Target Fish Species Research Articles

Microplastics in offshore fish from the Agulhas Bank, South Africa

The extent and type of microplastic (MP) contamination in South African open ocean marine resources is unknown. This study aims to report on MP ingestion in seven commercially targeted fish species from the Agulhas Bank, south of South Africa. MPs were found in all seven species sampled (N = 105) (Trachurus capensis, Merluccius capensis, Merluccius paradoxus, Etrumeus whiteheadi, Scomber japonicus, Chelidonichthys capensis and Argyrozona argyrozona). MPs were recorded in 86.67% fish sampled, with abundances ranging from 2.8 to 4.6 items/fish. Most MPs were fibres (95.14%), black (38.11%) and ranged from 1000 to 500 μm (35.55%) in size. There was no difference in microplastic concentration in relation to distance from shore (p > .05). This is the first record of MPs in offshore fish from southern Africa and the results indicate that more research is required to assess the extent of MP contamination in the region.

Current use and management of commercial fish vaccines in Korea

The aquaculture industry in Korea has grown rapidly since the 1960s, and it is a major food source. However, the expansion of aquaculture systems has increased the chances of infectious disease outbreaks, and vaccination plays an important role in commercial fish farming. This is the first comprehensive review of commercial fish vaccines in Korea. It not only provides an overview of commercially available fish vaccines and their associated approval processes and laws, but also some perspectives on research advances regarding fish vaccines in Korea. In Korea, fish vaccines are approved only after their safety and effectiveness have been verified according to the Pharmaceutical Affairs Act, and after approval, each vaccine lot must pass the national evaluation criteria. As of the end of 2019, 29 vaccines were approved for 10 fish pathogens, including both single and combination vaccines containing more than two inactivated pathogens. The approved fish vaccines consist of 2 immersion vaccines, as well as 1 intramuscular and 26 intraperitoneal vaccines, which require syringe injection. All the 29 vaccines are manufactured as formalin-inactivated vaccines; 1 is an adjuvant vaccine and 28 are non-adjuvant vaccines; 25 are bacterial vaccines, 2 are viral vaccines, 1 is a parasite vaccine, and 1 is a parasite and bacterial vaccine. In terms of the target fish species, 27 vaccines are used in the olive flounder (Paralichthys olivaceus), 1 in the starry flounder (Platichthys stellatus), and 1 in the red seabream (Pagrus major), striped beakfish (Oplegnathus fasciatus), and amberjack (Seriola quinqueradiata). This imbalance exists mostly because the olive flounder is the main farmed fish species in Korea. In 2018, 67.71 million vaccine doses were distributed following satisfactory performance in the national evaluation. They were used to vaccinate approximately 80.6% of farmed olive flounders.

A field study in support of the monitoring of priority substances in German freshwater fish: derivation of fillet-to-whole fish conversion factors

BackgroundBioaccumulating contaminants in surface waters are preferably monitored in fish for assessing the related risks to and via the aquatic environment. Consequently, the European Water Framework Directive (WFD) requires a monitoring of certain priority substances such as mercury, polybrominated diphenyl ethers (PBDE), perfluorooctane sulfonic acid and its derivatives (PFOS), hexachlorobenzene (HCB), hexabromocyclododecanes (HBCDD) and polychlorinated dioxins/dioxin-like compounds (dioxins) in freshwater and coastal fish. Tissue levels have to comply with biota environmental quality standards (EQSs) given in Directive 2013/39/EU. EQSs are justified either by risks for human health (assessed on the basis of fillet) or secondary poisoning of wildlife (based on whole fish). To support the practical implementation of the WFD biota monitoring in Germany, comparative investigations of target fish species caught at six sites were performed.ResultsAt each site, at least three fish species listed in a national guidance document were sampled (e.g., chub, roach, bream, perch). Beside biometric data, concentrations of seven priority substances were determined in pooled fillet and carcass samples and whole fish data were calculated. The EQSs for PBDE and mercury were exceeded in nearly all fillet and whole fish samples. PFOS was above the EQS at several sites especially in perch, while HCB exceeded the EQS only at one site (Elbe River). All fillet and whole fish samples complied with the EQSs for dioxins and HBCDD. Based on wet weight concentrations of a homogeneous set of 20 composite sample pairs of 3–5 year-old fish, the following fillet-to-whole fish conversion factors were derived: mercury 0.81, PBDE 5.4, HCB 3.6, PFOS 2.7, dioxins 5.3, and HBCDD 1.8.ConclusionsRecommendations on selection of target fish species, age or tissue given by EU and national guidance documents are practical and feasible. However, further adjustments of the samplings such as the determination of site-specific length–age relationships are required from both ecological and risk assessment perspectives. The derived conversion factors allow the translation of fillet-to-whole fish concentrations (and vice versa), and thus the EQS compliance assessment for the appropriate tissue (fillet for human health, whole fish for wildlife risks) if only one tissue is investigated.

