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  • 1.
    Stage, Jesper
    et al.
    Mid Sweden University, Faculty of Human Sciences, Department of Social Sciences.
    Zimmerman, Jenny
    Mid Sweden University, Faculty of Science, Technology and Media, Department of applied science and design.
    Crayfish management in the Ljungan river: Managing with shocks2012Conference paper (Other academic)
  • 2.
    Stage, Jesper
    et al.
    Mid Sweden University, Faculty of Human Sciences, Department of Social Sciences.
    Zimmerman, Jenny K M
    Mid Sweden University, Faculty of Science, Technology and Media, Department of applied science and design.
    Crayfish management in the Ljungan river: Managing with shocks2012In: Visible Possibilities: The Economics of Sustainable Fisheries, Aquaculture and Seafood Trade: Proceedings of the Sixteenth Biennial Conference of the International Institute of Fisheries Economics and Trade, July 16-20, Dar es Salaam, Tanzania / [ed] Ann L. Shriver, 2012Conference paper (Other academic)
    Abstract [en]
    • The noble crayfish fishery in the Ljungan river system in Sweden has been subjected to two major shocks; hydropower development in the 1970s, which reduced water flow throughout the system with attendant effects on the crayfish stocks, and an outbreak of crayfish plague in the 1990s which wiped out the noble crayfish in most of the river system. Differing ownership structures for the fishing rights in different parts of the river system have led to different management systems, ranging from sole private ownership through management by fishermen's associations through to effective open access fishing. We study how these different systems of management have affected the crayfish, and compare the outcomes to those from the hydropower development in the 1970s.

  • 3.
    Zimmerman, J K M
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
    Palo, Thomas R
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
    The decline and extinction of Noble crayfish in the river Ljungan, Mid-Sweden.: A case of non-sustainable harvest2007In: 92nd ESA/SER Joint Meeting, San Jose 5-10 August 2007, 2007Conference paper (Refereed)
  • 4. Zimmerman, Jenny K M
    Body growth of noble crayfish (Astacus astacus) after reintroduction to a northern river (Ljungan, Sweden)Manuscript (preprint) (Other academic)
    Abstract [en]

    Noble crayfish were introduced to the River Ljungan as part of a reintroduction program. Crayfish were caught at five sites and individually marked with passive integrated transponders (PIT-tags). At each sampling occasion, the crayfish were sexed and their total lengths measured before being released to the same spot where they were captured. The size structure and growth rates were compared between the different sites and a linear growth model was developed from recapture data. The analysis revealed that crayfish moulted once annually with length increments close to the maximum that is reported for the species. The relative growth increment of males was 20% greater than for females. The growth and size of the length increment were not associated to different habitats or water temperature at the sites. Growth was also measured in the River Ljungan in the 1960s. When compared to the conditions from the 1960s, it could not be precluded whether the differences in climate or population density from that time had a positive effect on the body size growth rate as observed today. A conclusion from this study is that noble crayfish have ability to grow just fast as at its southern locations as the northern edge of its distribution area.

  • 5.
    Zimmerman, Jenny K M
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences, Engineering and Mathematics.
    Conditions for sustainable crayfish populations in northern Sweden2009Report (Other academic)
  • 6.
    Zimmerman, Jenny K M
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences, Engineering and Mathematics.
    Kräftkokbok - om konsten att sköta ett kräftvatten2010Other (Other (popular science, discussion, etc.))
  • 7.
    Zimmerman, Jenny K. M.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of applied science and design.
    LOCAL ENGAGEMENT - A PREREQUISITE FOR SUCCESSFUL REINTRODUCTION2012Conference paper (Refereed)
  • 8.
    Zimmerman, Jenny K M
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Ecotechnology and Sustainable Building Engineering.
    Local engagement was a prerequisite for the comeback of the Noble crayfish (Astacus astacus) in the River Ljungan2012In: Crayfish News, ISSN 1023-8174, Vol. 34, no 1-2, p. 11-12Article in journal (Other academic)
  • 9.
    Zimmerman, Jenny K M
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Ecotechnology and Sustainable Building Engineering.
    Lokalt engagemang – en förutsättning för lyckad restaurering2012Conference paper (Other (popular science, discussion, etc.))
  • 10.
    Zimmerman, Jenny K. M.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of applied science and design.
    Noble Crayfish (Astacus astacus) in a Changing World: Implications for Management2012Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The noble crayfish (Astacus astacus) is critically endangered in Sweden. This is mainly due to the crayfish plague (Aphanomyces astaci), a lethal disease that, among other things, can be spread through the stocking of fish from contaminated water or contaminated fishing gear. The largest single propagation path is the illegal introduction of infected signal crayfish (Pacifastacus leniusculus). A conservation measure for crayfish is to re-introduce it to where it has a chance to survive, though a sustainable, locally regulated fishing can also serve as an indirect protection for the species. When the local inhabitants are allowed to keep their fishing culture and when fishing is acceptable, the incentive for illegal stocking of signal crayfish is low. However, it is important to avoid overfishing because the recovery, especially in the northern regions, can take several years. Therefore, it is important to know how crayfish respond long-term to fishing and environmental factors.

