Co-management is of increasing interest for fisheries management. We explore possibilities for, and barriers to, developing a co-management system, using threatened populations of landlocked Atlantic Salmon and Brown Trout as examples. Good management of natural resources requires not only knowledge about the resource, but also suitable tools to collect information and make decisions. In large ecosystems this can be difficult because many actors are involved, and various societal borders and traditions become barriers. Vänern is the largest lake in the European Union and it holds several distinct populations of large-bodied landlocked Atlantic Salmon and Brown Trout. The lake is used for commercial, subsistence, and sport fishing as well as for other recreational activities; in Klarälven, the largest river entering Vänern, sport fishing is popular. These salmonid populations were at critically low levels during the 1960s, but a stocking program since then has maintained the fishery. At least one wild stock appears to be recovering since being protected in 1993. Ecosystem users all have different needs: in the lake, sport fishermen say that catches of hatchery fish have declined, and commercial fishermen have focused on other species. In the river, wild salmon may be recovering: sport fishing is popular and an ongoing project investigates the possibilities for salmon to be able to circumvent hydro-electrical plants and reach historical Norwegian spawning areas. Not only do we lack information about the salmonids’ different life stages, we also lack a suitable socio-political organization to find sustainable solutions to the different needs of diverse user groups. We argue that a co-management system that enfranchises user groups in the Vänern-Klarälven ecosystem will improve sustainable management of wild and hatchery fish.

Introduction

To manage natural resources such as wild salmonid populations, we need good knowledge about the ecosystem, but we also need to overcome several sociopolitical, economic, intellectual and communicational barriers (Jacobsen et al., 2011). For migratory salmonids there is a need to understand the entire life cycle of the species, including both lake and river stages (Jonsson and Jonsson, 2011), despite the fact that most scientists work in either one or the other of these two ecosystems. Once research needs are determined, a monitoring program must be established to assess the effects of management decisions. Another barrier to progress is poor communication between scientists, managing authorities and user groups (Jacobsen et al., 2011). Finally, funding needs to be secured to address research needs and maintain management and monitoring programs.

Fisheries management is mostly about managing people, but a good knowledge of the resource is also required to inform policy development (Pitcher and Hart, 1982). For a large water body where resources are limited it can be difficult to obtain enough data to allow sound scientific advice. One way to deal with this is to form a partnership with the fishers who exploit the resource. They are out on the lake for a good part of the year and often have years of experience of the local conditions. This means that fishers can be employed to gather data, and that their local ecological knowledge can be gathered for evaluation and combined with scientific knowledge.

Efforts to bring fishers into the management system have been made through the establishment of co-management institutions. Co-management is defined by Jentoft (2003) as ‘… a collaborative and participatory process of regulatory decision-making between representatives of user-groups, government agencies, research institutions, and other stakeholders’. Co-management can be seen as a continuous problem-solving process, focusing on joint learning and understanding of how different management tasks are organized and solved (Walters, 1986).

The 2012 SOLVE symposium (State of Lake Vänern Ecosystem) brought together scientists and resource managers from Sweden, North America and beyond to assess the current knowledge level and future research needs for the Vänern ecosystem. Vänern supports a total commercial fishery of over 600 tonnes and c 2.9 million Euros per year. Although Salmon and Trout represent only a fraction of the total commercial value (4%) of the fishery, their ecology and fishery have been studied in some detail and the fish have an iconic status. Both species are well-recognized by the public and have high sport value due to a large recreational fishery. In this article we propose a co-management system, using Vänern’s migratory Salmon (Salmo salar) and Trout (S. trutta) as case studies. Vänern’s Salmon and Trout are also of interest because of their reliance on both lake and river habitats, so linking these ecosystems and their management.

