Critically examining the knowledge base required to mechanistically project climate impacts: A case study of Europe's fish and shellfish

An amalgam of empirical data from laboratory and field studies is needed to build robust, theoretical models of climate impacts that can provide science‐based advice for sustainable management of fish and shellfish resources. Using a semi‐systematic literature review, Gap Analysis and multilevel meta‐analysis, we assessed the status of empirical knowledge on the direct effects of climate change on 37 high‐value species targeted by European fisheries and aquaculture sectors operating in marine and freshwater regions. Knowledge on potential climate change‐related drivers (single or combined) on several responses (vital rates) across four categories (exploitation sector, region, life stage, species), was considerably unbalanced as well as biased, including a low number of studies (a) examining the interaction of abiotic factors, (b) offering opportunities to assess local adaptation, (c) targeting lower‐value species. The meta‐analysis revealed that projected warming would increase mean growth rates in fish and mollusks and significantly elevate metabolic rates in fish. Decreased levels of dissolved oxygen depressed rates of growth and metabolism across coherent species groups (e.g., small pelagics, etc.) while expected declines in pH reduced growth in most species groups and increased mortality in bivalves. The meta‐analytical results were influenced by the study design and moderators (e.g., life stage, season). Although meta‐analytic tools have become increasingly popular, when performed on the limited available data, these analyses cannot grasp relevant population effects, even in species with a long history of study. We recommend actions to overcome these shortcomings and improve mechanistic (cause‐and‐effect) projections of climate impacts on fish and shellfish.     

Qualitative and quantitative effects of reintroduced beavers on stream fish

Reintroduction of beaver (Castor spp) may facilitate rehabilitation of freshwater habitats providing a cost‐effective sustainable means of improving ecological conditions. Despite extensive research, debate and consultation, a general consensus on the impact of beaver on fishes has proven elusive because of variability in biological response. This paper provides a systematic review of the impacts of beaver dams on fishes and fish habitat based on a meta‐analysis of the literature and expert opinion. Research is regionally biased to North America (88%). The most frequently cited benefits of beaver dams were increased habitat heterogeneity, rearing and overwintering habitat and flow refuge, and invertebrate production. Impeded fish movement because of dams, siltation of spawning habitat and low oxygen levels in ponds were the most often cited negative impacts. Benefits (184) were cited more frequently than costs (119). Impacts were spatially and temporally variable and differed with species. The majority of 49 North American and European experts considered beaver to have an overall positive impact on fish populations, through their influence on abundance and productivity. Perceived negative effects related to the movement of aquatic organisms in tributary streams, including upstream and downstream migrating salmonids, and the availability of suitable spawning habitat.     

Mangroves enhance local fisheries catches: a global meta‐analysis

Mangroves are among the most productive ecosystems in tropical and subtropical regions. Historically, mangroves are assumed to support artisanal fisheries, leading decision‐makers to protect mangroves based on this premise. However, this relationship remains unclear, despite positive correlations obtained in different geographical regions. Here, we provide the first meta‐analysis of the mangroves–fisheries linkage at a global level. After conducting a systematic review, 23 publications containing 51 studies estimating the mangrove–fishery linkage were obtained. A random effect model was used to estimate the effect size (Pearson's correlation coefficient) of each individual study as well as the overall effect size. We found strong evidence for the mangrove–fishery linkage with an overall effect size of r = 0.72 (95% CI: 0.61–0.81), and substantial heterogeneity was observed (Q = 143.88, df = 50, P < 0.01). The countries where the studies were carried out were the only significant moderator (Q_M = 26.07, P < 0.01), while fisheries types (i.e. crab, fish, shellfish, prawn and total) and global regions were not good predictors of the relationship. Our results show that mangrove area is a good predictor of fishery catches overall, confirming the importance of conserving such habitats.     

A meta‐analysis of the effects of dietary marine oil replacement with vegetable oils on growth,feed conversion and muscle fatty acid composition of fish species

The effects of the replacement of marine oils (MO) with canola oil (CO), linseed oil (LO) and soybean oil (SO) on growth, feed conversion and major muscle fatty acid (FA) classes were quantified using a meta‐analysis of published results. There was an absence of relationships between levels of MO replaced and effect sizes for all outcomes. High heterogeneity when combining effects sizes according to fixed effects models imposed the stratification of values in MO replacement categories and the use of random effect models to calculate the summary statistics. Limited values at 50% and 60% hampered clear tendencies when compared to 100% MO replacement. A medium mean effect size (?0.3773, 95% confidence intervals = ?0.7325 to ?0.0222, n = 22) for growth was obtained when replacing all MO with CO, whereas LO (?1.5609, 95% confidence intervals = ?2.3584 to ?0.7633, n = 19) and SO (?1.0589, 95% confidence intervals = ?1.7197 to ?0.3980, n = 22) resulted in high negative effect sizes. This study quantified the extent of differences in production parameters caused by dietary MO replacement with VO and could serve as reference for future experimental studies.     

