Current issues with fish and fisheries: editor's overview and introduction

Authors


Prof. Steve Ormerod. Tel.: 01222 875871. Fax: 01222 874305. E-mail: ormerod@cardiff.ac.uk

Summary

1. By any measure, fishes are among the world's most important natural resources. Annual exploitation from wild populations exceeds 90 million tonnes, and fish supply over 15% of global protein needs as part of total annual trade exceeding $US 55 billion. Additionally, with over 25 000 known species, the biodiversity and ecological roles of fishes are being increasingly recognised in aquatic conservation, ecosystem management, restoration and aquatic environmental regulation.

2. At the same time, substantial management problems now affect the production, exploitable stocks, global diversity, trophic structure, habitat quality and local composition of fish communities.

3. In marine systems, key issues include the direct effects of exploitation on fish, habitats and other organisms, while habitat or water quality problems arise also from the atmospheric, terrestrial and coastal environments to which marine systems are linked. In freshwaters, flow regulation and obstruction by dams, fragmentation, catchment management, pollution, habitat alterations, exotic fish introductions and nursery-reared fish are widespread issues.

4. Management responses to the problems of fish and fisheries include aquatic reserves in both marine and freshwater habitats, and their effectiveness is now being evaluated. Policies on marine exploitation increasingly emphasise fishes as integral components of aquatic ecosystems rather than individually exploitable stocks, but the rationalisation of fishing pressures presents many challenges. In Europe, North America and elsewhere, policies on freshwaters encourage habitat protection, integrated watershed management and restoration, but pressures on water resources will cause continued change. All these management approaches require development and evaluation, and will benefit from a perspective of ecological understanding with ecologists fully involved.

5.Synthesis and applications. Although making a small contribution to the Journal of Applied Ecology in the past, leading work on aquatic problems and fish-related themes appear increasingly in this and other mainstream ecology journals. As this special profile of five papers shows, significant contributions arise on diverse issues that here include the benefit of aquatic reserves, river restoration for fish, the accumulation of contaminants, interactions with predators, and the fitness of salmonids from nurseries. This overview outlines the current context in which papers on the applied ecology of fish and fisheries are emerging, and it identifies scope for further contributions.

Introduction: the value of fish and fisheries

With considerable justification, fish and fisheries rank among the most important of all the world's natural resources. In 2000 alone – a good but not atypical year by recent trends – around 95 million tonnes of fish production was harvested directly from wild populations in the earth's seas and inland waters. A further 35 million tonnes was taken from aquaculture. Most of this combined total, or around 93 million tonnes, was used directly as food, equivalent to 16 kg for each of us, or 15% of our protein supply (FAO 2002). In order to secure this resource, some 35 million people were employed directly in fishing, including a surprisingly large number (12 million) dependent on inland waters often for their own subsistence. The international trade in fish products in this sample year, of $US 55 billion (FAO 2002), was greater than the individual gross domestic product of over 70% of the world's nations.

If these compelling economics are not sufficient to emphasise the value of fishes, consider also their intrinsic conservation importance (Leidy & Moyle 1998). Of the world's 25 000 known fish species, well over half occur in marine waters, the most extensive biogeographical realm on earth. Not only does it incorporate some of the earth's richest areas of fish endemicity (Roberts et al. 2002), but also, in the deep oceans, some of its most poorly known habitats (Angel 1993). While marine communities contain more species in total, freshwaters are far richer per unit habitat volume. Here, over 11 000 species occur at one per 15 km3 of water (cf. one per 100 000 km3 of sea water), reflecting the productivity, physiographic diversity and geographical isolation of freshwater habitats (Oberdorff, Guegan & Hugueny 1995; Amarasinghe & Welcomme 2002). As in marine environments, major instances of endemic richness have arisen, such as in Africa's Great Lakes (Miller 1989), but centres of species radiation in freshwater fishes are spread across all continents. While river catchments are naturally isolated, most are eventually connected to the oceans, and around 250 of diadromous fish species migrate regularly between inland waters and the sea. The resulting array of all fish species gives us some of the most remarkable examples of functional design, life cycles, behavioural ecology, physiological adaptations and ecological interactions in the whole of evolution.

