Eel Fishery Research Articles

Catch composition and bycatch from glass eel fisheries in Cimandiri River at Sukabumi, West Java

Bycatch is the catch of non-target fish, including what is brought to port which are not is main target of retain and what is discarded at fishing area. Sirib (a type of push net) and bubu (trap) are fishing gear to catch glass eel in the five rivers (both upriver and estuary) from Sukabumi, West Java. The research was conducted in July 2019 to January 2020. The aimed of this study to analyze the catch composition of glass eel from Cimandiri River. Result of the study shows that the catch composition from Cimandiri River consist of 8–9 species. However, catch composition of trap is lower than sirib/pushnet due to traps are more selective than sirib instead of the fishing location from the traps is in upriver.

Age-structured otolith chemistry profiles revealing the migration of Conger myriaster in China Seas

Conger myriaster is an eel species of considerable economic value in China Seas and around the Korean Peninsula and Japan, but its migration pattern remains largely unknown. This study used otolith microchemistry to investigate the migration and spawning of C. myriaster in the Yellow Sea and East China Sea. Samples were collected from three geographic regions, i.e. Middle Yellow Sea (QD), South Yellow Sea (DS) and East China Sea (ZS), and the micro-chemical compositions of otoliths were analyzed using laser ablation inductively coupled plasma mass spectrometry to produce continuous life history profiles of 4-year classes. The ratios of trace elements were analyzed with growth rings of otoliths to infer age-specific life-history profiles. Hierarchical cluster analysis showed no obvious partitioning in otoliths cores among samples, suggesting a similar environment at birth in these fish. The chemical compositions showed non-significant differences among sampling areas from core to metamorphosis zone, beyond which Ba:Ca ratio showed significant differences in the QD compared to other regions within the first year. This suggested that individuals might experience similar environmental conditions in the early life stages, and, during metamorphosis, QD individuals separated from the population and moved toward coastal waters of Shandong peninsula. The ZS and DS individuals shared similar chemical composition within the first year but differed in Ba:Ca and Sr:Ca ratios afterwards, suggesting a separation of the two groups at ages 1−2. The chemical signatures of the otoliths provide information on the spawning and separation of C. myriaster, which may contribute to the management of the eel fisheries.

Impaired antioxidant defenses and DNA damage in the European glass eel (Anguilla anguilla) exposed to ocean warming and acidification

The European eel (Anguilla anguilla) has attracted scientific inquiry for centuries due to its singular biological traits. Within the European Union, glass eel fisheries have declined sharply since 1980, from up to 2000 t (t) to 62.2 t in 2018, placing wild populations under higher risk of extinction. Among the major causes of glass eels collapse, climate change has become a growing worldwide issue, specifically ocean warming and acidification, but, to our knowledge, data on physiological and biochemical responses of glass eels to these stressors is limited. Within this context, we selected some representative biomarkers [e.g. glutathione peroxidase (GPx), catalase (CAT), total antioxidant capacity (TAC), heat shock proteins (HSP70), ubiquitin (Ub) and DNA damage] to study physiological responses of the European glass eel under distinct laboratory-climate change scenarios, such as increased water temperature (+ 4 °C) and pH reduction (− 0.4 units), for 12 weeks. Overall, the antioxidant enzymatic machinery was impaired, both in the muscle and viscera, manifested by significant changes in CAT, GPx and TAC. Heat shock response varied differently between tissues, increasing with temperature in the muscle, but not in the viscera, and decreasing in both tissues under acidification. The inability of HSP to maintain functional protein conformation was responsible for boosting the production of Ub, particularly under warming and acidification, as sole stressors. The overproduction of reactive oxygen species (ROS), either elicited by warming - due to increased metabolic demand - or acidification - through H+ interaction with O2−, generating H2O2 - overwhelmed defense mechanisms, causing oxidative stress and consequently leading to protein and DNA damage. Our results emphasize the vulnerability of eels' early life stages to climate change, with potential cascading consequences to adult stocks.