Developing a longline/jig sentinel survey program for an area with limited monitoring and fishing efforts

Areas, such as coastal eastern Gulf of Maine (GOM), perceived to have low density of target fish species and having high density fixed gear, are often subject to low fishing pressure and not well monitored. This can lead to a shortage of information regarding the fine scale dynamics of groundfish populations. Sentinel surveys are commonly developed for such areas with little monitoring and commercial fishing activity as a cost effective way to collect relevant data for monitoring the dynamics of fish stocks. In this study, we outline an approach that utilizes information from other survey programs and pilot study for designing a survey that satisfies both the wish of fishermen participants to contribute their knowledge and experience in determining groundfish abundance and distribution and the statistical rigor required for stock assessments. Through an analysis of spatial and density distribution of groundfish populations based on data from pilot seasons of the sentinel survey and other monitoring programs, we designed a survey that has good spatial and temporal coverage and captures the spatial variability in species composition and size structure of key species. The spatially explicit data collected in the program can contribute to a better understanding of groundfish stock status in the eastern GOM. The approach, although developed for the coastal eastern GOM, is also applicable to other areas with similar issues.

Re‐establishment of fish passage for conserving threatened migratory species of West‐Indian Himalayas

AbstractFish passes are structures (natural or manmade) bypassing barriers (e.g., dams), enabling satisfactory movement of migratory fish species. Reestablishment of fish passage, including facilitating overcoming barriers presented by impoundments or restoration of defunct structures, is attracting interest among scientists and policymakers as a mechanism to enable recovery of target fish species or fish communities. However, it is also important to note that fish passes may also act as ecological traps in some large neotropical rivers. A diversity of multispecies fish passage designs have been implemented in North and South America, Europe, and Australia, with varying efficacy for different species. However, field surveys between 2010 and 2018 supported by a review of published literature (N = 217) using Google Scholar search engine using six key terms reveal that few fish passes have been constructed in dams in the Indian Himalayan region, and their efficacy is largely unproven. Major problems associated with fish pass designs include uneven success across a range of species and largely untested effectiveness at the large scale of many major dams. The objective of this paper is to stress upon the requirement of a new approach to understand the operational drawbacks of different types of fish pass and to take an adaptive approach to both design and operation using field data to improve fish pass efficiency. These measures could contribute significantly to the conservation of threatened migratory fish in the increasingly impounded rivers of the Indian Himalayan region.

Review of fish trap fisheries from tropical and subtropical reefs: Main features, threats and management solutions

Fish traps are extensively used in tropical and subtropical reef fisheries. Despite this, there is a significant lack of extensive and consecutive research concerning the basic aspects of trap fishing. We herein compile the available information from the main coral and rocky reef fish trap fisheries, and compared their main aspects (i.e., mesh size, CPUE, catch composition, ghost fishing, and management) to assess the dynamics of these fisheries and their environmental impact. The analysis revealed that most fish stocks showed declining trends, with only few species under heavy management being capable of withstanding high fishing pressure. In other fisheries, due to fishing down the web, miscellaneous reef fish comprised the bulk of the catch, while the proportion of high-value landed species was insignificant. Gear restrictions remain the most common management method in trap fisheries; however, even the minimum mesh size has not been ubiquitously enforced, while due to great variability of targeted fish species, use of a uniform mesh size is highly unlikely. Other management tools, such as, restrictions in effort, size, and species, temporal and spatial closures were also widely used, but effective only when well enforced and interconnected. Rates of trap loss widely differed as well as the reported rates of ghost fishing mortality. In most cases, incorporation of escape panels resulted in almost complete elimination of ghost fishing. However, further research is required concerning these issues.