The Väner-Klarälven ecosystem

The lake and river habitats

Lake Vänern (58°55′N 13°30′E) is the largest lake in the EU, with a surface area of over 5650 km2 (Willén, 2001). The lake has a temperate fish fauna that was isolated from the sea some 9000 years ago (Willén, 2001), and the salmonids are more related to the Baltic stocks than to North Sea stocks (Palm et al., 2012). Klarälven (59°23′N 13°32′0″ E) is the largest river entering Vänern. It begins in Sweden, and then flows through Norway and back into Sweden before entering the lake (Figure 1). The river holds many fish species, for example, Salmon, Trout, Grayling (Thymallus thymallus), Whitefish (Coregonus spp.) and Pike (Esox lucius). The Salmon and Brown Trout grow to a large size and historically migrated as far as 400 km upstream to spawn in the northerly sections of the river. Klarälven Salmon is one of few stocks of landlocked Atlantic Salmon in Europe and is protected by the EUs habitat directive. Today there are 11 power stations in the main river channel (Figure 1) but no functional up- or downstream fishways. A number of other rivers are known to have held migratory salmonid stocks historically (Ros, 1981), but today they are known only to remain Gullspångsälven and Tidan.

Salmonid management

In the 1800s, catches in both Vänern and Klarälven were high, but decreased during the 1900s to critically low levels in the 1960s, resembling many large rivers around the world (Parrish et al., 1998; Piccolo et al., 2012). Timber floatation and hydroelectric power and high fishing pressure, lies behind these decreases (see Nordberg [1977] and Piccolo et al. [2012] for historical details). After the introduction of Smolt stocking during the 1970s, return rates have increased again (Figure 2) (Nordberg, 1977; Piccolo et al., 2012). Today the Vänern-Klarälven ecosystem holds both wild and hatchery reared stocks of Atlantic Salmon and Brown Trout (Piccolo et al., 2012). All hatchery Smolts are released downstream of the last hydro-electric plant (HEP) in Forshaga (Figure 1). Smolt spend two or more years in the lake and as returning spawners they swim 25 km up Klarälven before reaching the first HEP at Forshaga (Figure 1). There being no fish passes there is a “trap and hauling system” to catch fish for both hatchery purposes and for transportation to the spawning areas. Some fish are taken for the hatchery, but the rest are transported by truck past seven HEPs, and are released into the Klarälven again. Fish can reach upstream spawning areas in the Swedish part of the river. They cannot reach the pristine spawning areas in Norway (Nordberg, 1977).

Post-spawners descend either directly after they spawn in early November or after the winter in March. The Smolt run occurs in May to early July and the outward migrating Smolts are commonly 2–3 years old (Runnström, 1940; Norrgård et al., 2012; Bergman et al., unpublished data). All downstream migration occurs through power station turbines or spill gates.

Increasing wild population of salmon: A new pattern that changes everything

Prior to 1993 it was impossible to differentiate between wild and hatchery reared fish. Since then, all hatchery fish have received an adipose-fin clip, and there is a no-catch regulation for wild Salmon and Trout in the lake (Fiskeriverket, 1993). The number of wild salmon returning to Forshaga has increased since 1996 (Figure 3), while return rates of hatchery Salmon have decreased slightly (Piccolo et al., 2012). The proportion of wild Salmon and Trout combined in the commercial catch in Vänern has increased from a maximum of 5% in 1997 (Fiskeriverket and Länsstyrelsen i Värmlands län, 1998) to up to 30–50% by 2008 (Degerman, 2008; Hållén, 2008; Johansson et al., 2009). The increasing proportion of wild fish in the lake could be a result of (1) increased natural production and/or protection of wild fish and (2) declining numbers and/or decreased survival of hatchery Smolt (Eriksson et al., 2008). It is important to note that there is much uncertainty in the hatchery release data and catch statistics (Piccolo et al., 2012), and that the most obvious trend is the increasing returns of wild salmon to Forshaga, and apparent increasing proportions of wild fish caught in Vänern. Some of this uncertainty could be reduced in a co-management system through fishers gathering more systematic data on the species composition of catches.