Giants' shoulders 15 years later: lessons,challenges and guidelines in fisheries meta‐analysis

Meta‐analysis has been an integral tool for fisheries researchers since the late 1990s. However, there remain few guidelines for the design, implementation or interpretation of meta‐analyses in the field of fisheries. Here, we provide the necessary background for readers, authors and reviewers, including a brief history of the use of meta‐analysis in fisheries, an overview of common model types and distinctions, and examples of different goals that can be achieved using meta‐analysis. We outline the primary challenges in implementing meta‐analyses, including difficulties in discriminating between alternative hypotheses that can explain the data with equal plausibility, the importance of validating results using multiple lines of evidence, the trade‐off between complexity and sample size and problems associated with the use of model output. For each of these challenges, we also provide suggestions, such as the use of propensity scores for dealing with selection bias and the use of covariates to control for confounding effects. These challenges are then illustrated with examples from diverse subfields of fisheries, including (i) the analysis of the stock–recruit relationship, (ii) fisheries management, rebuilding and population viability, (iii) habitat‐specific vital rates, (iv) life‐history theory and (v) the evaluation of marine reserves. We conclude with our reasons for believing that meta‐analysis will continue to grow in importance for these and many other research goals in fisheries science and argue that standards of practice are therefore essential.     

Response of benthic fauna to experimental bottom fishing: A global meta‐analysis

Bottom‐contact fishing gears are globally the most widespread anthropogenic sources of direct disturbance to the seabed and associated biota. Managing these fishing disturbances requires quantification of gear impacts on biota and the rate of recovery following disturbance. We undertook a systematic review and meta‐analysis of 122 experiments on the effects‐of‐bottom fishing to quantify the removal of benthos in the path of the fishing gear and to estimate rates of recovery following disturbance. A gear pass reduced benthic invertebrate abundance by 26% and species richness by 19%. The effect was strongly gear‐specific, with gears that penetrate deeper into the sediment having a significantly larger impact than those that penetrate less. Sediment composition (% mud and presence of biogenic habitat) and the history of fishing disturbance prior to an experimental fishing event were also important predictors of depletion, with communities in areas that were not previously fished, predominantly muddy or biogenic habitats being more strongly affected by fishing. Sessile and low mobility biota with longer life‐spans such as sponges, soft corals and bivalves took much longer to recover after fishing (>3 year) than mobile biota with shorter life‐spans such as polychaetes and malacostracans (<1 year). This meta‐analysis provides insights into the dynamics of recovery. Our estimates of depletion along with estimates of recovery rates and large‐scale, high‐resolution maps of fishing frequency and habitat will support more rigorous assessment of the environmental impacts of bottom‐contact gears, thus supporting better informed choices in trade‐offs between environmental impacts and fish production.     

Ecosystem effects of invertebrate fisheries

Since the 1950s, invertebrate fisheries catches have rapidly expanded globally to more than 10 million tonnes annually, with twice as many target species, and are now significant contributors to global seafood provision, export, trade and local livelihoods. Invertebrates play important and diverse functional roles in marine ecosystems, yet the ecosystem effects of their exploitation are poorly understood. Using 12 ecosystem models distributed worldwide, we analysed the trade‐offs of various invertebrate fisheries and their ecosystem effects as well as ecological indicators. Although less recognized for their contributions to marine food webs, our results show that the magnitude of trophic impacts of invertebrates on other species of commercial and conservation interest is comparable with those of forage fish. Generally, cephalopods showed the strongest ecosystem effects and were characterized by a strong top‐down predatory role. Lobster, and to a lesser extent, crabs, shrimp and prawns, also showed strong ecosystem effects, but at lower trophic levels. Benthic invertebrates, including epifauna and infauna, also showed considerable ecosystem effects, but with strong bottom‐up characteristics. In contrast, urchins, bivalves, and gastropods showed generally lower ecosystem effects in our simulations. Invertebrates also strongly contributed to benthic–pelagic coupling, with exploitation of benthic invertebrates impacting pelagic fishes and vice versa. Finally, on average, invertebrates produced maximum sustainable yield at lower levels of depletion (~45%) than forage fish (~65%), highlighting the need for management targets that avoid negative consequences for target species and marine ecosystems as a whole.     

