The Efficiency of a Fish Ladder for Salmonid Upstream Migration in a Swedish Potential Impact of a Hydropower Station on Connectivity and Recruitment

Anton Larsson

Degree project for Master of Science in Biology

Animal Ecology, 30 hec, AT 2016 Department of Biological and Environmental Sciences University of Gothenburg

Supervisors: Johan Höjesjö, Lars-Olof Ramnelid, Daniel Johansson

Examiner: Charlotta Kvarnemo Abstract Assessments of the function of fish passages are typically rare, although the approach is frequently implemented to mitigate adverse effects of hydropower plants. In this study 249 electro fishing samples from 1979-2015, were used to assess the efficiency of a fish ladder to allow upstream migration of salmonids past a hydropower station in Örekilsälven, Sweden. Densities of brown trout (both young of the year, 0+, and older juveniles, >0+) did not increase in the area upstream the hydropower station after construction of the fish passage; neither did the densities of 0+. >0+ salmon had a higher density upstream the hydropower station after completion of the fish ladder, however this is most likely explained by extensive fish translocations. 0+ salmon were only found in 5 % of the sampling occasions upstream the power station when translocations were removed, whereas 0+ brown trout were found in 44.3 %. No effect of for ascension was found in the study. The efficiency of the passage was determined low and non-satisfactory for and brown trout, although the evaluation is more difficult for brown trout as a consequence of resident forms. Smolt models indicate that contemporary smolt escapement of both salmon and brown trout almost exclusively originate from the downstream areas. Improving the hydrological connectivity will probably increase the smolt escapement from the area upstream the power station, but the magnitude will depend on recolonization extent and mortality rates for smolts migrating seawards. Although vast suitable spawning areas exist upstream the hydropower station, natural features, including extensive migration distances and the presence of a lake compose natural constraints in smolt escapement from the upstream area. Future studies should include the aspect of downstream migration as a part of a holistic approach to improve hydrological connectivity.

Keywords: Salmonid migration, fish passage, fish ladder, hydrological connectivity, hydropower, electro fishing, smolt production

Cover photo: The fish ladder at the hydropower station in Torp, May 2016. Photo by the author.

1

1. Introduction Freshwater ecosystems sustain high biodiversity compared to their limited area, but are currently experiencing rapid declines in biodiversity, the rate exceeding those in the most affected terrestrial ecosystems (Dudgeon et al. 2006). and hydropower stations have been extensively constructed in the last century (Graf 1999, WCD 2000, Nilsson et al. 2005) and created impoundments by blocking transportation of water and altering the natural flow regime of (Nilsson and Berggren 2000, Nilsson et al. 2005, Moore et al. 2012). To date, existing dams retain a volume of more than 10 000 km3 of water, equivalent of five times the volume of all the world's rivers combined (Nilsson and Berggren 2000).

Although producing human services such as hydropower and water reservoirs, the foundation of dams modifies and freshwater systems resulting in ecological impacts that affect a wide array of taxa e.g. fish (e.g. Franchi et al. 2014, Poulos et al. 2014), amphibians (e.g. Naniwadekar and Vasudevan 2014), macroinvertebrates (e.g. Benitez-Mora and Camargo 2014, Holt et al. 2015) and influencing stream nutrient levels (Zhou et al. 2015). Perhaps the most imminent effect upon building a is the construction of a barrier to migration, potentially impeding all movement across the dam and thus reducing hydrological connectivity (Pringle 2001, Pringle 2003). The present study investigates the barrier effect of a hydropower station on salmonid migration and smolt production in the Örekilsälven on the Swedish west coast.

The Atlantic salmon (Salmo salar) and the brown trout (Salmo trutta) are two anadromous fish species migrating from marine environments to freshwater systems to breed and before returning to the ocean (Gibson 1993, Klemetsen et al. 2003). Strictly freshwater forms of brown trout are common (Klemetsen et al. 2003) but typically rarer in Atlantic salmon (Power 1958, Berg 1985, Klemetsen et al. 2003). Anadromous Atlantic salmon have a strong natal homing behaviour, returning to their natal stream for spawning (Stabell 1984, Hansen et al. 1993, Keefer et al. 2014). This trait restricts gene flow between different streams and facilitates genetic divergence in rivers (Saunder 1981, Taylor 1991) not necessarily separated by vast geographic distance (Verspoor 1997, Primmer et al. 2006, Vähä et al. 2007). Brown trout has also been considered to have strong natal homing behaviour (Stuart 1957, Ferguson 1989) but recent studies suggest that straying can be considerable (Frank et al. 2012, Degerman et al. 2012a, Östergren et al. 2012).

During the last centuries wild stocks of Atlantic salmon have decreased substantially or been extirpated throughout their native range and are at present at the lowest levels in known history (WWF 2001). The sources of decline are several and interconnected, including pollution, overexploitation, acidification, aquaculture and dam constructions (Parrish et al. 1998, WWF 2001); the latter known to have caused multiple extirpations and severe reductions of salmon populations (Limburg and Waldman 2009, Hall et al. 2012, Brown et al. 2013). Trends in population status of brown trout are limited and typically more complicated to assess, but the species seem to experience declines in some areas whereas in other regions it performs better (Pedersen et al. 2012, ICES 2013, Höjesjö et al. in press.A).

Due to the anadromous life cycle, dwindling stocks and commercial interest in salmonid species, barrier effects of dams have often been addressed with the construction of different types of fish passages as an attempt to allow upstream and downstream migration and ensure population viability (Clay 1995, Schilt 2007, Calles and Greenberg 2009). Fish passages include a variety of designs, i.e. fish ladders and bypasses, applied depending on location and intention. However, despite extensive construction, studies assessing the function of these

2 passages are scarce (Schmutz et al. 1998, Roscoe and Hinch 2010, Bunt et al. 2012, Hatry et al. 2013) and often indicate low efficiency (Noonan et al. 2012). Studies in this field use confusingly resembling terminology but the difference is crucial to apprehend. The term efficiency will in this report be applied as a quantitative concept defining the proportion of a fish stock successfully migrating upstream a hydropower station, whereas the term effectiveness will be used in a qualitative context, simply stating if target species are able to pass the fish passage at some point (Larinier 2001). Fish passage efficiency is generally determined by two aspects; (1) attraction efficiency meaning the proportion of individuals present downstream the passage able to find the entrance of the fish passage and (2) passage efficiency, the proportion of individuals locating the entrance that successfully ascend the fish passage (Aarestrup et al. 2003, Bunt et al. 2012). In one of the few reviews assessing fish passage efficiency, Noonan et al. (2012), reviewed 65 papers between 1960 to 2011 and concluded that fish passage efficiency was about 50 % on average for both upstream and downstream migration (although salmonids had slightly higher efficiency). Other studies have also shown limited upstream migration success for salmonids (Linløkken 1993, Rivinoja et al. 2001, Croze et al. 2008, Lundqvist et al. 2008) although some fish passages seem to perform better (Bryant et al. 1999, Gowans et al. 1999) indicating potential for improvement if dams are constructed properly.

In Sweden, having approximately 2100 dams (Havs- och vattenmyndigheten 2014), documentation and assessment of present fishways is also limited (Rivinoja 2015). One of few reports assessing the efficiency of fishways was conducted in the county of Västra Götaland (Andersson and Bäckstrand 2005). Investigating 62 fish passages (mostly pool and passages), the authors concluded that only 53 % of these passages worked satisfactorily (Andersson and Bäckstrand 2005). In other words, there is an increasing need to evaluate and potentially modify fish passages in order to allow efficient migration for fish and other fauna in lotic ecosystems with existing dams.

1.2 Study area Örekilsälven is located on the Western coast of Sweden running 90 kilometres from the county of Dalsland before entering the sea in the Gullmar fjord, close to Munkedal (Fig. 1). It is one of the few rivers in the Western parts of Sweden still supporting a genetically distinct salmon stock of high conservation value (Degerman et al. 1999). Brown trout is also present in the area and is considered of high conservation value (Thorsson 2009). The catchment area covers 1340 km2 and several larger add to the main stream . Forests cover the majority of the catchment area (76 %) whereas the proportion of lakes is limited (3.7 %), the largest lake being Kärnsjön (Fig. 1). Historically, Örekilsälven, has been subjected to human alterations through different dams and mills constructions and modifications such as log driving used for the transportation of timber for several centuries. At present, the river system is mostly affected by various dam operations which compose one of the major impacts in the system, potentially impeding and altering the natural flow regime of the stream (Andersson and Bäckstrand 2005, Thorsson 2009). The hydropower station at Torp, located approximately 10 kilometres upstream of the river mouth, constitute the first anthropogenic obstacle in the system (Fig. 1). The present dam was built in 1984 but previous dams and structures have existed at the location for centuries. Due to human modifications and degradation of the habitat for salmonid species, several conservation actions have been carried out throughout the years including legal compensatory release of foremost Atlantic salmon but also brown trout (of natural stock origin) and biotope restorations. More recently (year 2000-2011) both 0+ (young of the year) and adult salmon along with 0+ of brown trout have been transported manually upstream the hydropower

3

station of Torp. In 1991 a fish ladder, pool and weir type, was constructed to allow migration past the hydropower station and give access to the extensive rearing habitats upstream the dam. The fish ladder is 44 meters long, consisting of 22 chambers with a combined slope of approximately 17 % and designed for a discharge of 0.25-0.5 m3/s (Thorsson 2009). Quantitative assessment of passage efficiency is lacking but concerns about its efficiency have been raised repeatedly (Andersson and Bäckstrand 2005, Länsstyrelsen 2005, Thorsson 2009).