An overview of the Anguillid eel culture in Vietnam

The wild eel fishery and eel farming are playing an increasingly important role in aquaculture. Most of the Anguillid eel fries at their glass eel stage are caught in the two provinces of Vietnam, viz., Phu Yen and Binh Dinh, which accounts for over 80% and 10-15%, respectively. The stages of raising eels in Vietnam are very diverse with the survival rate of Anguilla Marmorata is approx. 60% through glass eel and elver stages. The major eel grow-out area of Vietnam is in Mekong delta. Ca Mau province is the highest in eel farming among the 14 provinces in the country. There are over 1,000 eel farms produced about 2,000–5,000 tons of eel in Vietnam at this moment. Around 95% of the total number of farms produced giant mottled eel (A. marmorata), and most of the production (70%) was used for domestic consumption, while30% was exported to the adjacent countries.

Development of the silver eel (Anguilla marmorata) gonad during downstream migration in the Lake Poso system, Central Sulawesi

The Lake Poso system is located in Central Sulawesi and is connected to the Tomini Bay by the Poso River. It is known that five out of nine Indonesian eel species were found at the Poso River. Anguilla marmorata is the most caught species. However, uncontrolled catching during downstream migration and the construction of a hydropower plant threaten the silver eel in the Lake Poso system. Research on silver eel (A. marmorata) in Lake Poso was conducted to determine and compare the condition of gonad development as part of the reproductive process. This represents essential information in eel fisheries management in Lake Poso. The eels were collected through bamboo traps (waya masapi). The present study calculates the GSI and HSI values, and histological analyses characterize the gonad. The GSI of eel ranges from 1.95 to 5.69%, and the HSI value ranges from 0.83 to 1.16%. Histological observation showed that eels from Tentena (Lake Poso outlet) and from the estuary of Poso River have ovaries in the early vitellogenic stage (III) and the vitellogenic stage (IV).

Fish catches diversity of the glass eel fishery in Cikaso and Cimandiri estuaries, Sukabumi, Indonesia

Cikaso and Cimandiri estuaries are well known as the central area of glass eel fisheries in Sukabumi Regency. Local fishermen catch glass eels using two main fishing gears, namely traps and lift nets. Although both fishing gears' target operation is glass eels, many other fish species are also caught as bycatch. The present study aimed to identify glass eels and bycatch ichthyofauna in glass eel fisheries of the Cikaso and Cimandiri estuaries, Sukabumi. The research was carried out monthly from November 2020 to January 2021. Glass eels fishing gears collected a total of 21 fish species belonging to 15 families in both estuaries. According to the percentage ano-dorsal length measurement to total length (AD/TL), 3 species of glass eel were identified, i.e. Anguilla bicolor bicolor, A. nebulosa, and A. marmorata. These three species were the most abundant fish catches in both estuaries. More than 18 bycatch ichthyofauna were recorded and most of them are economically important fish, such as Ambassidae, Eleotridae, Engraulidae, Gobiidae, and Polinemidae. To sustain fishery management, the recording bycatch from glass eel fishery in the Cikaso and Cimandiri estuaries is necessary to be done regularly because they contribute to fishing mortality.

Perspective plan for sustainable eel management in Lake Poso, Central Sulawesi

Lake Poso has high eel potential and a strategic position in supporting the development of eel fisheries in Sulawesi. Lake Poso is out of 15 national priority lakes in natural resources and environmental management programs. The catch of eel from Lake Poso is reported to have been decreasing for the last twenty years. Several factors causing the decline in eel populations are fishing activities, disruption in migration routes, and other factors such as changes in habitat and environmental conditions. The sustainability of the life of the Poso eel is determined by the success of the eel migration process. The migration of adult eels to the sea and young eels from glass eels to freshwater habitats must continue. The perspective plans that can be done to manage Poso's eel resources include 1) Socializing the eco-biological characteristics of eels as catadromous fish; 2) Establishing conservation areas and regulation of eel fishing; 3) Increasing eel population through restocking 4) Integrating fisheries and aquaculture activities; 5) Developing eel culture technology through size segmentation production; 6) Developing an eel migration monitoring system; 7) Building a cross-sectoral forum and put a joint action program; 8) Proposing the Poso eel Research and Conservation Center.

