By analyzing otolith microchemistry, we examined the use of freshwater and marine environments by brown trout Salmo trutta L. that spawn in the Swedish River Emån and migrate to the Baltic Sea. We estimated the time juveniles spent in freshwater and the number of times the fish returned to freshwater, presumably to spawn. Twenty-six percent of the fish migrated to sea by 1 year of age. However, 13% spent less than one year in the river. Most brown trout (48%) migrated to the sea between 1 and 2 years of age. On average, brown trout, which averaged 4.4 years in age (range 3–6 years), returned to freshwater 2.3 times, and there was an inverse relationship between time spent in freshwater after hatching and the number of visits to freshwater. Our results do not support the classical life history pattern, where brown trout spend one or more years in freshwater before migrating to the sea. Here, we found evidence that part of the population leaves freshwater during their first year. While the cause for precocial migration in the River Emån is not known, our results from this permanently flowing river do not support the idea proposed for other Baltic Sea populations, where the risk of drought has been suggested to be the cause. 

The Daugava River is the largest river in Latvia. Daugava Hydro Power Plants built in 1939 - 1974 are Latvia's most important renewable resource in generation of electricity. The absence of fish passage structures excludes upstream migration of diadromous species. Compensatory stocking activities are introduced annually. The need for studying alternative or additional impact mitigation measures is based on biodiversity conservation aspects and possible changes in EU legislation. The case study of solutions for improving the Daugava River connectivity is introduced and further strategies for mitigating the impact of HPP are proposed in the paper.

The focus of the research has been on restoration of rivers longitudinal connectivity for fish

migration, as stated in the research program title. The activities have consisted of a mix of

starting new studies* and continuing ongoing studies. All of the activities have involved a

cooperation between Olle Calles and Claudio Comoglio as well as several other partners.

The projects are described in detail in this report and their titles are:

1. Reintroducing marble trout to Dora Baltea (VdA): the impact of brown trout and

habitat modifications*

2. Reintroducing marble trout to highaltitude rivers in VdA*

3. The ecology and biology of a new Ligurian fish species *

4. Reestablishment of longitudinal connectivity on the River Nestos, Greece*

5. Introducing restoration ecology to Costa Rican rivers*

6. Reestablishing connectivity on the Torrente Chiusella, Piemonte*

7. Fish ladders or biocanals: on the potential of naturelike design

8. Reducing silver eel mortality at turbine intakes using lowsloping racks

9. The depth preference of silver eels approaching obstacles

10. Testing rehabilitative measures for downstream migrating diadromous fish at a

hydroelectric plant

En stor del av våra vattendrag är kraftigt påverkade av olika fysiska ingrepp. Denna skrift riktar sig i första hand till den som vill göra en insats för att förbättra en skadad vattenmiljö. Vattendomar och fiskevård en vägledning tar bland annat upp omprövning av vattendomar, vilka vanliga fysiska problem man kan stöta på i en vattenmiljö och vad man kan göra åt dem, samt olika exempel på fiskevårdsprojekt

The hydropower industry has altered connectivity in many rivers during the last century. Many fish species

depend on both an intact longitudinal connectivity to be able to migrate between spawning, feeding and

winter habitats, and vertical connectivity for development and survival of incubating embryos and larvae in

the gravel. The objective of this thesis was to examine problems and remedial measures associated with

disrupted longitudinal and vertical connectivity in regulated rivers.



The issue of longitudinal connectivity was studied in the River Emån by evaluating the efficiency of two

nature-like fishways for anadromous brown trout. Telemetry studies showed that the combined efficiency

for the two fishways in 2001-2004 was 60.5%. The passage efficiencies of both fishways were high for

trout (89-100%), but also for other species such as chub, perch, tench, burbot and roach (74%). The

attraction efficiencies were largely dependent on power plant operation, and generally high for the fishway

situated next to the tail-race and low for the fishway situated inside the former channel. More than half of

the trout spawners were also observed using the fishways for downstream passage. The densities of brown trout yearlings upstream of the fishways were higher after the fishways were built than during pre-fishway years. Smolts produced upstream of the fishways were observed migrating downstream in 2003-2005. The percentage of smolts that passed both power plants in was 51%, with

losses being attributed to predation (15%), turbine-induced mortality (16%) and other reasons (18%).

Turbine-induced mortality was higher (40%) at the power plant with four small Francis runners, than at the power plant with one large Kaplan runner (12%).