Figure 1. Örekilsälven and the electro fishing sampling sites included in the analysis. The location of Torp hydropower station is marked by the red triangle.

1.3 Aim and hypothesis The aim of this study is to assess the function (both effectiveness and efficiency) of the fish ladder at the hydropower station of Torp in Örekilsälven, Sweden, for Atlantic salmon, (Salmo salar) and brown trout (Salmo trutta), using data from electro fishing. The hypothesis is that recruitment of these species is lower upstream of the dam compared to downstream. The study also seeks to answer if the fish ladder is more functional during certain discharge. Lastly, the study aims to estimate contemporary and potential increase in smolt production of Atlantic salmon and brown trout if connectivity and accessibility to the suitable habitats upstream of the hydropower station could be improved.

4

2. Method

2.1 Data handling and analysis Electrofishing is a widely used method for estimating density of territorial salmonid fish species (Bohlin et al. 1989). In Sweden this method has been used at least since the 1940s (Degerman and Sers 1999) and today it is estimated that more than 2000 sites are sampled each year (Degerman et al. 2012b). To assess density of salmonids, data from the Swedish national electrofishing register (Svenskt ElfiskeRegiSter, SERS, 2016) were extracted. A total of 249 electrofishing samples, located downstream and upstream of the hydropower plant conducted between 1979-2015 were included. Sampling sites were selected from the main stream channel of Örekilsälven and from two major tributaries (Töftedalsån and Hajumsälven). No sampling sites upstream of the dam at Torpfors, the northernmost migration barrier 77 km from the sea, (Fig. 1) were included as suitable biotopes for salmonids in this upper reach are very scarce. Also, only sampling sites located downstream of anthropogenic barriers in the two tributaries, 58.7 km and 42.6 km respectively, were included in order to exclude the impact of other dams in the analysis.

Usually salmonid density from electrofishing is estimated by fishing the same river stretch repeatedly and successive removal of fish each time (Bohlin et al. 1989). However, in this area, the majority of electrofishing occasions included only 1 fishing opportunity. For these occasions, the density value calculated in SERS was used. The hypothesis of lower recruitment of both salmon and brown trout was analysed with a Mann-Whitney U test, comparing densities of 0+ (young of the year) in the areas downstream the hydropower station to the areas upstream. To analyse the effectiveness and efficiency of the fish ladder, densities during the episode before the fish ladder (1979-1991) and after construction of fish ladder (1992-2015) were compared using a Mann-Whitney U test. A nonparametric test was used since the data did not display normal distribution.

In order to investigate if the fish ladder had higher efficiency during certain discharge, hydrological data from the Swedish meteorological and hydrological institute (SMHI) were downloaded. As the adult salmonid fish in Örekilsälven are mainly autumn spawners, (migrating upstream in September-Novembers), an average autumn discharge (calculated as a monthly mean between September-November) was plotted against 0+ (young of the year) densities upstream of the ladder the following year. Data were not normally distributed (Kolmogorov-Smirnov P > 0.05, Shapiro-Wilk P > 0.05) and transformations using log10 (original value + 0.5) and √(original value + 0.5) both failed producing normality, hence no regression was used. Instead, average autumn discharge was plotted against densities of 0+ following year and visualized for any linear trends. All statistics and analyses were made in SPSS 22.

2.1.1 Correction of fish translocation and compensatory release Due to historic compensatory release and extensive fish translocation, attempts to exclude these effects were made. These corrections were only performed for density values of 0+ and by excluding density values for those years and localities where translocations or compensatory releases were conducted. Additionally, values of 0+ was removed the year after release of adult fish for the location of release. When the locality of release was unknown, all values from that year were removed from the analysis.

5

2.1.2 Smolt models Nilsson et al. (2013) and Höjesjö et al. (in press.B) used a model called the SBS-model (Swedish Biotope Survey) that combines electro fishing and biotope surveys of the whole stream to estimate smolt escapement of sea trout, defined as the number of smolts reaching the sea. The two smolt models used in this study follow the framework of Nilsson et al. (2013) except for excluding the division >0+ (juveniles older than one summer) into further year classes. Instead, a fixed smoltification value of >0+ was used for brown trout (30 %) and a range of 40-50 % used for Atlantic salmon (E. Degerman, Swedish University of Agricultural Science, personal communication). The smoltification value was multiplied with the mean density of >0+ and the area of each stream section derived from the SBS (retrieved from the Swedish Database for Biotope Surveys). The mean density value of >0+ for the area upstream of the hydropower stations after completion of the fish ladder (year 1992-2015) was used for present smolt escapement for all stream sections in this area, whereas the mean density value of >0+ from the downstream area after construction of the fish ladder, was used for all stream sections downstream the hydropower station. Two compensation factors, based on spawning habitat and rearing habitat class according to Nilsson et al. (2013) were then incorporated into the model. Depending on spawning habitat class, smolt production for each stream section was multiplied with a value of 0.25-1 (spawning habitat class 0 = 0.25, class 1 = 0.5, class 2 = 0.75, class 3 = 1; Nilsson et al. 2013) whereas rearing habitat was multiplied with a factor of 0-1 (rearing habitat class 0 = 0, class 1 = 0.26, class 2 = 0.57, class 3 = 1; Nilsson et al. 2013). The most suitable habitat for salmonid parr is classified as 3 whereas a non-suitable area receives the score of 0 (Halldén et al. 2002).

Finally, migration mortality is included in the model where lotic mortality is applied for the stream sections and lentic mortality utilized for lake sections (only relevant for smolts migrating from the upstream area). Two different lotic migration mortality scenarios were used in the model presented here. The first one, called lotic mortality 1, used the same mortality rate per kilometer as used in Nilsson et al. (2013). This mortality depends on the rearing habitat class (habitat class 0 = 10-17 %, class 1 and 2 = 3-12 % and class 3 = 0-5 %). The second lotic mortality rate, referred to as lotic mortality 2, used the same range of mortality for all stretches and originates from the review of Thorstad et al. (2012) where migration mortality of Atlantic salmon smolts ranged from 0.3-5 % per kilometer for wild smolts. The same lotic mortality was used for Atlantic salmon and brown trout as done by Aldvén et al. (2015).

For each stream section smolt production was multiplied with the lotic mortality rate raised to the distance of the specific stream section divided by 2 (Nilsson et al. 2013; se equation 1). This gives the average distance smolts produced in the specific stream section has to migrate before reaching next stream segment downstream and hence assumes that smolt production on each stream section is evenly distributed. To calculate the total smolt production, the number of smolts produced in the most upstream situated stream section was multiplied with the specific mortality of the adjacent downstream stream section. Secondly the smolts produced in adjacent stream section was added (equation 2). The process was repeated until the last stream section was added.

6

Equation 1 smolt production stream sectionn = area of stream sectionn (m2) * average density of >0+/m2 * smoltification value * spawning habitat compensation * rearing habitat compensation * specific migration mortality stream sectionn(length of stream section n/2)

Equation 2 smolt production stream sectionn * specific migration mortality stream sectionn+1length of stream section n+1 + smolt production stream sectionn+1

For smolts produced upstream the lake of Kärnsjön, three different lentic mortality spans were incorporated. The high mortality scenario used a mortality per kilometer of 25-71 % (Nilsson et al. 2013), the medium mortality scenario used a mortality rate of 15-20 % per kilometer (J. Höjesjö, Gothenburg University, personal communication) and the low mortality scenario used a mortality of 5 % per kilometer (E. Degerman, Swedish University of Agricultural Science, personal communication). The total distance in lake Kärnsjön is approximately 10 kilometers.

To calculate potential increase in salmon smolt production, two different scenarios of mean productivity in the upstream region were employed. The first one used an upstream mean density of 30 % of the downstream mean density and the second scenario used the same mean density as the mean density in the downstream section. For each scenario an average number of smolt escapement was extracted from 100 simulations with random values within the range of smoltification and migration mortality using Microsoft Excel®.

3. Results

3.1 Densities upstream and downstream the power station Densities was significantly higher in the downstream area for both Atlantic salmon 0+ (young of the year) (Mann-Whitney U test: U = 1380, n1 =129 n2 = 120, P < 0.001; Fig. 2) and brown trout 0+ (Mann-Whitney U test: U = 5307.5, n1 =129 n2 = 120, P < 0.001; Fig. 3) when compared with the area upstream the hydropower station. Densities was also significantly lower for the upstream stretches when adjusted for compensatory release and fish translocation (see section 2.2.1) (Atlantic salmon; Mann-Whitney U test: U = 466, n1 =126 n2 = 93, P < 0.001; Fig. 4; brown trout; Mann-Whitney U test: U = 4950, n1 =128 n2 = 115, P < 0.001; Fig. 5). Atlantic salmon had significantly higher densities of >0+ in the area downstream the power station (Mann-Whitney U test: U = 1665.5, n1 =129 n2 = 120, P < 0.001; Fig. 2). On the contrary densities of >0+ of brown trout was higher upstream (Mann- Whitney U test: U = 4406, P < 0.001; Fig. 3).

7

Figure 2. Boxplot showing 0+, >0+ and total density of Atlantic salmon in Örekilsälven downstream and upstream the hydropower station in Torp respectively between 1979-2015. The box-and-whisker plots show median values (black lines), the interquartile ranges (boxes; 25th and 75th percentiles), and the 5th and 95th percentiles (whiskers). Circles represent outliers, located 1,5-3 interquartile ranges from the end of the box and asterisks represent extreme values, located more than 3 interquartile ranges from the end of the boxes.

