. Considering that age is the potentially most important factor affecting estimates of , virtual population analysis (VPA) and cohort analysis (CA) are established using catch-at-age data. These methods could be used to reliably estimate fish stocks with long-term catch data. However, considering the incomplete and inaccurate statues of historical catch data in Chinese coastal fishes, the practicality of the VPA or CA models is relatively low. Meanwhile, taking and some coastal fish stocks as examples, this study compared estimation results through different methods and found that Pauly empirical equation is more reasonable to calculate . Then, this paper introduced the misapplications of Pauly empirical equation in inshore fisheries of China. The main misapplications were equation error, unit error and calculation mistake. According to the limited data and fishery exploitation status, we suggest that Pauly empirical equation has a positive meaning to assess the for major economic fish stocks in China. 参考文献 相似文献 引证文献

Approach to reduce the zoonotic parasite load in fish stocks: When science meets technology

The increasing public awareness on the presence of anisakids in the viscera and mostly the flesh of commercially important fish species provoked the search of technical solutions to reduce the abundance of infective viable larvae at sea. During the last decade, a technological device was tested and improved to check its viability to reduce the presence of parasites in a hot spot epidemiological area with high prevalence on anisakids. The device was monitored under laboratory conditions and at sea in Grand Sole fishing ground. The Technological Device for Avoiding Parasite Discarding at Sea (hereafter TEDEPAD®) is industrial equipment designed to process the viscera are generated on board commercial fishing vessels. This equipment inactivates the zoonotic parasites present in the viscera, especially those of the genus Anisakis (and congeners) affecting humans (anisakidosis and related allergies) and markets, before the offals are returned to the sea. This process would contribute to a substantial reduction of viable infective larvae returning to the water mass, which otherwise would reinfestate the food system if remained untreated. As a consequence, and bearing in mind than a single female of Anisakis spawn about 1.5 million eggs, a minimization of the incidence of infective parasite larvae (firstly in the water mass of the fishing grounds and later on major fish stocks of commercial interest) is expected. The cost-benefit analysis indicates important benefits from different perspectives: the minimization of the dispersion of viable larvae parasites, the reduction of the recruitment of parasites into fish species of commercial interest, the decrease of rejected fishing products, reduction in sanitary expenses to attend parasite-induced pathologies, and increase of the consumer confidence that derives in highest fish purchases. Overall, all these issues will improve the environmental health of the fishing grounds and, in parallel, will provide an important economic positive impact for the fishing sector.

Transform high seas management to build climate resilience in marine seafood supply

AbstractClimate change is projected to redistribute fisheries resources, resulting in tropical regions suffering decreases in seafood production. While sustainably managing marine ecosystems contributes to building climate resilience, these solutions require transformation of ocean governance. Recent studies and international initiatives suggest that conserving high seas biodiversity and fish stocks will have ecological and economic benefits; however, implications for seafood security under climate change have not been examined. Here, we apply global‐scale mechanistic species distribution models to 30 major straddling fish stocks to show that transforming high seas fisheries governance could increase resilience to climate change impacts. By closing the high seas to fishing or cooperatively managing its fisheries, we project that catches in exclusive economic zones (EEZs) would likely increase by around 10% by 2050 relative to 2000 under climate change (representative concentration pathway 4.5 and 8.5), compensating for the expected losses (around −6%) from ‘business‐as‐usual’. Specifically, high seas closure increases the resilience of fish stocks, as indicated by a mean species abundance index, by 30% in EEZs. We suggest that improving high seas fisheries governance would increase the resilience of coastal countries to climate change.