The pronounced biodiversity of fishes provides not only the many species exploited for food, but also those with potential in ecosystem management, for example in the control of mosquito vectors (Goodsell & Kats 1999), the management of invasive aquatic vegetation (Bain 1993), and in biomanipulations used sometimes for aquatic restoration (Lathrop et al. 2002). Increasingly, also, fish are recognised for their major roles in ecosystem processes that include trophic cascades, energy transfer between trophic levels, and the transport of nutrients between marine, freshwater and terrestrial ecosystems (Finney et al. 2000). With their importance increasingly recognised, fishes have been a central focus in conservation, pollution prevention and restoration in all aquatic environments. The value of these aquatic systems, in turn, is now strongly emphasized in environmental policy, planning and legislation throughout the world (Caddy 1999; Fluharty 2000; Baron et al. 2002; Sloan 2002).

All of these foregoing perspectives are, in their own right, enough to emphasize the need to understand the intrinsic dynamics of fish populations and the ecosystems of which they are a part. But this need is now being highlighted more than ever as aquatic systems are simultaneously viewed not only as the source of major goods and services, but also as systems whose use depends on long-term viability, integrity, sustainability and conservation (Pitcher 2001; Jackson et al. 2001). For fish species subject to regular, large-scale mortality through exploitation, this need for ecological understanding is paramount (Hilborn, Walters & Ludwig 1995). Most persuasive of all in the case for better ecological understanding, however, is the growing perception that fish conservation and management are now failing on a range of fronts, as expanded in this overview.

Given the importance of management issues involving fish, it is surprising that papers on this group have contributed less than 1–2% of the content of the Journal of Applied Ecology over recent years (Ormerod et al. 2002). Aquatic papers, in general, are relatively few by comparison with terrestrial (Edwards et al. 2000; Hogg et al. 2001; Robertson, Bacon & Heagney 2001; Muotka & Laasonen 2002). However, this situation is changing, with authors on aquatic themes increasingly keen to publish their leading work in the general ecological literature. Not only are these aquatic themes intrinsically important, but also they offer generic principles, concepts and applications with wider ecological relevance.

This short review, and the papers that follow, draw attention to some current aquatic issues, here exemplified by fish and fisheries, covered by a growing number of authors writing for Journal of Applied Ecology. In setting the scene for this ‘special profile’, this introduction overviews the context in which major papers on the applied ecology of aquatic systems are emerging, and it identifies scope for further contributions. Finally, as in all the Journal's ‘special profiles’, the papers collected and reviewed here illustrate the substantial contributions being made by ecologists in addressing real and present environmental problems (Ormerod et al. 2002).

Problems of exploitation

Reflecting the global importance of fisheries outlined above, the response of fish stocks to current patterns of exploitation are now among the most pressing of all of natural resource problems. The political, economic, consumer and conservation consequences are large. Data from the Food and Agriculture Organisation of the United Nations (FAO), collated at a global scale, suggest that c. 47% of fish stocks are already exploited to their maximum sustainable limits, while 18% are reported as over-exploited and 10% are depleted (FAO 2002). In other words, the FAO identify a clear requirement to reduce fishing pressure on a substantial proportion of the world's fisheries. Uncertainties in the data on many fish populations, difficulties in identifying constantly sustainable yields, risks that sustainable exploitation might be identified only after peaks yields are exceeded, and difficulties in controlling fishing effort, create major issues for fisheries ecologists and managers (Hilborn, Walters & Ludwig 1995; Larkin 1996; FAO 2002). Together, these issues have led to the widely publicised serial declines in stocks and catches (Cook, Sinclair & Stefansson 1997; Pauly et al. 2002), but also to less well known changes in the composition and ecological character of fish landed. Effects are most apparent in the northern hemisphere, and reflect a shift towards shorter-lived pelagic fish species feeding at lower trophic levels as larger piscivorous species have been fished out (Pauly et al. 1998). In the Journal of Applied Ecology, Pinnegar et al. (2002) illustrated how the Celtic Sea fish community has undergone trophic alterations of this type, with consequences for fishery yields and market prices. Symptoms of excessive exploitation also affect fishes in freshwaters, where fishery resources in general are considered important but under-valued (Pauly et al. 1998; FAO 2002).

