An overview of the current status of Lake Victoria fishery: Opportunities, challenges and management strategies

Lake Victoria is African's most important source of inland fishery production, exhibiting an annual catch of ≈500 000 mt. The lake moderates local climate, serves as a means of transport, and a source of human food and raw material for the fishmeal industry. The introduction of Nile perch transformed the fisheries from a locally based artisanal fishery to a national and international capital investment industry. The fisheries produce an annual income of $US 600 million, providing employment opportunities for over 3 million people. Although the benefits of transforming the fishery of Lake Victoria appear to be quite remarkable, the negative impacts of this development are even more dramatic. Several challenges face the lake fishery, including environmental degradation, the introduction of exotic species, overfishing, and a fish export ban. Nutrients inputs into the lake have resulted in eutrophication and increased algal blooms. Deteriorated water quality and increased anoxia have caused the displacement and decline of some fish species. Exotic tilapiines have hybridized, displacing the indigenous fish species. Nile perch predation has caused the disappearance of once abundant native fish species. The once complex food web is now dominated by Nile perch. Unhygienic fishing methods have led to several fish export bans, while water hyacinth invasion in the lake has affected water quality, fishing and transportation possibilities. The current top‐down management and use of different regulations by the riparian states have been a major drawback to sustainable management of the lake. There is a need for a paradigm shift, in which the lake is considered to be one ecosystem and relevant stakeholders are involved in the decision‐making process.     

Exotic introductions to the fishery of Lake Victoria: What are the management options?

Lake Victoria is Africa's most important source of inland fishery production, exhibiting annual catches of ≈ 400 000 mt. The predatory Nile perch, Lates niloticus, and the herbivorous tilapiines, Oreochromis niloticus, Oreochromis leucostictus, Tilapia zillii and Tilapia rendalii, were introduced in Lake Victoria in the 1950s and 1960s. Nile perch were introduced to convert the abundant, but bony, haplochromines to fish flesh, while the tilapiines were introduced to boost the declining fishery. Since that time, the fisheries of Lake Victoria have undergone dramatic social and ecological changes. The catches increased tremendously, changing the fishery from artisanal to commercial, in turn increasing fisher income and employment opportunities. However, there was a decline and, in some cases, the disappearance of many indigenous fish species, especially the haplochromine cichlids. This reduction was attributed to overexploitation, predation, and competition and hybridization with the introduced species. The decline of the native fish species has had impacts on the trophic and ecological status of the lake. Nile perch now dominate the formerly complex food web. The loss of phytoplanktivorous haplochromines has contributed to an increase in algal blooms, reduction in water quality and occasional fish kills. Water hyacinth, Eichhornia crassipes, invaded Lake Victoria in 1988, with high rates of infestation in shallow waters and bays, which are breeding and nursery grounds for most fish species. Catches of Nile perch decreased following the infestation, while those of Nile tilapia, lung fish (Protopterus aethiopicus) and mud fish (Clarias gariepinus) increased. Haplochromines species also showed some signs of recovery. In view of all these changes, the future of the Lake Victoria fishery is uncertain.     

Analysis of the technical efficiency of Nile perch (Lates niloticus) fishers in the Tanzanian portion of Lake Victoria: A stochastic frontier analysis

The Nile perch fishery sector in Tanzania is important for enhancing the livelihoods and food security for the majority of people living near the Tanzanian portion of Lake Victoria. Despite continued government efforts and other institutions, including the Food and Agriculture Organization (FAO), Lake Victoria Fisheries Organization (LVFO), European Union and World Bank regarding the management of Lake Victoria, the Nile perch fishers have remained relative inefficient in regard to improving their fish catches. The Nile perch small‐scale fisheries sector in particular faces a challenge regarding how to improve production performance while, at the same time, ensuring a sustainable level of fisheries resources. This reality necessitates the measurement and analysis of artisan fishers’ technical efficiency. Accordingly, the present study analyses Nile perch fishers technical efficiency, using a stochastic production frontier (SPF) model based on the sample of 268 Nile perch fishers in the Tanzanian portion of Lake Victoria. The translog stochastic frontier model results indicate the technical efficiency of Nile perch fishers range between 61% and 80%, with an overall average technical efficiency of 75%. This finding implies that, based on existing fishery resources, the current quantity of Nile perch catch can be improved efficiently by 25%, a reality highlighting mismanagement of the lake's fishery resources. The quantity of bait and petrol and the number of hooks used per trip are the most important fishing inputs, indicating a positive Nile perch fishing output–input elasticity. To address the Nile perch fisher inefficiency, it is important to provide subsidized inputs such as outboard engines and mesh gillnets. Provision of access to affordable credits will enable fishers to purchase less destructive fishing inputs and improve the current structure of fishery organizations.     