What we know and do not know

Until recently, much research is focused on achieving an estimate of the numbers of salmonids in their different life stages in the river, including both the downstream and upstream migration phases in the Swedish section. Wild and hatchery reared fish have been studied. In 2009 only about 20% of downstream migrating wild Smolt passed all eight HEPs (Norrgård et al., 2012; Figure 1). Among-year-variation has not been studied, and survival might be higher in some years.

Predation from both in-stream predators and terrestrial mammals or birds might add to the mortality caused by HEPs so limiting the population size of salmonids. In 2012 we explored the activity pattern and diet of pike in the lower part of Klarälven during the Smolt run. Concurrent studies explore migration behavior of both wild and hatchery reared Smolt in the same area and preliminary result show larger migration success for wild than hatchery reared Smolts. Experimental work has also shown that migratory behavior of Smolts is influenced by feeding regime and food quality (Lans et al., 2011; Bergman et al., unpublished data). Studies of the upstream migration of spawners and downstream migration of kelts started in 2011. These explored the upstream and downstream migration of early and late ascending Atlantic Salmon, wild and hatchery reared Atlantic Salmon, and Brown Trout. Aspects studied were the type of fish (i.e. wild or hatchery), the timing of migration, and the importance of gender and size. Concurrently we also follow ascending Atlantic Salmon in the lower part of the river, below the HEP closest to the lake, to explore their migration and evaluate the efficiency of the fish trap at the Forshaga HEP. A population model to describe the status of Atlantic Salmon in the Vänern-Klarälven ecosystem is being developed based on our Smolt, spawner and kelt studies together with population estimates from other sources, including the Norwegian Institute for Nature Research (NINA), Norway, and the Värmland County Administrative Board. There are also ongoing genetic analyses of the different Vänern salmonid stocks by the Swedish University of Agricultural Sciences (SLU) (Piccolo et al., 2012; Palm et al., 2012). Additional input from fishers would also be welcome but at present there is no easy way to obtain this. A formalized co-management system would provide the appropriate forum within which fishers could make their contribution.

In Vänern we still lack effort-related monitoring data on the present commercial, subsistence, and sport fishery for Salmon and Trout (Piccolo et al., 2012). It is in this area that a co-management system could make an important contribution as fishers, both recreational and commercial, are out on the lake for many days of the year and could easily contribute data on effort. Data on total catches exist on commercial, but not subsistence, fishery but there is a lack of data on effort. Until recently Salmon and Trout data were pooled so degrading the historical record. Recreational catches of hatchery reared fish in the lake is free and catches are not reported, but in 2013 a new study to estimate sport fishing pressure on the lake was started. In Klarälven it is possible to fish both wild and hatchery reared fish downstream of the 1st HEP in Forshaga, the fishery is managed by local landowner associations and total catches are reported annually. Piccolo et al. (2012) estimated that both commercial and subsistence fishery catches decreased during 1985–2009 whereas sport fishing catches increased to 50 tonnes. Alternative estimates of recreational catches have shown a decrease from 50 to 20 tonnes between 1998 and 2011 (Johansson and Andersson, 2011). There is an active but unreported sport fishery on wild and hatchery fish in the river upstream of the Forshaga HEP.

