Local Fish Research Articles

The role of the environment and connectivity with large rivers and streams on local fish diversity of tropical headwater streams

The role of the environment and connectivity with large rivers and streams on local fish diversity of tropical headwater streams

The analysis of chlorophyll-a distribution in fishing areas of Aceh Waters

The distribution and abundance of fish are strongly influenced by several oceanographic parameters, one of which is chlorophyll-a. Chlorophyll-a is one of the oceanographic parameters that play an important role in primary productivity in the sea. The distribution of chlorophyll-a contained in phytoplankton can be used as a measure of fertility in water. With advances in geographic information systems or remote sensing, the distribution of chlorophyll-a can be used to estimate fish catchment areas. This study aims to look at the distribution of chlorophyll-a in Aceh waters both spatially and temporally to predict fishing locations. This study used satellite imagery combined with a Geographic Information System (GIS) to detect chlorophyll-a’s distribution. The results of satellite image processing show that the average monthly value of chlorophyll-a in Aceh waters ranges from 2.71 – 23.54 mg/m3, areas with high chlorophyll-a are generally located in the western waters of Aceh to the southwestern waters of Aceh, while areas with The lowest chlorophyll-a is generally in areas far from the coast (towards the open sea) with a range of 0.04 – 0.5 mg/m3 where the lowest average occurs in the east monsoon. However, in general, the potential locations for fishing grounds are more in the waters west of Aceh than in the waters north of Aceh, Aceh waters.Keywords:Chlorophyll-aSatellite imageFishing areaGeographic information SystemAceh Waters

Regional dynamic co-management for sustainable fisheries and ecosystem conservation: a pilot analysis in the Catalan Sea

The complexity of coastal fisheries, which often involve many gears with cross-impacts on various species and life stages, requires a management system that is able to integrate these multiple interactions in order to gradually achieve sustainability. In this paper, we argue that regional co-management can appropriately address the complex interactions between fisheries, including those with other potentially conflicting human activities. Our results, notably obtained through a questionnaire to local fishers’ representatives mainly on bottom trawl fisheries in the Catalan Sea region, show, however, that improved mutual understanding through effective communication and long-term collaboration between stakeholders, and in particular between fishers and scientists, is essential to ensure the successful implementation of fisheries co-management. In addition to balancing the voices of the many stakeholders, co-management needs to be further improved by developing multi-species, multi-gear and multi-use approaches to the oceans. This improvement could in turn support the effectiveness of co-decisions, as they would be based on the recognised administrative structure of co-management committees and sound scientific guidance that addresses both ecosystem protection and sustainable fisheries profitability. Dynamic management over time and space, using real-time essential fish habitat from operational oceanography, can help to make the co-management process more robust by improving collaboration between stakeholders and the effectiveness of measures in a changing environment. The decision-making, social and ecological components are described as integral and dependent parts of the co-management system, with priority given to mutual understanding between stakeholders. This integrated co-management framework is flexible enough to take into account regional complexity, but also national legislation and the EU Common Fisheries Policy, which all promote sustainable use of the oceans and protection of the ecosystem.

‘Where there is fish, is where I put my head’: Challenges of mobile fishers in Elmina fishing community in Ghana

Small‐scale fisheries are crucial for improving livelihoods by providing fisher employment, and food security. As part of their work, fishers frequently move to different fishing communities to catch and trade in fish. This paper analyses the living circumstances of artisanal fishers and discusses their mobility patterns, lodging arrangements, and the difficulties they encounter as they carry out their work. This paper is based on a study that involved 385 artisanal fishers in the fishing community of Elmina in the Komenda Edina Equafo Abirem (KEEA) Municipality in the Central Region of Ghana. The results show that there are not many suitable places to stay for fishers when they travel from home to other fishing locations, and the few places that do offer affordable lodging also lack toilets, bathrooms and drinkable water. The paper also reflects on the gendered dynamics of these and related issues of insecurity for women in this case study. District authorities whose economies are heavily dependent on fishing ought to collaborate with private housing developers and the state to build affordable lodging facilities with standard household amenities like water, toilets and baths in fishing destinations to address the housing issues faced by fishers while travelling.