Figure 3. Boxplot showing 0+, >0+ and total density of brown trout in Örekilsälven downstream and upstream the hydropower station in Torp respectively between 1979-2015. The box-and- whisker plots show median values (black lines), the interquartile ranges (boxes; 25th and 75th percentiles), and the 5th and 95th percentiles (whiskers). Circles represent outliers, located 1,5-3 interquartile ranges from the end of the box and asterisks represent extreme values, located more than 3 interquartile ranges from the end of the boxes.

8

Figure 4. Boxplot showing density of Atlantic salmon 0+ in Örekilsälven downstream and upstream the hydropower station in Torp respectively between 1979-2015 after corrections for compensatory release and translocations. Boxes represent downstream and upstream areas of the hydropower station in Torp between 1979-2015. The box-and-whisker plots show median values (black lines), the interquartile ranges (boxes; 25th and 75th percentiles), and the 5th and 95th percentiles (whiskers). Circles represent outliers, located 1,5-3 interquartile ranges from the end of the box and asterisks represent extreme values, located more than 3 interquartile ranges from the end of the boxes.

Figure 5. Boxplot showing density of Atlantic salmon 0+ in Örekilsälven downstream and upstream the hydropower station in Torp respectively between 1979-2015 after corrections for compensatory release and translocationsBoxes represent downstream and upstream areas of the hydropower station in Torp between 1979-2015. The box-and-whisker plots show median values (black lines), the interquartile ranges (boxes; 25th and 75th percentiles), and the 5th and 95th percentiles (whiskers). Circles represent outliers, located 1,5-3 interquartile ranges from the end of the box and asterisks represent extreme values, located more than 3 interquartile ranges from the end of the boxes.

9

3.3 Functionality of the fish ladder Neither salmon 0+ nor brown trout of any age classes (0+, >0+, and total) showed an increase in density when comparing densities upstream the hydropower station before and after completion of the fish ladder. However, salmon >0+ had significantly higher density for the after the fish ladder was built compared to before the fish ladder existence (Table 1; Fig. 6 and 7). Salmon >0+ and brown trout densities were significantly lower in the downstream area after completion of the fish ladder (U test: P <0.05) whereas the was no difference for salmon 0+ (Mann-Whitney U test: U = 1484, n1 =41 n2 = 88, P > 0.1).

Table 1 . The table shows the result from a Mann-Whitney U test for Atlantic salmon and brown trout densities of two different year classes (0+, >0+) and total density for the upstream section of Örekilsälven before and after installation of the fish ladder. Before/After N Mean Mean Standard Mann- Asymp. fish passage Rank density deviation Whitney Sig (2- U tailed) Salmon Before 21 65.7 17.8 57.8 930.5 0.28 0+ After 99 59.4 5.4 16.9

Salmon Before 21 46.4 1.0 3.6 743.0 0.02 >0+ After 99 63.5 2.7 6.6

Salmon Before 21 57.1 18.8 57.7 968.0 0.59 total After 99 61.2 8.2 19.6

Brown Before 21 58.7 3.9 9.1 1003 0.78 trout 0+ After 99 60.9 3.4 8.8 Brown Before 21 54.8 3.0 4.6 920.5 0.41 trout >0+ After 99 61.7 3.4 5.1 Brown Before 21 54.8 6.9 12.2 920.5 0.41 trout tot After 99 61.7 6.8 11.3

Corrections for compensatory release and translocation showed no significant difference in 0+ density for Atlantic salmon (Mann-Whitney U test: U = 412.5, n1 =11 n2 = 80, P > 0.10) or 0+ density for brown trout (Mann-Whitney U test: U = 852.5, n1 =18 n2 = 97, P > 0.10).

For the upstream area salmon 0+ were found in 20 % of the cases (n=120). When corrections for compensatory release and translocations were performed salmon 0+ were only found in 5 % of the electrofishing samplings (n=100) and all these 5 occasions occurred after the construction of the fish ladder (years 2002, 2007 and 2009). Brown trout 0+ were found in 45 % of the electrofishing samplings (n=120) and in 44.3 % of the samplings after corrections for compensatory release and translocations (n=115).

10

Figure 6. Boxplot of Atlantic salmon 0+, >0+, and total density for the area upstream the hydropower station in Torp before and after the construction of the fish ladder. The box-and- whisker plots show median values (black lines), the interquartile ranges (boxes; 25th and 75th percentiles), and the 5th and 95th percentiles (whiskers). Circles represent outliers, located 1,5-3 interquartile ranges from the end of the box and asterisks represent extreme values, located more than 3 interquartile ranges from the end of the boxes.

Figure 7. Boxplot of brown trout 0+, >0+, and total density for the area upstream the hydropower station in Torp before and after the construction of the fish ladder. The box-and- whisker plots show median values (black lines), the interquartile ranges (boxes; 25th and 75th percentiles), and the 5th and 95th percentiles (whiskers). Circles represent outliers, located 1,5-3 interquartile ranges from the end of the box and asterisks represent extreme values, located more than 3 interquartile ranges from the end of the boxes. 11

3.4 Correlation with discharge Overall, no linear trend between discharge and density could be detected when plotting the mean autumn discharge against recruitment (density of 0+) the following year for Atlantic salmon (Fig. 8) or brown trout (Fig. 9). Correction of 0+ densities for fish translocations did not render a linear relationship either (Fig. 10, Fig. 11).

Figure 8. Mean monthly autumn discharge and salmon 0+ density for the following year in locations situated upstream the hydropower station. Y = 9.8-0.16x. Dashed lines represent mean confidence interval (95 %). The dashed and dotted line illustrates a quadratic model.

Figure 9. Mean monthly autumn discharge and brown trout 0+ density for the following year in locations situated upstream the hydropower station. Y = 5.04- 0.06x. Dashed lines represent mean confidence interval (95 %). 12

Figure 10. Mean monthly autumn discharge and salmon 0+ density for the following year in locations situated upstream the hydropower station after correct ion of fish translocations. Y =-0.48+0.05x. Dashed lines represent mean confidence interval (95 %).

Figure 11. Mean monthly autumn discharge and brown trout 0+ density for the following year in locations situated upstream the hydropower station after correction of fish translocations. Y = 4.66+-0.05x. Dashed lines represent mean confidence interval (95 %). 13

3.5 Smolt models The scenarios for upstream production, not including migration mortality, and the present production of the downstream area for Atlantic salmon are shown in Fig. 12. The mean number of salmon smolts produced today in the upstream area was calculated to 1556. Increasing the upstream mean >0+ density to 30 % of the overall downstream mean density of >0+ (future 1) increased this production to 2229 and using the same mean density upstream as found downstream (future 2) gave a smolt production of 7406 (Fig. 12). Downstream production had a mean value of 4123 and was constant since no increase in densities of >0+ was made. Production values are based on a mean of 100 simulations each.

8000

7000

6000

5000

4000

3000

2000

Numbersalmon of smolt produced 1000

0 Downstream Today Future 1 Future 2 Figure 12. Number of salmon smolt produced in the area downstream the hydropower station (blue ) and the upstream area today and two possible future scenarios (green bars). Note that the production presented here does not account for any migration mortality. The values represent the mean of 100 simulations each. Error bars denote standard deviation.

The number of smolts produced upstream and downstream (Fig. 12) are reduced by lotic and lentic migration mortality before reaching the ocean, resulting in the so called smolt escapement. The smolt escapement for the upstream region varied with lentic mortality, lotic mortality and upstream density of >0+ (Fig. 13 and 14). Downstream smolt escapement, however, was only affected by lotic mortality as the lake is located upstream this area and no additional density scenarios were made in this area. The percentage of smolts produced upstream and downstream reaching the ocean under different lotic and lentic mortality scenarios is shown in table 2. Total smolt escapment is derived by adding downstream escapement with any of the upstream escapement scenarios (Fig. 13 and 14). Hence, the estimated range of total present salmon escapement under lotic mortality 1 ranged between 2428-2547 (Fig. 13) and between 3469-3896 for lotic mortality 2 (Fig 14.). Future smolt escapement under lotic mortality 1 was estimated to 2428-3015 (Fig. 13) and to 3470-5409 for lotic mortality 2 (Fig 14.).

14

Figure 13. Salmon smolt escapement (measured as the number of smolts that were estimated to reach the sea) is affected by the mortality rate in lakes (lentic) and stream sections (lotic). In lotic mortality scenario 1, mortality rates from Nilsson et al. (2013) were used. Three different lentic mortalities (low, medium, high) are shown for today and two possible future scenarios for smolts produced in the upstream area. The length of the lake equals 10 kilometers. Downstream bar (blue) represents the number of salmon smolt produced downstream of the hydropower station that reach the ocean, thus unaffected by lentic mortality. Mean ± standard deviation.

Figure 14. Salmon smolt escapement (measured as the number of smolts that were estimated to reach the sea) is affected by the mortality rate in lakes (lentic) and stream sections (lotic). In lotic mortality scenario 2, mortality rates from Thorstad et al. (2012) were used. Three different lentic mortalities (low, medium, high) are shown for today and two possible future scenarios for smolt produced in the upstream area. The length of the lake equals 10 kilometers. Downstream bar (blue) represents the number of salmon smolts produced downstream of the hydropower station that reach the ocean, thus unaffected by lentic mortality. Mean ± standard deviation. 15

Table 2. The percentage of smolts produced in the downstream and upstream area of Örekilsälven reaching the ocean under the two different lotic mortality scenarios used. Smolt escapement in the upstream area is also

reduced by the three different lentic mortalities (low, medium, high) used. Percentage values were calculated from the mean of 100 simulations of the production of smolts (Fig. 12) and the smolt escapement for 100 simulations for each of the lake mortality scenarios (Fig. 13 and 14).