Fish assemblages in protected seagrass habitats: Assessing fish abundance and diversity in no-take marine reserves and fished areas

Marine reserves are an important management tool for conserving local biodiversity and protecting fragile ecosystems such as seagrass that provide significant ecological functions and services to people and the marine environment. With humans placing ever-growing pressure on seagrass habitats, marine reserves also provide an important reference from which changes to seagrass and their ecological assemblages may be assessed. After eight years of protection of seagrass beds (Posidonia australis) in no-take marine reserves (Sanctuary Zones) within the Jervis Bay Marine Park (New South Wales, Australia; zoned in 2002), we aimed to assess what changes may have occurred and assess continuing change through time in fish assemblages within these seagrass meadows. Using baited remote underwater videos (BRUVs), we sampled seagrass fish assemblages at three locations in no-take zones and five locations in fished zones three times from 2010 to 2013. Overall, we observed a total of 2615 individuals from 40 fish species drawn from 24 families. We detected no differences in total fish abundance, diversity, or assemblage composition between management zones, although we observed a significant increase in Haletta semifasciata, a locally targeted fish species, in no-take marine reserves compared with fished areas. Fish assemblages in seagrass varied greatly amongst times and locations. Several species varied in relative abundance greatly over months and years, whilst others had consistently greater relative abundances at specific locations. We discuss the potential utility of marine reserves covering seagrass habitats and the value of baseline data from which future changes to seagrass fish populations may be measured.

Meta-analysis of Queensland’s coastal Indigenous fisheries: Examining the archaeological evidence for geographic and temporal patterning

Marine fisheries have been a critical part of Aboriginal and Torres Strait Islander people’s connection to land and sea country in Queensland, Australia for millennia. However, no archaeological studies have examined regional variability in the role of fish within subsistence regimes or the distribution of targeted fish species throughout the Holocene. We utilised a meta-analysis approach to conduct the first comprehensive assessment of Indigenous fisheries along the eastern Queensland coast. Data from 44 archaeological sites were grouped according to marine bioregion to facilitate broad comparison between sites across the study area. These sites were predominantly associated with mid-to-late Holocene occupation, and provided an assemblage of 45,052 recovered fish bones, of which 6606 were identified most commonly to family-level. Results indicate clear geographic patterning in the ubiquity of fish species captured, and for some marine bioregions an increase through time in the range of species targeted. Archaeological data indicate mixed species fisheries, with a complex range of habitats and diverse fish species harvested by people in relative proximity to the sites. These harvesting decisions were mediated by local ecological knowledge, awareness of fish behaviour, and cultural preference for certain species. These outcomes support existing models for the region, which document a shift in subsistence regimes during the mid-to-late Holocene, particularly an increased reliance on marine resources and expansion in diet breadth. Future research needs to address geographic gaps in data availability and implement globally recognised ichthyoarchaeological quantification and identification protocols to comprehensively examine geographic and temporal variability in Queensland’s Holocene Indigenous fisheries, and contribute to regional models of long-term subsistence change.

Ecological drought monitoring through fish habitat-based flow assessment in the Gam river basin of Korea