Stomach contents and stable isotopes confirm ontogenetic diet shifts of Nile perch, Lates niloticus, in southern Lake Victoria

Nile perch (Lates niloticus), a main target for Lake Victoria's fisheries, shifts its diet from invertebrates to fish during its ontogeny. We combined stomach contents with stable isotopes to study these diet shifts in Mwanza Gulf, southern Lake Victoria. During four seasons between 2009 and 2011 we collected and analysed 6697 stomachs and 516 stable isotope samples of Nile perch. Caridina shrimp and haplochromine cichlids were the major food items in Nile perch of 5–40?cm. Based on stomach contents, the shift of dominance of Caridina towards haplochromines in the diet varied from 6.7?cm length in the southern part of the gulf, to >20?cm in the northern part, possibly related to the higher abundance of Caridina in the north. In general isotope-based and stomach-content-based estimates of Nile perch diets agreed. We observed only two discrepancies: in Nile perch >20?cm, the isotope-based estimates of the contribution of haplochromines to the diet were much lower than based on stomach contents and the contribution of juvenile Nile perch to the diet were much higher in the isotope-based estimates than in the stomach based-based estimates. This discrepancy may be explained by e.g. different timespan-coverages between isotopes and stomach contents, by movements of Nile perch between the Gulf and the rest of Lake Victoria, or by the overlapping isotopic profiles of haplochromines and juvenile Nile perch. With the recent recovery of haplochromines in Lake Victoria, Nile perch appears to rely more on this prey again, as it did in the 1980s.     

Shifts in the food of Nile perch (Lates niloticus) in Lake Victoria

The study investigated diet of Nile perch in Lake Victoria and compared results with past data from the same lake in order to analyse diet shifts over time. Fish samples (2020) were collected by seining and trawling from 2012 to 2016. In overall, Caridina nilotica (59%) was the dominant food item in the diet, while Rastrineobola argentea (5%) contributed the least. The diet of Nile perch of 1 cm was copepods, cladocerans and rotifers. The diet changed to only copepods and cladocerans at 2 cm. The proportion of the relatively large calanoids increased with Nile perch size in 1988/89, comprising between 35 and 80% of the diet of fishes of 3–4 cm. Nile perch of 6–25 cm TL fed more on C. nilotica in 2012/2016, compared to 1988/1989 and 2006/08. Haplochromines were fed on more in 2006/2008 than in 2012/2016 by Nile perch of 6–30 cm TL as fish size increased. The frequencies of occurrence of R. argentea in the diet were highest in 1988/1989, and lowest in 2006/2008, for fish size of up to 30 cm TL. The proportion of Odonata in the diet of size class 16–20 and 21–30 cm TL were highest in 2012/2016 and 1988/1989, respectively. Thus, shifts in Nile perch diet was observed from zooplankton to C. nilotica, then to haplochromines and finally to fish prey as size increased. Nile perch preferred haplochromines with C. nilotica as the substitute food. Cannibalism was observed to have decreased, only being evidenced in Nile perch above 35 cm TL, which could actually have a positive impact on the Nile perch fishery. The information on shifts in diet of Nile perch in Lake Victoria is of considerable ecological importance.     

