Intensification of Reservoir Fisheries in Tropical and Subtropical Countries

By now, most marine and inland fishery resources have been fully exploited or overexploited. To keep up with the growing demand for fish, only a few avenues for increasing fish production remain open. One of these is the intensification of fisheries in inland waters, such as reservoirs, lakes and small water bodies. Fish species transfer and culture-enhanced fisheries based largely on exotic species, mainly tilapias and cyprinids, is the current common strategy for increasing fishery benefits from tropical and subtropical inland water bodies. The growing human population and rising expectations require a steady growth in the number of reservoirs, both large and small. The development of cage and pen culture, especially in Asia, has substantially increased the reservoir fish production there. In Latin America, tilapias are the mainstay of many reservoir fisheries. By the year 2025, an additional 62 million tonnes of aquatic products will be required to maintain the present consumption of 19.1 kg/person. Much of it will have to come from inland waters, including reservoirs and small water bodies.     

Designing a global assessment of climate change on inland fishes and fisheries: knowns and needs

To date, there are few comprehensive assessments of how climate change affects inland finfish, fisheries, and aquaculture at a global scale, but one is necessary to identify research needs and commonalities across regions and to help guide decision making and funding priorities. Broadly, the consequences of climate change on inland fishes will impact global food security, the livelihoods of people who depend on inland capture and recreational fisheries. However, understanding how climate change will affect inland fishes and fisheries has lagged behind marine assessments. Building from a North American inland fisheries assessment, we convened an expert panel from seven countries to provide a first-step to a framework for determining how to approach an assessment of how climate change may affect inland fishes, capture fisheries, and aquaculture globally. Starting with the small group helped frame the key questions (e.g., who is the audience? What is the best approach and spatial scale?). Data gaps identified by the group include: the tolerances of inland fisheries to changes in temperature, stream flows, salinity, and other environmental factors linked to climate change, and the adaptive capacity of fishes and fisheries to adjust to these changes. These questions are difficult to address, but long-term and large-scale datasets are becoming more readily available as a means to test hypotheses related to climate change. We hope this perspective will help researchers and decision makers identify research priorities and provide a framework to help sustain inland fish populations and fisheries for the diversity of users around the globe.     

Stock Transfers in Spanish Brown Trout Populations: A Long-term Assessment

Synopsis Stocking of fish from other populations has been commonly employed for enhancement of wild brown trout, Salmo trutta, populations in north Spain. Young hatchery reared brown trout of central European origin were introduced into some Asturian rivers every year since 1984. Based on variation at the isozyme locus LDH-C1* and at the microsatellite locus BFRO 002, two genetic markers race-specific in Salmo trutta, we detected introgression of foreign genomes into native gene pools in some Spanish trout populations where only pure native individuals were present 10 years ago. We strongly suggest development of alternative management policies for conservation of Spanish natural brown trout populations without endangering the traditional recreational fisheries. Jorge I. Izquierdo, Ana G. F. Castillo: These two authors contributed equally to the article.     

Enhancement and conservation of inland fisheries resources in China

The inland aquatic ecosystem in China have been largely influenced by large-scale economic activities and over-exploitation of aquatic resources. Fisheries resource enhancement and conservation activities have been carried out throughout China. These activities include establishing artificial fish habitat and hatchery, releasing juvenile fish to rivers and lakes, forbidding illegal fishing, and setting up natural reserves. The purpose of these activities is to restore the quantity of inland fisheries resources, guarantee sustainable development of fisheries, maintain biological diversity and keep an ecological balance. These activities, conducted with a variety of methods, numerous species, extensive water areas and large scale programs have played an active role in fisheries resource enhancement and conservation. As a consequence the inland water environment has been improved; the biological diversity and fish catch increased, and the social, ecological and economic benefits have been significantly improved. However, problems such as inappropriate technology and nonstandard operations continue to affect fisheries resource enhancement, conservation and ecological stability. This paper reviews the history and practice of inland fisheries resource enhancement and conservation in China, analyzes the existing problems and deficiencies in the activities, and finally make some recommendations on technology and procedures to sustain inland fisheries resources.     