    Crayfish populations became extinct in the River Ljungan for unknown reasons in 1999. The water flow of the river has been used for activities such as fishing, timber transport and hydroelectric power since the 1500s, and the noble crayfish has been part of the fauna since the last century. The River Ljungan was known as one of Sweden's best fishing areas for crayfish and fishing became an important part of the local tradition. When the crayfish populations became extinct, a reintroduction program was a natural step, and crayfish are nowadays re-established in the river.

    From 1963 to 1990 the Swedish Board of Fisheries collected data from crayfish fishing in the River Ljungan to determine the economic damage to fishery owners caused by the construction of a power plant. After each season the fishermen reported the catch. In this thesis, the data was used to investigate which factors influence the long-term size of the crayfish catch and how the crayfish catches were affected by the power plant building. After re-introduction of the crayfish to the River Ljungan, the local fishermen monitored the population development in a simple, standardized way. To examine the validity of their measurements and to investigate the body growth of the individuals, a capture-recapture technique with a permanent marking of the crayfish was used.

    The crayfish catches were primarily impacted by the previous years' catch size, and a large catch the previous year resulted in a reduced catch the following year. A mild winter climate (NAO-index > -0.7) six years before the catch implied a large catch, whereas a high water flow during the autumn or spring (>95m3s-1) two years before the catch, implied a poor catch. Major habitat changes in the form of greatly reduced water flow (~90%) were negative for crayfish catches. The standardized method of fishing used by the local fishermen to monitor the development of the crayfish population was precise enough to detect population trends and this method can therefore be recommended to monitor future re-introductions of crayfish. Although the River Ljungan is located at the northern edge of the species' range, noble crayfish in the river presently have a body growth rate that is close to the maximum measured for crayfish (8 mm/moult for females and 10 mm/moult for males).

    Based on the results, the most important advice for sustainable fisheries in Ljungan and other northern rivers is to:

    • Monitor the population trends, NAO-index and water flow in May and October. 
    • Use the results from the monitoring to determine the number of allowed fishing days and traps.
    • Collect data about the catch size and efforts from legal fishing and use it to evaluate the sustainability of the fishing.
    • Enhance the buildup of the harvestable cohort by

    -saving reproductive females

    -introduce a size limit of 10 cm

    -provide proper shelters for the non-harvestable cohort.

  • 11.
    Zimmerman, Jenny K M
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences, Engineering and Mathematics.
    Slutrapport Förstudie för Älvens Hus: Ett LEADER-projekt i samarbete med Mittuniversitetet, Ånge kommun, 16 lokala fiskevårdsområden och en entreprenör2011Report (Other (popular science, discussion, etc.))
    Abstract [sv]

    Arbetet med förstudie för ”Älvens Hus” visar att det går att överbrygga både läns- och kommungränser när det gäller fiske. Det går att diskutera förvaltningsfrågor över gränserna. Arbetet visar också att det finns ett behov av lättförståelig information och utbildning om hur man förvaltar den utrotningshotade flodkräftan. Projektet har visat att det finns förutsättningar i vår region för att utveckla en uthållig, ekologisk verksamhet kring flodkräftan och fiske, men att det saknas entreprenörer i form av kunniga fiskeguider som kan länka samman deltagare, fiskevårdsområden och besöksnäring. Projektet har visat att naturum Ånge kan arbeta tematiskt över ett vidare geografiskt område och vara ett fönster för hela Mittlandregionen samt att naturum Ånge behöver förnya sin utställning för att klara detta. Projektet har visat att naturum Ånge har behov av att inleda nya samarbeten; både av ekonomisk och av kunskapsmässig natur. Detta är ett tidsödande arbete, men nödvändigt för att få till stånd en utveckling.