Economic development in times of population decline—a century of European eel fishing on the Swedish west coast

Abstract The European eel stock is in a multi-decadal decline. When fishing yield diminished throughout Europe, the small-scaled fyke-net fishery for eel on the west coast of Sweden gradually increased. This contrary trend lasted from the early-1900s, until the 1990s when fishing restrictions eventually limited the catch. We identified the processes driving this aberrant historical development. Using data on the fisheries from 1914 to 2006, we analysed the relation of total landed quantities to stock abundance indices, weather conditions, technical development, and market indicators. No relation between landed volumes and abundance indices was found, but market price (inflation-adjusted) was clearly correlated. Weather and technical development had a minor influence on landed volumes. This indicates that the commercial eel fishery on the west coast developed due to increasing demand and increasing eel prices. We found no evidence that the local stock has been fully exploited, though the increasing catch must have gradually reduced the contribution to the international spawning stock. These results stress the importance of considering economic processes when interpreting historical catch data as a source of information on population size in stock assessments, and ultimately, understanding the collapse of the eel stock.

Design features of constructed floodplain ponds influence waterbird and fish communities in northern New Zealand

Abstract Ponds can provide important refuges for aquatic biota on developed floodplains and are increasingly being constructed in an effort to enhance native biodiversity and ecosystem services in degraded landscapes. This study examined 34 constructed ponds to investigate the influence of design features on community composition, native biodiversity, and the biomass or abundance of common fish and waterbirds on the lower Waikato River floodplain, northern New Zealand. Inundation frequency appeared to be a key factor affecting biomass of the native shortfin eel Anguilla australis and three invasive fish species (common carp [Cyprinus carpio], brown bullhead [Ameiurus nebulosus], and goldfish [Carassius auratus]), suggesting that colonisation occurred during flooding by adjacent waterbodies. Linear models indicated that shortfin eel abundance and total eel biomass were positively associated with the biomass of potential fish prey, the area occupied by islands and cover by trees in the riparian zone. Native waterbird species richness was strongly related to water area, edge length (including islands) and area:perimeter ratio, with little increase in richness for ponds >1 ha in area, perimeters longer than 800 m, and ratios over 20. The protected grey teal (Anas gracilis), and the recreationally hunted species phenotypically assigned as mallard (Anas platyrhynchos + hybrids) and grey duck (Anas superciliosa + hybrids) appeared most strongly influenced, respectively, by perimeter length, water depth, and biomass of potential macroinvertebrate food supplies, suggesting variable effects of pond design attributes among waterfowl species. Overall, these results indicate that constructed ponds can be designed to promote native waterbird diversity, enhance eel fishery and waterfowl gamebird services, and also limit the proliferation of some non‐native invasive fish species in degraded floodplain landscapes. A hierarchy of constructed pond design attributes was identified, involving landscape position and connectivity, pond morphology and complexity, and riparian maturity and buffering, which were associated with direct (habitat) and indirect (food supply, physicochemistry) effects on biodiversity and provisioning services.

Stock assessment and potency of sustainable yield of glass eel (Anguilla spp.) in Cimandiri River Estuary, West Java

The demand for glass eel (Anguilla spp.) as a source of seeds for aquaculture activities depended on natural catches continue to increase. It has caused glass eel fishing activities to increase and potentially affect the biological condition and sustainability of fishing activities. The study aims to assess the potential stock, maximum sustainable yield (MSY) and the level of utilization of glass eel in the Cimandiri river estuary, West Java. The data were obtained from data on fisherman catches in the period 2014-2018. Potential stock calculation using the CPUE method is based on the Leslie model. Calculation of MSY based on the surplus production model from Schaefer. Utilization rates are determined based on the percentage of actual catch to the total allowable catch (TAC). The results of the study obtained an estimated glass eel potential stock of 4,575 kg. The maximum sustainable yield (MSY) was 991.20 kg.years−1 and the effort (fMSY) was 1050 trip.years−1. The average of glass eel production was 725.55 kg.years−1 and fishing effort 1031 trip.years−1. The TAC which set at 80% from the MSY was 792.96 kg.years−1. The average of the utilization rate of glass eel reached 91.50%. Utilization rates exceeding the TAC value occurred in 2014 and 2017. Management of glass eel fisheries is needed through limiting fishing efforts and the number of catches.