The applied ecological consequences of fishery exploitation go well beyond these emerging impacts on our own resource needs. For example, the pronounced effects of some types of fishing methods on aquatic habitats and their fauna are increasingly well known, while more subtle consequences arise from impacts on populations of ‘ecosystem engineers’ (Watling & Norse 1998; Jennings et al. 2001; Coleman & Williams 2002). The latter organisms, by their actions, alter the architecture of aquatic habitats or have significant effects on biogeochemical cycles. Exploitation effects from fishing cascade to other trophic levels with consequences for wider ecosystem quality and conservation (Pinnegar et al. 2000). Management issues arise through the incidental by-catch of species that are discarded after capture, sometimes in large tonnages (Hall, Alverson & Metuzals 2000). By-catch also affects predatory fishes, turtles, birds and mammals whose populations can be extremely sensitive to the resulting increase in mortality because of their own low fecundity and long life-cycles (Schindler et al. 2002). In the Journal of Applied Ecology, Tuck et al. (2001) have provided one of the most seminal studies so far, drawing attention to the demographic consequences for a large, long-lived seabird, the wandering albatross Diomedea exulans. Other contributions to the Journal have addressed the activity, trends and distribution of marine mammals sometimes considered important predators of near-shore fishes, but which are also at risk from operations such as gill netting (McConnell et al. 1999; Thompson, Van Parijs & Kovacs 2001; Hammond et al. 2002; Van Parijs, Smith & Corkeron 2002). Many have distributions that reflect the richness and productivity of fish distributions – exactly the features sought also for commercial fishing activity.

The consequences of fishing can be pronounced for organisms with which people compete for harvestable stocks, while natural predators sometimes affect commercial fish species (Furness 2002). Some of the key studies published in the Journal have involved the Southern Ocean system, and in particular the interactions among marine predators (Antarctic fur seal Arctocephalus gazella and macaroni penguin Eudyptes chrsolophus), commercial fin-fish Champsocephalus gunnari and krill (including Euphausia superba; Everson et al. 1999; Boyd 2002). These species share interactions that highlight particularly clearly the importance of ecosystem approaches to fisheries management: even in relatively simple marine food webs, commercial species cannot be managed in isolation from the ecosystems that they occupy (FAO 2002). This view will have resonance for researchers on fisheries other than fin-fishes; for example, commercial wild shell-fisheries. Recent work in the Journal has illustrated, for example, the wider and sometimes major ecological impacts of commercial bivalve harvesting both at the exploitation stage (Ferns, Rostron & Siman 2000; Piersma et al. 2001) and through possible competitive impacts on other wild predators (Stillman et al. 2001).

Unexploited fish populations might not normally be sensitive to natural predation, with the population consequences damped out by density compensation. However, as fishes are affected increasingly from other environmental changes or from the sheer pressure of human exploitation, the control of natural predators may resurface as a management issue (Beamesderfer 2000; Swain & Sinclair 2000). Decisions to cull or control fish predators can lead to management conflicts where the predators in question have their own conservation importance (Swain & Sinclair 2000; Ormerod 2002). In this issue, Gremillet et al. (2003) continue to address the potential impact of growing populations of cormorants Phalacorax carbo on commercial fishery interest (Frederiksen, Lebreton & Bregnballe 2001). This most recent contribution offers an improved and regionally transportable bioenergetics model for assessing daily food intake in this species – now providing one of the best case studies of any wild fish predator.

The value of aquaculture?

Aquaculture is often lauded as a potential solution to fishery problems because it allows the economic and efficient production of fish protein, and because production can occur over a wide range of climates. Aquacultural performance is particularly favourable in warmer regions where poverty often limits access to other protein sources, but production has also grown substantially in north-temperate regions such as NW Europe. Aquaculture, however, brings its own range of difficulties. Although currently delivering a net addition to world fish production, in some locations where piscivorous species are farmed aquaculture can be a net user of fish production from wild populations. Negative environmental effects arise also through habitat modifications for installations, from the collection of seedstock, and from local adverse changes in water quality (Naylor et al. 2000). Many such ecological effects are only now being addressed as aquaculture expands, but appropriately designed experimental assessments are still scarce, and none has yet been published in the Journal of Applied Ecology.