Discussion

The potential for wild salmonids in Klarälven and Vänern

Nilsson (1979) proposed a food web for Vänern’s pelagic zone. His research focused on salmonids and their prey because they attract so much worldwide attention (Bottom et al., 2009). They have unsurpassed food and sport value, and many populations are endangered (Piccolo, 2011 and references therein). When Nilsson (1979) studied Vänern, salmonid populations were at an all-time low, and as in many other ecosystems hatchery production seemed the logical answer (Behnke, 2002). Indeed, hatchery production has brought Vänern’s salmonids back from the brink of extinction while simultaneously maintaining a considerable commercial fishery. In addition, a rapidly-expanding sport fishery has developed since hatchery production peaked in the 1990s. Over the past decade, production of wild Smolt in Klarälven has increased dramatically while survival of hatchery Smolts has decreased (Piccolo et al., 2012; Bergman et al., unpublished data). Authorities overseeing the Vänern ecosystem are now faced with difficult decisions as to how the fish community and the fisheries ought to be managed: What emphasis should be placed on restoring wild, native salmonid populations in Klarälven, and other tributaries? To what extent can hatchery production be replaced by wild production? How will continued increases in wild fish affect survival of the hatchery Smolts upon which all of the fisheries depend? Alternatively, how might proposed changes in strategies for the release of hatchery Smolt influence the success of the wild fish conservation programs? And finally, how will the future management of Vänern’s salmonids effect the complex food web interactions of the lake as a whole, and the myriad ecosystem services these provide to the region? Below we argue that much key scientific knowledge about the Vänern ecosystem is still lacking, even for Atlantic Salmon and Brown Trout, and that the most successful way to improve this situation might be to develop a co-management system in which all stakeholders are engaged in the common goal of long-term sustainability.

Barriers to overcome

Scientists are now expected to collaborate with a range of stakeholders to produce good management plans. For salmonids in the Vänern-Klarälven ecosystem we must develop a holistic understanding of the ecosystem. This means producing knowledge of all stages of the life cycle of Salmon and Trout, which will demand collaboration between habitat specialists. Further, efforts must develop communication between scientists, managing authorities and other stakeholders in both Sweden and Norway. In addition, the large size of the catchment area of this ecosystem generates complications. There are several separate authorities involved in the management of the lake as there are two counties in each of the two countries involved in this bi-national-ecosystem. This presents a major challenge!

Since the compensatory Smolt stocking started during the 60s data has been collected on the stocked fish. Commercial and recreational fishermen have been involved in data collection but neither group has a clear and unified goal for data collection and their numbers have decreased (Brendan et al., 2010). Furthermore, as the goals have changed over time the “sample characteristics” of the marked fish have varied, making it hard to evaluate the data set. For the Vänern-Klarälven ecosystem, this means that despite long-term data collection efforts, we still lack essential information of the salmonid populations and the role of hatchery reared salmonids in the ecosystem. Although all elements of the ecosystem are being monitored (Vänerns vattenvårdsförbund, 2011; AL Control, 2012), there is a strong need for well-coordinated monitoring programs and for a continuous analysis of the data set.

A new management plan?

Ecosystem based fishery management is now a goal of many management agencies (Link, 2010). This recognizes the fact that fish resources are embedded in an ecosystem, but requires more knowledge than we yet have. A major deficiency is the lack of well tested models of and sufficient data for exploited ecosystems. Developing workable models is the job of scientists and can be achieved by a few, but obtaining good data requires a larger group. In the Vänern-Klarälven ecosystem our understanding is best for the river part of the ecosystem. We also have indirect measurements of survival of fish in the lake. Data collection from Vänern could be improved and a preliminary analysis of an ecosystem can be facilitated by scientists collaborating with resource users, who spend much time on the lake, and managing authorities. Fishers’ knowledge can be gathered through interviews and used to develop a preliminary understanding of how the ecosystem is structured and functions (Olsson and Folke, 2001). Fishers can also be engaged in a joint research program and can help to develop management policies, especially if they are drawn into the scientific enterprise through workshops (Walters, 1986).

We propose that Vänern fishery is best documented and managed through co-management. To do this we need to understand that co-management means paying attention to what resource users know and want. Here, it is important to establish a trusting relationship between authorities and stakeholders, since fishermen who actively choose to work with scientists are motivated by the possibility of influencing and improving management, but there is also a fear that there might be hidden agendas possessed by the authorities and that research results could be used against them (Jacobsen et al., 2011). All stakeholders must be motivated to achieve sustainable management. Achieving this will need models of the lake ecosystem that predict sustainable levels of fishing. Sweden’s second largest lake, Vättern, could serve as an example with a well-established fisheries co-management group acting as a working committee in the Lake Vättern Society for Water Conservation, LVSWC (Stöhr et al., 2014). They take part in an participatory research project bringing fishers, scientists and policy makers together to work towards sustainable fisheries for the benefit of society (http://gap2.eu/case-studies/case-study-6/ [last accessed 26 September 2013]; Mackinson et al., 2011; Jacobsen et al., 2011) which has been an important stimulus for the introduction of co-management.