Abstract Global warming has reinforced irregular hydrologic cycle patterns causing serious changes and threats to the ecosystem. This study targeted the Gam River in South Korea and assessed ecological droughts that could occur in the river ecosystem due to long-term meteorological droughts. To assess ecological droughts, this study (1) focused on a representative fish species in the river, (2) analyzed the required ecological flow in the river to ensure a healthy fish habitat, (3) developed a fish habitat-based ecological drought index (EcoDI_FH) calculated by analyzing the river’s ecological flows and flow regimes with double thresholds to monitor how ecological droughts proceed in extreme low flow, and (4) evaluated the applicability of the EcoDI_FH. The following are the salient points of this study: (1) The dominant species, Zacco platypus, and endangered species, Squalidus gracilis majimae were chosen as the target fish species in the study area. To determine the ecological flow considering its habitat the optimal ecological flow was estimated using the River2D hydrodynamic model. (2) Due to the construction of Buhang Dam in the Gam river basin, the pattern of river flow has changed significantly. (3) By applying the developed ecological drought index, the ecological flow was used as the first threshold for determining drought occurrence. Droughts were divided into four stages, and the extreme low flow calculated using indicators of hydrologic alteration was set as a second threshold or a serious stage. (4) For the past drought periods that took place in the Gam river basin, the drought state was analyzed before and after the construction of the dam. In the drought period that occurred before Buhang Dam was built, an ecological drought occurred in the serious stage during the drought period. During the droughts that occurred after the dam was built, the serious drought stage was alleviated quite substantially. It is expected that the results of this study will be utilized as one of the main tools for establishing countermeasures and adaptation strategies against ecological droughts in the river ecosystem.

The value artificial lake ecosystems provide to recreational anglers: Implications for management of biodiversity and outdoor recreation

Small lakes largely outnumber large lakes among the world's lentic ecosystems. Despite being common landscape elements, however, little is known about the value small lakes provide to recreationists. This paper presents results of an economic valuation study concerned with small gravel pits in Lower Saxony, Germany. Gravel pits are artificially created lake ecosystems that, particularly in Europe, are regularly used and managed by privately organized recreational anglers in an angling club context. A stated choice experiment provided insights into anglers' preferences for the abundance of target fish species, biodiversity of taxa other than fishes in the lakes as well as in the lake surroundings, and about the use of gravel pits by other recreationists for walking, swimming or boating. Latent class analysis identified five segments that varied in preferences. For the majority of anglers, the value of angling at gravel pit lakes was improved by an increase in the abundance of predatory fishes. Additionally, the presence of aquatic and terrestrial endangered species at the lakes increased the value of the ecosystems as perceived by the majority of anglers. By contrast, the presence of other recreational uses reduced the value of angling, with swimming being considered the most disturbing, while the degree of shoreline development had the least impact on the recorded choices. The results suggest that managing the gravel pit lakes for high biodiversity and the presence of desired game fish species maximizes the value for anglers. However, also two smaller segments with anglers revealing lexicographic preferences were identified. These anglers expressed either strong preferences against swimming in the lakes or strongly preferred the opportunity to use boats. Lake management may address the preference heterogeneity and the aversion against other recreational uses, such as swimming, by spatial zoning.

Traditional Ecological Knowledge Supports Ecosystem-Based Management in Disturbed Coastal Marine Social-Ecological Systems

A growing number of studies suggest a participatory ecosystem approach to support decision-making towards resilience and sustainability in social-ecological systems. Social-ecological resilience (SER) principles and practices are recommended to manage natural crises. However, it is necessary to broaden our understanding of SER on human-induced disturbances driven by economic development projects. In this paper we present the social-ecological system of Araca Bay (Brazil), a small-scale fishery community that has experienced successive disturbances due to development projects since the 1930s. There was a lack of studies about the impacts of development projects in this bay. As part of a major project that aimed to build an ecosystem-based management plan for Araca Bay through a participatory planning process, we focused on investigating fishers’ traditional ecological knowledge (TEK) to understand Araca Bay’s small-scale fisheries social-ecological system. The objectives were to: (1) investigate fishers’ TEK regarding management practices and linked social mechanisms, human-induced disturbances and their consequences for the social-ecological system, ecosystem goods and services, and future threats; and (2) provide information based on TEK to the participatory planning process and analyze its contribution to Araca Bay’s ecosystem-based management plan. Combined methods were used during 3 years of intense research-action (2014-2017): in-depth ethno-oceanographic interviews with expert fishers; monitoring Araca Bay participatory meetings; and participant observation. Genuine local practices and social mechanisms from traditional culture were recorded, as well as TEK about 57 target fish species and methods to protect habitats and natural resources. Fishers also reported ecosystem disturbances and recovery processes. TEK was codified through SWOT analysis to assist the participatory planning process. Ecosystem services and threats based on TEK were brought to the participatory process, acknowledged by the participants, and incorporated into the management plan. TEK analysis proved to be an important methodology to provide historical environmental data regarding the impacts of development projects and support planning in disturbed ecosystems. In order to support coastal marine ecosystem-based management strategies towards SER and sustainability, researchers and practitioners should consider traditional territories in planning, recognize local practices and social mechanisms, and consider TEK on ecosystem goods and services and on historical human-induced disturbances.