湛江港区底泥悬浮物对2种海洋动物的致死效应研究

为评价湛江沿海涉海工程建设过程中引起的悬浮物质对附近海区海洋动物的影响,研究了底泥液相及不同浓度底泥悬浮物对川纹笛鲷和尖吻鲈的致死效应。试验结果表明,在8d的试验时间里,底泥水相对川纹笛鲷和尖吻鲈均无致死效应。底泥悬浮物浓度≤160mg/L时,川纹笛鲷和尖吻鲈的死亡率均处于较低水平。底泥悬浮物浓度≥2560 mg/L时,川纹笛鲷死亡率达75%,尖吻鲈死亡率达70%。通过概率单位法计算得出川纹笛鲷的8d半致死浓度为716.14 mg/L,尖吻鲈的8d半致死浓度为1105.096 mg/L。     

Potential effects of global warming on northern European freshwater fish and fisheries

Abstract Global warming is expected to result in considerable changes in northern European freshwater fish populations, fisheries and aquaculture. Shifts towards cyprinid and percid dominance in fish assemblages are expected, together with a decrease and collapse of salmonid and other coldwater fish populations. Most of the evident changes will occur in shallow lakes, where no thermal stratification occurs. The potential ranges of some fish species will shift northwards but pronounced changes will occur in the relative abundance of individual fish species. Total fish production will increase but because of changed composition of fish communities the commercial and recreational value of catches will decrease. Salmonid aquaculture productivity will increase provided that fish farmers adapt to new circumstances and cold, oxygenated water is available in larger quantities during summer.     

Examining the knowledge base and status of commercially exploited marine species with the RAM Legacy Stock Assessment Database

Meta‐analyses of stock assessments can provide novel insight into marine population dynamics and the status of fished species, but the world’s main stock assessment database (the Myers Stock‐Recruitment Database) is now outdated. To facilitate new analyses, we developed a new database, the RAM Legacy Stock Assessment Database, for commercially exploited marine fishes and invertebrates. Time series of total biomass, spawner biomass, recruits, fishing mortality and catch/landings form the core of the database. Assessments were assembled from 21 national and international management agencies for a total of 331 stocks (295 fish stocks representing 46 families and 36 invertebrate stocks representing 12 families), including nine of the world’s 10 largest fisheries. Stock assessments were available from 27 large marine ecosystems, the Caspian Sea and four High Seas regions, and include the Atlantic, Pacific, Indian, Arctic and Antarctic Oceans. Most assessments came from the USA, Europe, Canada, New Zealand and Australia. Assessed marine stocks represent a small proportion of harvested fish taxa (16%), and an even smaller proportion of marine fish biodiversity (1%), but provide high‐quality data for intensively studied stocks. The database provides new insight into the status of exploited populations: 58% of stocks with reference points (n = 214) were estimated to be below the biomass resulting in maximum sustainable yield (B_MSY) and 30% had exploitation levels above the exploitation rate resulting in maximum sustainable yield (U_MSY). We anticipate that the database will facilitate new research in population dynamics and fishery management, and we encourage further data contributions from stock assessment scientists.     

A decision support system for setting legal minimum lengths of fish

Abstract  The use of legal minimum lengths is one of the oldest forms of regulation in fisheries management. Management objectives using minimum legal lengths are varied, often conflicting and generally poorly communicated. This paper introduces a decision support system that will assist fisheries managers in determining optimal legal minimum lengths. The system uses multi-criteria decision analysis to enable the integration of objective scientific and biological information into a system that assesses the success of any potential length limit in achieving each of the management objectives. The system can also document trade-offs between options that achieve management objectives and short-term socio-economic impacts. The decision support system is demonstrated using 13 commercially and recreationally important coastal species from New South Wales, Australia.     