Reconciling stock assessment paradigms to better inform fisheries management

AbstractFor several decades, the fisheries stock assessment paradigms of virtual population analysis (VPA) and statistical catch-at-age (SCA) models have been routinely applied to major fish stocks, and their prevalence often dictated by historical continuity, local experience, and geographical differences in standard practices. Similarly, there is a growing split among models using short and long time-series. In one approach, only the recent time-series, where the data are relatively complete, and the assumptions about stationarity in population and sampling processes are relatively simple, are included. In the other, long time-series include far more historical data, but necessitate the relaxation of many common assumptions regarding stationarity. Unlike scientific paradigms in fields outside of fisheries science where empirical validation can provide a growing body of irrefutable evidence (such as physics), there is no expectation that some “truth” will emerge or that a single best stock assessment modelling approach will ultimately displace the others. The 2013 Pacific halibut SCA stock assessment, with the addition of a VPA-based analysis, is used to illustrate how an ensemble approach can represent a more complete description of the uncertainty in management quantities, relative to selecting just one of these competing model paradigms. We suggest that risk assessment for fisheries management, based on stock assessment models, should seek to avoid binary decisions about which models to include, and instead seek better approaches to incorporate alternative models. The ensemble approach to stock assessment also provides a conceptual link between traditional “best model” analyses and fully developed management strategy evaluation of harvest policy and management procedures.

Iron fertilisation by Asian dust influences North Pacific sardine regime shifts

Forcing factors and mechanisms underlying multidecadal variability in the production of the world’s major fish stocks are one of the great mysteries of the oceans. The Japanese and California sardine are species that exhibit the regime shifts. It is shown in the present work that during two periods of frequent Asian dust events over the last 100years, sardines on opposite sides of the Pacific Ocean only flourished under a dust-active regime. The earlier such regime that peaked in the 1930s was strong, and it brought synchronous changes in the two species that were linked to the frequency of Asian dust events. However, there is an apparent mismatch in the rise and fall of abundance between the two species in the current dust-active regime. The massive increase in Japanese sardine stock in the 1970s was related to high levels of ocean precipitation and strong winter mixing, whereas the stock collapse since 1988 has been attributed to diminished winter mixing. High levels of ocean precipitation in the western North Pacific effectively cause wet deposition of Asian dust and enhance Japanese sardine stock, whereas it reduces dust flux that can be transported to the eastern North Pacific, delaying the increase of California sardine stock. Analysis further indicates that productivity of Japanese sardine stock is jointly controlled by wet deposition of Asian dust and winter mixing, which supplies macronutrients from depth. California sardine productivity is inversely related to precipitation in the western North Pacific and is positively affected by precipitation off western North America. This indicates that Asian dust influx dominates productivity of the species because of iron-limited ocean productivity in the California sardine ranges. The analysis suggests that dust regime shifts influence shifts in sardine productivity regimes and that iron input from Asian dust during trans-Pacific transport is directly responsible. It appears that in addition to enhancing phytoplankton growth and carbon sinks, atmospheric iron deposition can regulate the production of living ocean resources, which is an extension of Martin’s iron hypothesis.

Commercial fish and shellfish in the Barents Sea: Have introduced crab species affected the population trajectories of commercial fish?

The Barents Sea shelf system, particularly the southwestern, western and southern parts, is one of the most productive ocean regions in the world due to the influence of warm Atlantic water. We conducted an analysis of long-term data based on original and published sources focused on the trends in abundance of key commercial species in the Barents Sea. We specifically examined the patterns and characteristics of both invasive species and invasion processes, using the example of two introduced crabs: the red king crab (Paralithodes camtschaticus) and the snow crab (Chionoecetes opilio), which in polar ecosystems may provide an important case study for improving our ability to predict the impact of new invaders. Warm temperature anomalies were observed in the Barents Sea in the 20th century and in the early twenty-first century, with peaks from 2001 to 2007 and in 2012, associated with a pronounced decrease in total ice cover since 1999. Since their introduction, the stock biomass of red king crabs has varied widely. These fluctuations were associated with high levels of illegal fishing of red king crab. The total biomass of commercial snow crabs increased exponentially in the last decade. Since the late 1990s the stock of northern shrimp has varied with an overall rising trend, although landings in more recent years were relatively stable. Cod, haddock, and saithe stocks remained at relatively high levels. Capelin stock size is characterized by large fluctuations that are likely to reflect natural processes. Cross-correlation analysis suggests that neither crab species had negative effects on the stocks of important fish. However, a potential negative impact of snow crab on the northern shrimp population could not be rejected due to their overlapping distribution and predator–prey interactions. The high overall productivity of the Barents Sea in recent years, as evidenced by high abundances of major fish stocks, is more likely associated with warming in the Arctic region, and the introduction of both crab species has had no apparent detrimental effects on fish stocks while resulting in positive economic benefits.