Why fishers end up in social-ecological traps: a case study of Swedish eel fisheries in the Baltic Sea

Unsustainable fishing can be surprisingly persistent despite devastating social, economic, and ecological consequences. Sustainability science literature suggests that the persistence of unsustainable fisheries can be understood as a social-ecological trap. Few studies have explicitly acknowledged the role of historical legacies for the development of social-ecological traps. Here, we investigate why fishers sometimes end up in social-ecological traps through a reconstruction of the historical interplay between fishers’ motivations, capacities, and opportunities to fish. We focus on the case of a Swedish fishery targeting the critically endangered European eel (Anguilla Anguilla) in the Baltic Sea. We performed the case study using a unique quantitative data set of social and ecological variables that spans over eight decades, in combination with earlier literature and interviews with fishers and fisheries experts. Our analysis reveals that Swedish archipelago fishers are highly dependent on the eel to maintain their fishing livelihood. The dependence on the eel originates from the 1930s, when fishers chose to intensify fishing for this species to ensure future incomes. The dependence persisted over time because of a series of changes, including improved eel fishing technology, heightened competition over catch, reduced opportunities to target other species, implementation of an eel fishing license, and the fishers’ capacity and motivation to deal with dwindling catches. Our study confirms that social-ecological traps are path-dependent processes. In terms of management, this finding means that it becomes progressively more difficult to escape the social-ecological trap with the passage of time. The longer entrapment endures, the more effort it takes and the bigger change it requires to return to a situation where fishers have more options so that unsustainable practices can be avoided. We conclude that fisheries policies need to be based on the premise that unsustainable fishing emerges through multiple rather than single causes.

Increasing or decreasing? - Current status of the Japanese eel stock

Although Japanese eel, Anguilla japonica, is listed as endangered on the International Union for Conservation of Nature Red List of Threatened Species, a previous stock assessment of the Japanese eel estimated that the age 1+ stock of the species has been recovering since 1990. To help understand the population dynamics of wild Japanese eels, eel fisheries in coastal and estuarine areas in Japan were investigated, because inland fisheries cooperative associations have conducted eel stocking that is presumed to bias the fisheries data in inland waters of Japan. We conducted a questionnaire survey of 1509 fisheries cooperative associations in coastal and estuarine areas of Japan, where the possible bias of eel stocking is expected to be relatively low. Based on the questionnaire, exploitable eel (yellow and silver eels) catch and effort data from 2003 to 2018 were obtained from six fisheries cooperative associations. A standardized catch per unit effort (CPUE) was developed using a generalized linear model for each fisheries cooperative association. The results indicated that the standardized exploitable eel CPUE was significantly lower in four of the six associations. As for the other two associations, significant relationships between CPUE and year was not found. Additionally, of the 227 fisheries cooperative associations that confirmed they catch eels, 1.3%, 5.3%, 21.6%, and 71.8% answered that the eel stock is “relatively increasing,” “stable” “relatively decreasing,” or “decreasing,” respectively, with no association stating that the eel stock is “increasing.” Moreover, reported glass eel CPUE in nine prefectures in Japan was significantly lower in both periods of 1977–2018 and 2003–2018. Because the dataset used in this study is likely to be one of the best currently available, the wild Japanese eel stock appears to be currently declining in Japanese coastal and estuarine waters, where the bias of eel stocked eels on stock dynamics is thought to be relatively low.

Challenges to reconcile conservation and exploitation of the threatened Anguilla anguilla (Linnaeus, 1758) in Santo André lagoon (Portugal)

The adoption of the EC Regulation 1100/2007 for the recovery of the European eel required EU member states to implement and periodically report on their Eel Management Plans (EMPs) with the goal of achieving at least 40% of the silver eel escapement relative to the best estimate of escapement that would have existed if no anthropogenic influences had impacted the stock. The specific measures to achieve such a goal have spurred a harsh debate among the different stakeholders with the need to mediate among multiple conflicting interests. In this investigation the study of the dynamics of the eel fishery in the Santo André Lagoon, a small-scale fishery in the southwest of Portugal, is presented. Through the description of the management structure, the analysis of 40 years of catch and effort data, and the analysis of socio-economic data, the existing enforcement and the way forward is discussed. Day-to-day logbooks of catch and effort data from five professional fishermen, for two fishing seasons (that is, 2011/2012 and 2016/2017), and surveys to the community, were used to independently estimate total harvest and income of the eel fishery in Santo André Lagoon, and the perception of the fishermen toward regulation and management. The results showed that both catch per unit effort and fishing yield increased during the study period and now ranges between 68 and 169 kg/ha, with eel fishing making a significant fraction of the fishermen's revenue. Although the existing regulation does not satisfy the fishing community, their disagreement decreased during the studied period. The analysis of the fisheries management in the lagoon and its impact on eel harvesting and, on the stock, revealed opportunities to adjust the set of regulations enforced at the national level under the Portuguese EMP to the specific context of the Santo André Lagoon. Specifically, a co-management approach would promote legitimacy and contribute to a better acceptance of the regulations by the fishing community.