Spatial and Temporal Variability in a Large‐Reservoir Fish Assessment and Application of a Stratified Random Sampling Approach

AbstractSampling is often standardized with regard to time and space to monitor population characteristics. Effective sampling of large reservoirs can be complicated by the inherit bias of habitat variability along the reservoir gradient. Our objective was to assess spatial and seasonal distribution patterns of target and nontarget fish species in a large reservoir to identify potential sources of bias. A multitude of fish community and habitat characteristics were measured during seasonal (spring, summer, and fall) gill‐net surveys in 2015 and 2016 at Lake McConaughy, Nebraska. Spatial assessments along the longitudinal gradient (up‐reservoir to down‐reservoir) and between opposing shorelines were made for fish metrics from the seven most common species, and associations between species‐specific relative abundance and habitat data were examined. Spatial differences in relative abundance and size structure occurred for nearly all species, with the greatest spatial variability occurring between the upper and lower reservoir zones, but few strong correlations were observed between species‐specific relative abundances and habitat data. Seasonal differences occurred in relative abundance and size structure for most species, and size structure was lowest in the fall for most species. To reduce the impact of spatial variability, we determined the minimum required sampling effort to achieve precise estimates of mean catch per net‐night using two resampling strategies, with 16 or fewer gill‐net sets required for five of seven species and 14 or fewer required if a stratified random approach is utilized. This research quantifies the extent of spatial and temporal variability in standardized sampling on a large reservoir and provides novel insight for managers of similar systems considering a stratified random approach to reduce sampling effort while maintaining desired levels of precision.

The dynamics of target fishes resources in coral reef fisheries at coastal area of Ternate Island

Abstract. As one of the coastal ecosystem, coral reef ecosystem is a magnificent marine ecosystem, where their species richness and composition play an important role for the ability of coral reef ecosystem to respond to the fishing activity and other stressors, where fishing has impacted the fish community, target or non-target reef fish species. The dynamic of reef fish resources, especially the target species, become one of the aspects that must be considered in the management and utilization of the fisheries resources in the coral reef ecosystem and their surrounding area. The purpose of the study was to analyze the dynamics of the target fish in the coral reef fishing activity at the coastal area of Ternate Island, from the growth, mortality and exploitation ratio aspect. The research was conduct from April to August 2018 in the coastal area of Ternate Island. The data sampling was growth parameters data through length and weight measurement. Total sample measure along the research time was 6245 sample (consist of seven family and 11 species). The result shows that the target fish have asymptotic length (L∞) range from 263.16–483.16 mm, with growth coefficient (K) ranging from 0.61–0.92 per year. The theoretic age at length 0 (t0) ranges from minus 0.0825–0.1669 year (equal to 30-61 day). The fishing mortality rate (F) is lower than the natural mortality rate (M), which resulting the exploitation rate (E) for the target fish mostly under 50%, which indicated that the utilization of the reef fishes in the coastal area of Ternate Island is still under-exploited.Keywords: Exploitation rate, Growth parameters, Length-weight relationship, Mortality rate, Stock assessment

Comparison of diver operated stereo-video and visual census to assess targeted fish species in Mediterranean marine protected areas