The issue of vertical connectivity was studied in three rivers in Värmland, one unregulated, and two regulated, one of which had no minimum flow requirements. In the unregulated river, temporal patterns in hyporheic water chemistry correlated to variation in surface water chemistry and discharge as expected. In the regulated rivers, the hyporheic water chemistry showed little correlation to discharge or surface water chemistry. The intra-gravel water chemistry conditions for brown trout eggs were more favourable in the unregulated river, characterised by high oxygen levels, than in the two regulated rivers. The regulated river with no minimum flow requirements had critically low oxygen levels at the end of the incubation period

The Baltic Sea in northern Europe is one of the most thoroughly studied marine environments in the world. Shallow bays in the coastal areas, so called flads, have however until recently been poorly investigated. The present study includes a comparison of the benthic fauna of two flads in southern Bothnian Sea, Skatviken

and Långörsviken, in early spring. Skatviken is target to human activities whereas Långörsviken is largely unaffected. This spatial comparison is complemented by a seasonal comparison with a study performed at fall the year before. Core samples were taken from three vegetation communities in each bay, dominated by one of the macrophytes Chara tomentosa, C. aspera and Potamogeton pectinatus respectively. In these samples the benthos were identified, quantified and weighed, and macrophytes present were identified and weighed. Parameters like oxygen, depth, temperature and salinity were measured. No clear differences between the two bays were detected on a community level in regards of abundance, biomass nor diversity.

Instead these parameters showed signs to be more dependent on type of vegetation and associated parameters. The shallow C. aspera community held both higher abundance and diversity of benthos than the other two. The taxonomic composition of the benthic communities of the two bays was slightly different. Several taxa that previously have been identified as indicators of a degraded water quality, were

significantly more abundant in Skatviken e.g. Asellus aquaticus (Crustacea: Isopoda), and Endochironomus sp. (Diptera: Chironomidae). Likewise, taxa indicating a high water quality were significantly more abundant in Långörsviken e.g. Gammarus sp. (Crustacea: Amphipoda), Microtendipes sp. , Paratanytarsus sp. and Pseudochironomus sp. (all three, Diptera: Chironomidae). In addition to this the use of Ecological quality classes, based on certain indicator taxa present, illustrated that Skatviken showed clear effects of stress whereas Långörsviken showed no or

insignificant effects of stress. The seasonal variation indicated an increased dominance by a few very abundant taxa at fall e.g. Stylaria lacustris (Oligochaeta: Naididae), resulting in a lowered diversity. The total number of taxa was surprisingly

similar at spring and fall, even though several organisms are likely to have left the aquatic juvenile phase by August. The use of easily detected and identified indicator taxa is recommended for future investigations of benthic fauna as indicators of

environmental conditions of flads

Fiskarter som är beroende av att kunna röra sig mellan sötvatten och hav för att fullfölja sina livscykler stöter ofta på problem i reglerade vattendrag, eftersom vattenkraftverk skapar vandringshinder. Vanligen försöker man lösa dessa problem genom att anlägga fiskvägar vid hindren, för att åter göra det möjligt för fisken att passera. Fokus för sådana åtgärder har legat på just uppströms passage, medan nedströms passage av kraftverk sällan uppmärksammats och ytterst sällan åtgärdats. Denna rapport beskriver nedströmspassagen för ål vid ett vattenkraftverk i Ätran, före och efter åtgärd.

Före åtgärd satt en fingaller med 20 mm spaltvidd och 63,4° lutning i intagskanalen till Ätrafors kraftverk i Ätran. Förlusten för ål på väg nedströms mot havet var omfattande och dödligheten var 72 %. De flesta ålar som dog klämdes fast på intagsgallret eller skadades vid turbinpassage. Åtgärden bestod i att sätta in ett nytt fingaller i intagskanalen med 18 mm spaltvidd och 35° lutning. Dessutom anlades flyktöppningar i gallrets övre del för att erbjuda ålen en alternativ väg förbi kraftverket. Efter åtgärd minskade dödligheten för ål till 10%. Ca. 80% av ålarna hittade ut genom flyktöppningarna och ingen av dem fastnade på det nya gallret. Det nya gallrets utökade yta ledde även till att fallförlusten minskade med som mest 170 mm, vilket innebär en ökad framtida produktion vid kraftverket om man lyckas med att hålla gallret rent från löv och drivgods.