Operational,environmental, and resource productivity factors driving spatial distribution of gillnet and longline fishers targeting Nile-perch (Lates niloticus), Lake Victoria

Operational and environmental factors limited available resource space of gillnet and longline fishers targeting Nile perch in the Speke gulf and open lake of southern Lake Victoria and drove their encounter rates with patches of fish resulting in gear specific distributional patterns. Catch-rate patterns were similar by region and gear: large (>50?cm) Nile-perch densities increased over distance from homeport and deeper in the water column while small Nile perch (<50?cm) densities decreased. Effects of season, (setting) depth and region were present but small and obscured by high variation in daily catch-rates and individual fisher strategies. Both fisheries distributed themselves over the size-productivity spectrum of Nile perch but reacted differently to patterns in size distribution of Nile perch: gillnetters focused more on numbers of productive juveniles between 30 and 60?cm at on average 5?km distance (59?min travel time) from homeport and longliners on larger sized 40–80?cm Nile perch deeper in the water column at 7?km (108?min). Sampled fishers likely were representative of most of the Nile perch fisheries. If so, this means that fishing pressure is mainly exerted on nearshore lake areas, and more lightly fished offshore areas may act as a refuge for adult Nile perch. Total catch-rates by gear were generally equalized over the resource space, increasing slightly with distance from homeport, according to ideal free distribution predictions. Nile perch fishers on Lake Victoria appear to distribute themselves according to the underlying productivity distribution of the resource within the constraints of their available resource space.     

Ontogenic Changes in Prey Ingested by Nile perch (Lates niloticus) Caught in Nyanza Gulf of Lake Victoria,Kenya

A total of 289 fish were analysed in this study, with Caradina nilotica (44%) being the dominant food item in their diet, while tilapia (8%) contributed the least. Haplochromines, unidentified fish prey and juvenile Nile perch also were observed. An ontogenic shift was observed, with C. nilotica contributing highest (61.1%) of the diet of fingerlings, but decreasing to 21% in the diet of adults. Nile perch contributed 35.7% of the diet in the adults and 8.1% in the fingerlings. This study indicates Nile perch is a predatory fish, feeding mainly on C. nilotica, haplochromines, tilapia, Nile perch and other fish materials.     

Lake Victoria fisheries: Outlook and management

The past subsistence of the Lake Victoria fishery was dominated by rich, diverse haplochromine cichlids. This multispecies fishery has undergone a decline over the past four decades, evolving into a commercial fishery consisting mainly of Nile perch (Lates niloticus), Nile tilapia (Oreochromis niloticus) and cyprinid (Rastrineobola argentea species). To better understand Lake Victoria fisheries, studies dating as far back as the 1920s have been carried out to assess the status of the fish stocks. These past studies indicated the lake fisheries were declining because of numerous major challenges, including intense fishing, invasive species, loss of biodiversity, ecological alterations, climate change, inadequate information to inform management and unharmonized policies. Numerous policies and regulations have been developed and implemented over the years to address these issues and manage the fisheries sustainably. Most of the interventions have been sectorial, disjointed and unharmonized and have not reduced the declining fish catch rates. With reestablishment of the East Africa Community (EAC) with several institutions in 1994, the Lake Victoria riparian states initiated an ecosystem approach to manage the Lake Victoria fishery resources in a sustainable manner. This study reviews the development of the Lake Victoria fisheries, outlines major past and present management challenges and provides a set of new strategies to manage the lake's fisheries resources, with emphasis on an ecosystem approach.     

A review on the status of some major fish species in Lake Victoria and possible conservation strategies