Underwater visual census (UVC) is currently the primary tool used to survey shallow water fish assemblages in the Mediterranean Sea. However, the rapid development of digital technologies, such as underwater video cameras and photogrammetric techniques, are providing new sampling opportunities in marine ecosystems. In this study we compare two non-destructive sampling methods, UVC and diver operated stereo-video systems (stereo-DOVs), to characterize assemblages of targeted fish species. Surveys were undertaken in three zones with different levels of protection from fishing (MR, marine reserve; PP, partially protected reserve; NP, non-protected area) in the Montgrí, Medes Islands and Baix Ter Natural Park (NW Mediterranean Sea). There were no statistically significant differences between stereo-DOVs and UVC surveys in terms of species richness, relative abundance and biomass of targeted fish species across the three protection levels. Both methodologies found statistically significant differences between areas closed to fishing (MR) and areas where fishing is regulated (PP) or allowed (NP), whereby higher fish biomass, density, species richness and larger sizes were found in MR surveys. Length estimates of fish were comparable between methods albeit with some species-specific differences in the size-distribution, and a tendency for UVC to overestimate the size of larger fishes. Our results suggest that stereo-DOVs provide an equivalent and complementary technique to UVC to survey assemblages of targeted fish species. In addition to structural data (e.g., biomass, abundance, and length) recorded by UVC, stereo-DOVs provide a permanent visual record of a fish community and enable additional factors such as fish behaviour, precise distance and length, and benthic composition to be quantified. Stereo-DOVs may, therefore, facilitate the continuity and expansion of long-term monitoring programs of fish assemblages in the Mediterranean Sea.

Study of key technologies for fishways in the plateaus of western China

Determining how to restore fish migration routes blocked by large dams is the subject of great debate. Fishways are effective engineering measures restoring fish migration routes. However, most fishways in China do not carry out their target functions. Additionally, no studies have investigated key fishway technologies in the plateaus of Western China. In this research, the relationship between fish behavior and hydrodynamics was assessed by conducting quantitative descriptions of flow speed, turbulence, and other hydraulic indicators. First, target fish species of the plateaus of Western China were determined; then, swimming capabilities and migration characteristics of target fish were assessed. Then the preliminary hydraulic conditions for fishway projects in the plateaus of Western China were proposed. Finally, on-site migration experiments in the fishways were conducted to validate the preliminary hydraulic conditions.

Mesoscale eddies release pelagic sharks from thermal constraints to foraging in the ocean twilight zone

Mesoscale eddies are critical components of the ocean's "internal weather" system. Mixing and stirring by eddies exerts significant control on biogeochemical fluxes in the open ocean, and eddies may trap distinctive plankton communities that remain coherent for months and can be transported hundreds to thousands of kilometers. Debate regarding how and why predators use fronts and eddies, for example as a migratory cue, enhanced forage opportunities, or preferred thermal habitat, has been ongoing since the 1950s. The influence of eddies on the behavior of large pelagic fishes, however, remains largely unexplored. Here, we reconstruct movements of a pelagic predator, the blue shark (Prionace glauca), in the Gulf Stream region using electronic tags, earth-observing satellites, and data-assimilating ocean forecasting models. Based on >2,000 tracking days and nearly 500,000 high-resolution time series measurements collected by 15 instrumented individuals, we show that blue sharks seek out the interiors of anticyclonic eddies where they dive deep while foraging. Our observations counter the existing paradigm that anticyclonic eddies are unproductive ocean "deserts" and suggest anomalously warm temperatures in these features connect surface-oriented predators to the most abundant fish community on the planet in the mesopelagic. These results also shed light on the ecosystem services provided by mesopelagic prey. Careful consideration will be needed before biomass extraction from the ocean twilight zone to avoid interrupting a key link between planktonic production and top predators. Moreover, robust associations between targeted fish species and oceanographic features increase the prospects for effective dynamic ocean management.

Differential responses by two closely related native fishes to restoration actions

Globally, river degradation has decimated freshwater fish populations. To help reverse this trend in a southeastern Australia river, we used multiple restoration actions, including reintroduction of instream woody habitat, riparian revegetation, removal of a weir hindering fish movement, fencing out livestock, and controlling riparian weeds. We monitored the responses of native fish at the segment scale (20 km) and reach scale (0.3 km) over 7 years to assess the effectiveness of the different restoration strategies. Two closely related species, Murray cod Maccullochella peeli and trout cod Maccullochella macquariensis, increased at the restored segment compared with the control segment. However, inherent differences between river segments and low sample size hampered assessment of the mechanisms responsible for segment‐scale changes in fish abundance. In contrast, at the reach scale, only M. peeli abundance significantly increased in reaches supplemented with wood. These differential responses by 2 closely related fish species likely reflect species‐specific responses to increased habitat availability and enhanced longitudinal connectivity when the weir improved passage around a fishway. Changes in M. peeli abundance in segments supplemented with and without wood suggest an increase in carrying capacity and not simply a redistribution of individuals within the segment, facilitated the observed expansion. Our findings confirm the need to consider individual fish species' habitat preferences carefully when designing restoration interventions. Further, species‐specific responses to restoration actions provide waterway managers with precise strategies to target fish species for recovery and the potential to predict fish outcomes based on ecological preferences.