Stream section Lentic mortality Percentage of smolts produced reaching the ocean Lotic Lotic mortality 1 mortality 2

Downstream 58.9 % 84.1 %

Upstream Low 7.67 % 27.5 %

Medium 1.93 % 6.67 % High 0.02 % 0.05 %

Present smolt escapement for brown trout ranged between 86-186 for lotic mortality scenario 1 (Fig. 15) and 124-470 for lotic mortality scenario 2 (Fig. 16). The range of estimated smolt escapement is affected by the lentic mortality scenario applied in the model (low, medium, high). Percentage of smolts produced in the downstream and upstream section under different lentic mortalities are shown in table 2.

Figure 15. Present smolt escapement for brown trout (measured as the number of smolts that were estimated to reach the sea) is affected by the mortality rate in lakes (lentic) and stream sections (lotic). In lotic mortality scenario 1, mortality rates from Nilsson et al. (2013) were used. Three different lentic mortalities (low, medium, high) are shown for smolts produced in the upstream area. The length of the lake equals 10 kilometers. Downstream bar (blue) represents the number of brown trout smolt produced downstream of the hydropower station that reach the ocean, thus unaffected by lentic mortality. Mean ± standard deviation. 16

Figure 16. Present smolt escapement for brown trout (measured as the number of smolts that were estimated to reach the sea) is affected by the mortality rate in lakes (lentic) and stream sections (lotic). In lotic mortality scenario 2, mortality rates from Thorstad et al. (2012) were used. Three different lentic mortalities (low, medium, high) are shown for smolts produced in the upstream area. The length of the lake equals 10 kilometers. Downstream bar (blue) represents the number of brown trout smolt produced downstream of the hydropower station that reach the ocean, thus unaffected by lentic mortality. Mean ± standard deviation.

4. Discussion Recruitment, indicated as density of 0+, of both Atlantic salmon and brown trout was higher in the area downstream of the hydropower station compared to the area upstream. This was in accordance with the hypothesis and hence not surprising. The stream section downstream the hydropower station provides large areas of suitable spawning and rearing habitats whereas the upstream area stresses a longer migration for the fish with several migration obstacles. Although densities of 0+ were lower upstream for both salmon and brown trout, the densities of >0+ showed a contrasting result between the two species, where salmon >0+ density was higher downstream and brown trout >0+ was lower downstream. Habitat choice of both Atlantic salmon and brown trout usually leads to spatial overlap to some degree (Heggenes et al. 1999, Klemetsen et al. 2003) and interspecific competition in juveniles of both species, when co-occurring, is common (Harwood et al. 2002, Stradmeyer et al. 2008). Traditionally, juvenile brown trout has been considered competitively superior to juvenile Atlantic salmon (Stradmeyer et al. 2008, Van Zwol et al. 2012). However, emerging studies suggest that this might not always be the case (Berg et al. 2014). As 0+ Atlantic salmon are typically more often found further away from the stream banks (Bremset and Berg 1999) and brown trout typically prefer shallower waters (Heggenes 1996, Linnansaari et al. 2010, Berg et al. 2014), it is possible that juvenile salmon have a higher competitive ability compared to brown trout in the lower stretches of Örekilsälven where the depth and distances from the stream banks are higher. In the more upstream parts of Örekilsälven where discharge is lower, brown trout may instead have the competitive advantage resulting in a higher density of >0+ trout. In addition, brown trout in the upstream area is considered resident to a high degree and would be less affected by a poor passage at the hydropower station in Torp, resulting in reduced competition between brown trout and salmon in this area. Resident trout have been

17 recognized to produce fewer juveniles than anadromous trout (Bohlin et al. 2001) which also could explain why 0+ density is higher downstream the hydropower station compared to the upstream area where resident life form of brown trout is more extensive.

4.1 Fish ladder effectiveness and efficiency No increase in densities of brown trout (total) or salmon 0+ upstream the hydropower station could be detected for the period after completion of the fish ladder, indicating low efficiency. However, densities of brown trout (total) were significantly lower during this time in the downstream area compared to the period before the fish ladder. This could indicate that a lower amount of brown trout found their way to Örekilsälven during the second time period. Hence fewer fish was possibly available for ascension to the upstream area and therefore could conceal any potential effect of the fish ladder. Although, no overall trend in decreasing brown trout stocks has been recognized (Höjesjö et al. in press.A), marine survival seems to be site specific, where decreases in survival have been observed in some rivers (Jonsson and Jonsson 2009) and not in others (Jensen et al. 2015).

The increase in salmon >0+ upstream after the construction of the fish ladder contrasts the fact that no increase in salmon 0+ were observed. Fish translocations that have been extensive after construction of fish ladder could explain this result as no correction of >0+ density was possible. Still, the fact that translocations, when included, did not affect the outcome of salmon 0+, confounds the observed increase in >0+ (Table 1). Parr typically move within the river system between seasons (McCormick et al. 1998, Stickler et al. 2008) but it is highly unlikely that the increase in >0+ density upstream the hydropower station is a result of parr produced downstream ascending the fish ladder due to their limited swimming capacity. Instead, the increase could be due to an increased survival rate for 0+ in the upstream area resulting in a significantly higher density of salmon >0+ but not for salmon 0+.

Median density for salmon 0+ and >0+ for the upstream area after construction equalled zero, but several outliers of higher densities were found (Fig. 6). When corrected for fish translocation for this period, most of these outliers were discarded and only five occasions with salmon 0+ remained. These occasions were electro fishing samples where the presence of salmon 0+ could not be directly associated with a translocation according to the correction criteria used in this study. Despite carefully performed it cannot be completely ruled out that the five remaining occasions with 0+ are not a result of spontaneous ascent through the fish ladder. It is possible that translocated adult fish move from the release spot in the river and spawns somewhere else and hence biasing the correction for translocations. Salmon (0+) have been observed to drift downstream, probably as a strategy adopted when individuals are displaced from suitable habitats by intraspecific competition, (Johnston 1997, Bujold et al. 2004). In a river system such as Örekilsälven, with very low densities of 0+ and vast suitable habitat upstream, it is highly unlikely that 0+ released in the upstream area would have to drift any longer distances before finding a suitable habitat without being displaced. For instance, one locality occupied by salmon 0+ is located 10 kilometres downstream of the release spot of adult fish previous year and 15 kilometres downstream the closest release point of 0+. The second time salmon 0+ were found in the same location, no translocations of adult fish had been performed the year before and no translocation of 0+ were made the concerned year. In other word, these occasions strongly imply that the fish ladder has successfully allowed ascent of Atlantic salmon during certain years indicating that there is a motivation for adult salmon to migrate higher in the system. However, these occasions are rare and represent only 5 % (n=100) of the electro fishing samplings when corrected for fish translocations. This, along, with low densities, indicates that although allowing salmon to migrate upstream occasionally,

18 the fish ladder has an overall poor function for salmon and cannot be said to be efficient (Lucas and Baras 2001, Fergusson et al. 2002, as cited in Noonan et al. 2012).

Densities of brown trout did not increase in the upstream area following the construction of the fish ladder. Fish translocations of brown trout in Örekilsälven are scarce, and are not believed to have had a major impact on the observed densities and occurrence of brown trout upstream the hydropower station. Compared to Atlantic salmon, spontaneous recruitment was found in a much higher extent in brown trout (in 44.3 % of the samplings for brown trout compared to 5 % for the Atlantic salmon). However, this does not necessarily prove a higher efficiency of the fish ladder for brown trout but is more likely explained by the high degree of resident trout in the upstream area (SERS 2016). Partial anadromy in brown trout populations is common (Jonsson and Jonsson 1993, Klemetsen et al. 2003, del Villar-Guerra et al. 2014) and this in most likely also the case in Örekilsälven. Truly, anthropogenic migration barriers have existed in the location of the contemporary hydropower station for centuries. If connectivity has been impaired for such a long time, it is likely that brown trout have adopted a more resident life history, as this would be advantageous in a system with several migration barriers downstream (Jonsson and Jonsson 1993). Judging from the low densities of brown trout and the absence of increase in density after construction of the fish ladder, the efficiency is most likely deficient also for brown trout. It cannot be ruled out that the fish ladder has allowed ascent for some individuals in certain years as for salmon, but the recommendation of 90-100 % of the migrating adults to ascend safely and rapidly to mitigate fragmentation from anthropogenic barriers (Lucas and Baras 2001, Fergusson et al. 2002, as cited in Noonan et al. 2012) is most probably violated. The high degree of resident trout also implies a limited function of the fish ladder as an efficient fish ladder would offer high connectivity and allow brown trout to migrate to the ocean, growing bigger and hence increase their egg clutch (Bohlin et al. 2001). As the migratory behavior seems to be plastic, with resident parents giving birth to both migratory and resident offspring (Jonsson and Jonsson 1993), a system with high connectivity would be expected to favor anadromy over residency if migration distances are not too far.

A fish ladder with a low efficiency does not only fail in mitigating the barrier effect of dams, but may also affect individual spawning performance by spending resources in trying to ascend (Gowans et al. 2003, Castro-Santos et al. 2009). This is of special importance for anadromous Atlantic salmon and brown trout that completely cease or dramatically decrease their feeding when migrating upstream to spawn (Bardonnet and Baglinière 2000, Degerman et al. 2001, Klemetsen et al. 2003). If ascent is managed nevertheless, not only is the energy storage for spawning reduced (Gowans et a. 2003), but migration is delayed (Castro-Santos et al. 2009, Roscoe and Hinch 2010, Marschall et al. 2011) and thus less time can be spent on spawning. It is therefore crucial that a fish ladder works efficiently, not just for the number of fish ascending, but also for the time and energy being invested in ascent.