Beside production effects, aquaculture brings spin-offs in the development of fish-breeding and husbandry. In the Salmonidae, for example, techniques are so well developed that threatened populations or important sport fisheries – major economic resources in their own right – are entirely supported or substantially reinforced from hatchery releases (Dannewitz et al. 2003). As well as benefits, however, there are potential costs or adverse impacts. They include possible genetic introgression into wild stocks (Hansen et al. 2000), reduced fitness among the released fish (Fleming et al. 1996), the invasion of wild communities by exotic salmonid species (McMichael & Pearsons 2001), competitive displacement of closely related species (Levin & Williams 2002), and the release of pathogens (Noakes, Beamish & Kent 2000). As with many fishery-related management issues, these effects occur over large spatio-temporal scales, particularly where the species involved are long-range migrants. Controlled investigations into the eventual effects on ecosystems are thus challenging, although novel approaches are being developed as revealed in this issue of the Journal of Applied Ecology by Dannewitz et al. (2003). These authors use a particularly elegant method of planting eggs from carefully contrasted wild or sea-ranched stock into a semi-natural stream, and then comparing subsequent fitness. Other assessments of the performance of hatchery-reared fish at a range of experimental scales will appear in forthcoming issues of the Journal.

Fish, fisheries and environmental change

As in many other environments, those occupied by fish are not stable, but characterised by natural and anthropogenic change. Natural environmental variations present their own challenges to fishery managers, for example in the changing yield of the large Peruvian anchovy fishery that follow El Niño events in the Pacific (FAO 2002). It is anthropogenic effects on fisheries, however, that fall mostly within the scope of the Journal of Applied Ecology because both their causes and consequences present management problems (Hall 2002). Issues of environmental change cut across the whole field of fish exploitation, conservation, restoration and management, and are increasingly sources of policy concern (FAO 2002).

With many fish stocks already exploited to their limits, additional stressors could have important repercussions. For example, since most fish species in marine systems occur in waters on the earth's continental shelves (Leidy & Moyle 1998), many feed or breed in exactly those shallow marine environments where the future climatic effects on temperature, upwelling and primary production will be most pronounced. Climate is recognised already as one of the strongest influences on the growth, assemblage composition and abundance of juvenile fish during their residency in estuarine or coastal waters with consequences for recruitment, production and nutrient flux (Finney et al. 2000; Attrill & Power 2002). Consequences might arise not only for exploitation, but also, as species’ distributions change, for marine protected areas designated for fish conservation (Soto 2001). Prediction to allow adaptive management in anticipation of future global change is still in need of considerable development (Hall 2002; Jurado-Molina & Livingston 2002).

While climate change reflects pollution through complex indirect pathways, changes in water quality have effects on fish that are more direct. Traditionally, the effects of aquatic pollutants have been disproportionately larger in freshwaters than marine waters. Previously widespread problems from organic effluents and some industrial discharges have been largely controlled, at least in economically richer countries, although some substances continue to cause concern (Hall 2002; Mason 2002). This includes pollutants whose ecological effects have been geographically extensive and long-standing despite large management efforts. After first becoming apparent as a major problem in the 1960s, eutrophication continues to have major effects on some lake systems (Verschuren et al. 2002). Similarly, impacts from acidification occurred over large areas of Europe and North America during the 19th and 20th centuries, but recovery among fish communities is far from complete. In some cases, populations are still maintained only by programmes of liming (Sandoy & Langaker 2001). In addition to these well-established problems, novel pollution issues arise as new chemicals are synthesised and ultimately released as contaminants. For example, the physiological effects of endocrine disrupting chemicals are now widely investigated by ecotoxicologists, although comparatively little effort has so far gone into assessing any ecological consequences (Sumpter & Jobling 1995). More generally, large ecotoxicological research efforts on fish provide an important basis for setting water quality objectives and for understanding pattern among wild populations (Robinet & Feunteun 2002), although critics argue that such work needs greater ecological relevance (Power & McCarty 1997). Investigations evaluating the ecological relevance or extensions of ecotoxicological research have occasionally made important contributions to the Journal of Applied Ecology, and we expect similarly seminal contributions in future (Sibly, Williams & Jones 2000).

In marine systems, pollution mostly affects estuaries, reefs and near-shore coastal waters, although consequences permeate to offshore areas following alterations to inshore marine nurseries, or due to changes in near-shore food-webs that cascade outwards (Micheli 1999; Hall 2002). Offshore pollution effects can be particularly pronounced where large, eutrophic rivers enter marine areas, for example in the well-known case involving the Mississippi and the Gulf of Mexico (Rabalais, Turner & Wiseman 2002). Marked pollution events can also occur following shipping incidents (Carls, Marty & Hose 2002), or chronically from low-level continuous waste disposal, particularly involving persistent or physiologically active compounds (Matthiessen & Law 2002).