Elasmobranch Diversity at Reunion Island (Western Indian Ocean) and Catches by Recreational Fishers and a Shark Control Program

Elasmobranchs are declining worldwide due to overfishing. In developing countries and island states in tropical regions, small-scale and recreational fisheries can significantly impact the dynamics of neritic species. We investigated elasmobranch diversity at Reunion Island, a marine biodiversity hotspot in the Western Indian Ocean. Combining information from the literature, catches from the local shark control program, results from a survey of local recreational fishing, and through barcoding of some specimens, we updated the list of elasmobranchs to 65 species. However, uncertainties remain about the actual presence of some species, such as the three sawfish species. Results highlight the disappearance of most coral reef-associated species, as already suspected. Results also suggest that local populations of scalloped hammerhead shark (Sphyrna lewini) and bottlenose wedgefish (Rhynchobatus australiae) seem healthy, in contrast with their decline in the region. For some species, such as bull sharks (Carcharhinus leucas) and scalloped hammerhead sharks, Reunion Island is a site of reproduction, and as such, the species are exploited at both juvenile and adult stages, which likely increases their vulnerability. In the context of global elasmobranch decline, it is urgent to clarify the conservation status and evaluate the degree of isolation of local populations to identify research and conservation priorities.

An advanced Bangladeshi local fish classification system based on the combination of deep learning and the internet of things (IoT)

Fish classification leads to the automated machine-based fish separation system. In terms of classification and real-time data monitoring, deep learning and the Internet of Things (IoT) each provides an efficient solution. This paper focuses on the development of an embedded system based on the principles of Deep Learning and IoT. The proposed methodology is classified into interconnected parts. The first part describes the working principles of DL with along the dataset building, model analysis and overall system architecture. A new dataset from eight different Bangladeshi fish species. In the process of DL, First, two sets of datasets have been created namely, setup-1(S1) containing original images and setup-2(S2) containing Unsharp masked photos. Then, seven conventional ImageNet pertained state-of-the-art deep learning models on both benchmarking setups: InceptionV3, Xception, DenseNet121, DenseNet169, DenseNet201, InceptionResNetV2, and ResNet152V2. In the process of IoT, the architectural design of a smart contained has been deployed with the aid of several kinds of sensors and microcontrollers. This research has found satisfactory results with the DL models and IoT-based components. The best benchmark accuracy for setup-1 was 96% for all of the DenseNet121, DenseNet169, and DenseNet201 architecture, and for setup-2, it was 96% for the Xception model. Finally, we have constructed a hybrid (CNN + Convolutional LSTM) model, for which the accuracy was 97%, outperforming all of the abovementioned state-of-the-art methods. Besides, the research has performed some experiments with the IoT-based Solution. Though the proposed solution has exhibited some drawbacks, but it can be practicable in real-time solutions.

Market demand of conventional and non-conventional fish species and price comparison between BFDC landing center and two popular fish markets, the Baharchora and Borobazar, in Cox’s Bazar, Bangladesh

The study of conventional (common commercial fish species which is consumed by people in Bangladesh like Seabass,Ribbon fish, Hilsha, Bombay ducketc.) and non-conventional (fish species which is consumed by people in Bangladesh like Milk shark, Stingrayetc.) fish species at BFDC landing center was conducted to know the current condition of fish, their market demand, prices and price difference between BFDC landing center and two popular fish market Baharchora and Borobazar. There were about 32 varietiesof conventional fish species and most common were Seabass,Ribbon fish, Hilsha,Bombay duck, Mackerel, Silver pomfret, Red snapper, etc. The average price for most demandable fish were Hilsha (TK. 600-1000 kg), Silver pomfret(TK. 550-900 kg), Seabass (TK.500- 650 kg),Bombay duck(TK. 100 kg), Ribbon fish (TK. 300 kg) which varied with size and season. There were about 20 species of non- conventional fish includingMilk shark, Stingray,Long Tung Sole,Mud spiny lobster, Mud crab etc. observed. Milk sharkand Dog shark was common at the landing center. Their average size and weight were 1-2 feet and 1-3 kg which were sold for TK. 120-140 kg. The regular price of Stingray was TK.180-220 kg at the landing center with average weight of 2-8 kg. Normally marketing channel of both fish was maintained by middle men. A large number of fish from the landing center was sold to them by auction. The landing center is the common place from where local fish seller collects fish and sell by for around 15-25% of the profit. Usually, unsold raw fishes were preserved in the freezer and rests were sold to dry fish processors mainly in Nazirartek. The study shows a variation of conventional and non-conventional fish species, their price, and market demand in Cox’s Bazar region.