4.2 Influence of discharge Discharge is often of high importance for initiating and stimulating upstream migration in salmonids (Aarestrup et al. 2003, Arnekleiv and Rønning 2004, Jonsson and Jonsson 2002, Mitchell and Cunjak 2007). However, in this study, no linear trend between discharge (defined as mean per month for the period September-November) and recruitment upstream the hydropower station was found for either brown trout or salmon (Fig. 8-11). Still, it is possible that discharge had an effect at a smaller temporal scale than autumn monthly mean as used in the study. Data on daily discharge showed relatively large fluctuations over few days and potentially the few confirmed spontaneous ascent of salmon coincided with a specific

19 discharge not identified here. Four of the five proposed spontaneous salmon ascents had a relatively high discharge previous year (Fig. 10) but this might only be circumstantial due to scarce data. Both lower and higher discharge were associated with increased densities of brown trout 0+, although the high proportion of resident trout in the upstream area complicates any conclusions. A higher discharge could be beneficial for upstream migration as seen in Arnekleiv and Kraabøl (1996), Gowans et al. (1999) and Thorstad et al. (2005). In many cases an increase in discharge increases the attraction flow of the fish passage which is a crucial part for successful ascent (Lundqvist et al. 2008, Calles and Greenberg 2009, Bunt et al. 2012). The fish ladder in Torp, however, is only designed for a discharge of 0.25-0.5 m3/s, meaning that a high elevation in diversion of water from the turbines to the fish ladder potentially would increase the attraction but also, most likely, impede passage efficiency. In aspect of the proposed low efficiency of the fish ladder in this study, the observed fluctuations in 0+ density are more likely to be contingent or explained by other factors such as environmental circumstances affecting the spawning success.

4.3 Smolt production The present smolt escapement of Atlantic salmon smolts, as calculated in the smolt models, ranged between 2428-3896 depending on lotic and lentic mortality (Fig. 13 and 14). However, the habitat survey for the upstream area was made in 1985 and changes after this would affect the accuracy of the estimation which is important to consider. Most of today’s escapement of salmon smolts originate from spawning sites located downstream the hydropower station, ranging between 87.66-99.99 % of the total contemporary production (Fig. 13 and 14). Considering the large areas of suitable spawning and rearing habitat upstream these values might appear to be low. Still, estimation of upstream escapement of salmon smolts originate from mean values upstream (median values were 0.00), hence including all outliers (Fig. 6) and not accounting for the artificially increased densities due to fish translocations. Moreover, the model does not account for the presence of hydropower stations during downstream migration. Hydropower stations often induce an elevated mortality if smolts pass through the turbines (Larinier 2008, Greenberg et al. 2012, Norrgård et al. 2013) or by increasing the risk of predation when smolts aggregate upstream the dam construction (Aarestrup and Koed 2003, Schilt 2007, Castro-Santos et al. 2009). In other words, the large range of estimated escapement of 0.31-428 for salmon smolts and 0.26-347 for brown trout smolts from the upstream area is more likely an overestimation than the opposite.

Future production of salmon smolt in the upstream area, not including migration (lotic and lentic) mortality, is likely to increase with improved connectivity (Fig. 12). Comparable systems are rare but Rolfsån in the county of Halland shares the feature with large lakes in the system and has recently gained increased access to upstream areas for salmonids. At present, results from electro fishing in Rolfsån shows that densities of salmon >0+ upstream the lakes are 30 % of the densities downstream the lakes (future 1 scenario on this study). However, it is possible that there is a lag phase in colonization of these new accessible habitats and that densities of salmon could be equal upstream to the present densities downstream downstream (E. Degerman, Swedish University of Agricultural Science, personal communication). Upstream areas in Örekilsälven provide suitable habitats and the natural migration mortality for adult salmonids travelling upstream in this area is thought to be limited (Bohlin et al. 2001). Therefore, an equal density of salmon upstream the hydropower station and downstream is not unrealistic but speculated to occur over time with restored hydrological connectivity in Örekilsälven. Restoring the hydrological connectivity would probably also increase the density of brown trout in the upstream area, but the actual magnitude of this is hard to assess and therefore no estimation of future smolt escapement was performed.

20

Facilitating migration in the river system will most likely increase the anadromous proportion of the brown trout population as this will be evolutionary advantageous when the migration distance is not too far (Jonsson and Jonsson 1993, Bohlin et al. 2001, Brenkman et al. 2008). An increase in anadromy will likely increase the densities of brown trout due to the beneficial feeding grounds at sea (Bohlin et al. 2001). Future densities of salmon and brown trout in Örekilsälven will also depend on interspecific interactions and competition.

Colonization of newly accessible habitat has been documented for salmonid species (e.g. Bryant et al. 1999, Gardner et al. 2013, Hogg et al. 2015). Time and success of the colonization is considered to depend on four factors: (1) accessibility, (2) proximity to donor stock, (3) productivity and condition of donor stock, and (4) habitat suitability for the species and life history variant (Pess et al. 2014). In Örekilsälven, the relatively long distance from the presently accessed habitat to suitable areas upstream could halt colonization of the upstream area. In addition, the strong natal homing displayed in Atlantic salmon (Stabell 1984, Hansen et al. 1993, Keefer et al. 2014) would also impede fast exploitation of new habitats (Pess et al. 2014). However, the fact that spontaneous upstream migration has occurred indicates a motivation to ascend within the salmon population and implicates a probable colonization if connectivity is improved. Brown trout typically has higher straying rates than Atlantic salmon (Frank et al. 2012, Degerman et al. 2012a, Östergren et al. 2012) and is also more widespread in the upstream area at present. Thus, colonization of the upstream area for brown trout is likely to be more rapid compared to Atlantic salmon.

The smolt model predicts that apart from upstream density of salmon and brown trout, the rate of lotic and lentic mortality is paramount for the actual escapement of smolts (Table 2). Tagging and tracking smolt migration downstream in other river systems have given a wide range of migration mortality per kilometre in lotic sections (Jepsen et al. 2000, Olsson et al. 2001, Calles and Greenberg 2009, Thorstad et al. 2012) as well as in lentic migration pathways (Jepsen et al. 1998, Jepsen et al. 2000, Olsson et al. 2001). These discrepancies indicate that migration mortality (lotic and lentic) varies both spatially and temporally (Olsson et al. 2001).

In lotic mortality 1 (Fig. 13 and 15), mortality rates were based on the different ranks of rearing quality, as done in Nilsson et al. (2013). To evaluate the estimated smolt escapement from the model, Nilsson et al. (2013) used a smolt trap to estimate actual brown trout smolt escapement in two Swedish streams. Results from this evaluation showed that the model tended to estimate a lower production than observed for several years in Kävlingeån, a river of comparable size to Örekilsälven. Potentially, the underestimations were derived by using exaggerated migration mortality in the lotic section. In another tagging and tracking study, smolt migrating downstream in Högvadsån, a to Ätran, showed an average migration mortality of 5 % per kilometre in slow flowing sections (E. Degerman, Swedish University of Agricultural Science, personal communication). In addition, the six studies reviewed in Thorstad et al. (2012), investigating migration mortality for wild salmon smolt, all fitted within the range of 0.3-5 %. These results could indicate that mortality rates in Örekilsälven are closer to the lower mortality rate in scenario 2 (Fig. 14 and 16). Still, higher mortality rates per kilometre have been found (Jepsen et al. 1998, Olsson et al. 2001, Calles and Greenberg 2009). Additional data collection, using tagging and tracking of down migrating smolts in Örekilsälven, are necessary for more accurate estimations. Moreover, performing new habitat surveys of the upstream area of Örekilsälven is crucial for a more precise picture of the contemporary production in this area.

21

Data on mortality rates experienced by smolts migrating through lentic systems are scarce but typically show an elevated mortality compared to stream sections (Jepsen et al. 1998, Jepsen et al. 2000, Olsson et al. 2001). The three different mortality rates used in the model rendered large differences in smolt escapement (Fig. 13-15). Applying the high mortality rate (25-71 % mortality per kilometre) virtually prevented any smolts from the upstream region to reach the sea, whereas incorporating a medium or a low lentic mortality allowed some smolt escapement from the upstream area (Table 2). Hence, the mortality rate in the lake could act as a natural bottleneck for the escapement of smolts in Örekilsälven. Although studies assessing migration mortality of smolts in lentic systems demonstrated mortality rates within the high mortality scenario (Jepsen et al. 2000, Olsson et al. 2001), there is evidence that mortality rates can be lower and within the medium mortality scenario used here (Jepsen et al. 1998). It is crucial to bear in mind that the studies identifying a high migration mortality in lentic systems observed mortality rates in human made reservoirs, where mortality rates are expected to be higher compared to natural lakes (Jepsen et al. 2000). In fact, in their study in the Bygholm reservoir, Jepsen et al. (2000) recorded an average survival time of brown trout smolts of 4 days and concluded that difficulties in finding the outlet probably had a major impact on mortality rates. Thus, if migrating smolts in Örekilsälven are able to find the outlet in lake Kärnsjön and proceed the migration, mortality rates in the lake are likely to be reduced. In addition, lentic mortality of smolts descending trough lake Kärnsjön will be determined by the swimming speed of migrating smolts as well as the presence and amount of smolt predators e.g. pikeperch and pike. Based on the natural features of lake Kärnsjön and assumed that downstream passage is made optimal for salmonid smolts, I speculate that lentic mortality in lake Kärnsjön is closer to the medium and low mortality scenarios than the high. Despite a high potential in salmon smolt production for the upstream area (Fig. 12), it is important to remember that features such as the presence of a lake and long migration pathways entail natural constraints on the possible smolt escapement from the upstream area in Örekilsälven even if high connectivity is achieved in the future. Still, improving the efficiency of the fish ladder and thus increasing the connectivity, smolt escapement of both Atlantic salmon and brown trout from the upstream area is likely to increase substantially and aid in the restoration of this historically and extensively modified stream.