Among the Journal's recent papers assessing the ecological consequences of pollutants for fish have been those assessing the bioaccumulation and biomagnification of contaminant body burdens. These issues are still highly topical due to the implications for people or other top consumers, and mercury, radionuclides and persistent organic pollutants are major research subjects (Hessen et al. 2000). Power et al. (2002) recently provided one of the few case studies of mercury accumulation in sub-arctic lakes where Inuit people rely heavily of subsistence fish harvests, thereby revealing yet another instance in which applied ecology has direct relevance to human well-being. In this issue of the Journal of Applied Ecology, Sundbom et al. (2003) examine the long-term dynamics of 137Cs in fish from Swedish lakes following the Chernobyl accident, in particular demonstrating how the effects of such contaminant pulses in fish can be modelled highly effectively.

Exotic fish introductions – accidentally and on purpose

In addition to being impacted by adverse environmental change, fish can be the cause of applied ecological problems, particularly as exotic species. While fishes have sometimes been accidentally introduced outside their normal range, for example in ship ballast, purposeful introductions have been far more common. The intentions include biocontrol, aquaculture, addition to recreational fisheries, use as bait and the release of former companion animals (Kolar & Lodge 2002). Quantitative data on the exact incidence of exotic fish introductions are few, reflecting the difficulty of identifying all instances of this artificial form of dispersal, particularly where it occurs within national boundaries. During the 1980s, Welcomme (1988) documented 1354 introductions of 237 non-indigenous species into the freshwaters of 140 countries, although this is now almost certainly an underestimate. Each such introduction often has its own profound impacts (Adams & Maitland 1998), but some of the consequences for conservation reach global significance (Miller 1989; Saunders, Meeuwig & Vincent 2002). The management problems that result include predatory, competitive or deplacement effects on indigenous fishes (Levin et al. 2002); general homogenisation of fish assemblages across areas that were previously distinct (Rahel 2000); the erosion of genetic biodiversity in otherwise isolated populations (Douglas & Brunner 2002); impacts on native vegetation (Lake et al. 2002); substantial structural and functional alterations to aquatic food webs (Townsend 1996); impacts on other vertebrates, such as amphibians or birds, with which fishes interact as predators, prey or competitors (Adams & Maitland 1998; Goodsell & Kats 1999; Gillespie 2001). Invasions may well become more likely following release in future as global change proceeds (Fausch et al. 2001). While steps are sometimes taken to minimise risks that exotic fish species will establish breeding populations, for example by releasing only sterile triploid forms (Bain 1993), in many other instances releases are made without control, licence or precautions. Increasingly, research efforts are turning to methods of controlling or eradicating exotic fish species, but the difficulties are substantial. In marked contrast to the regular contributions to the Journal of Applied Ecology on terrestrial exotic species (see Barlow 2000 for a review; for recent examples, see Bryce, Johnson & Macdonald 2002; Craze & Mauremootoo 2002; Somers & Morris 2002; Stapp 2002), there have been no recent contributions on exotic fishes despite the magnitude of this issue.

Unfavourable habitat and fragmentation

Compounding the potentially negative effects of exploitation, introductions, and adverse water quality on the integrity of fish communities, changes in habitat character also have major implications. In freshwaters, flow-regulation, insensitive catchment management and alterations to riparian or in-river habitats are perceived among dominant sources of change (Jones et al. 1999; Saunders, Meeuwig & Vincent 2002), but examples of research published in the Journal have been few (Manel et al. 2000). In addition, barriers such as dams can remove, fragment and isolate fish populations (Morita & Yamamoto 2002), also affecting survival and fitness by disrupting normal patterns of migration (Zabel & Williams 2002). Already, people probably appropriate over half of all accessible freshwater runoff, with demands set to increase further (Jackson et al. 2001). The resulting requirements to develop and exploit water resources will increasingly affect geographical regions that are rich in aquatic species, but currently poorly known ecologically (Ormerod 1999).

Alterations in river discharge and sediment transport have consequences for near-shore marine systems. Other major agents of change in habitat quality for marine fishes include the loss of some coastal habitats, waste disposal, installations for aquaculture, exploitation for both fin- and shell-fish, and exploitation of non-living resources such as fossil-fuels or renewable energy (Hall 2002). Habitat effects from some types of fishery exploitation have been particularly strongly researched (Watling & Norse 1998), but the effects of offshore energy or mineral exploitation are less well known, particularly in the growing sector of renewables.