One way to convince fishers and other stakeholders that co-management is worth doing is to involve them at ALL levels of the co-management process. The idea of participatory research in Vänern is not new, there are some ongoing projects involving scientists and stakeholders, but several earlier attempts have failed as a result of disagreements among stakeholders (A. Sandström and M. Johansson, Swedish University of Agricultural Sciences, Department of Aquatic resources, Institute of Freshwater Research, Drottningholm, Sweden, pers. com.). However, the first steps towards co-management have already been taken by the County Administrative Boards of Västra Götaland and Värmland, together with Vänerns Vattenvårdsförbund.

A major problem influencing the success of the co-management is the relationship between fisher, scientist and manager. Traditionally, fishers have not been involved in data gathering and management. Although some fishers in the last quarter of the 19th century raised the question of overfishing (Smith, 1994), they have become passive elements in the fishery and are manipulated by a top-down management system. This has led to alienation of the fisher from the scientists and managers, an alienation partly caused by the separation of intellectual outlook and training and partly by the professionalization of science and management which leads to institutional traditions and methods that exclude those that are not members (Finlayson, 1994). True advances in developing successful co-management will only be made once the fisher has accepted a role as a leader in setting the management goals. Persuading fishers to take this lead will be aided by showing that sustainable exploitation has benefits for marketing the resource.

It is self-evident that a robust funding model must be developed if the co-management approach is to be implemented successfully. If the co-management institution or consortium cannot guarantee its own economic sustainability over the long term it will be difficult to attract stakeholders to voluntarily take part in the process. Also, good monitoring and regular evaluation of the monitoring efforts and management constraints require long term funding. Previous efforts to produce a fisheries management plan for Vänern have documented an existing set of interested fishers, managing authorities and scientists willing to work towards a co-management consortium. But ultimately, whether or not this set is supported financially is a political issue! Politicians and decision makers have to be convinced that the ecosystem services provided by the lake are in danger of being seriously damaged if their role is not well enough appreciated and managed. This is an issue that concerns all who live in the Vänern catchment.

Conclusions

As ecosystem-based management is a possible way towards sustainability, co-management seems to be a natural way to implement that. We identify four major barriers: (1) ecosystem borders and state/county borders are rarely the same; (2) different stakeholders have different needs and perspectives; (3) coordinating the monitoring that is needed for salmonids with their complex life cycle in a large ecosystem is difficult and expensive; (4) it is difficult to attract adequate funding. We argue that by creating a Väner-Klarälven ecosystem management consortium we have a better chance to overcome these barriers. In such a consortium scientists, managers and stakeholders meet and work together. Through this process, not only can they better coordinate research and management efforts, they can also better understand each other’s perspectives and find acceptance for necessary trade-offs. Further, we argue that by using Atlantic Salmon and Brown Trout as example species we can show the full complexity of the problem, as these species need both river and lake habitat to complete their life cycle. Finally, we hope that a co-management group that clearly holds a holistic perspective will find it easier to gain public support needed to attract the sustainable funding for ecosystem management.

Funding

We thank the European Union and the European regional development fund for supporting the project Vänerlaxens fria gång (S30441-48-10), Fortum Generation AB, Karlstad University and The County Administrative Board of Värmland for supporting different parts of the research in Klarälven.