A Review of Genetic Engineering in Current Aquaculture Practises

Fish represent the main food protein eaten worldwide. Farming of fish has been a traditional practice in South East Asia for over 500 years [1], but with the recent collapse of major fish stocks around the globe and the increasing demand for fish, farming of fish species has turned into an intensive practice that is raising important concerns about its sustainability. With recent advances in genetics and marine biotechnology, aquaculture may undergo a further transformation with the addition of genetically modified organisms (GMOs) to farmed stocks. Genetic engineering of fish and shellfish has been under development for decades but until recently this has been restricted to research experiments [2]. However, after 20 years of pressures from aquaculture and biotechnology companies, the US Food and Drug Administration (FDA) is on the verge of approving genetically modified salmon in US markets [3]. This has opened major debates about the potential environmental outcomes and the possibility of approval by the global market. This article discusses the development of aquaculture over recent years with the advance of genetic engineering using salmon, ‘the king of fish’, as a case study.

Overfishing and the replacement of demersal finfish by shellfish: an example from the English Channel.

The worldwide depletion of major fish stocks through intensive industrial fishing is thought to have profoundly altered the trophic structure of marine ecosystems. Here we assess changes in the trophic structure of the English Channel marine ecosystem using a 90-year time-series (1920–2010) of commercial fishery landings. Our analysis was based on estimates of the mean trophic level (mTL) of annual landings and the Fishing-in-Balance index (FiB). Food webs of the Channel ecosystem have been altered, as shown by a significant decline in the mTL of fishery landings whilst increases in the FiB index suggest increased fishing effort and fishery expansion. Large, high trophic level species (e.g. spurdog, cod, ling) have been increasingly replaced by smaller, low trophic level fish (e.g. small spotted catsharks) and invertebrates (e.g. scallops, crabs and lobster). Declining trophic levels in fisheries catches have occurred worldwide, with fish catches progressively being replaced by invertebrates. We argue that a network of fisheries closures would help rebalance the trophic status of the Channel and allow regeneration of marine ecosystems.

Implementing ecosystem-based fisheries management: from single-species to integrated ecosystem assessment and advice for Baltic Sea fish stocks

Abstract Theory behind ecosystem-based management (EBM) and ecosystem-based fisheries management (EBFM) is now well developed. However, the implementation of EBFM exemplified by fisheries management in Europe is still largely based on single-species assessments and ignores the wider ecosystem context and impact. The reason for the lack or slow implementation of EBM and specifically EBFM is a lack of a coherent strategy. Such a strategy is offered by recently developed integrated ecosystem assessments (IEAs), a formal synthesis tool to quantitatively analyse information on relevant natural and socio-economic factors, in relation to specified management objectives. Here, we focus on implementing the IEA approach for Baltic Sea fish stocks. We combine both tactical and strategic management aspects into a single strategy that supports the present Baltic Sea fish stock advice, conducted by the International Council for the Exploration of the Sea (ICES). We first review the state of the art in the development of IEA within the current management framework. We then outline and discuss an approach that integrates fish stock advice and IEAs for the Baltic Sea. We intentionally focus on the central Baltic Sea and its three major fish stocks cod (Gadus morhua), herring (Clupea harengus), and sprat (Sprattus sprattus), but emphasize that our approach may be applied to other parts and stocks of the Baltic, as well as other ocean areas.