Risks of fish extinction

Reflecting the sum total of all adverse environmental impacts on freshwaters, globally around 20% of all freshwater fish species are considered threatened by extinction (Jackson et al. 2001). In locations characterised by high diversity or marked endemicity, this proportion can be much higher (Leidy & Moyle 1998). However, extinction appears to be equally widespread across different ecological groups of fishes, suggesting widespread extrinsic causes (Duncan & Lockwood 2001). Future losses may well accelerate, and for example in North America fish extinction rates could exceed 4% per decade during this century (Ricciardi & Rasmussen 1999).

Indications of fish population trends and extinction risks in all aquatic systems can be difficult to detect, but problems are particularly acute in marine environments. Here, risks of extinction may have been overlooked perhaps because of previous misunderstandings about the sensitivity of marine systems to change, but also because aquatic organisms can seldom be observed directly (Roberts & Hawkins 1999). Factors that might pre-dispose species to extinction are known in relatively few groups (Dulvy & Reynolds 2002), although some ecological factors are emerging. As in freshwaters, extinction risks appears to be particularly high in regions of pronounced endemism, such as coral reefs (Roberts et al. 2002), that are also sensitive to rapid environmental change (Nystrom, Folke & Moberg 2000).

Management responses and conservation

Even in fish such as salmonids – among the most intensively researched of all vertebrates – the precise identification of causes and solutions in population decline can be difficult (Armstrong et al. 1998; Parrish et al. 1998; Ruckelshaus et al. 2002). Negative effects often operate in combinations that vary across spatio-temporal scales, particularly where fish species are migrants. Moreover, the scale of the problems involved mean that the required management actions are intrinsically challenging (Ruckelshaus et al. 2002). The exact balance of management aims for exploitation and conservation vary widely between species and locations, particularly in marine and freshwater systems.

Conservation or fish protection measures in freshwater systems increasingly aim for some blend of sustainable watershed management, flow maintenance, protection of water quality, exclusion of exotic species, and more localised conservation designation focused on specific water bodies (Baron et al. 2002; Saunders, Meeuwig & Vincent 2002). The last of these is still a minority approach, with surface waters considerably under-represented in reserve networks by comparison with terrestrial ecosystems. Fish figure infrequently in their designation or monitoring, so that important populations are often dispersed outside protected locations (Keith 2000). For example, in Britain, around 8% of the total land area is notified as Sites of Special Scientific Interest – still the major planning designation used for nature conservation – by comparison with less than 2–4% of main river and a considerably smaller percentage of total river length (i.e. including headwaters). However, very substantial river lengths in Britain are designated under the Fresh Water for Fish Directive (78/659/EEC), aiming to protect freshwater fish through water quality standards. Moreover, recent re-emphasis on freshwater conservation throughout Europe has followed the European Union Habitats Directive (92/43/EEC), which cited several fishes. As a result, some UK rivers are now identified as candidate ‘Special Areas of Conservation’ (SACs), specifically with these fish species in mind (Scottish Executive 2000). Further substantial implications will arise with implementation of the European Union directive on integrated river basin management with its strong emphasis on ecological quality (2000/60/EC). The consequences and effectiveness for fish conservation of these types of legislation, and for the status of protected freshwaters per se, are major issues that will have to be assessed over the coming years.

With the ideal conditions for basin-scale freshwater conservation for fish seldom met, compromise objectives can involve riparian-zone management or compensatory water discharges from impoundments (Saunders, Meeuwig & Vincent 2002). As occasionally revealed in the Journal of Applied Ecology, problems are particularly acute in less developed regions of the world where resources for aquatic conservation are fewer and rates of environmental change rapid (Ormerod 1999; Manel et al. 2000). In some high-profile locations for fish conservation, such as Lake Victoria, catchment-scale improvements in land use remain one of the few remaining options for halting and reversing major system changes (Verschuren et al. 2002).