Challenges in assessments of Japanese eel stock

Although Japanese eel, Anguilla japonica, is one of the most important fish species in East Asia, only one study has assessed Japanese eel stocks to date. That study estimated the stock status and dynamics of this species mainly based on Japanese fishery data on recruiting glass eel, growing-phase yellow eel, and maturing silver eel. That study also used data on biological characteristics, such as the growth, maturity and natural mortality of both Japanese eel and European eel, A. anguilla, to develop an age- and sex-structured production model. However, Japanese fishery statistics for glass eel are not an appropriate data source for stock assessment because there are non-negligible illegal and unreported glass eel catches occur in Japan. Moreover, yellow and silver eel fishery data in Japan are biased by those pertaining to stocked individuals, although most of the data are for eels originating from Japan as opposed to other countries and regions within the species distribution range. In addition to these problems in data collection, the biological parameters might be biased by contamination from stocked individuals. Therefore, it is difficult to assess the stock status of Japanese eels using an age- and sex-structured production model based on official Japanese eel fisheries statistics. The legality and traceability of glass eel fisheries and eel trading should be improved to enable appropriate stock assessment in future, and data on catch per unit effort (CPUE) in areas where eel stocking is not conducted should be collected throughout the species distribution range.

On the actual recruitment of European eel (Anguilla anguilla) in the River Ems, Germany

AbstractData from the historical River Ems glass eel fisheries in the 20th Century have been used for the ICES recruitment series. Commercial catches ceased from 1980 and dropped to zero; thus, eel recruitment data are since lacking. The present study assessed the actual eel recruitment to the River Ems with regard to the local tidal conditions. Standardised measurements were performed on relative glass eel occurrence at the tidal weir from 2014 and quantitative sampling at the next weir upstream from 2013. Eel migration at the tidal weir was dominated by glass eels and increased 2–3 month earlier than at the upstream weir, where migration was dominated by pigmented eels. In 2016, glass eels were marked at the tidal weir and pigmented elvers were sampled at the upstream weir. The 2016 eel recruitment was estimated at about 1% of the mean historical recruitment. Eel recruitment at the two weirs was not directly linked. Many eels seem not to pass the upstream weir. Further investigations are needed to reveal whether the results represent a regular pattern. In the long run, the perpetuation of the recruitment series is also foreseen.

First examination of the Lough Neagh European eel (Anguilla anguilla) population for eel virus European, eel virus European X and Anguillid Herpesvirus-1 infection by employing novel molecular techniques.

Lough Neagh is home to the largest wild-caught European eel (Anguilla anguilla) commercial fishery in the EU, producing 14% of the EU catch and worth £3.2 million to the local economy. Viral infections have been suggested to play a contributory role in the decline of the worldwide eel stock, but previous studies of the Lough Neagh European eel population had not observed either acute or chronic viral signs. Eel virus European (EVE), Eel virus European X (EVEX) and Anguillid herpesvirus-1 (HVA) have been detected throughout Europe and as the Lough Neagh eel fishery is supplemented by re-stocking of eels from France, Spain and the United Kingdom and these viral infections may be asymptomatic, it is vital that the viral pathogen prevalence in the Lough is accurately determined. This study aimed to ascertain the presence of these viruses in the Lough Neagh European eel population by employing novel molecular techniques testing specifically for the presence of EVE, EVEX and HVA. No evidence was found of HVA infection, whereas EVE and EVEX were found, albeit at a very low prevalence.