Cultured fish: integrative biology and management of domestication and interactions with wild fish

Fish aquaculture for commodity production, fisheries enhancement and conservation is expanding rapidly, with many cultured species undergoing inadvertent or controlled domestication. Cultured fish are frequently released, accidentally and deliberately, into natural environments where they may survive well and impact on wild fish populations through ecological, genetic, and technical interactions. Impacts of fish released accidentally or for fisheries enhancement tend to be negative for the wild populations involved, particularly where wild populations are small, and/or highly adapted to local conditions, and/or declining. Captive breeding and supplementation can play a positive role in restoring threatened populations, but the biology of threatened populations and the potential of culture approaches for conserving them remain poorly understood. Approaches to the management of domestication and cultured‐wild fish interactions are often ad hoc, fragmented and poorly informed by current science. We develop an integrative biological framework for understanding and managing domestication and cultured‐wild fish interactions. The framework sets out how management practices in culture and for cultured fish in natural environments affect domestication processes, interactions between cultured and wild fish, and outcomes in terms of commodity production, fisheries yield, and conservation. We also develop a typology of management systems (specific combinations of management practices in culture and in natural environments) that are likely to provide positive outcomes for particular management objectives and situations. We close by setting out avenues for further research that will simultaneously improve fish domestication and management of cultured‐wild fish interactions and provide key insights into fundamental biology.     

A brief history of aquatic resource use in medieval Europe

Humans have exploited European aquatic resources since at least the Palaeolithic, but during the Middle Ages rising human populations and demand initiated great changes in many fisheries. To help understand the past and present of the Wadden Sea, this paper sets the main developments of medieval fisheries in the context of changing larger European social and aquatic environments ca. 500–1500 A.D. Anthropogenic influences on fish populations and aquatic habitats interacted with natural environmental variations. Both nutritional and cultural needs shaped human consumption of aquatic organisms. Many fisheries met the demand for food by economic reorientation from subsistence to artisanal and then even fully commercial purposes. Exploitation slowly shifted from limited or deteriorating local inland and inshore fish populations to frontier, commonly marine, and increasingly pelagic resources. Some inland regions developed aquaculture to enhance local supplies of fresh fish. General processes are illustrated by case studies of selected indicator species from freshwater and marine habitats generally pertinent to the region surrounding the Wadden Sea. Anadromous salmon (Salmo salar) and sturgeon (Acipenser sturio) were negatively affected by overfishing and by unintentional human alteration of critical habitat. Habitat preferences of catadromous eel (Anguilla anguilla) and exotic carp (Cyprinus carpio) let these species gain from medieval human activities. In the case of herring (Clupea harengus), Europes largest early commercial marine fishery, technological innovations which raised production and consumption played off against long-term consequences of intensely exploiting sensitive natural systems.     

Paradigm shifts in fish conservation: moving to the ecosystem services concept

Various factors constrain the existence and development of inland fishes and fisheries, such as pollution, habitat degradation, alien invasive species, local user conflicts, low social priority and inadequate research and funding. In many cases, however, degradation of the environment and loss of aquatic habitat are the predominant concerns for the conservation of freshwater aquatic biota. The need for concerted effort to prevent and reduce environmental degradation, as well as protection of freshwater fishes and fisheries as renewable common pool resources or entities in their own right, are the greatest challenges facing the conservation of fishes in inland waters. Unfortunately, traditional conservation practices such as regulation of exploitation, protected areas and habitat restoration have failed to arrest the alarming increase in number of threatened freshwater fish species worldwide. This paper examines the shifting paradigm of fisheries management from rule-based regulation, through fishery enhancement towards the ecosystem approach to fisheries, with reference to inland waters, and how the emerging concept of ecosystem services coupled with traditional fish conservation management practices, institutional restructuring and integrated management planning should provide a more sustainable thrust to formulation and promotion of fish conservation initiatives.     