Probarbus jullieni and Probarbus labeamajor: the management and conservation of two of the largest fish species in the Mekong River in southern Laos

• 1. Probarbus jullieni and Probarbus labeamajor are two of the largest carps in the Mekong River Basin, each reaching a maximum weight of about 70 kg. P. jullieni is listed in Appendix 1 of the Convention on the International Trade in Endangered Species, and both are listed on the IUCN Red List of Threatened Species, the first as ‘endangered’ and the second as ‘data deficient’.
• 2. Six years of quantitative monitoring of a large‐meshed gill net fishery for Probarbus just below the Khone Falls in Khong district, Champasak province, in southern Laos shows that 78% of the overall catch is comprised of Probarbus, with P. jullieni making up 65% of landings.
• 3. Over the 6‐year period catches of Probarbus declined significantly. However, catch‐per‐unit effort statistics do not indicate that the fishery is in decline, although fishers are convinced that real stock reductions are a large part of the reason for catch declines and decreases in fishing effort.
• 4. A number of ecological and social factors are affecting the number and quality of gill nets in use, the length of fishing seasons, and gill net efficiency, making it difficult to compare catch‐per‐unit effort between years.
• 5. There has been a shift from using large‐meshed gill nets for catching Probarbus to targeting smaller species using gill nets with smaller mesh‐sizes. This is an example of the ‘fishing down’ of a Mekong fish community, in which large long‐lived species are the first to be affected by heavy fishing pressure.

Copyright © 2006 John Wiley & Sons, Ltd.     

A comparison of freshwater mussel assemblages along a land‐use gradient in Minnesota

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A tale of two seas: a meta‐analysis of crustacean stocks in the NE Atlantic and the Mediterranean Sea

Meta‐analysis of marine biological resources can elucidate general trends and patterns to inform scientists and improve management. Crustacean stocks are indispensable for European and global fisheries; however, studies of their aggregate development have been rare and confined to smaller spatial and temporal scales compared to fish stocks. Here, we study the aggregate development of 63 NE Atlantic and Mediterranean crustacean stocks of six species (Nephrops norvegicus, Pandalus borealis, Parapenaeus longirostris, Aristeus antennatus, Aristaeomorpha foliacea and Squilla mantis) in 1990–2013 using biomass index data from official stock assessments. We implemented a dynamic factor analysis (DFA) to identify common underlying trends in biomass indices and investigate the correlation with the North Atlantic Oscillation (NAO) index. The analysis revealed increasing and decreasing trends in the northern and southern NE Atlantic, respectively, and stable or slowly increasing trends in the Mediterranean, which were not related to NAO. A separate meta‐analysis of the fishing mortality (F) and biomass (B) of 39 analytically assessed crustacean stocks was also carried out to explore their development relative to MSY. NE Atlantic crustacean stocks have been exploited on average close to F_MSY and remained well above B_MSY in 1995–2013, while Mediterranean stocks have been exploited 2–4 times above F_MSY in 2002–2012. Aggregate trends of European crustacean stocks are somewhat opposite to trends of fish stocks, suggesting possible cascading effects. This study highlights the two‐speed fisheries management performance in the northern and southern European seas, despite most stocks being managed in the context of the European Union's Common Fisheries Policy.     

基于GAM的长江口鱼类资源时空分布及影响因素

根据2006至2017年长江口及其邻近海域鱼类资源调查,运用广义加性模型研究长江口鱼类资源密度与环境因子之间的关系,并对2017年鱼类资源密度的时空分布进行预测。结果显示,春夏秋冬四个季节最佳GAM偏差解释率分别为69.6%、55.9%、51.4%和47.4%,交叉验证回归线斜率的平均效应为0.62～0.88。盐度、水温和溶解氧是影响长江口鱼类资源密度的主要环境影响因子且在不同季节对鱼类资源密度有不同的影响机制。总体上,在春、夏、秋季,盐度与鱼类资源密度之间存在正向相关性;在夏、秋、冬季,水温对鱼类资源密度有显著影响,在秋季与鱼类资源密度之间存在正向相关性;在春、秋、冬季,溶解氧对鱼类资源密度有显著影响,在冬季与鱼类资源密度之间存在正向线性相关。研究表明,2017年夏季鱼类资源密度较高;在长江口南支的自然延伸水域存在鱼类资源密度的相对低值,在崇明岛向海自然延伸方向水域存在鱼类资源密度的相对高值。后续研究将对长江口鱼类资源进行不同生态类型区分,以期更加准确地掌握影响各生态类型鱼类时空分布的环境因素及其时空分布信息。     

Ontogeny matters: Climate variability and effects on fish distribution in the eastern Bering Sea

Analyses of climate effects often ignore differences in life history for individual species. We analyzed a 34‐year time series of eastern Bering Sea fish surveys to evaluate changes in distribution by length and between cold and warm shelf‐wide average water temperatures for 20 species over inhabited depth, temperature, and location. All species showed evidence of ontogenetic migration. Differences in distribution between years with warm and years with cold shelf‐wide water temperatures varied among species and within species at different lengths. For species where shelf‐wide temperature effects were detected, the mid‐sized fish were most active in changing spatial distribution. For aquatic organisms ontogenetic migration occurs because life history stages have different environmental requirements. This study illustrates the need to consider species responses to climate change over different life history stages, and that studies on ecosystem responses should take ontogenetic differences into consideration when assessing impacts.     

