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Loss of Biodiversity in Aquatic Ecosystems: Evidence from Fish Faunas
Abstract
Fishes are appropriate indicators of trends in aquatic biodiversity because their enormous variety reflects a wide range of environmental conditions. Fish also have a major impact on the distribution and abundance of other organisms in waters they inhabit. Examination of trends in freshwater fish faunas from different parts of the world indicate that most faunas are in serious decline and in need of immediate protection. Species most likely to be threatened with immediate extinction are either specialized for life in large rivers or are endemic species with very small distributions. We conservatively estimate that 20 percent of the freshwater fish species of the world (ca. 1800 species) are already extinct or in serious decline. Evidence for serious declines in marine fishes is limited largely to estuarine fishes, reflecting their dependence on freshwater inflows, or to fishes in inland seas. The proximate causes of fish species’ decline can be divided into five broad categories: (1) competition for water, (2) habitat alteration, (3) pollution, (4) introduction of exotic species, and (5) commercial exploitation. Although one or two principal causes of decline can be identified for each species, the decline is typically the result of multiple, cumulative, long-term effects. Ways to protect aquatic biodiversity include the implementation of landscape-level management strategies, the creation of aquatic preserves, and the restoration of degraded aquatic habitats. Without rapid adoption of such measures we are likely to experience an accelerated rate of extinctions in aquatic environments as human populations continue to expand.
... A decreasing trend in crab fishery production was prominent from the surveyed area within four years which was very similar to the report of Moyle and Leidy (1992) and Chakraborty (2009;2010). ...
JIFSI is now online, please visit http://epubs.icar.org.in/ejournal/index.php/JIFSI http://ifsi.res.in NAAS RATING 5.71
... The extinction rate of all fish was reported to be 112 times higher than what would be expected naturally (Dias et al. 2017) and more recently, Sayer et al. (2025) reported that one quarter of freshwater fauna is threatened with extinction. Anthropogenic pressures that are affecting both marine (Doney et al. 2012;Hoegh-Guldberg and Bruno 2010) and freshwater fishes (Moyle and Leidy 1992;Su et al. 2021) are becoming so serious that current efforts may be insufficient to avert biodiversity loss in the coming decades (Dudgeon and Strayer 2024). Fish are particularly affected by climate change (Nye et al. 2009;Rose 2005), industrial (Tsikliras et al. 2015) and recreational (Hyder et al. 2020) fishery overexploitation, water pollution (Malik et al. 2020) and changes in hydrological conditions (Anufriieva and Shadrin 2018; Wrona et al. 2016). ...
Effective monitoring strategies are key for aquatic species conservation, but traditional methods often require significant resources, especially in large aquatic systems. The emergence of quantitative environmental DNA (eDNA) is a promising alternative. Yet, few studies have evaluated the possibility of quantifying Atlantic salmon abundance with eDNA when individuals are at low abundance and occur in large river systems. In this study, we tested the efficacy of eDNA to monitor and quantify daily variation in smolt counts during their downstream migration in a large river system with low abundance of smolts. During the 2021 and 2022 downstream migrations, trap nets were used to conduct a daily census of smolts in the Romaine and Puyjalon rivers (Québec, Canada) while eDNA samples were collected daily over a transect perpendicular to the riverbank. Using quantitative real‐time qPCR, we showed that discharge‐corrected eDNA concentrations were positively correlated with daily smolt counts for both years. In addition, we found that controlling for temperature and precipitation improved model transferability between years, showing the importance of considering environmental correlates when using eDNA for abundance quantification. Finally, smolt counts were correlated with eDNA concentrations on the same day, but not with eDNA concentrations 1 or 2 days prior, highlighting the capacity of the model to track daily fluctuations in smolt abundance. Our results underscore the potential of using eDNA to monitor Atlantic salmon in large river systems with low smolt abundance when the river hydrology and environmental conditions are documented.