5. Conclusions Electro fishing samples revealed low densities of foremost Atlantic salmon in the area upstream of the hydropower station of Torp despite extensive suitable habitats. Densities of 0+ brown trout were higher downstream whereas densities of brown trout >0+ was higher upstream presumably due to high proportion of upstream residency and lower competition with salmon in the upstream area. No increase in brown trout density or salmon 0+ density was apparent in the upstream area after construction of the fish ladder, whereas salmon >0+ increased after the fish ladder was completed. Extensive translocations of adult and 0+ salmon during this period complicates the picture and is probably the explanation for the increase in salmon >0+. When corrected for translocations, salmon 0+ were only found in 5 % of the electro fishing occasions after construction of fish ladder and 0+ brown trout in 44.3 %. This indicates that salmon has successfully ascended the fish ladder but only occasionally. The few spontaneous ascents along with overall low densities of salmon upstream point to a low and not satisfactory efficiency of the fish ladder. The absent increase in brown trout density together with a high proportion of residency also indicates a low efficiency of the ladder for brown trout. No effect of discharge was apparent but due to the low number of verified spontaneous ascents for salmon and the high degree of residency in brown trout, discharge probably influenced on a much finer time scale than the one used in the study. In order to minimize the barrier effects of the hydropower station and provide high longitudinal

22 connectivity, a new fish passage, alternatively decommission of the dam is needed. would also benefit other migrating species in the system such as sea lamprey and European eel.

The smolt model used revealed that only a fraction of the present smolt escapement originates from the upstream area. Improved hydrological connectivity will probably increase the escapement of both Atlantic salmon and brown trout in the upstream area, but the actual numbers depend on multiple factors. The colonization extent and time is affected by straying rates and interspecific interactions between brown trout and Atlantic salmon and other fish species. Densities of Atlantic salmon upstream the hydropower station are expected to be equal to densities in the downstream area, whereas brown trout is assumed to adopt anadromy to a higher degree once connectivity is improved. The actual number of smolts escaping the system is likely to vary temporally and be dependent on site specific mortality in both lotic and lentic sections. Referring to current knowledge and features of Örekilsälven, I speculate that migration mortality in lotic sections will be in the lower range and in the low-medium range for the lentic sections. Based on these speculations, future smolt escapement of both Atlantic salmon and brown trout from the upstream area will increase substantially and contribute to a considerable part of the total smolt escapement if high connectivity is achieved. Still, the major part of the smolt escapement will also in the future originate from the downstream area. This is a is a result of natural constraints in the upstream area including the presence of a lake and long migrations distances. Downstream migration pass the hydropower dam is not assessed in this study but is of equal importance as upstream migration to ensure high connectivity. Future efforts in Örekilsälven should focus on downstream migration, contemporizing the habitat survey in the upstream part for more accurate estimation of smolt production, monitoring and emphasizing additional parts of the native fish fauna.

23

Acknowledgement Many people have been involved in the work of this essay and contributed to its present content. Without your input and support, the writing of this paper would not have been possible. Firstly, I want to thank Lars-Olof Ramnelid and Daniel Johansson at the county administration board in Västra Götaland for giving me the opportunity to work with this project. Your feedback, help, knowledge and open attitude has been invaluable and inspiring. The county administration board in Vänersborg with personnel were always welcoming and helpful whenever I needed something. I owe special thanks to Lars Thorsson who helped with electro fishing protocol and shared with his knowledge of Örekilsälven. There are many other persons to thank and some of them are Lars-Åke Winbladh, Martin Dellien, Ingvar Lagenfelt, Key Höglind, Emil Larsson, Badreddine Bererhi, Johanna Ek, Magnus Lovén Wallerius, Ida Hedén, the staff at the Department of Biological and Environmental Sciences at University of Gothenburg and the municipality of Södertälje. Erik Degerman contributed with ideas and input about the calculations of smolt production. Lastly, I want give my deepest gratitude to my supervisor Johan Höjesjö for guidance and feedback on the manuscript and for inspiration and encouragement in the field of .

24

References Aarestrup, K., Koed, A. (2003). Survival of migration sea trout (Salmo trutta) and Atlantic salmon (Salmo salar) smolts negotiating in small Danish rivers. Ecology of Freshwater Fish 12: 169-176. Aarestrup, K., Lucas, M. C., Hansen, J. A. (2003). Efficiency of a Nature-like Bypass Channel for Sea Trout (Salmo trutta) Ascending a Small Danish Stream Studied by PIT Telemetry. Ecology of Freshwater Fish 12: 160-168. Aldvén, D., Degerman, E., Höjesjö, J. (2015). Environmental cues and downstream migration of anadromous brown trout (Salmo trutta) and Atlantic salmon (Salmo salar) smolts. Boreal Env. Res. 20: 35-44. Andersson, M., Bäckstrand, A. (2005). Fungerar våra fiskvägar? Miljömålsuppföljning i Västra Götalands län. Länsstyrelsen i Västra Götalands Län. 2005:56. 41 pp. Arnekleiv, J. V., Kraabøl, M. (1996). Migratory behavior of adult fast-growing brown trout (Salmo trutta L.) in relation to water flow in a regulated Norwegian river. Regulated Rivers: Research & Management 12: 39-49. Arnekleiv, J. V., Rønning, L. (2004). Migratory patterns and return to the catch site of adult brown trout (Salmo trutta L.) in a regulated river. River Research and Applications 20: 929-942. Bardonnet, A., Baglinière, J-L. (2000). Freshwater habitat of Atlantic salmon (Salmo salar). Can. J. Fish. Aquat. Sci. 57: 497-506. Benítez-Mora, A., Camargo, J. A. (2014). Ecological Responses of Aquatic Macrophytes and Benthic Macroinvertebrates to Dams in the Henares River Basin (Central Spain). Hydrobiologia 728: 167-178. Berg, O. K. (1985). The Formation of Non-anadromous Populations of Atlantic salmon, Salmo salar L.,in Europe. Journal of Fish Biology 27: 805-15. Berg, O. K., Bremset, G., Puffer, M., Hanssen, K. (2014). Selective segregation in intraspecific competition between juvenile Atlantic salmon (Salmo salar) and brown trout (Salmo trutta). Ecology of Freshwater Fish 23: 544-555. Bohlin, T., Hamrin S., Heggberget T. G., Rasmussen G., Saltveit S. J. (1989). Electrofishing Theory and Practice with Special Emphasis on Salmonids. Hydrobiologia 173: 9-43. Bohlin, T., Pettersson, J., Degerman, E. (2001). Population density of migratory and resident brown trout (Salmo trutta) in relation to altitude: evidence for migration cost. Journal of Animal Ecology 70: 112-121. Bremset, G., Berg, O. K. Three-dimensional microhabitat use by young pool-dwelling Atlantic salmon and brown trout. Animal Behaviour 58: 1047-1059. Brenkman, S. J., Pess, G. R., Togersen, C. E., Kloehn, K. K., Duda, J. J., Corbett, S. C. (2008). Predicting Recolonization Patterns and Interactions Between Potamodromous and Anadromous Salmonids in Response to Dam Removal in the Elwha River, Washington State, USA. Northwest Science, Special Issue 82: 91-106. Brown, J. J., Limburg, K. E., Waldman, J. R., Stephenson, K., Glenn, E. P., Juanes, F., Jordaan, A. (2013). Fish and Hydropower on the U.S. Atlantic Coast: Failed Policies From Half- way Technologies. Conservation Letters 6:4 280-286. Bryant, M. D., Frenette, B. J., McCurdy, S. J. (1999). Colonization of a Watershed by Anadromous Salmonids following the Installation of a Fish Ladder in Margaret Creek, Southeast Alaska. North American Journal of 19: 1129-1136. Bujold, V., Cunjak, R. A., Dietrich, J. P., Courtemanche, D. A. (2004). Drifters versus residents: assessing size and age differences in Atlantic salmon (Salmo salar) fry. Can. J. Fish. Aquat. Sci. 61: 273-282. Bunt, C. M., Castro-Santos, T., Haro, A. (2012). Performance of Fish Passage Structure at Upstream Barriers to Migration. River Research and Applications 28: 457-478. Calles, O., Greenberg, L. (2009). Connectivity is a Two-way Street - The need for a Holistic Approach to Fish Passage Problems in Regulated Rivers. River Research and Applications 25: 1268-1286. Castro-Santos, T., Cotel, A., Webb, P. (2009). Fishway evaluations for better bioengineering: an integrative approach. American Fisheries Society Symposium 69: 557-575.