    De erfarenheter vi har fått i projektet visar att det är viktigt att låta samverkan och nätverksbyggande ta tid. Det tar tid att bygga upp förtroende. Vår projekttid på ett och ett halvt år var tillräcklig när det gällde fiskevårdsområdena, men för att inleda nya samarbeten för naturum Ånge var tiden för kort.

    Projektet har fört samman fiskevårdsområden från hela regionen i ett gemensamt nätverk och bidragit till ökad kunskap om flodkräftan till en bredare allmänhet genom ”Kräftkokbok – om konsten att sköta ett kräftvatten”. Projektet har också bidragit till att naturum Ånge får behålla sin status som naturum och att det kommer anläggas en naturstig med vatten- och kräfttema i anslutning till naturum Ånge.

  • 12.
    Zimmerman, Jenny K M
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Ecotechnology and Sustainable Building Engineering.
    Vattenkraften - hot eller möjlighet för flodkräftan?2013Conference paper (Other academic)
  • 13.
    Zimmerman, Jenny K M
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Ecotechnology and Suistainable Building Engineering.
    Grönlund, Erik
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Ecotechnology and Suistainable Building Engineering.
    van den Brink, Paul
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Ecotechnology and Suistainable Building Engineering.
    Is Astacology Environmental Science?2019In: Book of abstracts.: IAA Gotland 2019 Crayfish Conference, 2019Conference paper (Refereed)
    Abstract [en]

    Environmental Science aims to study the relationships between human beings influence on and dependence of nature, the interaction and integration of ecological, social and technical systems as well as the strategies for sustainable use of natural resources. The linking of social, ecological and economical aspects in Environmental Science can provide useful tools for the study, management and conservation of freshwater crayfish from a broad social perspective. Therefore, it is of interest to explore the relationships between Environmental Science and Astacology. By analysing the aims of the International Association of Astacology and the content of some volumes of Freshwater Crayfish from an Environmental Science perspective we found that Astacology is operating within the field of Environmental Science. The focus is mainly on identifying underlying mechanisms of environmental issues. We will point out unexplored scientific perspectives and propose some advice of how to study freshwater crayfish from a broad systems perspective.

  • 14.
    Zimmerman, Jenny K. M.
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of applied science and design.
    Palo, R Thomas
    Mid Sweden University, Faculty of Science, Technology and Media, Department of applied science and design.
    Time series analysis of climate-related factors and their impact on a red-listed noble crayfish population in northern Sweden2012In: Freshwater Biology, ISSN 0046-5070, E-ISSN 1365-2427, Vol. 57, no 5, p. 1031-1041Article in journal (Refereed)
    Abstract [en]

    1. Global climate change is predicted to raise water temperatures and alter flow regimes in northern river systems. Climate-related factors might have profound impacts on survival, reproduction and distribution of freshwater species such as red-listed noble crayfish (Astacus astacus) in its northern limit of distribution.2. In this study, noble crayfish capture data over 27 years from the River Ljungan, Sweden, were examined. Time series of catch per unit effort (CPUE) were analysed in relation to the North Atlantic Oscillation (NAO) index, regional weather factors and water flow. CPUE was assumed to reflect differences in population size. Two models were constructed to explore the relative impact of different climate factors and density dependence on variability of catch sizes.3. The most parsimonious model for CPUE time series, explaining 72% of the variance in CPUE, included density-dependent population dynamics of the crayfish and climate or weather factors. The specific effect from density dependence in the model was 37%, while climate/weather factors contributed with 35% of the variation. The most important climate/weather factors are variations in NAO index and water flow. Temperature did not improve the model fit to capture data.4. The best model was evaluated using independent data sets that gave correlations between model predictions and data ranging from 0.44 to 0.53. The density dependence shows a time lag of 1 year, while climate variables show time lags from 2 to 6 years in relation to CPUE, indicating effects on different cohorts of the crayfish population.5. Both density dependence and climatic factors play a significant role in population fluctuations of noble crayfish. A 6-year time lag for NAO index is puzzling but indicates that some as yet unidentified factors related to NAO might act on the juvenile stages of the population. Water flow shows a 2-year lag to the CPUE, and high flow in the river may affect adult survival. The reasons for fluctuation of crayfish catches in response to climate need to be identified, and fishing quotas should consider the different cohort sizes because of variation in environment. Reintroduction programmes for crayfish need to consider effects of climate change when designing management strategies.

