| 1. |
|
|
| 2. |
- Andersson, Magnus, et al.
(författare)
-
Fiskbestånd och miljö i hav och sötvatten : Resurs- och miljööversikt 2012
- 2012
-
Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Detta är den nionde utgåvan av den samlade översikten över fisk- och kräftdjursbeståndens status i våra vatten. Kunskap om fiskbestånden och miljön är en förutsättning för att utnyttjandet av fiskresurserna skall bli bärkraftigt. För svenska vattenområden beskrivs miljöutvecklingen i ett ekosystemsperspektiv, dels för att tydliggöra fiskens ekologiska roll och beskriva yttre miljöfaktorer som påverkar fiskbestånden, dels för att belysa fiskets effekter på miljön.Fiskbestånd och miljö i hav och sötvatten är utarbetad av Sveriges lantbruksuniversitet (SLU), Institutionen för akvatiska resurser (SLU Aqua), på uppdrag av Havs- och vattenmyndigheten. Rapporten sammanfattar utveckling och beståndsstatus för de kommersiellt viktigaste fisk- och kräftdjursarterna i våra vatten. Bedömningar och förvaltningsråd är baserade på Internationella Havsforskningsrådets (ICES) rådgivning, SLU Aquas nationella och regionala provfiskedata, samt yrkesfiskets rapportering.
|
|
| 3. |
- Ragnarsson Stabo, Henrik, et al.
(författare)
-
Can multi-frequency acoustics improve the monitoring of large zooplankton in large temperate lakes?
- 2014
-
Ingår i: Aquatic Ecosystem Health and Management. - : Michigan State University Press. - 1463-4988 .- 1539-4077. ; 17, s. 374-381
-
Tidskriftsartikel (refereegranskat)abstract
- Large zooplankton has an important role for the functioning of the ecosystem in many lakes. Most are predatory, which makes them both competitors as well as food for many planktivorous fish species. In general, it has been elusive to measure the abundance of this group of zooplankton with traditional sampling methods, particularly in large volumes of water. In this study we tested the potential and adequacy of multi-frequency hydroacoustics as a method to map the spatial patterns in abundance of the large zooplankton in Lake Vanern, Lake Vattern and Lake Malaren. In addition, we used a plankton net to groundtruth biovolume estimates vertically, and a Tucker trawl for the horizontal distribution. Two frequencies were used to separate the acoustic backscattering from fish, mysids and plankton. The main target species were Leptodora kindtii, Bythotrephes longimanus and Limnocalanus macrurus.The plankton communities were very heterogeneous both within and among the lakes. Lake Vanern and Lake Malaren were dominated by Leptodora, whereas Lake Vattern was dominated by Limnocalanus. Bottom depth at the sample site was the most important community structuring factor.Our results indicate that the biomass of large predatory zooplankton is comparably high and in most surveyed areas even higher than the biomass of planktivorous fish. Consequently, they are more important for the dynamics of lake food webs than previously assumed. Using multi-frequency hydroacoustics show promising results and with some alterations to the sampling design this would be a valuable addition to the traditional zooplankton monitoring in large lakes.
|
|
| 4. |
- Ragnarsson Stabo, Henrik, et al.
(författare)
-
Kvantifiering av stora djurplankton i de stora sjöarna
- 2012
-
Ingår i: Rapport - Vänerns vattenvårdsförbund. - 1403-6134. ; , s. 89-106
-
Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Large zooplankton (>2 mm) are important for the functioning of the ecosystem in many large lakes. In several cases they have severely altered the food web where they have invaded. Most are predatory, which makes them both direct competitors to, and the dominant food of, many planktivorous fish species. In addition, juveniles of several predatory species, such as zander (Sander lucioperca) have been reported to utilize them extensively. In this case study we used different methods to map the spatial patterns in abundance of the large zooplankton in Lake Vänern, Lake Vättern and Lake Mälaren. The cladocerans Leptodora kindtii and Bythotrephes longimanus are predators whereas the copepod Limnocalanus macrurus is an omnivore. Generally, quantitative measurements of large zooplankton in large volumes of water are difficult to obtain with traditional sampling methods. In this case study we sampled plankton with a large plankton net - to obtain biovolume estimates horizontally, and with a tucker trawl for the vertical distribution[TA1]. A total of 58 samples were collected. In addition, multi-frequency hydroacoustics was tested as a monitoring method, with the tucker trawls as ground truth. Two frequencies were used to separate the acoustic backscattering from fish, mysids and plankton. The plankton communities were very heterogenous both within and among the lakes. Both Lake Vänern and Lake Mälaren were dominated by Leptodora, whereas Lake Vättern was dominated by Limnocalanus. The depth at the sample site was most important for the structure of the community, with Limnocalanus predominantly present below the thermocline. The hydroacoustics showed some potential for sampling the species that do not share habitat with mysids. The high densities of predatory zooplankton found in all lakes indicate that they have the potential of being important prey species for fish as well as competitors, and thus any ecosystem models in these lakes should include them. Our results indicate that large predatory zooplankton are found in the same amount (biomass) as planktivorous fish. Consequently, they are important in the food web of all three lakes. Hydroacoustic monitoring of some of the species show promising results and with some alterations in the sampling methods this could be a useful addition to the regular zooplankton monitoring of the large lakes.