A further problem in fish conservation is that issues depend not only on actions implemented now and in the future, but also on conditions inherited from the past. With many aquatic systems, and possibly most freshwater systems, already substantially altered by past environmental change, fish conservation will often require habitat restoration (Baron et al. 2002). This is emphasised particularly by the growing legislative drive in Europe and elsewhere to return systems to ‘good ecological status’ (2000/60/EC). Actions typically sought for fish restoration include solving past problems of water quality (Ludsin et al. 2001) or habitat degradation (Nislow, Folt & Parish 1999); restoring semi-natural flow regimes, for example by removing dams (Bednarek 2001); rebuilding fish populations, sometimes even with re-introductions following contractions in species’ range or local extinction (Pitcher 2001; Harig & Fausch 2002); and eradicating or at least containing introduced species of fish or other damaging aliens (Saunders, Meeuwig & Vincent 2002). In some instances, fishery restoration or rehabilitation measures have been successful both locally (Nislow, Folt & Parish 1999), and more extensively, for example in parts of the Great Lakes where eutrophication has been reversed (Ludsin et al. 2001). However, a common assumption in restoration ecology – that restoring past physical or chemical conditions is always sufficient to engender ecosystem recovery– has not always been validated (Ormerod 2003). Pretty et al. (2003) provide a further example in this issue of the Journal of Applied Ecology in an assessment of the effects of river-habitat rehabilitation on fish populations in lowland Britain. Their work reveals only negligible beneficial effects from physical manipulations alone, hinting at the potential importance of other limits on fish recovery such as connectivity, water quality or ecological attributes in the target species, all of which should ideally be addressed in aquatic restoration. In providing a badly needed systematic and replicated study of rehabilitation, Pretty et al. (2003) offer a model approach that will be valuable in addressing other stream-scale problems in river systems.

With terrestrial land use and pollution sometimes responsible for impacts on offshore fish habitats of global importance, some marine management issues have their solutions onshore (Ducrotoy, Elliott & De Jonge 2000; Brodie et al. 2001). In large contrast to freshwater systems, however, most management actions for fish and fisheries in marine systems emphasise the effects of exploitation on habitats and fish species. In recognition of the risks of present exploitation trends, Pauly et al. (2002) recently reinforced the importance of reducing fishing capacity to appropriate levels by reducing financial subsidies, and by zoning the oceans to safeguard unfished marine reserves. In addition to preserving important locations against damage by fishing activities (Watling & Norse 1998), the goals include restoring depleted stocks, supplying gametes or progeny to adjacent areas, halting loss rates of genetic diversity, and in general allowing more sustainable fishing practice alongside functional, diverse ecosystems. Despite controversy and clear difficulties associated with marine reserves (Sloan 2002), there is growing evidence of benefit not only to general marine conservation, but also to adjacent fisheries (Roberts et al. 2001). This issue of the Journal of Applied Ecology brings yet another example, in this case from New Zealand involving a mobile indicator species, further emphasising that the value of marine reserves generalises across marine regions and fish taxa (Willis, Millar & Babcock 2003). As with the work in this special profile by Pretty et al. (2003), Willis et al. (2003) also illustrate the value of a replicated design in assessing such large-scale questions as reserve designation.

A special profile: current issues with fish and fisheries

Together, this overview of recent work, and the small set of papers collected for this special profile, emphasize some of the current issues affecting fish and fisheries. Perhaps more importantly in view of the wider resource value of the earth's aquatic systems per se, they illustrate some of the major management issues affecting the ecosystems of which fish are a part. In turn, these issues are generated both from intrinsic aquatic factors, and from changes in the atmospheric and terrestrial environments to which the earth's aquatic systems are inextricably bound. In this respect, the current state of the world's fish, fisheries and aquatic ecosystems not only reflect aquatic management problems, but also they offer an integrating indication of wider environmental change.

Although the five papers that follow are apparently disparate – the benefit of aquatic reserves, river restoration for fish, the accumulation of contaminants, interactions with predators, and the fitness of salmonids from nurseries – they illustrate significant contributions from our authors on themes whose diversity matches today's most topical aquatic management issues. But even more, their single, unifying message is that the management of fish and fisheries – whether for nature conservation, restoration, predation, exploitation or ecosystem management – operates most effectively from a perspective of ecological understanding. Not only does this add weight to the growing view that fish management must consider target species as integral parts of aquatic ecosystems, but also it illustrates that the process of fish and fisheries management is one to which ecologists have much to contribute (Larkin 1996; Fluharty 2000; Pitcher 2001; FAO 2002).

Ancillary