A meta‐analysis of haddock size‐selection data

Many jurisdictions have introduced management regimes prohibiting or limiting discarding, and a key objective of the European Union Common Fisheries Policy is the gradual elimination of discards. One way of reducing the catch of unwanted fish is to use more size‐selective gears. Gear‐based management options can best be explored using models that predict size selection across a wide range of variables related to gear design. Such a model is developed for haddock (Melanogrammus aeglefinus) through a meta‐analysis of 21 trials of codend selection and 19 trials of the combined selection of the codend and a square mesh panel. Individual‐haul estimates of the 50% retention length (l₅₀) and the selection range (SR) are related to a set of explanatory variables through a structural model that describes the dual process of panel and codend selection. Codend l₅₀ and SR are positively related to codend mesh size and negatively related to the codend twine diameter. Codend l₅₀ is also negatively related to the number of open meshes around the codend circumference. Panel l₅₀ increases with panel mesh size. The panel contributes more to gear selection as it is moved closer to the codline. The panel is most effective between November and January and least between May and July, periods which broadly coincide with peak and poor haddock condition. The results are illustrated for a typical trawler targeting haddock in the Scottish whitefish sector, and the utility of the model for gear design and legislation is discussed.     

The relative influence of temperature and size‐structure on fish distribution shifts: A case‐study on Walleye pollock in the Bering Sea

Research has estimated associations between water temperature and the spatial distribution of marine fishes based upon correlations between temperature and the centroid of fish distribution (centre of gravity, COG). Analysts have then projected future water temperatures to forecast shifts in COG, but often neglected to demonstrate that temperature explains a substantial portion of historical distribution shifts. We argue that estimating the proportion of observed distributional shifts that can be attributed to temperature vs. other factors is a critical first step in forecasting future changes. We illustrate this approach using Gadus chalcogrammus (Walleye pollock) in the Eastern Bering Sea, and use a vector‐autoregressive spatiotemporal model to attribute variation in COG from 1982 to 2015 to three factors: local or regional changes in surface and bottom temperature (“temperature effects”), fluctuations in size‐structure that cause COG to be skewed towards juvenile or adult habitats (“size‐structured effects”) or otherwise unexplained spatiotemporal variation in distribution (“unexplained effects”). We find that the majority of variation in COG (including the north‐west trend since 1982) is largely unexplained by temperature or size‐structured effects. Temperature alone generates a small portion of primarily north–south variation in COG, while size‐structured effects generate a small portion of east–west variation. We therefore conclude that projections of future distribution based on temperature alone are likely to miss a substantial portion of both the interannual variation and interdecadal trends in COG for this species. More generally, we suggest that decomposing variation in COG into multiple causal factors is a vital first step for projecting likely impacts of temperature change.     

A meta‐analysis of steady undulatory swimming

The mechanics underlying undulatory swimming are of great general interest, both to biologists and to engineers. Over the years, more data of the kinematics of undulatory swimming have been reported. At present, an integrative analysis is needed to determine which general relations hold between kinematic variables. We here perform such an analysis by means of a meta‐analysis. Using data of 27 species, we examine the relationships between the swimming speed and several kinematic variables, namely frequency and amplitude of the tail beat, length and speed of the propulsive wave, length of the body, the Reynolds number, the Strouhal number and the slip ratio U/V (between the forward swimming speed U and the rearward speed V of the propulsive wave). We present results in absolute units (cm) and in units relative to the length of the organism (total length, TL). Our data show several kinematic relations: the strongest influence on swimming speed is the speed of the propulsive wave, and the other variables (amplitude and frequency of the tail beat, length of the propulsive wave and length of the body) influence it more weakly (but significantly). In several cases, results differ when variables are expressed in different units (absolute or relative to length). Our data reveal significant differences between kinematics of swimming of shallow‐bodied and deep‐bodied individuals, with shallow‐bodied ones swimming with a shorter propulsive wave length and a higher Strouhal number. The slip ratio U/V and the Strouhal number appear to depend on the Reynolds number in a non‐linear manner.