Non-native freshwater fishes in Norway: history, consequences and perspectives

At present, there are 43 self-sustaining fish species in Norwegian fresh waters, 11 (26%) of which are non-native, representing four families (Salmonidae, Cyprinidae, Centrarchidae and Ictaluridae). Human-mediated fish introductions probably began in the 15th century with common carp Cyprinus carpio, but most have occurred between the late 1800s and late 1900s. The number of known established populations varies from one (goldfish Carassius auratus ) to nearly 250 (tench Tinca tinca ). Dispersal risk is also highest with tench, which is being spread by anglers for its appeal as a trophy fish. Intentional introductions to improve amenity angling have been part of fisheries management programmes ( e.g. brook trout Salvelinus fontinalis ), so this appears to be an increasingly common introduction vector despite the prohibition under legislation of introducing any species of non-native fishes. Some introduced species, such as brook trout, have declined in abundance and number of populations as the quality of acidified waters has been restored, being replaced by native brown trout Salmo trutta . Further range expansion by some species ( e.g. common carp, goldfish and pumpkinseed Lepomis gibbosus ) is probably restricted by current climatic conditions.     

Estimating Fish Exploitation and Aquatic Habitat Loss across Diffuse Inland Recreational Fisheries

The current state of many freshwater fish stocks worldwide is largely unknown but suspected to be vulnerable to exploitation from recreational fisheries and habitat degradation. Both these factors, combined with complex ecological dynamics and the diffuse nature of inland fisheries could lead to an invisible collapse: the drastic decline in fish stocks without great public or management awareness. In this study we provide a method to address the pervasive knowledge gaps in regional rates of exploitation and habitat degradation, and demonstrate its use in one of North America’s largest and most diffuse recreational freshwater fisheries (Ontario, Canada). We estimated that 1) fish stocks were highly exploited and in apparent danger of collapse in management zones close to large population centres, and 2) fish habitat was under a low but constant threat of degradation at rates comparable to deforestation in Ontario and throughout Canada. These findings confirm some commonly held, but difficult to quantify, beliefs in inland fisheries management but also provide some further insights including 1) large anthropogenic projects greater than one hectare could contribute much more to fish habitat loss on an area basis than the cumulative effect of smaller projects within one year, 2) hooking mortality from catch-and-release fisheries is likely a greater source of mortality than the harvest itself, and 3) in most northern management zones over 50% of the fisheries resources are not yet accessible to anglers. While this model primarily provides a framework to prioritize management decisions and further targeted stock assessments, we note that our regional estimates of fisheries productivity and exploitation were similar to broadscale monitoring efforts by the Province of Ontario. We discuss the policy implications from our results and extending the model to other jurisdictions and countries.     

Ecological, environmental and socioeconomic aspects of the Lake Victoria's introduced Nile perch fishery in relation to the native fisheries and the species culture potential: lessons to learn

Inland fishery ecosystems in Africa are characterized by patterns of overexploitation, environmental degradation and exotic species introductions. Ecological complexity and diversity of aquatic habitats dictate that fishes in general are not evenly distributed in a water body. However, fisheries management regimes tend to ignore this basic principle, assume generalized conditions in a water body, and focus more on ‘desired’ objectives such as maximizing catch. The result is to disregard fish habitat boundaries and anthropogenic influences from the catchment that influence fish production. Overexploitation and environmental degradation disrupt sustainable socioeconomic benefits from the fisheries, create uncertainty among investors, but leave some managers calling for more information with the expectation that the fisheries will recover with time. Open access to the fisheries and full control of fishing effort remain challenges for managers. Exotic species introductions and fish farming can increase production, but such interventions require firm commitment to sound ecological principles and strict enforcement of recommended conservation and co‐management measures in capture fisheries. The general tendency to downplay fishing effort issues, other ecosystem values and functions or rely on temperate fisheries models until a new cycle of overexploitation emerges, characterizes many management patterns in inland fisheries. Aquaculture is not an option to challenges in capture fisheries management. Aquaculture should be developed to increase fish production but even this practice may have negative environmental impacts depending on practice and scale. Decades of information on Lake Victoria fisheries trends and aquaculture development did not stop the collapse of native fisheries. The successfully introduced Nile perch (Lates niloticus) has shown signs of overexploitation and aquaculture has again been considered as the option. By reviewing significant trends associated with Nile perch and its feasibility in aquaculture this paper uses Lake Victoria to illustrate ‘special interest management’ targeting selected species of fish rather than the fisheries.     