Lake Victoria, the second largest freshwater lake in the world, supports an enormous flora and fauna biomass, with a large human population around the Lake. The lake is a source of food (fish), water for domestic use and crop and livestock production, transportation and tourism, among other uses. As a result of these varied uses, human intervention within the lake and its catchment has resulted in several ecological changes in the lake in recent years, with profound effects on its fish resources. One of the most notable changes is the reduction and risk of extinction of some fish species, including the endemic tilapiine species (Oreochromis esculentus and Oreochromis variabilis), catfishes (Xenoclarias eupogon), haplochromines and cyprinids (Labeo victorianus and Barbus altinialis) in the lake. The reduced biodiversity, as well as extinctions within the lake, has been attributed to the introduction of alien fish species (e.g. Nile perch (Lates niloticus) and Nile tilapia (Oreochromis niloticus) into the lake, habitat loss and cultural eutrophication. If left unchecked, these changes will have devastating effects on the lake's resources, as well as to people living around the lake and beyond who depend on the lake fisheries for their livelihood. Thus, there is an urgent need for management measures based on sound scientific research to be implemented in order to curb the loss of ichthyodiversity within the lake, as well as to save the livelihoods of those stakeholders who are either directly or indirectly dependent on the lake.     

Management issues in the Lake Victoria watershed

Lake Victoria is the largest lake in Africa (68 800 km²) and is the eighth largest lake in the world by volume. The three East African countries of Tanzania, Uganda and Kenya share Lake Victoria and its resources. The total annual catch of fish from the lake ranges between 400 × 10⁶ kg and 500 × 10⁶ kg, bringing these riparian countries a combined annual income of approximately US$250 000–500 000 from exports alone. Approximately 30 million people live in the riparian region and the catchment, with about 2 million of these depending directly or indirectly on fishing activities. Tragically, Lake Victoria’s extremely diverse fauna was decimated in only 30 years following the introduction of non‐native Nile perch in the early 1960s. An estimated 200 endemic cichlid species became extinct. Dramatic increases in overfishing, pollution from various sources, effects of noxious water weeds and other associated problems threaten the sustainability of the lake’s resources and the economies of the riparian governments and peoples. Regulations governing Lake Victoria’s resources are different in each country. The laws concerning treatment of effluents from point sources in the three countries are not harmonized, neither are implementation or enforcement provisions. The governments of Kenya, Uganda and Tanzania have begun to put in place regional mechanisms to address the lake’s many problems including the creation of a permanent regional international institution through the establishment of the Lake Victoria Fisheries Organization (LVFO). A strategic vision document and action plans have been developed. Efforts are being made at local, national and regional levels to control the water hyacinth, including manual pulling, mechanical harvesting and introduction of weevils that weaken hyacinth root systems. To address the problem of overfishing, fishermen committees at landing beaches have been put in place. Each country has committed to take all necessary measures including legislation to implement the decisions of the LVFO governing bodies. All three countries have agreed to adopt and enforce legislation and regulations prohibiting the introduction of non‐indigenous species to the lake and to enforce existing regulations regarding fisheries. A Global Environment Facility project which provides funding to the Lake Victoria Fisheries Organization addresses land use management, catchment forestation, fisheries research and management, water hyacinth control, industrial effluent treatment and municipal waste treatment.     

Land‐use impacts on small‐scale Mpologoma wetland fishery,eastern Uganda: A socio‐economic perspective

Small‐scale fisheries in developing countries are characterized by uncertain futures attributable to ever‐increasing pressures on wetland resources. Data on the interconnectivity between wetland fishery, land‐use changes and the socio‐economic situation in the Mpologoma wetland, Uganda, were obtained through interviews and structured questionnaire surveys at sampling sites exhibiting differing different levels of environmental disturbance (ranging from less disturbed to highly disturbed). Rice production was the major economic activity at the highly disturbed sites, while maize production was the major activity at the less‐disturbed sites. Of the secondary activities, the Clarias gariepinus (Burchell, 1815) and Protopterus aethiopicus (Heckel, 1851) fishery was more important at the less‐disturbed sites. The high daily fish sale income ranging from US$ 8 to 12 and the high‐percentage (52%) catch preference of all large wetland fish species were observed for the less‐disturbed sites. A high percentage of respondents from the area of the less‐disturbed sites had higher annual incomes, resulting in more accumulated wealth than for the highly disturbed Nsango site, whose fishery was affected by large‐scale rice schemes. The overall socio‐economic impact of the small‐scale fishery, based on the data regarding the number of fishermen and their dependents, and the income from fish sales and other wetland activities, was low, with differences between sites being attributed to the level of wetland disturbance. The Mpologoma wetland is threatened by overexploitation of its fisheries services, but also overlooked and undervalued by policymakers because of inadequate fisheries statistics. Thus, the information derived from this study will facilitate the formulation and design of riverine wetland‐specific and small‐scale fisheries management strategies.     