... Elevated nitrogen and phosphorus levels from Acacia litter deposition can harm aquatic ecosystems, reducing biodiversity and productivity by encouraging nutrient accumulation (Chislock et al., 2013;Forrester et al., 2010). These changes negatively affect stream biodiversity and aquatic life, such as fish populations, further emphasizing the need to understand and manage the impacts of Acacia invasions (Moyle & Leidy, 1992). ...
Acacia invasion has shown a negative impact on the water resources of forest streams. Therefore, studies need to be conducted demonstrating the importance of managing invasive species to preserve stream and forest ecosystems. This study investigates the effects of Acacia invasion on the water quality of Kerangas forest streams in Brunei. Water samples were collected from an Acacia-invaded (IN) stream and a non-invaded (NIN) stream during the dry season at three locations along each stream. Water properties, including pH, conductivity, salinity, total dissolved solids (TDS), phosphate, nitrate, ammonia, and nitrite, were analyzed using in situ and laboratory methods. The results showed that Acacia invasion significantly increased pH (from 4.01 to 5.68), nitrate (by 256%), and phosphate (by 250%) levels, while reducing conductivity (by 208%) and salinity (by 20%) compared to non-invaded streams. These findings suggest that Acacia invasion alters water chemistry, potentially posing risks to aquatic ecosystems. Effective management strategies, such as controlling Acacia spread and restoring native vegetation, are essential to mitigate these impacts and preserve forest water resources.
... The freshwater habitats are discrete, and fishes are contained within particular geographic bounds, leading to the differentiation of many independent populations with individual stock characters developed due to isolation (Maitland 1995). This makes the freshwater fishes more vulnerable to environmental stresses and contributes to population depletion upon exploitation (Moyle and Leidy 1992). Different techniques have been used for identifying populations, which include traditional morphology, truss images, molecular markers, otoliths, fatty-acid profile and several other methods (Ramya et al. 2021;Sajina et al. 2015;Shanmughan et al. 2024). ...
Hypselobarbus curmuca is an endemic fish species of Family Cyprinidae found in rivers and reservoirs of the Western Ghats, India. An interdisciplinary study was conducted to assess the population genetic structuring of the species with the help of conventional morphometric, image‐based truss network and genomic data of a nonprotein encoding mitochondrial DNA region (partial D‐loop −494 bp) ( n = 106). Fishes were collected from five rivers of the Western Ghats, namely, Kali, Sharavathi and Chalakudy (west‐flowing) and Ghod and Tungabhadra (east‐flowing) ( n = 294). Multivariate analysis of body measurements and truss distances revealed very weak separation among populations. The D‐loop sequence analysis showed that genetically distinct populations of fishes inhabit the studied rivers. Principal component analysis (PCA) and linear discriminant analysis (LDA) could not completely distinguish morphologically distinct populations. D‐loop sequence analysis indicated 13 haplotypes with low nucleotide diversity and 15 polymorphic sites, with location‐specific haplotypes. An overall haplotype diversity of 0.80 and nucleotide diversity of 0.00849 were found. The haplotype network and maximum likelihood phylogenetic tree showed three clusters with two most probable ancestors. Analysis of molecular variance (AMOVA) showed a high value (0.898) of the fixation index (F ST ) among the populations ( p > 0.05). Neutrality test and mismatch distribution results indicated that the populations are currently subjected to selection. Application of an integrated approach to characterise the populations of H. curmuca in the wild supports the hypothesis of geographical barriers as major drivers of population genetic differentiation. Different riverine environments have not selected for morphological differences during the evolutionary process in the recent past and showed weak separation of populations. These findings can be utilised while designing conservation strategies for the species in the rivers of the Western Ghats, as the species faces threats due to exploitation in capture fisheries and trade in aquaculture.
... Freshwater fishes stand out as one of the most endangered groups of organisms in the world (Moyle and Leidy, 1992;Dudgeon et al., 2006). Understanding the life history characteristics of species is a fundamental step in evaluating their conservation status and planning for their management. ...