Managing conflicts arising from fisheries enhancements based on non‐native fishes in southern Africa

Southern Africa has a long history of non‐native fish introductions for the enhancement of recreational and commercial fisheries, due to a perceived lack of suitable native species. This has resulted in some important inland fisheries being based on non‐native fishes. Regionally, these introductions are predominantly not benign, and non‐native fishes are considered one of the main threats to aquatic biodiversity because they affect native biota through predation, competition, habitat alteration, disease transfer and hybridization. To achieve national policy objectives of economic development, food security and poverty eradication, countries are increasingly looking towards inland fisheries as vehicles for development. As a result, conflicts have developed between economic and conservation objectives. In South Africa, as is the case for other invasive biota, the control and management of non‐native fishes is included in the National Environmental Management: Biodiversity Act. Implementation measures include import and movement controls and, more recently, non‐native fish eradication in conservation priority areas. Management actions are, however, complicated because many non‐native fishes are important components in recreational and subsistence fisheries that contribute towards regional economies and food security. In other southern African countries, little attention has focussed on issues and management of non‐native fishes, and this is cause for concern. This paper provides an overview of introductions, impacts and fisheries in southern Africa with emphasis on existing and evolving legislation, conflicts, implementation strategies and the sometimes innovative approaches that have been used to prioritize conservation areas and manage non‐native fishes.     

The effects of population density and lake characteristics on growth and size structure of brook trout Salvelinus fontinalis (Mitchill, 1815) in boreal forest lakes in Canada

This paper examines the effect of lake characteristics on population density and how this variation affects growth, mortality and population size structure of brook trout, Salvelinus fontinalis. The study was conducted on 17 recreationally fished, reproductively isolated boreal forest lakes in Newfoundland, Canada from 1993 to 2000. A standardized sampling program, the Fyke Littoral Index Netting program (FLIN) was used to collected data that describes brook trout population parameters and life history attributes. Regression analyses showed significant relationships between fish density and biomass and characteristics of the lakes. Variation in fish density and biomass was explained by lake surface area and littoral habitat area. Significant relationships were found when growth, mortality and size structure were regressed against density. The proportional stock distribution and theoretical maximum size of brook trout were negatively related to density, and natural mortality was positively related to density. The largest maximum length and highest proportional stock densities occurred at brook trout densities of less than 30 fish/ha. In general, the higher the proportion of littoral habitat area the higher the densities of brook trout, which correspondingly had important effects on growth, natural mortality and size structure of the brook trout populations. This information is critical to the development of management strategies aimed at altering size distribution to produce specific fisheries management outcomes.     

Wild brown trout Salmo trutta: an important national and international resource

SUMMARY. 1. Brown trout were once given a variety of latin and common names, but are now regarded as belonging to only one polymorphic species, Salmo trutta L. A review of their geographical distribution shows that this species was originally native to Europe but has been successfully introduced in at least twenty-four countries outside Europe.
2. Brown trout provide valuable commercial and sports fisheries, e.g. commercial and rod catches of sea-trout in England and Wales averaged 110,547 fish per year from 1983 to 1986 and the minimum value of these fisheries is estimated to be £55M.
3. It is concluded from this brief review that the major objectives of scientific research on wild brown trout should be: (a) an assessment of the current status of stocks; (b) the maintenance of existing populations; (c) the development and improvement of mathematical models that can be used as tools for the conservation and management of this important national and international resource.     

The selection of the ‘wild’: A combined molecular approach for the identification of pure indigenous fish from hybridised populations

The identification of pure indigenous fish from hybridised populations represents a key issue in fisheries management and conservation biology. In the present study an approach for selection of purebred marble trout (Salmo trutta marmoratus C.) individuals out of admixed populations was set up and assessed. In a first step, baseline data sets of pure marble trout and pure brown trout specimens based on twelve microsatellite loci were used to simulate five consecutive generations of admixture. The baseline and the resulting simulation data sets were then combined with data of a ‘real’ hybridised marble trout population to perform a single individual assignment test as implemented in STRUCTURE. By this procedure the assignment approach was calibrated and it was possible to compare admixture coefficients obtained for individuals from different populations. The ranking of individual admixture coefficients on a plot and comparison with simulated data revealed that the test population was composed of pure marble trout individuals, first generation hybrids between marble trout and brown trout, and hybrid backcross specimens between both groups. However, by defining a critical q-value of 0.1 and additionally integrating individual sequence data of the mtDNA control region, it was possible to indicate individuals, which could be selected for the establishment of a pure marble trout strain.     