  • 15.
    Zimmerman, Jenny K. M.
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of applied science and design.
    Palo, R Thomas
    Mid Sweden University, Faculty of Science, Technology and Media, Department of applied science and design.
    WHERE SHOULD YOU PUT THE CRAYFISH - DOES THE ACTUAL REINTRODUCTION SITE MATTER?2012Conference paper (Refereed)
  • 16.
    Zimmerman, Jenny K M
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences, Engineering and Mathematics.
    Palo, Thomas R
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences, Engineering and Mathematics.
    Do global cimate or local weather influence influence crayfish catches in the river Ljunjan in Sweden?2010In: 18th IAA Symposia, Program and  abstracts / [ed] Allert Annie, 2010, p. 35-35Conference paper (Refereed)
  • 17.
    Zimmerman, Jenny K M
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences, Engineering and Mathematics.
    Palo, Thomas R
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences, Engineering and Mathematics.
    Reliability of catch per unit effort (CPUE) for evaluation of reintroduction programs – A comparison of mark-recapture method with standardized trapping2010In: European Crayfish food, Flagships and Ecosystem Services / [ed] Souty Grosset Catherine, 2010, p. 28-29Conference paper (Refereed)
  • 18.
    Zimmerman, Jenny K M
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences, Engineering and Mathematics.
    Palo, Thomas R
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences, Engineering and Mathematics.
    Reliability of catch per unit effort (CPUE) for evaluation of reintroduction programs – A comparison of mark-recapture method with standardized trapping2011In: Knowledge and Management of Aquatic Ecosystems, ISSN 1961-9502, E-ISSN 1961-9502, no 401, p. Art no. 7-Article in journal (Refereed)
    Abstract [en]

    Catch per unit effort (CPUE) is used as a standardized trapping method by local fishermen and in monitoring studies. In this study, CPUE was compared with population estimates made with a capture-recapture method based on the passive integrated transponder (PIT-tag) marking of individuals. The results show a stronger positive correlation between the estimated population sizes from the capture-recapture method with an estimated CPUE effort of 120 traps. The fishermen used 15 traps, and even this effort showed a fair correlation with the mark-recapture estimates. This indicates that the standardized way of trapping with 15 traps can be used to evaluate reintroduction programs and monitor crayfish populations

  • 19.
    Zimmerman, Jenny
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences, Engineering and Mathematics.
    Palo, Thomas
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences, Engineering and Mathematics.
    Influence of water regulation and water flow on noble crayfish (Astacus astacus) catch in the River Ljungan, Sweden2008In: International association of Astacology, IAA18 konferens in Kuopio, August 2008. / [ed] Japo Jussila, James M. Furse & James W. Fetzner Jr, 2008, p. 141-144Conference paper (Refereed)
    Abstract [en]

    Free-flowing water is thought to be of importance for reproduction and body growth of noble crayfish, Astacus astacus (Linnaeus), in the northern edge of its distribution area. A hydroelectric power plant with a bypass tunnel was built in the River Ljungan, Sweden, in 1976. This reduced the mean water flow in the old river bed from about 60 m3 s-1 to 3 m3 s-1. The sites with the largest reduction of water flow had the largest decline in catch per unit effort of crayfish. At one site the catches were reduced by > 60%, but the catch success varied between locations. At all sites, water regulation seemed to have an effect, even though catch per unit effort was possibly affected by a number of other factors. © 2010 International Association of Astacology.

  • 20.
    Zimmerman, Jenny
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences, Engineering and Mathematics.
    Palo, Thomas
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences, Engineering and Mathematics.
    Influence of water regulation and water flow on Noble crayfish (Astacus astacus) catch yield in Ljungan a Northern Swedish River after building of a power plant2010In: Freshwater Crayfish, ISSN 2076-4324, Vol. 17, p. 141-144Article in journal (Refereed)
    Abstract [en]

    Free-flowing water is thought to be of importance for reproduction and body growth of noble crayfish (Astacus astacus (Linné)) in the northern edge of its distribution area.

    A hydroelectric power plant with a bypass tunnel was built in the river Ljungan in 1976.  This reduced the mean water flow in the old river bed from about 60m3/s to 3m3/s. The sites with the largest reduction of water flow had the largest decline in catch per unit effort of crayfish.  At one site the catches were reduced by >60%, but the catch success varied between locations.  In all sites the regulation seemed to have an effect, even though catch per unit effort was possibly affected by a number of other factors.

    KEY WORDS: Catch yield, noble crayfish (Astacus astacus), water flow, water level regulation

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