... Fish are an excellent gauge of the biodiversity of aquatic ecosystems due to the vast variety of species found in a wide array of environmental settings (Moyle & Leidy, 1992). Numerous fish species from various aquatic habitats such as riverine, lagoonal, estuarine, and inshore or near-shore and offshore areas were present in the Godavaya sample (Table 5 and Figures 25-26), highlighting the diversity in the local aquatic ecosystems exploited by early HGF groups. ...
Archaeological evidence suggests that middle Holocene hunter-gatherer-fisher (HGF) populations set up camps on coastal shell ridges of Sri Lanka. From the middle to late Holocene, coastal areas were subjected to several localized episodes of marine transgression and regression due to sea level oscillation. During highstands the Godavaya hill in southeastern Sri Lanka was a coastal headland jutting into the Indian Ocean between two submerged coastal embayments. We present an analysis of data collected from the rescue excavation conducted in 2014 at the Godavaya mid-Holocene coastal HGF camp site, including supporting information from surveys conducted on the surrounding coastal landscape. Through studying the stratigraphy of the profile walls of the gravel pits adjacent to the Godavaya hill, we summarize the geological process associated with site formation, contextualizing the prehistoric cultural phases. The analysis of the lithic and faunal remains recovered from the Godavaya midden refuse, provide insights to middle Holocene coastal adaptations that suggest the existence of multiple sub-ecosystems abundant in aquatic resources. This abundance may have been a key pull-factor that attracted HGF groups to aggregate along the shorelines during the sea-level highstands allowing a relatively higher density of occupation, as evidenced by numerous encampments along former bay beaches. Based on the presence of previously excavated human burials at Godavaya hill, similar to the burials found at interior shell ridge habitations, and support from ethnographic analogy, we propose that inhumation of the dead may have created an ancestral link to the locality, forming a sense of territorial right and ownership
... Human health benefits also accrue from aquatic ecosystems through experiencing nature and biodiversity [74]. Fish and aquatic resources supply food, provide recreational opportunities, play an important role in maintaining aquatic food webs [75], and can act as indicators of ecosystem health [76]. However, native freshwater biodiversity has been reduced [67][68][69] because beneficial goods and services from freshwater ecosystems are adversely affected by anthropogenic impacts, e.g., [59,[77][78][79]. ...
A common problem for interdisciplinary sustainability research is that scientists trained in different disciplines are often not rowing their boat effectively in the same direction. Sustainability tools can aid the implementation of this team-melding process. Here, our purpose is to illustrate our Multi-step Integrated graphical and structured discussion eXercise (MIX) tool that transforms diverse disciplinary experts into an interdisciplinary team. We use a visual puzzle-solving approach based on the blind men and the elephant metaphor (BMEM) because this story illustrates the shortcomings of siloed viewpoints and the need to integrate multiple perspectives. Our six-step MIX tool provides step-specific objectives, group activities, discussion questions, and learning outcomes. Activities promote experiential learning for team problem solving. The step-specific structured discussions are designed to get each individual to change their focus from their own discipline (i.e., an elephant trunk, tail, leg, or other isolated pieces of the whole animal) to the team’s interdisciplinary goal (i.e., the whole elephant or the entire multi-faceted problem). In our example proof of concept, we show that a narrow focus on only economic yield (trunk), ecological conservation (legs), or human values (tail) misrepresents the biologically involved sustainability problem (elephant) and blocks innovative solutions.
This study documents the presence of congaturi halfbeak Hyporhamphus limbatus (Valenciennes, 1847), belonging to Hemiramphidae family, for the first time in the Wainganga River of Maharashtra State, India. Three specimens were collected from the river near Kardha village in Bhandara district, on November 10th, 2022. The collected specimens ranged from 221.31 mm to 243.95 mm in length and 279.62 to 314.23 g in weight. 20 morphometric and 6 meristic traits were examined using standard keys. The presence of the congaturi halfbeak along the Wainganga River signifies an extension of its geographical distribution. This publication provides essential insights into H. limbatus occurrence and briefly describes the collected specimens in the Wainganga River, Maharashtra.