The myths and realities in the management of the Kapenta fishery at Lake Kariba (Zimbabwe)

Biological considerations have dominated the management of the Kapenta fishery since its inception. State fisheries' managers employed the traditional scientific models that proved useful in managing temperate fisheries. This study uses both secondary and primary data to discuss the problems of using scientific models to manage tropical river‐fed lakes. Where fish stock size fluctuates in response to environmental factors such as river flows and lake level (which influence the level of nutrients in the water body), the concepts of maximum sustainable yield (MSY) and maximum economic yield (MEY) become problematic. This study demonstrated that, in an unstable environment, and where the target species is resilient to high levels of fishing effort, biological models lose their predictive power, allowing the state to determine the proportion of the resource to be distributed among its nationals. The redistribution of access rights or fishing licences (as a way of redressing a legacy of an unequal distribution of resources between emerging local entrepreneurs and companies established during the colonial era) is a major management issue in Zimbabwe. This study uses historical appraisal to illustrate how biological growth models failed to determine the optimal level of fishery exploitation upon which informed decisions could be made regarding whether to redistribute fish access rights or to broaden participation (or just recruit more fishers into the industry). This study also investigates tensions between the industry (advocating for broadening of access) and the state (seeking to redistribute existing resource use rights). Each stakeholder group has evoked institutions and discourses supporting their positions in influencing the strategies to eliminate the existing imbalances.     

Management of the Nile tilapia (Oreochromis niloticus (L.)) fishery in the Kenyan portion of Lake Victoria, in light of changes in its life history and ecology

This study reports on the population parameters, catch distribution and feeding ecology of Nile tilapia (Oreochromis niloticus) from bottom trawls and commercial catches obtained in the Kenyan portion of Lake Victoria during 1997–2006. The population parameters were analysed using the FAO‐ICLARM stock assessment tool (FISAT). The fish biomass and the food ingested by the fish were estimated using the swept area and point methods, respectively. Immature fish comprised ≈70% of the total fish population. The asymptotic length, maximum weight, maximum age, exploitation rate (E) and length at 50% maturity of Nile tilapia have decreased, whereas the growth curvature and fishing mortality have increased. The commercial catches increased from 13.93 t in 1997, to 23.70 t in 1999, decreasing thereafter to 18.73 t in 2005. The bottom trawl catches increased from 46.90 kg ha^?1 in 1997, to 401.48 kg ha^?1 in 2000, decreasing thereafter to 15.57 kg ha^?1 in 2006. The major food items ingested by the fish were algae, insects and other fish. Population parameters, and the catch and diet of O. niloticus, have changed over the years in Lake Victoria. The population characteristics suggest a population under stress, attributable to intense catch exploitation. Even under intense exploitation (E = 0.68), however, the mature fish constituted ≈30% of the population. The commercial catches are still high, indicating a very resilient fishery. Nevertheless, despite this resilience, the future of Oreochromis fishery is threatened by increased fishing capacity in the lake, and there is need to re‐evaluate the effectiveness of current fishery management measures, with the goal of possibly adopting new measures. Enactment of new fishery policies also should provide for co‐management to enhance the management process. Furthermore, there is a need to reduce fishing capacity and illegal fishing methods, and to seek alternative livelihoods for lake fishers and other stakeholders.     