Productivity development in Icelandic, Norwegian and Swedish fisheries

This article analyses the Total Factor Productivity (TFP) performance of fisheries in Iceland, Norway and Sweden during the period 1973 to 2003. We measure TFP growth using real gross value added as output and capital input, labour input and a stock input index based on the major fish stocks. In developed neighbouring countries, we expect rapid diffusion of fishing technology innovations contributing to productivity convergence. In addition, innovations in the public regulation and the industrial organization may also have influenced productivity growth during the period. We find that Iceland had the highest annual TFP growth. Accounting for stock changes, it amounts to 3%, while the corresponding figures for Sweden and Norway are 2.8% and 0.8%, respectively. Despite best practice fishing technologies being widely available, we find no evidence of productivity convergence among the three countries.

Fishing industry borrows from natural capital at high shadow interest rates

Fish stocks can be considered as natural capital stocks providing harvestable fish. Fishing at low stock sizes means borrowing from the natural asset. While fishing a particular quantity generates immediate profits and income, an interest rate has to be paid in terms of foregone future fishing income, as the fish stock's reproductive capacity remains low and fishing costs stay high. In this paper we propose to apply the concept of shadow interest rate to quantify the degree of overfishing. It incorporates the relevant biological and economic information and compares across fish stocks. We calculate the shadow interest rates for 13 major European fish stocks and find these rates to range from 10% to more than 200%. The concept of the shadow interest rate can be used to make the economic consequences of overfishing transparent and to evaluate the profitability of short-term catch reductions as investments in natural capital stocks.

Estimating the consumption of Calanus finmarchicus by planktivorous fish in the Norwegian Sea using a fully coupled 3D model system

Energy flow and trophic regulation are often well understood in closed freshwater ecosystems. Such regulation is harder to understand in large marine ecosystems, as they extend over vast areas and are influenced by adjacent marine areas. Fully coupled biophysical models have increased in popularity during recent years, but these models are still in their infancy. Here we present a coupled model system of the Norwegian Sea, including an ocean model, a phytoplankton model and individual-based models of the copepod Calanus finmarchicus and planktivorous fish. The fish migration model is driven by survey observations, but the C. finmarchicus densities also affect the fish migrations. This leads to a realistic predation pressure on zooplankton by fish in time and space. The predation pressure of fish on zooplankton is calculated by modelling individual fish growth using bioenergetics models. We estimated that the major pelagic fish stocks in the Norwegian Sea, herring, mackerel and blue whiting, consumed a total of 82 million tonnes of zooplankton, including 35 million tonnes C. finmarchicus, in 1997. Furthermore, the interspecific competition has the greatest effect on blue whiting consumption, while herring consumption is unaffected by the other fish species in this one-year simulation. We also analysed the spatial distribution of C. finmarchicus in June and August and found the highest densities in the northern Norwegian Sea and around Iceland. The results give us a better understanding of the effect from fish predation on the Norwegian Sea ecosystem, and how it affects the C. finmarchicus stock.

From common to rare: The case of the Mediterranean common dolphin

Although overfishing has been recognized as responsible for the decline of major fish stocks, it has been less easy to demonstrate its indirect and detrimental effects on marine mammals, particularly dolphins. Competition with fisheries for the same food resources has been hypothesized to have led to the decline of several species of dolphins, including the endangered Mediterranean short-beaked common dolphin. Based on an ecosystem model for the Inner Ionian Sea Archipelago, a former hotspot for common dolphins in the Mediterranean Sea, we investigated the effect of increasing fishing effort on common dolphins, its prey and on marine biodiversity and we evaluated the outcomes of different fisheries closures (1 – closure of the purse seine fishery, 2 – closure of purse seine, trawl and beach seine fisheries, 3 – entire area closed to fisheries) ran between the years 2011 and 2030. Our results showed that local fisheries have negatively impacted the marine biodiversity of the ecosystem causing sharp declines of common dolphins and major fish stocks and weakening the robustness of the marine food web. The implementation of fisheries closures would gradually recover fish stocks, while common dolphins would increase more pronouncedly only if the study area was to be closed to all fisheries. As shown in this study, common dolphins have reflected ecosystem changes and degradation over time. Ensuring the survival of dolphin populations is thereby essential to enhance marine ecosystems and ensure sustainable fishing.