Fish and fisheries of the Prespa lakes

Twenty-three taxa of fish have been identified fromthe Prespa lakes. Eleven of these have been introducedor translocated, and 7 of the remaining 12 are endemicto the Prespa lakes. This high proportion of endemismrequires confirmation because the systematic positionof several of the species and subspecies remainsuncertain. The absence of a predatory fish in MikriPrespa, the occurrence of trout in Megali Prespa, thepresence of eels in both lakes and the occurrence ofmany rheophilous fish species typifies the fishcommunities of these two lakes. Monitoring of the fishpopulation in Mikri Prespa, from 1984 to 1994, showedapparent stability or a slight increase in catchesduring this period. Not all the introduced specieshave been able to establish populations and theirimpact on the indigenous populations is yet to bedefined. A spectacular re-establishment of the carppopulation, following the crash of the stock of thisspecies in the 1970s–1980s, was recorded in the springof 1991. The past and present situation of thefisheries in lakes Mikri and Megali Prespa isdescribed, and their productivity and yields areanalysed. Particular attention is given to atraditional fishing method unique to the Presparegion: pelaizia fishing. The factors involved inthe temporal trends in the fisheries are identifiedand analysed. Recommendations for the management ofthe fish populations and the fisheries are proposed,so that the sustainability of this resource and thesurvival of the endemic fish species can beensured.     

Alteration of Nutrient Cycles and Algal Production Resulting from Fish Introductions intoMountain Lakes

The introduction of salmonid fishes into naturally fishless lakes represents one of the most prevalent environmental modifications of aquatic ecosystems in western North America. Introduced fish may alter lake nutrient cycles and primary production, but the magnitude and variation of these effects have not been fully explored. We used bioenergetics modeling to estimate the contributions of stocked trout to phosphorus (P) cycles across a wide range of fish densities in lakes of the Sierra Nevada, California. We also assessed the larger effects of fish-induced changes in phosphorus cycling on primary production using paleolimnological analyses from lakes in the southern Canadian Rockies. Our analyses showed that total P recycling by fish was independent of fish density but positively related to fish biomass in the Sierra Nevada. In lakes with fish populations maintained by continued stocking, fish recycled P at over twice the rate of those in lakes where introduced fish populations are maintained by natural reproduction and stocking has been discontinued. We estimate that P regeneration by introduced fishes is approximately equivalent to atmospheric P deposition to these lakes. Paleolimnological analyses indicated that algal production increased substantially following trout introductions to Rocky Mountain lakes and was maintained for the duration of fish presence. The results of our modeling and paleolimnological analyses indicate that introduced trout fundamentally alter nutrient cycles and stimulate primary production by accessing benthic P sources that are not normally available to pelagic communities in oligotrophic mountain lakes. These effects pose a difficult challenge for managers charged with balancing the demand for recreational fisheries with the need to maintain natural ecosystem processes. Received 28 March 2000; accepted 4 January 2001.     

Effects of brown trout (Salmo trutta L.) stocking and catch‐release practice on angling catches in the River South Rena in southeast Norway

Preserving of fish species and populations is important whether it is for exploitation or just for conservation. Management of fisheries aim to maintain fishable stocks that are attractive to anglers, and different means are performed. In this study from the River South Rena in southeastern Norway, conducted during 1991–2005, the effects of supportive stocking of hatchery reared brown trout (Salmo trutta L.) from 1996, and bag limit (BL) and catch‐release (CR) practice for the target species brown trout, from 2002, were explored. Effects of supplemental brown trout stocking was not noticeable, except from one year following a year of exceptional high number of stocked fish, actually 41% of the catches, whereas in the following years this proportion remained constant about 10%, and the catches remained high in 2003 and 2004, mainly due to increased angling success rate after BL‐CR introduction.     