Spatio‐temporal variability of suspended sediments in rivers and ecological implications of reservoir flushing operations

AbstractHigh suspended sediment concentrations during reservoir flushing are known to be harmful to biota in downstream river stretches. Therefore, it is common practice to set legal concentration limits for upstream reservoir management operations such as flushings or controlled drawdowns. However, as shown by measurements, there is a considerable spatio‐temporal variability of suspended sediment concentrations both in the longitudinal profile of rivers and in river cross‐sections. To consider this variability in management operations, SED‐FISH—a three‐dimensional modelling approach—was developed to study this variability in a wider context by upscaling cross‐sectional measurements of suspended sediments to high‐resolution three‐dimensional information on the reach scale in an alpine river. The resulting patterns of suspended sediment concentrations were integrated over their respective time of occurrence for various scenarios in order to calculate severity of harmful impacts for target fish species. The modelling results identified refugial habitats with reduced negative impacts in near‐bank zones even for relatively high suspended sediment concentrations in the centre of the river. Moreover, a substantially larger variability of both suspended sediment concentrations and associated harmful impacts was found for a winding riverbed morphology as compared with a straight reach. Both these findings and the developed modelling tool could assist in establishing individual case‐based concentration limits for reservoir management operations in the future and should also be taken into account when planning river regulation or restoration measures.

Small-scale fish buyers' trade networks reveal diverse actor types and differential adaptive capacities

The importance of understanding how social-ecological interdependencies deriving from global trade influence sustainability has been argued for decades. Even if substantial progress has been made, a research gap remains regarding how the adaptability of small-scale fish buyers, whose daily operations have implications for the livelihood of more than 100 million people, are affected by networks of trade relationships. Adaptability is here defined as fish buyers´ abilities to adapt using their relationships with others. We elaborate how these capacities relate to the precise patterns in which a fish buyer is entangled with other fish buyers, with the fishers, and with the targeted fish species, by combining a multilevel social-ecological network model with empirical data from a small-scale fishery in Mexico. Further, we also identify types of fish buyers distinguishable by how they operate, and how they are embedded in the trading network. Our results suggest that adaptability differs substantially amongst these types, thus implying that fish buyers' abilities to respond to changes are unevenly distributed. This study demonstrates the need for a more profound understanding of the consequences of the different ways in which fish buyers operate commercially, and how these operations are affected by patterns of social and social-ecological interdependencies.

A numerical model for river habitat restoration: a case study of the Chin-sha River in China

<p>Currently, the ecosystem is being damaged in many rivers and subsequently the fish species living there are also facing decline or even extinction. This situation urges to model the habitat and to design suitable restoration strategies in order to increase the capabilities of ecological modeling. In this paper, we proposed a numerical model to assess the ecosystem habitat situation and investigated the impacts of two ecological restorations strategies for the target fish species. The model includes a hydrodynamic model, a habitat model and habitat restoration schemes. The hydrodynamic model simulated the flow properties while sediments in the riverbed were also surveyed. Based on these parameters and fish preference curves, the habitat suitability indices were calculated. In order to analyze the river habitat quality, the weighted usable areas and overall suitability index were also calculated and the effects of the restoration strategies on selected fish species (Freshwater Reeves shad - Tenualosa reevesii) in the Chin-sha River were evaluated. The two ecological restoration strategies: addition of side-channel (scheme I) and river bank reconstruction (scheme II) enhanced the Freshwater Reeves shad habitat suitability level, with the high suitability index proportion increasing from 19.5% to 33.1% for scheme I and to 36.1% for scheme II. Based on the modelling results, we concluded that our numerical model could potentially provide suitable scenarios for successful fish habitat restoration.</p>