Measuring Detection Efficiency of High-Residency Acoustic Signals for Estimating Probability of Fish–Turbine Encounter in a Fast-Flowing Tidal Passage

Semidiurnal tidal currents can exceed 5 ms−1 in Minas Passage, Bay of Fundy, where a tidal energy demonstration area has been designated to generate electricity using marine hydrokinetic turbines. The risk of harmful fish–turbine interaction cannot be dismissed for either migratory or local fish populations. Individuals belonging to several fish populations were acoustically tagged and monitored by using acoustic receivers moored within the Minas Passage. Detection efficiency ρ is required as the first step to estimate the probability of fish–turbine encounter. Moored Innovasea HR2 receivers and high-residency (HR) tags were used to obtain detection efficiency ρ as a function of range and current speed, for near-seafloor signal paths within the tidal energy development area. Strong tidal currents moved moorings, so HR tag signals and their reflections from the sea surface were used to measure ranges from tags to receivers. HR2 self-signals that reflected off the sea surface showed which moorings were displaced to lower and higher levels on the seafloor. Some of the range testing paths had anomalously low ρ, which might be attributed to variable bathymetry blocking the line-of-sight signal path. Clear and blocked signal paths accord with mooring levels. The application of ρ is demonstrated for the calculation of abundance, effective detection range, and detection-positive intervals. High-residency signals were better detected than pulse position modulation (PPM) signals. Providing that the presently obtained ρ applies to tagged fish that swim higher in the water column, there is a reasonable prospect that probability of fish–turbine encounter can be estimated by monitoring fish that carry HR tags.

Twenty years of monitoring reveal overfishing of bony fish stocks in the coastal national park Banc d’Arguin, in Mauritania

Abstract Along Africa’s western coast, many local communities rely on the ocean for their livelihood. Over the last decades, introductions of new fishing techniques along with globalizing trade have strongly changed local fishing practices. The Parc National du Banc d’Arguin (PNBA) in Mauritania had for centuries been subjected to an artisanal, low‐impact, fishery. This fishing was exclusively oriented towards migratory bony fish species, mullet (Mugil cephalus) and meagre (Argyrosomus regius). Since the 1980s, these species have been replaced by illegal catches of internationally traded elasmobranchs (sharks and rays) and by non‐migratory and relict species (resident) such as tilapias (Sarotherodon melanotheron) and catfishes (Arius sp.). To date, most monitoring and management efforts have been dedicated to evaluating changes in elasmobranch populations and less focus has been on bony fish species. Data from a fishery monitoring programme are used to analyse the trends in effort, catch and catch per unit of effort of bony fish species by fitting non‐parametric generalized additive models to capture changes in the fish community over the last 20 years. Mullet and meagre became overfished early on, and the contribution of resident species (tilapias and catfishes) increased in the catches. Together with a pattern of increased effort on the traditionally targeted species, such a change in the catch could reflect a change in the fish community. These results call for the implementation of sustainable fishing practices within PNBA. We propose the need to implement closures of fisheries during the species’ breeding periods as well as the use of biological reference points such as the size at first capture and maximum sustainable yield targets for resident species.

Feasibility Analysis of Koi Fish Cultivation with the Use of Rice Fields as Cultivation Sites

Indonesia's biodiversity is very diverse, especially ornamental fish, both seawater and fresh water ornamental fish. Commodities of freshwater ornamental fish cultivated in Indonesia are not only local ornamental fish but imported freshwater ornamental fish such as Koi (Cyrpinus carpio) have also been cultivated in several regions of Indonesia. Kediri is a very potential area, especially in the field of ornamental fish cultivation. The Koi fish cultivation center in Kediri is not inferior to the cultivation in the Blitar area which is already famous for Koi fish cultivation. The traditional pond pattern using rice fields as a place for Koi fish cultivation has proven that with makeshift facilities the people of Pranggang Village are able to help their economy. These advantages make this commodity have business prospects that can be developed through cultivation activities. so it is necessary to do a business feasibility analysis to develop a koi fish farming business in the future. Retrieval of data used in this study is the method of observation, interviews and documentation. while for the analysis using qualitative methods, where the researcher as the key instrument, data collection techniques were carried out by means of triangulation (combined). Qualitative method analysis carried out in this study includes business management, production inputs, production processes, outputs, marketing and business development plans.