Changes in Abundance and Growth Characteristics of White Perch from the Mouth of the Bay of Quinte

White perch became established in Lake Ontario in the 1950s, and by the mid 1960s were a major commercial species in the Bay of Quinte area. Commercial catches have fluctuated markedly, ranging from approximately 60,000 to 230,000 kg/yr between 1964 and 1978. Experimental trap nets set inshore of the mouth of the Bay of Quinte during May to July suggest a decline in white perch abundance from 1973 through 1978. However, the commercial catch did not similarly decline until 1979 when the commercial catch fell to a low of 30,000 kg/yr. The reason for this difference may be due to the fact that the bulk of the commercial catch is harvested during the winter when white perch congregate at the mouth of the bay, making fishing relatively productive. The growth of white perch was also considered, based on back-calculated growth curves of white perch caught in the experimental nets. Lee's phenomenon—a tendency for back-calculated lengths at a given age to become progressively smaller as the age of the fish from which they were computed increases—was apparent among the fish caught during this study although lacking in an earlier study. Due to the size selective nature of the fishery, an increased commercial harvest in recent years may have removed a disproportionate number of faster growing individuals from the population.     

Self-Regulation of Commercial Fisheries of the Outer Long Point Bay,Lake Erie

We examined self-regulation among commercial fishermen of Outer Long Point Bay, and found evidence of it with respect to avoidance of crowding among gillnets, avoidance of gillnet-trawl conflicts, fishermen's attitudes toward smelt and perch quotas, fish size limits, and gillnet mesh size. Some of these are primary fishermen-controlled, and many are industry-controlled, for example, through the processors. While the fishermen and the fishing industry have some ability to self-regulate, fishermen may not be able to manage fisheries successfully because of conflicts among themselves and factors external to their control. Given the scope of management issues discussed in this paper, it is clear that self-regulation alone cannot meet the need for resource protection. Rather, we are suggesting that fishery regulations be designed to take account of existing self-regulation, and biological objectives for stock protection be reconciled with socio-economic objectives for the industry.     

Ecosystem models of Lake Victoria (East Africa): Can Ecopath with Ecosim and Atlantis predict similar policy outcomes?

Ecosystem simulation models are valuable quantitative decision tools for supporting ecosystem-based fisheries management. However, the application of ecosystem models in fisheries management is still undermined by the lack of simple procedures to test the effect of model uncertainty on policy outcomes. The use of multiple ecosystem models is viewed as “insurance” against the effects of uncertainty emanating from modelling complex systems, which calls for investigations to ascertain whether models with different structure and assumptions can give consistent policy evaluations. We compared two structurally-distinct ecosystem models, Ecopath with Ecosim (EwE) and Atlantis, for Lake Victoria by varying fishing mortality of the key functional groups: Nile perch (the top predator) and haplochromines (key prey species). We compared model behaviour at the ecosystem level and at the level of functional groups, by evaluating changes in biomass of targeted groups and the consequent effects of changes in target groups on non-target groups. Results showed qualitative similarities (direction of change) for the major harvested groups; however, the cascading effects on non-target species varied across models, depending on the species interaction feedbacks. We conclude that: EwE and Atlantis, despite the huge differences in ecological processes between the models, can give consistent qualitative advice, which is needed for strategic management decisions; consistency in the representation of trophic interactions may help to minimize variations in simulated fishery responses due to model structure. This study helps to highlight scenarios that are robust to model choice, and for which simpler models (such as EwE) could also provide reliable advice.     

The relevance of species-based indicators as a tool for evaluating the structure of exploited fish assemblages: a comparative study of two tropical lakes in Mali, West Africa

A comparative study of the fish communities in two lake ecosystems in Mali (Lakes Manantali and Selingue) was based on monitoring small‐scale fishery landings for a 13‐month period. The main difference between the two lakes is the fishing pressure, being higher in Lake Selingue and lower in Lake Manantali. The effects of fishing on the structure of the fish communities in the two lakes were analysed with the use of diversity indices, rank species abundance (RSA) and abundance–biomass comparative curve (ABC) methods. The diversity differed significantly between the lakes, being higher for Lake Selingue. Analysis of the community structure, using RSA curves, indicated a more regular distribution of the weights between fish species for Lake Selingue than for Lake Manantali. The two lakes exhibited different exploited fish community structures. For Lake Selingue, the fishery was based on smaller‐sized species, compared to that for Lake Manantali. The indicators based on the species composition of exploited fish communities, in terms of abundance and life‐history traits, seemed to be more relevant in this study. Indicators such as diversity indices and RSA curves depend strongly on the exploitation strategy, being unreliable for evaluating exploited fish communities from catch data.     