Assessing the status of British wild brown trout, Salmo trutta, stocks: a pilot study utilizing data from game fisheries

SUMMARY. 1. This paper describes an analysis of results from a questionnaire (Giles, 1987) which requested information on the status of game fish stocks (especially wild brown trout Salmo trutta L.) from those Game Conservancy members who own or manage fisheries. Also included are data arising from fishery log book records which are used to indicate trends in brown trout catch per unit effort (CPUE) over past decades.
2. The key finding from questionnaire returns was the widespread reporting of apparent declines of wild brown trout stocks in a total of twenty-seven sites throughout Britain. The affected waters are geographically widespread from the south-west of England through southern and south-east England, south Wales, northern England and Scotland including the Western Isles. Suspected stock declines of migratory (sea) trout, salmon Salmo salar L. and grayling Thymallus thymallus L. were also reported. Where brown trout occur alone, a significantly higher proportion of questionnaire returns recorded a stock decline compared with fisheries containing both brown and rainbow trout Salmo gairdneri Richardson.
3. Trout catch records from a small selection of differing fishery types are presented and the value of such data in fish stock assessment is discussed.     

Movement in a large predatory fish: coral trout, Plectropomus leopardus (Pisces: Serranidae), on Heron Reef, Australia

 Movement by the larger more mobile species of coral reef fish plays a significant role in determining patterns in abundance and population structure. Fish movement is also relevant to the use and effectiveness of marine reserves in managing fish populations. Coral trout are large piscivorous serranids supporting major fisheries on the Great Barrier Reef (GBR). This study reports on the within-reef movement of the common coral trout, Plectropomus leopardus, at Heron Reef, southern GBR, over a twelve month period, investigated by tagging and underwater tracking. Tracking of coral trout revealed no apparent relationship between the area moved and stage of tide or time of day. However, movement areas were affected by the size of fish: in spring a linear relationship between fish size and area of movement was measured, but in summer the largest (male) fish moved over significantly smaller areas than medium-sized fish. Movement of males may be related to cleaning behaviour and spawning. Fifty nine percent (n=101) of the tagged fish were resighted over periods of 4–5 months, in “home sites” measuring ∼2000 m². Coral trout were not restricted to home sites, but moved on average 2 km along the reef slope; maximum distances of 7–7.5 km were measured. Coral trout appear to range as mobile, opportunistic predators, but also maintain home sites for access to shelter and cleaning stations. Accepted: 1 August 1996     

Sustainability of the Lake Superior Fish Community: Interactions in a Food Web Context

The restoration and rehabilitation of the native fish communities is a long-term goal for the Laurentian Great Lakes. In Lake Superior, the ongoing restoration of the native lake trout populations is now regarded as one of the major success stories in fisheries management. However, populations of the deepwater morphotype (siscowet lake trout) have increased much more substantially than those of the nearshore morphotype (lean lake trout), and the ecosystem now contains an assemblage of exotic species such as sea lamprey, rainbow smelt, and Pacific salmon (chinook, coho, and steelhead). Those species play an important role in defining the constraints and opportunities for ecosystem management. We combined an equilibrium mass balance model (Ecopath) with a dynamic food web model (Ecosim) to evaluate the ecological consequences of future alternative management strategies and the interaction of two different sets of life history characteristics for fishes at the top of the food web. Relatively rapid turnover rates occur among the exotic forage fish, rainbow smelt, and its primary predators, exotic Pacific salmonids. Slower turnover rates occur among the native lake trout and burbot and their primary prey—lake herring, smelt, deepwater cisco, and sculpins. The abundance of forage fish is a key constraint for all salmonids in Lake Superior. Smelt and Mysis play a prominent role in sustaining the current trophic structure. Competition between the native lake trout and the exotic salmonids is asymmetric. Reductions in the salmon population yield only a modest benefit for the stocks of lake trout, whereas increased fishing of lake trout produces substantial potential increases in the yields of Pacific salmon to recreational fisheries. The deepwater or siscowet morphotype of lake trout has become very abundant. Although it plays a major role in the structure of the food web it offers little potential for the restoration of a valuable commercial or recreational fishery. Even if a combination of strong management actions is implemented, the populations of lean (nearshore) lake trout cannot be restored to pre-fishery and pre-lamprey levels. Thus, management strategy must accept the ecological constraints due in part to the presence of exotics and choose alternatives that sustain public interest in the resources while continuing the gradual progress toward restoration. Received 10 December 1999; accepted 13 June 2000.