Differences in Recreational Fishers’ Motivations for Utilising Two Estuarine Fisheries

Effective fisheries management requires an understanding of human dimensions. This study elicited the salient motivations for recreational blue swimmer crab and black bream fishing in Western Australia and whether these views differed depending on the fishing location and/or the characteristics of the fisher. Crab fishers were strongly consumption-orientated and aimed to “catch big crabs” and “catch enough crabs to eat”. Furthermore, 91% consumed their catch, with only 2% practicing catch-and-release fishing. In contrast, 81% of black bream fishers did so for the sport/challenge, with the strongest motivation being to catch a bream considerably above legal size and with food only selected by 15% of respondents; most fishers released caught fish. The marked differences between the fisheries for the two species, which co-occur in the same estuaries, are likely driven by the accessible nature of the crab fishery, ease of catching crabs, the low cost of fishing equipment, and their taste. Fishing for black bream, however, requires more expensive equipment, patience, and a greater skill level. Fishers considered crabbing to be as important as other fishing and outdoor activities, whereas bream fishers considered bream fishing considerably more important, reflecting the trophy nature of this fishery.

Importance of coastal vegetated habitats for tropical marine fishes in the Red Sea

Marine vegetated habitats such as seagrass, mangroves, and macroalgae are common along tropical coastlines globally and provide habitats for a diversity of fishes, including juvenile fish and species found on coral reefs. Understanding the use of these habitats by different fish species and life stages is fundamental to spatial planning, fisheries management, and conservation. While previous studies have focused on the habitat potential of seagrass, macroalgae, or mangroves for coral reef fish independently, it is important to consider their combined roles, as tropical seascapes are often mosaics of such habitats. In this study, we evaluated habitat associations across life stages for fish species in coral reefs, seagrasses, macroalgae, and mangroves in Saudi Arabia’s central Red Sea. Through in situ visual surveys, we documented 36% of local coral reef fish species in one or more vegetated habitats, with the fraction of coral reef species utilizing macroalgae or seagrass much greater than that of mangroves (29%, 18%, and 6%, respectively). Mangroves hosted mainly juvenile fish (83% of observed population) and macroalgae hosted the largest proportion of herbivores (39% of observed population), suggesting that each environment offers different combinations of resources (food and shelter), and a mix of these habitats could support biological connectivity across a seascape. Species targeted by local fisheries made up 37% of the species documented in vegetated habitats. The use of multiple habitat types by juvenile and commercially important fishes in the Red Sea underscores the need for a holistic approach to habitat protection.Graphical abstract

Paired passive acoustic and gillnet sampling reveal the utility of bioacoustics for monitoring fish populations in a turbid estuary

Abstract Estuaries worldwide provide critical habitat to many ecologically and socioeconomically important fish species. However, the high turbidity and strong environmental gradients inherent to many estuaries make the monitoring of fish populations a challenging task. To assess the health and diversity of local fish populations, resource managers often employ fisheries-independent sampling methods, which result in valuable population assessments, but suffer from low-temporal resolution and high rates of mortality. Passive acoustic monitoring (PAM) provides a near-continuous, non-invasive means for monitoring soniferous fish activity over extended periods, but its utility for quantifying entire fish communities is largely untested, especially in turbid estuaries. Here, we use synchronized acoustic and gillnet sampling at 51 locations in the Mission-Aransas Estuary (TX), across two sampling seasons to test correlations between acoustic indices and gillnet catch. Positive correlations were observed between gillnet catch and sound pressure levels in both broadband (50–22050 Hz) and low-frequency (50–2500 Hz) bands. Additionally, sciaenid calling activity was positively correlated with sciaenid catch during the spring, when most spawning activity occurs. Our results indicate that PAM can be used to monitor the relative abundances of fish in Gulf of Mexico estuaries and beyond, although this is subject to species identity and seasonal dynamics.