Impacts of the Victoria Nile Bujagali hydropower dam on fisheries and livelihoods

The Upper Victoria Nile (UVN) flows from Lake Victoria into Lake Kyoga, spanning 117 km and supports a diverse aquatic fauna that sustains livelihoods of riverside communities. The UVN is habitat to critically endangered (Labeo victorianus), near threatened (Oreochromis variabilis and Oreochromis esculentus), and rare species (Neochromis simotes). Four hydropower dams were built on the UVN to provide energy for industrial and socioeconomic development, notwithstanding consequential environmental and socioeconomic impacts. The impacts of Bujagali hydropower (BHP) dam on fisheries and livelihoods were assessed biannually (April and September) from 2006 to 2019, using fishing effort, species abundance, catch composition, and economic beach revenue at upstream, mid-reservoir, and downstream transects. The fishing boats increased from 31 in 2009 to 293 in 2019 and fishers from 83 to 500 over the monitoring period. Maximum annual catch of 461.4 t was recorded in 2014 and lowest of 54.2 t in 2009. In all transects, Protopterus aethiopicus and Labeo victorianus were least in the commercial catches and the use of Mormyrus kannume juveniles as bait for Nile perch fishery corresponded with increased catches from 3.3 t in 2009 to 148.2 t in 2019. Women were mostly engaged in post-harvest activities such as fish drying, smoking, and food vending. These observations suggest coupling effects of the hydropower dam and ineffective fisheries management. The harvest of M. kannume wild stocks for bait should be banned and research in possible domestication of the species undertaken. There is a need to strengthen fisheries enforcement to curb illegal effort and overexploitation and to implement conservation actions to mitigate potential biodiversity impacts from the hydropower dam operations.     

Catch per unit effort estimation and factors influencing it from recreational angling of sockeye salmon (Oncorhynchus nerka) and management implications for Lake Toya,Japan

The present study examined the factors influencing catch per unit effort (CPUE) and standardized the CPUE of sockeye salmon (Oncorhynchus nerka) from offshore angling in Lake Toya, northern Japan. A generalized linear model (GLM), based on a negative binomial error distribution, was used to standardize the catch‐and‐effort data collected from anglers, using questionnaires and interview surveys during the fishing season (June) in 1998, 1999 and 2001–2012. Year, week, fishing area, number of fishing rods, fishing duration and Year × Week were the factors that significantly (P < 0.05) influenced CPUE. Anglers' fishing experience had no significant effect (P = 0.06) on CPUE. Limiting fishing duration, number of anglers and fishing rods may reduce fishing pressure and ensure sustainable management of the fishery. The results of the present study on standardized CPUE can also be useful in fine‐tuning age‐based models, such as Virtual Population Analysis (VPA–ADAPT), for the fish species in the lake, studies that are currently lacking. Regular and interdisciplinary studies that include biophysical factors are required to provide more understanding of the variations in the abundance of the fish species in the lake and in the ecosystem at large.     

Challenges to collective action in the management of the Kapenta fishery in lake Kariba

This study focused on the Kapenta fishing industry at Lake Kariba to illustrate that variations in economic situation, and in biophysical attributes of the resource users, make it difficult to institute collective conformity with fishery management regulations. The paper discusses how the Kapenta fishing companies in the Lake Kariba region have differing preferences regarding fishery resource management, and assign different priorities to various objectives of the resource management. The differences in personal objectives regarding management of the fishery resources, and the differences in the degree of control and access over the fishery, led to situations where users had varying incentive structures. The differences in incentive structures lead to fishery management regulations based on the average characteristics of users and the biophysical environment, fuelling conflicts between fishery resource managers and users. The variations of micro‐biophysical attributes of the resource, combined with the behaviour of the resource users, make it difficult to bring resource users together for developing and initiating collective action.