|
|
| 5. |
- Ragnarsson Stabo, Henrik, et al.
(författare)
-
Kvantifiering av stora djurplankton i de stora sjöarna
- 2012
-
Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Stora djurplankton (>2 mm) fyller en viktig funktion i många sjöekosystem. De flesta är rovdjur, vilket leder till att de är både konkurrenter och föda till många planktonätande fiskar. Dessa storväxta planktonarter kan också utgöra viktig föda för unga rovfiskar, t.ex. gös (Sander lucioperca). I denna studie testades olika metoder för att kartlägga och kvantifiera förekomsten av stora djurplankton i Vänern, Vättern och Mälaren. Det har visat sig att den traditionella provtagningen ofta missar de stora djurplantonarterna. Här testade vi en stor och grovmaskig planktonhåv för att få ett mått på biomassorna av plankton per ytenhet. Tuckertrål kombinerat med hydroakustik användes för att få ett mått på arternas vertikalfördelning och rumsliga fördelning. Flera frekvenser användes för att skilja på den detekterade energin från fisk och djurplankton som vid ekolodning reflekteras från organismerna. Totalt samlades 58 håv- och trålprover in. Planktonsamhället varierade starkt både mellan och inom sjöar. Vänern och Mälaren dominerades av Leptodora, medan Vättern dominerades av Limnocalanus. Djupet var avgörande för vilka arter som förekom i proverna, speciellt tydligt var det hos Limnocalanus som främst förekom i det kalla vattnet under språngskiktet. Hydroakustisk visade sig vara en möjlig metod för att mäta mängden stora djurplankton i de stora sjöarna. Mysider har tidigare visats ge starka och urskiljningsbara signaler i Vättern. Vår undersökning visade att även tofsmygglarver (Chaoborus) gav mycket starka signaler, som riskerar att överskugga de svagare signalerna från djurplankton. Vi föreslår därför att eventuell framtida hydroakustisk övervakning ska ske i dagsljus då både mysider och tofsmygglarver håller sig nära eller på botten. Våra resultat visar att biomassan stora djurplankton per ytenhet är i samma storleksordning som mängden fisk. Det indikerar att de är viktiga i födoväven och bör övervakas. Hydroakustik kombinerad med håvning eller Tucker-trålning skulle utgöra ett värdefullt komplement till den vanliga djurplanktonprovtagningen.
|
|
| 6. |
- Sandström, Alfred, et al.
(författare)
-
Assessing the potential of remote sensing-derived water quality data to explain variations in fish assemblages and to support fish status assessments in large lakes
- 2016
-
Ingår i: Hydrobiologia. - : Springer Science and Business Media LLC. - 0018-8158 .- 1573-5117. ; 780, s. 71-84
-
Tidskriftsartikel (refereegranskat)abstract
- Remote sensing techniques may provide a higher temporal and spatial resolution than traditional water monitoring methods. We tested if this auxiliary information can be used to (i) explain patterns in fish assemblage composition and (ii) test candidate metrics to assess ecological status in large lake water bodies. We used MERIS-derived layers describing chlorophyll a, total suspended matter, and colored dissolved organic matter (CDOM) overlaid on all available fish monitoring data from the four largest Swedish lakes (Vanern, Vattern, Malaren, and Hjalmaren). We assessed the influence of remote sensing-derived parameters in the pelagic, offshore benthic, and the inshore benthic habitats. Our results demonstrated that chlorophyll a and CDOM together with depth at the sampling site explained a significant part of the variation in the distribution of fish assemblages. These predictors were particularly important not only in pelagic, but also in inshore benthic areas. Furthermore, we identified three potential candidate metrics to assess pressure from eutrophication in large lakes: density of pelagic fishes, biomass of planktivorous species, and the proportion of cyprinids when roach was excluded. Remote sensing was considered a useful tool to support analyses of fish community composition and dynamics.
|
|
| 7. |
- Sandström, Alfred, et al.