Carcass and Cooked Meat Acceptance of Broilers Chickens Fed the Diet Containing Fermented Moringa with the Addition Corn and Fishmeal

The purpose of this study was to evaluate the organoleptic acceptance on the carcass and cooked meat of broilers fed the diet containing the fermented moringa leaves and yellow corn with the addition of fish meal or none.This study used 100 broiler chicks strain MB 90 and a commercial diet CP511 Bravo (CD). The substitute feed ingredients were composted of fermented domesticated Moringa oleifera leaf(FDMOL), yellow corn (YC), rice bran (RB), top mix (TM), and local commercial fish meal (FM). The study was performed in a Completely Randomized Design (CRD) with subsampling consisting of 5 treatments, 4 replicates, and 2 subsamples. The experimental diets were C 1 = 100% CD, C 2 =84.5% CD + 7.5% YC + 7.5% RB + 0.5% TM, C 3 = 84.5% CD + 5% YC + 5% RB + 5% TM + 0.5% TM, MCR= 84.5% CD + 5%FDMOL + 5% YC + 5% RB + 0.5% TM (moringa+), and MCF= 84.5% CD + 5% FDMOL + 5% YC + 5% FM + 0.5% TM (moringa++). The results indicated that carcasses from broilers fed the moringa-base diets were significantly higher (P<0.05) yellow coloration than those fed the control diets but the panelists’ acceptances for carcass organoleptic either fresh or cooking were not significantly different (P>0.05). In conclusion, there were no impacts on the acceptance of fresh carcass characteristics(conformation, color, and odor) or cooked meat (color, flavor, and taste) from the broilers fed the diets containing the moringa leaves compared to the control.

Microplastic Occurrence in Mugil Cephalus

Microplastic (MP) ingestion by fish can not only impact the environment but also human health. This study determines the abundance and composition (polymer, shape, size) of MPs ingested by gray mullet (Mugil cephalus). A total of 30 specimens were purchased from local fish market collected from Lake Cernek located in Kızılırmak Delta, Türkiye by local fishermen. The digestive tracts of the fish were removed and digested with hydrogen peroxide (H2O2) to extract microplastics. The share of the contaminated fish with microplastics was 90%. The average microplastic abundance by individual and weight were 2.87±0.27 MP/ind and 0.014±0.001 MP/g respectively. The length, weight, and condition factor of the fish did not correlate with MP abundance (Spearman’s correlation, p > 0.05). Four different polymer types were determined in the digestive tract of the specimens. The composition of polymers consisted of 44.58% polyethylene terephthalate (PET), 34.94% polypropylene (PP), 10.84% polyethylene (PE), and 9.64% polyamide (PA). The determined shapes were fiber (67.47%), fragment (20.48%), and film (12.05%). The size range of MP particles was ranged between 132 μm to 4850 μm, and the average was 1522.45±131.22 μm.

Morphological variability of the white carp (Hypophthalmichthys molitrix) during domestication

Acclimatized in the last century in the reservoirs of Russia, the white silver carp is the only consumer of phytoplankton in our country. In conditions of artificial reproduction and domestication, uncontrolled deterioration of fish habitus often occurs. In this regard, a comparative analysis of the variability of the most informative morphological parameters, namely length, mass, head length, body girth and their main indices in the samples of the white silver carp of varying degrees of domestication, was carried out. The Chinese, Amur and local lineages, the Ergenin sample and the Romanian population were studied, of which the least domesticated is the Chinese line. The presented materials show that the Chinese white carp line of the second generation of domestication differs in a smaller head, high indices of relative head length and physical development from the local and Ergeninsky fish samples domesticated for several decades. In pond lines domesticated in several generations, there is an increase in the relative size of the head and a deterioration in the index of physical development, which indicates the presence of selection for fitness to insufficient food supply in conditions of weak flow. It is recommended in the breeding program when growing reproductive herds of white carp in ponds to provide for selection to preserve the commercial qualities of fish.

First records of ratan goby Ponticola ratan in the Kaniv Reservoir and Desna River (Ukraine): A discreet invader of rip-raps

Monitoring of nearshore fish communities carried out in 2019 and 2022 in the Kaniv Reservoir and lower Desna River (Dnieper River basin, Ukraine) showed the presence of the ratan goby (Ponticola ratan), which has never been observed in these water bodies before and naturally inhabited marine and brackish waters of the Black and Azov Sea basins. The ratan goby was detected only on rip-rap structures and not on any other surveyed substrates including sand, mud, clay, and gravel which suggests a narrow habitat preference for this species. In all instances, the ratan goby co-occurred with the round goby (Neogobius melanostomus). Occurrence on all surveyed rip-raps, high abundances and the presence of a variety of size classes of the ratan goby in samples suggest that this species penetrated the Kaniv Reservoir quite long ago and successfully established there and has become a common component of the local fish fauna. Based on the obtained data, this gobiid should be listed among freshwater fishes of Europe as a euryhaline species that can potentially colonize other rivers flowing into the Black Sea including the Danube.