25

Clay, C. H. (1995). Design of Fishways and Other Fish Facilities. 2nd edn. Lewis Publishers, Boca Raton, FL. Croze, O., Bau, F., Delmouly, L. (2008). Efficiency of a Fish Lift for Returning Atlantic Salmon at a Large-scale Hydroelectric Complex in France. Fisheries Management and Ecology 15: 467-476. Del Villar-Guerra, D., Aarestrup, K., Skov, C., Koed, A. (2014). Marine migrations n anadromous brown trout (Salmo trutta). Fjord residency as a possible alternative in the continuum of migration to the open sea. Ecology of Freshwater Fish 23: 594-603. Degerman, E., Almer, K, Höglind, K. (1999). Västkustens laxåar. Fiskeriverket Information 1999:9, 156 pp. Degerman, E., Sers, B. (1999). Elfiske. Fiskeriverket, Sötvattenslaboratoriet, Lokalkontor. Fiskeriverket information 1999:3 3-63. Revised 2001-08-24. (In Swedish). Degerman, E., Nyberg, P., Sers, B. (2001). Havsöringens ekologi. Fiskeriverket informerar 2001:10, ISSN 1404-8590, 122 p. In Swedish. Degerman, E., Leonardsson, K., Lundqvist, H. (2012a). Coastal Migrations, Temporary use of Neighbouring Rivers, and Growth of Sea Trout (Salmo trutta) from Nine Northern Baltic Sea Rivers. ICES Journal of Marine Science 69(6): 971-980. Degerman, E., Petersson, E., Sers, B. (2012b). Analys av elfiskedata. Länsstyrelsen i Jönköpings Län 2012:2, 79 pp. (In Swedish). Dudgeon, D., Arthington, A. H., Gessner, M. O., Kawabata, Z-I., Knowler, D. J., Lévêque, C., Naiman, R. J., Prieur-Richard, A-H., Soto, D., Stiassny, M. L. J., Sullivan C. A. (2006). Freshwater Biodiversity: Importance, Threats, Status and Conservation Challenges. Biological Reviews, 81: 163-182. Ferguson, A. (1989). Genetic Differences Among Brown Trout, Salmo trutta, Stocks and Their Importance for the Conservation and Management of the Species. Freshwater Biology 21: 35-46. Franchi, E., Carosi, A., Ghetti, L., Giannetto, D., Pedicillo, G., Pompei, L., Lorenzoni, M. (2014). Changes in the Fish Community of the Upper Tiber River After Construction of a Hydro-dam. Journal of Limnology 73(2): 203-210. Frank, B. M., Gimenez, O., Baret, P. V. (2012). Assessing Brown Trout (Salmo trutta) Spawning Movements with Multistate Capture-recapture Models: a Case Study in a Fully Controlled Belgian Brook. Canadian Journal of Fisheries and Aquatic Science 69: 1091-1104. Gardner, C., Coghlan Jr, S. M., Zydlewski, J., Saunders, R. (2013). Distribution and abundance of stream fishes in relation to barriers: implications for monitoring stream recovery after barrier removal. River Research Applications 29: 65-78. Gibson, R. J. (1993). The Atlantic Salmon in Fresh Water: Spawning, Rearing and Production. Reviews in Fish Biology and Fisheries 3: 39-73. Gowans, A. R. D., Armstrong, J. D., Priede, I. G. (1999). Movements of Adult Atlantic Salmon in Relation to a Hydroelectric Dam and Fish Ladder. Journal of Fish Biology 54: 713-726. Gowans, A. R. D., Armstrong, J. D., Priede, I. G., Mckelvey, S. (2003). Movements of Atlantic salmon migration upstream through a fish-pass complex in Scotland. Ecology of Freshwater Fish 12: 177-189. Greenberg, L., Calles, O., Andersson, J., Engqvist, T. (2012). Effect of trash diverters and overhead cover on downstream migrating brown trout smolts. Ecological Engineering 48: 25-29. Hall, C. J., Jordaan, A., Frisk, M, G. (2012). Centuries of Anadromous Loss: Consequences for Ecosystem Connectivity and Productivity. BioScience 62: 723-731. Halldén, A., Liliegren, Y., Lagerkvist, G. (2002) Biotopkartering -vattendrag, metodik för kartering av biotoper i och i anslutning till vattendrag. Länsstyrelsen i Jönköpings Län. Meddelande 2002:55. 86 pp. (In Swedish). Hansen, L. P., Jonsson, N., Jonsson, B. (1993). Oceanic Migration in Homing Atlantic Salmon. Animal Behaviour 45: 927-941. Harwood, A. J., Metcalfe, N. B., Griffiths, S. W., Armstrong, J. D. (2002). Intra- and inter-specific competition for winter concealment habitat in juvenile salmonids. Can. J. Fish. Aquat. Sci. 59: 1515-1523. Hatry, C., Binder, T. R., Thiem, J. D., Hasler, C. T., Smokorowski, K. E., Clarke, K. D., Katopodis, C., Cooke, S. J. (2013). The status of Fishways in Canada: Trends Identified Using the National CanFishPass Database. Reviews in Fish Biology and Fisheries 23: 271-281.

26

Havs- och vattenmyndigheten. (2014). Strategi för åtgärder i vattenkraften. Avvägning mellan energimål och miljökvalitetsmålet Levande sjöar och vattendrag. Havs- och vattenmyndighetens rapport 2014:14. 45 pp. Heggenes, J. (1996). Habitat selection by brown trout (Salmo trutta) and young Atlantic salmon (S. salar) in streams: static and dynamic hydraulic modelling. Regulated River Research & Management 12: 155-169. Heggenes, J., Baglinière, J. L., Cunjak, R. A. (1999). Spatial niche variability for young Atlantic salmon (Salmo salar) and brown trout (S. trutta) in heterogeneous streams. Ecology of Freshwater Fish 8: 1-21. Hogg, R. S., Coghlan Jr, S. M., Zydlewski, J., Gardner, C. (2015). Fish community response to a small-stream dam removal in a Maine coastal river tributary. Transactions of the American Fisheries Society 144(3): 467-479. Holt, C. R., Pfitzer, D., Scalley, C., Caldwell, B. A., Batzer, P. (2015). Macroinvertebrate Community Response to Annual Flow Variation from River Regulation: An 11-year Study. River Research Applications 31: 798-807. Höjesjö, J., Aldvén, D., Grimsrud Davidsen, J., Pedersen. S, Degerman, E. Perspectives on sea trout stocks in Sweden, Denmark & Norway: monitoring, threats and management. In press.A. Höjesjö, J., Nilsson, N., Degerman, E., Halldén, A., Aldvén, D. Calculating smolt production of sea trout from habitat surveys and electrofishing; pilot studies from small streams in Sweden. In press.B. ICES. (2013). Report of the Workshop on Sea Trout (WKTRUTTA), 12–14 November 2013, ICES Headquarters, Copenhagen, Denmark. ICES CM 2013/SSGEF:15. 243 pp. Jensen, A. J., Diserud, O. H., Finstad, B., Fiske, P., Rikardsen, A. H. (2015). Between-watershed movements of two anadromous salmonids in the Arctic. Canadian Journal of fisheries and Aquatic Sciences: 1-9. Jepsen, N., Aarestrup, K., Økland, F., Rasmussen, G. (1998). Survival of radio-tagged Atlantic salmo (Salmo salar L.) and trout (Salmo trutta L.) smolts passing a reservoir during seaward migration. Hydrobiologia, 371/372: 347-353. Jepsen, N., Pedersen, S., Thorstad, E. (2000). Behavioral interactions between prey (trout smolts) and predators (pike and pikeperch) in an impounded river. Regulated Rivers: Research & Management 16: 189-198. Johnston, T. A. (1997). Downstream movements of young-of-the-year fishes in Catamaran Brook and the Little Southwest Miramichi River, New Brunswick. Journal of Fish Biology 51: 1047-1062. Jonsson, B., Jonsson, N. (1993). Partial migration: niche shift versus sexual maturation in fishes. Reviews in Fish Biology and Fisheries 3: 348-365. Jonsson, N., Jonsson, B. (2002). Migration of anadromous brown trout Salmo trutta in a Norwegian river. Freshwater Biology 47: 1391-1401. Jonsson, B., Jonsson, N. (2009). Migratory timing, marine survival and growth of anadromous brown trout Salomo trutta in the River Imsa, Norway. Journal of Fish Biology 74: 621-638. Keefer, M. L., Caudill, C. C. (2013). Homing and Straying by Anadromous Salmonids: A Review of Mechanisms and Rates. Reviews in Fish Biology and Fisheries 24: 333-368. Klemetsen, A., Amundsen, P-A., Dempson, J. B., Jonsson, B., Jonsson, N., O’Connell, M. F., Mortensen, E. (2003). Atlantic Salmon Salmo salar L., Brown Trout Salmo trutta L. and Arctic Charr Salvelinus alpinus (L.): a Review of Aspects of Their Life Histories. Ecology of Freshwater Fish 12: 1-59. Larinier, M. (2001). Environmental Issues, Dams and Fish Migration. In: Marmulla, G (ed) Dams, fish and fisheries. Opportunities, challenges and conflict resolution. FAO Fisheries technical paper no. 419, Rome, pp 45-90. Larinier, M. (2008). Fish passage experience at small-scale hydro-electric power plants in France. Hydrobiologia 609: 97-108. Limburg, K. E., Waldman, J. R. (2009). Dramatic Declines in North Atlantic Diadromous Fishes. BioScience 59(11): 955-965. Linløkken, A. (1993). Efficiency of Fishways and Impact of Dams on the Migration of Grayling and Brown Trout in the Glomma River System, South-Eastern Norway. Regulated Rivers: Research and Management 8: 145-153.