(författare)
-
Has climate variability driven the trends and dynamics in recruitment of pelagic fish species in Swedish Lakes Vanern and Vattern in recent decades?
- 2014
-
Ingår i: Aquatic Ecosystem Health and Management. - : Michigan State University Press. - 1463-4988 .- 1539-4077. ; 17, s. 349-356
-
Tidskriftsartikel (refereegranskat)abstract
- We analyse trends and dynamics in time-series of recruitment in Smelt and Vendace in the Swedish large Lakes Vanern and Vattern, with particular emphasis on the importance of climate variability. Climate-related predictor variables in our analyses were air temperature, water temperature, ice coverage and duration of ice winters. The variation between years with successful recruitment and years with low recruitment was considerable in both species and especially for Vendace. Ultra-oligotrophic Lake Vattern was characterized by strong pulses in Vendace recruitment, occurring mainly in four year intervals. Smelt recruitment was positively related to recruitment pulses of Vendace. In meso-oligotrophic Lake Vanern, Vendace pursuit was more successful in years with long ice winters that lasted until the middle of March or longer. Smelt recruitment in Lake Vanern was positively correlated to the air temperature in April. There was no obvious synchrony in recruitment patterns between the two lakes. Recruitment of Smelt in Lake Vanern's two main basins was, however, positively correlated. The results indicated that climate factors may influence the recruitment of important pelagic species, but that the effects may differ between lakes, even though the systems are adjacent and situated at the same latitude.
|
|
| 8. |
- Sandström, Alfred, et al.
(författare)
-
Kan fredningsområden förbättra fisket i Sveriges stora sjöar? : Bilaga till uppföljningsrapport för fas 2 av projektet "Områdesbaserad förvaltning".
- 2012
-
Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- The usefulness and function of areas protected from fishing has been a major issue of scientific as well as political debate over the last decade. With a few exceptions, the vast majority of both case-studies and theoretical models are from marine environments. Although fisheries management in lakes faces similar problems as in marine systems, fishery closures has not been as frequently used as a management method and subsequently, the numbers of studies from lakes are few and rather limited. Nevertheless, large lakes in temperate areas could provide excellent study objects of the mechanistic processes that govern the success of protected areas, mainly due to lower number of species and habitat complexity and less complex dispersal mechanisms of early life-stages of fishes. In addition, the lakes are often closed systems that thus facilitate monitoring of whole populations. This report summarizes early results from an assessment of fishery closures in the largest lakes of Sweden. Particular emphasis has been given to monitor the impacts of fishery closures in Lake Vättern, the fifth largest lake in Europe. The commercial catch of the important fish species; whitefish (Coregonus lavaretus, L) and Arctic char (Salvelinus alpinus, L) have declined markedly since the mid 70s and as a means of remediation, three large areas, comprising 15 % of the lake's surface, were closed for all fishing in autumn 2005. We report our results monitoring the response of the fish communities within and outside the protected areas as well as the response of the fishery sector. Almost seven years after the closure, the overall catch per unit effort of Arctic char has increased substantially. There are no clear differences in abundance or biomass of Arctic char between protected and not protected areas. There are, however, some differences between closed areas and fished areas. The mean size and age of Arctic char has a more positive trend in the protected areas. There was also a significant effect of the size of the closures. The development of Arctic char was positively related to closure size. These results indicate that at least 25 % of the feeding areas of a mobile fish such as Arctic char must be protected in order to achieve a clear positive influence on a population under substantial pressure from fisheries. In parallel there was also a significant effect of the distance from the edge of the closures on Arctic char mean size, which decreased with increasing distance from the core of the largest protected areas. Several other species have also increased after the introduction of closures but in those cases there were no clear differences between closures and areas with fishing. Similar to the results in other monitoring programmes there has also been a sharp increase in the density of large fishes recorded in hydroacoustic surveys, particularly in deeper parts within protected areas. It is concluded that the positive development of Arctic char in particular and some other commercial species (particularly brown trout) is a product of a combination of fishery closures and other fishery regulations together with a marked reduction in the effort of the commercial fishery that has switched its attention to the more economically beneficial introduced signal crayfish. The total catch in the fisheries in Lake Vättern, when adding all types of fisheries, has mainly responded positively to the new fishery regulations. After an initial drop after the introduction of closures, the total catch of Arctic char has increased to approximately 38 tonnes in 2010 compared to 23 tonnes in 2003 and 17 tonnes in 2006. A similar positive trend was also observed for the catches of trout, which has more than doubled after the introduction of closures. Besides an increased total catch in many species, the fisheries have shifted in dominance from commercial to recreational fishing. Particularly the catches in trolling have increased markedly over time and at present contribute to the largest part of the overall fisheries mortality in Lake Vättern. 