Heterogeneity of adaptation strategies to climate shocks: Evidence from the Niger Delta region of Nigeria

There is overwhelming evidence to suggest that climate shocks undermine food security and livelihood well-being of the climate-impacted Niger Delta region of Nigeria. Employing survey data collected from farming and fishing households in the Niger Delta region of Nigeria, the study investigated the range of adaptation practices prevalent in the region, as well as factors influencing the adoption of these adaptation strategies. Five hundred and three (503) households (252 fishing households and 251 farming households) were selected using multi-stage sampling techniques. Multinomial logit model was used to determine factors affecting the household choice of adaptation strategies. The results show that adaptation strategies adopted by farming households were livelihood diversification (78.5%), crop management (77.7%), and soil and water management (64.5%). Factors influencing their choice of adaptation strategies were age, gender, household size, education, extension, and farm size. The adaptation strategies employed by the fishing households were livelihood diversification (83.61%) and intensification [which include the use of improved fishing gears (80.33%), varying fishing locations (67.21%), and expanding area of fishing (40.98%)]. Uncovering the heterogeneity in adaptation and resilience aspects to climate shocks has immense practical significance, particularly in providing targeted assistance for the two livelihood groups’ adoption.

Environmental and economic impacts of retrieved abandoned, lost, and discarded fishing gear in Southwest Nova Scotia, Canada

Abandoned, lost, and discarded fishing gear (ALDFG), negatively impacts marine environments. Managing ALDFG in Atlantic Canada is challenging due to knowledge gaps on loss rates, locations, data availability/accuracy, impacts, and regulatory barriers for retrieval. This study removed ALDFG in Southwest Nova Scotia in collaboration with local fishers (with local knowledge and practical ALDFG removal expertise), government, non-profit organizations, and academia. A total of 29,298 kg of ALDFG was retrieved, including 24,630 kg using towed grapples covering ~3986 km of seafloor and 4668 kg from shorelines (comprising, 68 % lobster traps and 12 % dragger cable by weight). Traps ranged from <1 to 37 years old (median, 10 years). Traps continued to catch target and non-target species with 25 species released, including 652 individual lobsters (82 % were market-sized) and 57 fish (42 were species-at-risk). Based on estimated 2 % trap losses, annual commercial losses from ALDFG were $155,836 CAD in Lobster Fishing Area 34.

Local intensity of artisanal gold mining drives mercury accumulation in neotropical oxbow lake fishes

Driven by surges in global gold prices and additional socio-economic factors, artisanal small-scale gold mining (ASGM) in the Global South is increasing and driving emissions of significant quantities of mercury (Hg) into the air and freshwater. Hg can be toxic to animal and human populations and exacerbate the degradation of neotropical freshwater ecosystems. We examined drivers of Hg accumulation in fish that inhabit oxbow lakes of Peru's Madre de Dios, a region with high biodiversity value and increasing human populations that depend on ASGM. We hypothesized that fish Hg levels would be driven by local ASGM activities, by environmental Hg exposure, by water quality, and by fish trophic level. We sampled fish in 20 oxbow lakes spanning protected areas and areas subject to ASGM during the dry season. Consistent with previous findings, Hg levels were positively associated with ASGM activities, and were higher in larger, carnivorous fish and where water had lower dissolved oxygen levels. In addition, we found a negative relationship between fish mercury levels associated with ASGM and the occurrence of the piscivorous giant otter. The link between fine-scale quantification of spatial ASGM activity and Hg accumulation, as indicated by the result that in the lotic environment, localized effects of gold mining activities are stronger drivers (77 % model support) of Hg accumulation than environmental exposure (23 %) constitutes a novel contribution to a growing body of literature on Hg contamination. Our findings provide additional evidence of high Hg exposure risks to neotropical human and top carnivore populations subject to the impacts of ASGM, which depend on freshwater ecosystems undergoing gradual degradation. The documented spatial variation in Hg accumulation and increased Hg levels in carnivorous fish should serve as a warning to human communities in Madre de Dios to avoid the proximity of high-intensity gold mining areas and minimize local carnivorous fish consumption.