The critical situation for European eel population was addressed in 2007 by a new Council Regulation (No 1100⁄2007⁄EC), which required all member states to develop national eel management plans. The goal of each of these national eel management plans is to allow with high probability the escapement of the silver eel to the sea is at least 40% of the best estimate of escapement biomass that would have existed if no anthropogenic influences had impacted the stock. The four main actions of the Swedish eel management plan are: 1) reduction of the fishery, 2) improved possibilities for downstream migration (reduced turbine mortality), 3) stocking of glass eel and 4) increased control measures.”Krafttag ål” was initiated in 2010 to contribute to reduced turbine mortality with the goal of allowing at least 40% of downstream migrating eels in rivers with hydropower dams to reach the sea. This letter of intent was signed by the Swedish hydropower industry and the Swedish Agency for Marine and Water Management. The reduced turbine mortality shall be achieved by implementing measures where they are expected to give the largest effect (“most bang for the buck”). The Swedish rivers have been ranked in a priority list, with the following eleven rivers listed as “top priority rivers”: 1) Göta älv, 2) Motala ström, 3) Rönne å, 4) Lagan, 5) Norrström, 6) Mörrumsån, 7) Nyköpingsån, 8) Kävlingeån, 9) Örekilsälven, 10) Dalälven and 11) Skräbeån. These 11 rivers are believed to have the greatest potential for increasing survival of eels after rehabilitative measures have been implemented.According to the Swedish eel management plan, the silver eel mortality at all hydroelectric plants in the top priority rivers has been set to 70%. It is unclear how realistic the assumed passage mortality of 70% is, and thus the aim of this study is to obtain information about the passage conditions in the top priority rivers by: 1) collecting information about studies carried out in the top priority rivers, 2) estimating turbine-induced mortality in the top priority rivers using a newly developed model, and 3) identifying what is known and not known about eel downstream passage conditions in the top priority rivers and proposing future activities within this context.Estimates of silver eel escapement to the sea, based on a constant 70% turbine induced mortality (old estimate), generally differed from model estimates using empirical data (new estimate). In most cases the new estimate is higher than the old, i.e. more eels are expected to reach the sea, but in some cases the combined mortality is even higher than the assumed mortality of 70% per plant. In addition, eel production is not known for most rivers, which means that even with accurate estimates of passage survival will not help us in estimating total escapement to the sea. It is not even known if eels are still present in some of the rivers, and thus we recommend further investigations be conducted in these rivers. For the small rivers, such as Rönne å, Kävlingeån, Örekilsälven, Nyköpingsån, Skräbeån and Borgvikeälven, proven methods to improve passage or collect eels are available for implementation. In large rivers like Göta älv, Motala ström and Norrström, it is more difficult, but technically possible. We recommend that rehabilitative measures be implemented and tested in one or several of these large rivers.

To reach the goals of Krafttag ål, more effort needs to be put into identifying the current situation and the current eel production in the top priority rivers. After identifying the most productive areas, actions are needed to ensure a sustainable eel production by enabling juvenile eels to reach these rearing areas. The next step will be to implement measures to allow silver eels to migrate from freshwater rearing areas to the sea. The current knowledge is rather good on such rehabilitative measures in small to medium sized rivers, whereas there is an urgent need to gain more knowledge about measures passing or collecting silver eels at plants in large rivers.

Det europeiska ålbeståndet har minskat drastiskt under de senaste årtiondena och år 2007 antog därför EU en förordning, som innehåller åtgärder för återhämtning av beståndet av europeisk ål och som innebar att alla medlemsländer måste upprätta en nationell ålförvaltningsplan. I Sveriges ålförvaltningsplan anges minskad dödlighet i vattenkraftverk som en viktig åtgärd för att öka mängden blankålar som når havet. För att sådana åtgärder ska få stor effekt, måste man veta var mest ål produceras och vilken skada som orsakas av de kraftverk ålen passerar på sin väg mot havet. Denna kunskap är bristfällig för de flesta vattendrag i Sverige.

Ätran har en lång historia som ett ålproducerande vattendrag soch lämpar sig väl för en fallstudie för svensk ålförvaltning för att belysa ålproduktionens omfattning, dess lokalisering och därmed åtgärdsnyttan. Blankålsfångst på sex platser i Ätrans avrinningsområde under 2010-2011 visade att Ätran prducerar minst 950 blankålar/år och den totala produktionen för hela Åtrans avrinningsområde skulle kunna vara >5500 blankålar/år. Vår studie visar att man utöver redan genomförda och beslutade åtgärder endast behöver åtgärda ytterligare ett kraftverk för att merparten av Åtyrans blankålar ska nå havet.