Tidal wetland restoration is integral to achieving the Delta coequal goals. Deeply subsided islands limit the potential for tidal wetland restoration. Floating peats may offer an opportunity to create tidal habitat in the subsided western and central Delta. We conducted a mesocosm experiment to assess the feasibility of floating peat blocks, and the potential food-web benefits, biomass production, carbon sequestration, methane emissions, and water-quality effects. We evaluated the effect of varying water residence time and initial peat-block density. The peat blocks floated during the entire experiment, and accreted biomass at rates consistent with those reported for Delta non-tidal managed wetlands. Peat blocks placed in mesocosms with 45% open water expanded horizontally about 21% per year. We estimated average vertical accretion rates of 5.5 to 8.6 cm yr – 1 for all the mesocosms. Vertical and horizontal expansion increase floating peat-block stability. We measured a 3-fold zooplankton population increase during the first year after deployment, relative to the Mokelumne River, which was the mesocosm’s water source. Measured and modeled methane emissions were lower than those reported in Delta non-tidal managed wetlands. Aqueous methane concentrations and methane fluxes were significantly lower for the shorter water-residence-time of about 5 days compared to longer residence times of about 11 days. Elevated dissolved oxygen (DO) concentrations generally corresponded with low methane concentrations. Our estimated net ecosystem carbon balance of – 820 +/– 137 g C m – 2 yr – 1 indicates that the floating wetlands are potentially greater carbon sinks than Delta non-tidal wetlands. Nitrogen data indicated consumption by wetland plants, and denitrification and dissimilatory nitrate reduction in the mesocosms. Our preliminary results point to potential ecosystem benefits of floating peats on a larger scale.
Man's activities have had profound, and usually negative, influences on freshwater fishes from the smallest streams to the largest rivers. Some negative effects are due to contaminants, while others are associated with changes in watershed hydrology, habitat modifications, and alteration of energy sources upon which the aquatic biota depends. Regrettably, past efforts to evaluate effects of man's activities on fishes have attempted to use water quality as a surrogate for more comprehensive biotic assessment. A more refined biotic assessment program is required for effective protection of freshwater fish resources. An assessment system proposed here uses a series of fish community attributes related to species composition and ecological structure to evaluate the quality of an aquatic biota. In preliminary trials this system accurately reflected the status of fish communities and the environment supporting them.
This report synthesizes extant literature detailing the ecology of bottomland hardwood swamps in the Southeast. The geographic scope focuses the report to the hardwoods occupying the floodplains of the rivers whose drainages originate in the Appalachian Mountains/Piedmont and Coastal Plain (NC, SC, GA, and FL). The origin and dynamics of the floodplains are described and related to hydrology and physiographic provinces. The biogeochemistry and interactions between the riverine and floodplain environments are discussed in conjunction with floodplain biology. Plant and animal community structure and ecological processes (productivity) are detailed and organized by ecological zones. The final chapter discusses the ecological value of the floodplain ecosystems and the nature of their relationships to adjacent uplands, downstream coastal estuaries and the atmosphere.
Peak annulus formation occurs in March and April, followed by the period of maximum growth. Scale patterns illustrate a variable growing season. Maximum growth in length is in the first 3 yr of life; after that males begin to grow faster than females. Females mature at 3 or 4 yr (352-484 mm), and males mature at 2 or 3 yr (299-445 mm). Both ovum size and fecundity are a function of fish size. Distribution patterns vary on a seasonal basis, with maximum activity during late fall and winter. Management objectives are presented and recommendations are discussed. -from Sport Fishery Abstracts