4 Besides permanent no-take closures there are also seasonal closures aimed to protect spawning areas of sensitive species. In Lake Vänern the catches of sander (Sander lucioperca) in areas with seasonal fishery closures were compared to other adjacent areas where fishing was allowed and with other lakes without fishery closures. Two of the investigated areas with spawning closures had low catches of pikeperch and very few young pikeperch in the catch indicating that these areas probably are not very important spawning areas. In the remaining areas in northern Lake Vänern on the other hand the catches of pikeperch were high and a significant part of the catch was constituted of young pikeperch. The comparison with other areas and lakes showed that the size distribution of pikeperch in Lake Vänern did not differ significantly from lakes without fishing closures. This study however is only comprised of data from two years and should be interpreted with care. An analysis of migration patterns and influence of fisheries on asp (Aspius aspius) in Lake Mälaren was conducted in collaboration with Sigtuna Naturskola and the County Administration of Stockholm. The results indicate that asp may migrate downstream for spawning and that the recreational fisheries on the species have changed as a response to introduction of spawning closures. General considerations when arranging zoning activities in Swedish large lakes are discussed. The importance of adapting the size and distribution of closed areas to the life-history and migration tendency of the target species is emphasised. The results from Lake Vättern show that fishery closures could be a powerful tool to remediate fisheries in crisis but since they constitute a significant violation of the livelihood of fishermen they should be used with care and only in situations where they can be fully legitimate. Involving stakeholders in zoning activities and using stakeholders local knowledge combined with modern spatial modelling techniques is concluded as a promising way to implement and facilitate the use of fishery closures in large lakes.
|
|
| 9. |
- Sandström, Alfred, et al.
(författare)
-
Satellitdata för miljöövervakning och fiskeriförvaltning i Sveriges stora sjöar
- 2015
-
Rapport (övrigt vetenskapligt/konstnärligt)abstract
- The report is a full description of the work accomplished within the SNSB user project "MERIS and hydroacoustic data for fisheries management, assessment of ecosystem status and identification of essential habitats in Sweden's large lakes". The project goal was to develop MERIS based water quality indicators for the large lakes and to employ these to predict the distribution of essential and sensitive habitats, to assess ecological status and to optimize fish monitoring. MERIS based water quality products have been developed and the possibility to use these as pressure variables in assessments of ecological quality based on metrics originating from fish monitoring has been investigated. Our results verify that predictors acquired from MERIS based water quality products can be useful for many purposes. Chlorophyll a as well as CDOM (Colored Dissolved Organic Matter), together with depth at the sampling site explained a significant part of the variation in fish assemblage composition. The major changes that normally follow eutrophication, i.e. a dominance shift to cyprinids in benthic fish communities and to young smelt in the pelagic zone, could be successfully predicted using MERIS data. Particularly CDOM and Chl a, which were highly correlated, were both strong predictors. MERIS based data layers could be a useful contribution to model the distribution of individual species and assemblages as well as the characteristics of their habitats. However, since depth in many cases is the single most important environmental factor, bathymetry maps must be markedly improved to enable modelling of the distribution of essential habitats in these systems. Another important factor that could improve the potential to model distributions would be to collect data on fish abundance and presence more evenly along the environmental gradients described by MERIS data. One example is monitoring data from hydro-acoustics that has been focused on the very largest open basins and thus do not cover the entire productivity gradient. We tested several candidate metrics to describe the influence of eutrophication on fish assemblages in large lakes using MERIS data as proxy pressure variables. In total, we were able to assess the status in thirty-one different water bodies. There were two metrics that appeared to be very promising: the density of pelagic fishes (number per hectare) and the percentage of cyprinids (when roach is excluded). We recommend that these two metrics are further explored as primary candidates for assessment of ecological status when the pressure variable is eutrophication and that the potential of a third candidate metric comprising information on age/size structure of fish communities also is investigated. To conclude, MERIS based data was a relatively powerful predictor of variation in fish monitoring data. It could be used for modelling distribution and to describe the pressure of eutrophication on water bodies in large lakes. Additionally, since the continuous maps derived from MERIS cover the majority of the lakes surface indicates that they also can be used to improve the design of field based monitoring efforts. The information can be used to ensure that the existing fish assemblages are covered and that data is representatively collected and covers the majority of the existing habitats of the monitored systems.
|
|