References

AL control
,
2012
.
Norra Vänern 2010, Norra Vänerns intressenter. (North Lake Vänern 2010, North Lake Vänerns stakeholders. In Swedish.)
.
AL control laboratories
,
Karlstad, Sweden
.
Behnke, R. J.,
2002
.
Trout and salmon of North America
.
The Free Press
,
New York
.
Bottom, D. L. , Jones, K. K. , Simenstad, C. A. , Smith, C. L.,
2009
.
Reconnecting social and ecological resilience in salmon ecosystems
.
Ecology and Society
14
,
5
.
Brendan, T. O. , Jones, M. L. , Ebner, M. P.,
2010
.
Sensitivity of tag-recovery mortality estimates to inaccuracies in tag shedding, handling mortality, and tag reporting
.
J. Great Lakes Res.
36
,
100
109
.
Degerman, E.,
2008
.
Vänern–hur många laxar och öringar är vildproducerade–en spekulation. (Lake Vänern–how many salmon and trout are wild produced–a speculation. In Swedish)
.
PM Fiskeriverkets Sötvattenslaboratorium
,
2008-08-04
.
Eriksson, L.-O. , Rivinoja, P. , Östergren, J. , Serrano, I , Larsson, S.,
2008
.
Smolt quality and survival of compensatory stocked Atlantic Salmon and Brown Trout in the Baltic Sea
.
Department of Wildlife, Fish, and Environmental studies
,
Umeå, Sweden
.
Report 62
.
Finlayson, A. C.,
1994
.
Fishing for truth. A sociological analysis of northern cod stock assessments from 1977–1990
.
Social and Economic Studies No 52, Institute of Social and Economic Research, Memorial University of Newfoundland
.
Fiskeriverket
,
1993
.
Fiskeriverkets föreskrifter för vissa sötvattensområden. (Regulations form some freshwater areas by the Board of Fisheries. In Swedish)
.
FIFS
1993
:
32
.
Fiskeriverket, Länsstyrelsen i Värmlands län
,
1998
.
Lax- och öringfisket i Vänern. (Salmon- and trout fishery in Lake Vänern. In Swedish)
.
Fiskeriverket Information nr 8
.
Hållén, A.,
2008
.
Hur stor del av Vänerns lax är vild? En undersökning av andelen vild respektive odlad lax i Vänern. (What proportion of the Vänern salmon is wild? An investigation of the proportion wild and hatchery reared salmon in Vänern. In Swedish)
.
Länsstyrelsen i Västra Götalands län
,
Rapport 2008, 78
.
Jacobsen, R. B. , Wilson D. C. K. , Ramirez-Monsalve, P.,
2011
.
Empowerment and regulation–dilemmas in participatory fisheries science
.
Fish and Fisheries
13
(
3
),
291
302
.
Jentoft, S.,
2003
.
Co-management–the way forward
. In Wilson, D. C. , Nielsen, J. R. , Degnbol, P. (Eds.)
The fisheries co-management experience. Accomplishments, challenges and prospects
, pp.
1
14
.
Kluwer Academic Publishers, the Netherlands
.
Johansson, M. , Andersson, M.,
2011
.
Trollingtävlingarna Kinnekulle och Sunnanå 2010 samt en skattning av trollingfisket i Vänern perioden 1997–2009. (Trolling competition at Kinnekulle and Sunnanå 2010 and an estimation of the trolling fishery in Vänern during 1997–2009. In Swedish)
.
Fiskeriverket
,
Stockholm, Sweden
.
Dnr 26-2011, 11 sidor
.
Johansson, M. , Degerman D. , Steénson, S.-G.,
2009
.
Vänerns bestånd av odlad lax och öring 1997–2008 – data från Kinnekulleträffen. (Vänern stock of reared salmon and trout. In Swedish)
.
PM 2009-04-09
.
Jonsson, B. , Jonsson, N.,
2011
.
Ecology of Atlantic Salmon and Brown Trout-Habitat as a template for Life Histories
.
Fish and Fisheries Series
.
Springer
,
New York
.