Downstream passage problems for diadromous fish are rarely addressed in regulated rivers in northern Europe. Some attempts to decrease the mortality among downstream moving fish are now tested in southern Sweden, ranging from the use of trash gates to

testing of low-sloped fine-spaced racks. This presentation describes the efficiency of two

such measures at hydroelectric facilities in the River Ätran. The targeted species were Atlantic salmon, anadromous brown trout and European eel. Smolt (N=66, 2007), kelt (N=20, 2007) and silver eels (N=170, 2007-2008) were radio-tagged and tracked in

passing the facilities.



An open trash gate proved to have a very low efficiency for smolt (7%) and most individuals passed through the racks and turbines. The efficiency was intermediate for kelt (40%) and several individuals died on the trash racks or remained upstream until the

end of the study. The route seeking time was limited for smolts, but substantial for kelts. Since no control groups were used the extent of the delays could not be quantified. The overall passage success was 50% for kelts and 85% for smolts, illustrating the need for a more efficient measure for kelts in particular.



The passage for silvers eels of the two lower most hydroelectric plants (HEPs) in the River Ätran revealed a 28% passage success at HEP 2 (N=50), with a 23,5 m head and Francis turbines. The corresponding success for the control group released downstream of

the HEP was 92% (N=50). The following year the old rack (20 mm / 43°) was replaced by a new rack (18 mm / 35°) with exits at the surface. With the new rack in place 80% of the eels released upstream were successfully diverted and caught, resulting in a total

success of 90% (compared to 28% with the old rack). The success at HEP 1 was 76% (N=58), but no individuals entered the open trash gate. The success rate was somewhat uncertain because of the short distance to sea and the possibility for injured (but not dead) individuals to reach sea but not surviving in the long run

The European eel population is critically endangered due to a multitude of human-induced factors such as habitat fragmentation, parasites, fishing, and climate change. In freshwater, downstream migrating silver eels encountering hydroelectric plants often suffer substantial delays and increased mortality from trash-rack impingement and turbine-induced mortality. Downstream passage problems can be ameliorated by implementing different types of downstream passage solutions that show variable but promising results for salmonids, but their performance for silver eels remains largely unknown. To address these knowledge gaps, radio telemetry was used to monitor the downstream migration of silver eels during 2 years past a hydroelectric plant recently equipped with two new fish passage solutions, consisting of an angled bar rack with a full-depth bypass, and a nature-like fishway. No tagged eels passed through the turbines, but bypassed the dam evenly between the two passage solutions, resulting in a 95% impediment passage efficiency and a median passage time of 1 h. Movement patterns and route selection were associated with variation in discharge and most individuals approached both passage solutions before passing, resulting in route-specific efficiencies of 69% for the angled rack and bypass, and 46% for the nature-like fishway. We conclude that the combination of a new bypass, paired with an angled rack, and a large nature-like fishway provided downstream migrating silver eels with a highly effective combination of passage solutions, with high impediment passage success and relatively low passage times.

We evaluated the function of two nature-like fishways for re-establishing connectivity for anadromous salmonids in the regulated River Emån. Between 90 and 100% of the salmonids that entered the fishways actually passed through them, with median speeds of 180–190mh  1. Only 50% of the anadromous brown trout that passed the first fishway also passed the second one, indicating that the fish might have had problems locating the upstream fishway. The fishways were also observed to function as a passage for downstream post-spawning migrants. The densities of brown trout yearlings upstream of the fishways were higher in 2002, after the fishways were built, than during pre-fishway years. In control sites in other parts of the river as well as in a nearby river, no changes in yearling densities were observed. Thus, the fishways are working for upstream spawners, albeit at a recolonization rate that is slower than expected.

We studied the use of two nature-like fishways by 15 fish species (N ¼ 240) in the River Emån in southern Sweden. Use of the fishways for both passage and as a habitat was studied by electrofishing, trap catches and PIT telemetry. Of the 187 PIT-tagged fish, 52 individuals from 10 different species ascended one of the fishways for a total passage efficiency of 74%. For the five species that most frequently ascended the fishways, the passage efficiency was 100% for tench (Tinca tinca L.) and perch (Perca fluviatilis L.), 86% for chub (Leuciscus cephalus L.), 60% for burbot (Lota lota L.) and 50% for roach (Rutilus rutilus L.). Individuals that failed to pass the fishways were typically small cyprinids or species that were assumed to have taken up residence in the fishways, such as juvenile brown trout (Salmo trutta L.) and burbot. The nature-like fishways have re-established longitudinal connectivity for most of the studied species and also functioned as rearing and winter habitat for a number of species.