Modelling the bycatch of Anguilla marmorata using a generalized depletion model with an example from the Taiwanese glass eel fisheries for Anguilla japonica

Aquaculture of freshwater eels (genus Anguilla) relies solely on the glass eel fisheries for production stock. The countries where multiple anguillid species occur have become important sources for supplying glass eels. In East Asia, the giant marble eel Anguilla marmorata was a bycatch species in the glass eel fisheries for A. japonica, whose population has declined dramatically over the recent three decades. We quantify the impact of glass eel fisheries on the bycatch of A. marmorata using a generalized depletion model with transit stock structure and examine the possible ecological origin of the bycatch. The catch and effort data from the glass eel fisheries targeting A. japonica in the estuary of the Shuang River, northeastern Taiwan, from 1981 to 1994 was used as an example. Compared to A. japonica, A. marmorata had lower catches, lower estimates of abundance, and higher variability in abundance among recruitment waves. The number of recruitment waves, exploitation rate, and relative escapement for A. marmorata were generally similar to those for A. japonica, implying similar impacts from the glass eel fisheries. The abundance estimates did not correlate with minimum annual sea surface temperature. Similarities in the early life history characteristics of A. marmorata and A. japonica could indicate possible ecological origins for the bycatch of A. marmorata, such as a similar splitting mechanism controlled by eddies during larval-stage oceanic migration. Lower abundance and higher variability in A. marmorata might result from a year-round opportunistic spawning pattern, or a strategy corresponding to the distribution edge. The generalized depletion model applied to anguillid glass eel fisheries for multiple vulnerable species showed that similar exploitation pressures may occur for both targeted and non-targeted species. This finding may be applicable to countries in Southeast Asia and Africa where multiple species of anguillid eels occur.

The history of commercial fisheries for European eel commenced only a century ago

AbstractThe stock of the European eel is in decline throughout its distribution area—for decades, if not for centuries. Its population dynamics are not well understood. The extremely scattered occurrence, as well as the general lack of quantified information before 1950, prevents a straightforward analysis. This article discusses the history of eel fisheries across Europe, reviewing the literature published before 1940. A follow‐up study is advocated, to unearth primary information in archives across Europe.In the late 1800s, development programmes were initiated in central Europe, complementing the widespread subsistence fisheries with “modern” commercial exploitation of new areas, new markets and new products. In the early 1900s, increasing fisheries and trade were reported throughout northern Europe, and new developments started in the south. This lasted until about 1950—when the current multidecadal decline set in. The eel fisheries have never experienced a period of stable, sustainable exploitation. The decline in the stock is probably not a simple case of overfishing, but a continent‐wide serial depletion of local resources—eventually depleting the whole stock—in times of growing non‐fisheries impacts. Consequences for the European eel protection programme and for the derivation of restoration targets are discussed.

Effect of illegal glass eel (Anguilla anguilla) fishery on estuarine fish stocks: a case study in the Mondego Estuary, Portugal

Illegal fishing is a critical activity that affects a wide range of species, leading to a decline in total abundance and the overexploitation of target and non-target species. In Portugal, despite fishing for eel juveniles not being allowed, a substantial amount of illegal fishing takes place during the migratory season (October–March). The aim of this study was to investigate the effects of glass eel fishing in the Mondego estuary on target and non-target species. Samples were collected between November 2011 and March 2013 during the autumn and winter (dry and regular respectively with regard to hydrological characteristics) in 2 years. No differences in glass eel catches were observed between fishing seasons; however, a higher number of non-target species was observed in 2012–13 (regular year). There was higher species diversity in the regular year, as well as the highest number of individuals. Higher catches of the most abundant species were also observed in the regular year, compared with the dry year, suggesting that the magnitude of the effect of these illegal practices is related to hydrological cycles. Despite the low replication (2 years), the present study shows that non-selective practices have considerable effects on the species captured, as well as on the functioning of the estuarine ecosystem.

A stock assessment model for transit stock fisheries with explicit immigration and emigration dynamics: Application to upstream waves of glass eels

Fisheries for catadromous fish migrating through the fishing grounds are conceptualized as transit stock fisheries, whose local population dynamics is completely controlled by immigration and emigration. We present an extension to generalized depletion models to estimate the abundance and natural mortality rate of transit stock fishes using detailed fishery catch and effort data. We apply the model to 13 annual seasons of the Anguilla japonica glass eel fishery in the Shuang River estuary, northeast Taiwan. Estimates of abundance and natural mortality compare well with estimates for other species obtained from experimental studies or from data-rich stock assessment models at similar spatial scales. Parameter estimates are generally robust to biases and imprecision in the fisheries catch and effort data. The size of migration waves arriving at the estuary support a splitting mechanism controlled by eddies during oceanic migration. This extension of generalized depletion model provides a useful tool for the assessment of glass eel fisheries in East Asia, South East Asia, Europe and North America when only fisheries-dependent data are available.