Lans, L. , Greenberg, L. A. , Karlsson, J. , Calles, O. , Schmitz, M. , Bergman, E.,
2011
.
The effects of ration size on migration by hatchery-raised Atlantic Salmon (Salmo salar) and Brown Trout (S trutta)
.
Ecology of Freshwater Fish
20
,
548
557
.
Link, J.,
2010
.
Ecosystem-based fisheries management, Confronting tradeoffs
.
Cambridge University Press
,
Cambridge, UK
.
Mackinson, S. , Wilson, D. C. , Galiay P. , Deas, B.,
2011
.
Engaging stakeholders in fisheries and marine research
.
Marine Policy
35
,
18
24
.
Nilsson, N.-A.,
1979
.
Food and habitat of the fish community of the offshore region of Lake Vänern, Sweden
.
Report for the Institute for Freshwater Research, Drottningholm
,
50
,
133
167
.
Nordberg, P. O.,
1977
.
Laxplan för Klarälven. (Salmon plan for Klarälven. In Swedish)
.
Sundsvall. 354
.
Norrgård, J. R. , Greenberg, L. A. , Piccolo, J. J. , Schmitz, M. , Bergman, E.,
2012
.
Multiplicative loss of landlocked Atlantic Salmon Salmo salar L. Smolts during Downstream Migration through Multiple Dams
.
River Research Applications
29
,
1306
1317
.
Olsson, P. , Folke, C.,
2001
.
Local ecological knowledge and institutional dynamics for ecosystem management: a study of Lake Racken Watershed, Sweden
.
Ecosystems
4
,
85
104
.
Palm, S. , Dannewitz, J. , Johansson D. , Laursen, F. , Norrgård, J. R. , Prestegaard, T. , Sandström A.,
2012
.
Populationsgenetisk kartläggning av Vänerlax. (Population genetical mapping of Vänern salmon. In Swedish)
.
Aqua reports 2012, 4
.
Parrish, D. L. , Behnke R. J. , Gephard S. R. , McCormick S. D. , Reeves G. H.,
1998
.
Why aren’t there more Atlantic Salmon (Salmo salar)?
Can. J. Fish. Aq. Sci.
55
(
l
),
281
287
.
Piccolo, J. J.,
2011
.
Challenges in the conservation, rehabilitation and recovery of native stream salmonid populations: A letter from Luarca, 2010
.
Ecology of Freshwater Fish
20
,
346
351
.
Piccolo, J. J. , Norrgård, J. R. , Greenberg, L. A. , Schmitz, M. , Bergman, E.,
2012
.
Conservation of endemic landlocked salmonids in regulated rivers: a case-study from Lake Vänern, Sweden
.
Fish and Fisheries
13
,
418
433
.
Pitcher, T. J. , Hart, P. J. B.,
1982
.
Fisheries ecology
.
Kluwer Academic Publishers
,
Dordrecht, Netherlands
.
Runnström, S.,
1940
.
Vänerlaxens ålder och tillväxt. (Age and growth of Vänern salmon. In Swedish)
.
Meddelanden från Statensundersöknings- och försöksanstalt för sötvattensfisket No. 18
.
Smith, T. D.,
1994
.
Scaling fisheries: the science of measuring the effects of fishing 1855–1955.
Cambridge University Press
,
Cambridge, UK
.
Stöhr, C. , Lundholm, C. , Crone, B. , Chabay, I.,
2014
.
Stakeholder participation and sustainable fisheries: an integrative framework for assessing adaptive comanagement processes
.
Ecology and Society
19
(
3
),
14
.
Vänerns vattenvårdsförbund
,
2011
.
Årsskrift 2011. (Yearbook 2011. In Swedish)
.
Vänerns vattenvårdsförbund
,
Mariestad
.
Report No 66
.
Walters, C. J.,
1986
.
Adaptive management of renewable resources
.
Macmillan Publ. Company
,
New York
.
Willén, E.,
2001
.
Four decades of research on the Swedish large lakes Mälaren, Hjälmaren, Vättern and Vänern: significance of monitoring and remedial measures for a sustainable society
.
Ambio
30
,
458
466
.