27

Linnansaari, T. Keskinen, A., Romakkaniemi, A., Erkinaro, J., Orell, P. (2010). Deep habitats are important for juvenile salmon Salmo salar L. in large rivers. Ecology of Freshwater Fish 19: 618- 626. Lundqvist, H., Rivinoja, P., Leonardsson, K., McKinnell, S. (2008). Upstream Passage Problems for Wild Atlantic Samon (Salmo salar L.) in a Regulated River and its Effect on the Population. Hydrobiolobia 602: 111-127. Länsstyrelsen Västra Götalands Län (2005). Bevarandeplan för Natura 2000-område. SE0520163 Örekilsälven. Länsstyrelsen Västra Götalands Län. Diarienummer: 511-36828-2005. 22 pp. Marschall, E. A., Mather, M. E., Parrish, D. L., Allison, G. W., McMenemy, J. R. (2011). Migration delays caused by anthropogenic barriers: modeling dams, temperature, and success of migrating salmon smolts. Ecological Applications 21(8): 3014-3031. McCormick, S. D., Hansen, L. P., Quinn, T. P., Saunders, R. L. (1998). Movement, migration and smolting of Atlantic salmon (Salmo salar). Can. J. Fish. Aquat. Sci. 55: 77-92. Mitchell, S. C., Cunjak, R. A. (2007). Relationship of upstream migrating adult Atlantic salmon (Salmo salar) and stream discharge within Catamaran Brook, New Brunswick. Can. J. Fish. Aquat. Sci. 64: 563-573. Moore, J. N., Arrigoni, A. S., Wilcox, A. C. (2012). Impacts of Dams on Flow Regimes in Three Headwater Subbasins of the Basin, United States. Journal of the American Association 54(5): 925-938. Naniwadekar, R., Vasudevan, K. (2014). Impact of Dams on Riparian Frog Communities in the Southern Western Ghats, India. Diversity 6: 567-578. Nilsson, C., Berggren, K. (2000). Alterations of Riparian Ecosystems Caused by River Regulation. BioScience 50: 783-792. Nilsson, C., Reidy, C. A., Dynesius, M., Revenga, C. (2005). Fragmentation and Flow Regulation of the World’s Large River Systems. Science 308: 405-408. Nilsson, N., Degerman, E., Eklöv, A., Andersson, H. C., Halldén, A. (2013) Validering av modell för beräkning av öringsmoltproduktion i Kävlingeån, 1999-2005, och Åvaån, 2010. Del 3 i Vättern- FAKTA no: 4. 104 pp. (In Swedish). Noonan, M. J., Grant, J. W. A., Jackson, C. D. (2012). A Quantitative Assessment of Fish Passage Efficiency. Fish and Fisheries 13: 450-464. Norrgård, J. R., Greenberg, L. A., Piccolo, J. J., Schmitz, M., Bergman, E. (2013). Multiplicative loss of landlocked Atlantic salmon Salmo salar L. smolts during downstream migration through multiple dams. River Research and Applications 29: 1306-1317. Olsson, I. C., Greenberg, L. A., Eklöv, A. G. (2001). Effect of an Artificial Pond on Migrating Brown Trout Smolts. North American Journal of Fisheries Management 21(3): 498-506. 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)?. Canadian Journal of Fisheries and Aquatic Sciences 55 (Supplement 1): 281-287. Pedersen, S., Heinimaa, P. & T. Pakarinen (Eds). (2012). Workshop on Baltic sea trout. Helsinki, Finland, 11-13 October 2011. DTA Aqua report no. 248, 95 pp. Pess, G. R., Quinn, T. P., Gephard, S. R., Saunders, R. (2014). Re-colonization of Atlantic and Pacific rivers by anadromous fishes: linkages between life history and the benefits of barrier removal. Rev. Fish. Biol. Fisheries 24: 881-900. Poulos, H. M., Miller, K. E., Kraczkowski, M. L., Welchel, A. W., Heineman, R., Chernoff, B. (2014). Fish Assemblage Response to a Small Dam Removal in the Eightmile River System, Connecticut, USA. Environmental Management 54: 1090-1101. Power, G. (1958). The Evolution of Freshwater Races of the Atlantic Salmon (Salmo salar L.). Arctic 11: 86-92. Primmer, C. R., Veselov, A. J., Zubchenko, A., Poututkin, A., Bakhmet, I., Koskinen, M. T. (2006). Isolation by Distance Within a River System: Genetic Populations Structuring of Atlantic Salmon, Salmo salar, in Tributaries of the Varzuga River in Northwest Russia. Molecular Ecology 15: 653-666. Pringle, M. C. (2001). Connectivity and the Management of Biological Reserves: A Global Perspective. Ecological Applications 11(4): 981-998.

28

Pringle, M. C. (2003). What is Hydrological Connectivity and Why is it Ecologically Important? Hydrological Processes 17: 2685-2689. Rivinoja, P., McKinnell, S., Lundqvist, H. (2001). Hindrance to Upstream Migration of Atlantic Salmon (Salmo salar) in a Northern Swedish River Caused By a Hydroelectric Power-station. Regulated Rivers: Research Management 17: 101-115. Rivinoja, P. (2015). Effekter av faunapassager. En sammanställning med fokus på fiskvägar i Norden. SWECO Environment AB. Uppdragsnummer 1655133000. 34 pp. Roscoe, D. W., Hinch, S. G. (2010). Effectiveness Monitoring of Fish Passage Facilities: Historical Trends, Geographic Patterns and Future Directions. Fish and Fisheries 11: 12-33. Saunders, R. L. (1981). Atlantic Salmon (Salmo salar) Stocks and Management Implications in the Canadian Atlantic Provinces and New England, USA. Canadian Journal of Fisheries and Aquatic Sciences 38(12): 1612-1625. Schilt, C. R. (2007). Developing Fish Passage and Protection at Hydropower Dams. Applied Animal Behaviour Science 104: 295-325. Schmutz, S., Giefing, C., Wiesner, C. (1998). The Efficiency of a Nature-like Bypass Channel for Pikeperch (Stizostedion lucioperca) in the Marchfeldkanalsystem. Hydrobiologia 371/372: 355- 360. Spjut, D., Degerman, E. (2016). Laxhabitat på västkusten. Aqua reports 2016:XX. Sveriges lantbruksuniversitet, Drottningholm. 45 pp. Stabell, O. B. (1984). Homing and Olfaction in Salmonids: a Critical Review with Special Reference to the Atlantic Salmon. Biological Reviews 59: 333-388. Stickler, M., Enders, E. C., Pennell, C. J., Cote, D., Alfredsen, K., Scruton, D. A. (2008). -related movement and growth of Atlantic salmon parr during winter. Transactions of the American Fisheries Society 137(2): 371-385. Stradmeyer, L., Höjesjö, J., Griffiths, S. W., Gilvears, D. J., Armstrong, J. D. (2008). Competition between brown trout and Atlantic salmon parr over pool refuges during rapid dewatering. Journal of Fish Biology 72: 848-860. Stuart, T. A. (1957). The Migration and Homing Behaviour of Brown Trout (Salmo trutta L.). Freshwater Salmon Fisheries Research 18:1-27. Svenskt ElfiskeRegiSter (SERS). (2016). Sveriges Lantbruksuniversitet (SLU), Institutionen för akvatiska resurser: http://www.slu.se/elfiskeregistret [2016-02-02]. Taylor, E. B. (1991). A Review in Local Adaptation in Salmonidae, with Particular Reference to Pacific and Atlantic Salmon. Aquaculture 98: 185-207. Thorsson, L. (2009). Torpdammen i Örekilsälven. Förbättring av fiskens vandringdmöjligheter. Förstudie och underlag för samråd. Thorsson & Åberg Miljö och Vattenvård AB, Terra- Limnogruppen AB. 24 pp. Thorstad, E. B., Fiske, P., Aarestrup, K., Hvidsten, N. A., Hårsaker, K., Heggberget, T. G., Økland, F. (2005). Upstream migration of Atlantic salmon in three regulated rivers. In Aguatic Telemtry: Advances and Applications, M, Spedicato Marmulla G, Lembo G (eds). FAO/UN – COISPA: Rome; 191-202. Thorstad, E. B., Whoriskey, F., Uglem, I., Moore, A., Rikardsen, A. H., Finstad, B. (2012). A critical life stage of the Atlantic salmon Salmo salar: behaviour and survival during the smolt and initial post-smolt migration. Journal of Fish Biology 81: 500-542. Tian, K., Liu, G., Xiao, D., Sun, J., Lu, M., Huang, Y., Lin, P. (2015). Ecological Effects of Dam Impoundment on Closed and Half-closed Wetlands in China. Wetlands 35: 889-898. Van Zwol, J. A., Neff, B. D., Wilson, C. C. (2012). The effect of competition among three salmonids on dominance and growth during the juvenile life stage. Ecology of Freshwater Fish 21: 533-540. Verspoor, E. (1997). Genetic diversity among Atlantic salmon (Salmo salar L.) populations. ICES Journal of Marine Science 54: 965-973. Vähä, J-P., Erkinaro, J., Niemelä, E., Primmer, C, R. (2007). Life-history and Habitat Features Influence the Within-river Genetic Structure of Atlantic Salmon. Molecular Ecology 16: 2638- 2654. World Comission on Dams (WCD). (2000). Dams and Development: a new Framework for Decisions-making. London: Earthscan Publications.

29

WWF (2001). The Status of Wild Atlantic Salmon: A River by River Assessment. AGMV Marquis, Quebec, Canada. Zhou, J., Zhang, M., Lin, B., Lu, P. (2015). Lowland Fluvial Phosphorus Altered by Dams. Water Resources Research 51: 2212-2226. Östergren, J., Nilsson, J., Lundqvist, H. (2012). Linking Genetic Assignment Tests with Telemetry Enhances Understanding of Spawning Migration and Homing in Sea Trout Salmo trutta L. Hydrobiologia 691: 123-134.

30