GRADIENT RELATED MOVEMENT OF ATLANTIC SALMON PARR DURING A FREEZE UP EVENT IN A SMALL, NATURAL RIVER

GRADIENT RELATED MOVEMENT OF ATLANTIC SALMON PARR DURING A FREEZE UP EVENT IN A SMALL, NATURAL RIVER.

Morten Stickler*1, Eva C. Enders2, Curtis J. Pennell2, David Cote3, David A. Scruton2 and Knut Alfredsen1

*Corresponding author. Phone: +47 73598388, fax: +47 73591298, e-mail: [email protected]

1 Department of Hydraulic and Environmental Engineering, Norwegian University of Science and Technology, 7491 Trondheim, Norway

2 Fisheries and Oceans Canada, Science Branch, P.O. Box 5667, St. John’s, NL A1C 5X1 Canada. Phone: +17097726416, fax: +17097725315

3Parks Canada, Terra Nova National Park of Canada, Glovertown, NL, A0G 2L0, Canada. Phone: +17095332801; fax: +1 7095332706

Key words: Atlantic salmon (Salmo salar), physical habitat, movement, river ice, gradient

ABSTRACT Though there has been an increased focus on the interaction between the physical habitat and the behaviour of Atlantic salmon parr (JAS; Salmo salar L.), only a few studies have attempted to link winter conditions using hydraulic variables and ice conditions with behaviour and habitat use in natural flow environments. In this study, mobility of Atlantic salmon parr was studied during a freeze up event in late January in a small, natural river located in north-east Newfoundland, Canada. Two river sections with different gradients were selected as study reaches. The low gradient section (LGS) had a bed slope of 0.3 % and the high gradient section (HGS) had a bed slope of 1.8 %. Passive Interactive Transponder (PIT) technology was used to collect data on movement of 71 parr by using both fixed antennae and mobile tracking devices. Meteorological and physical conditions were continuously monitored. In the LGS, formation of surface ice dominated, giving stable conditions. In the HGS, formation of anchor ice and anchor ice dams occurred periodically leading to a dynamic environment. Parr inhabiting LGS moved significantly more than parr in HGS indicating a higher activity. In both sections the parr did not tend to explicit exploit ice edges, nor day or night. However, parr in HGS inhabited locations closer to the edge compared to parr in LGS. The obtained results imply different behavioral

Proceedings oh the 18th IAHR InternationalSymposium on Ice (2006)

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strategies within the fish population in relation to local, physical winter habitat conditions. Furthermore, the results underline the importance of considering the physical habitat when monitoring fish behavior and movement in lotic environments.

INTRODUCTION Physical habitat and behavior of stream fishes has traditionally been investigated in relation to the stream flow variables depth and velocity, and substrate (Alfredsen and Tesaker, 2002; Berg, 1994; Cunjak, 1996; Tesaker, 1998). These characteristics have been extensively studied over the last two decades, primarily during summer conditions. Even though winter has been suggested as a critical period for survival of stream fishes (Annear et al., 2002; Bradford and Higgins, 2001; Cunjak et al., 1998; Power et al., 1993), few investigations have been carried out. This is particularly true in relation to physical conditions, (Roussel et al., 2004). However, the physical conditions during winter in lotic environments can be severe (Prowse and Gridley, 1993), and thus potentially affect fish distribution, mobility, habitat use and survival. In boreal regions winter prevails a significant part of the year. Different types of river ice form and alter the environment by changing flow conditions (Prowse, 1994; Stickler, 2003; Stickler and Alfredsen, 2005). It has been suggested that river reaches with riverbed gradients lower than 0.004, static (surface-) ice formation dominates while in river reaches with bed gradients > 0.004 dynamic ice formation dominates (Tesaker, 1998). Between these two gradients differences in physical conditions are likely to be found, and thus potential effects on fish behaviour. In such dynamic environments, where marked seasonal changes occur, adaptive changes in behaviour and activity of animals are expected (Chapman, 1966). For example, previous studies have shown that juvenile stream fishes decrease their activity (Fraser and Metcalfe, 1997; Fraser et al., 1993; Scruton et al., 2005) and are often found in deeper sections of the river during the cold season (Bremset and Berg, 1999; Cunjak, 1988; Cunjak et al., 1998; Hiscock et al., 2002b). These locations are expected to be important in relation to energy expenditure and survival for juvenile stream fishes during winter (Cunjak, 1988). Reduced flow velocity gives stable conditions and require less energy usage for the fish (Alfredsen et al., 2004) and formation of surface ice creates cover against predators (Meyers et al., 1992; Young, 1995). In addition, surface ice cover has also been found to benefit juvenile Atlantic salmon (Salmo salar) in terms of energy storage due to decreased light (Finstad et al. (2004) and as refuge from high velocity fields (Cunjak and Randall, 1993; Maciolek and Needham, 1952; Whalen et al., 1999). In contrast, other winter studies have found an increased activity of stream fish during specific winter episodes. E.g. Heggenes (1993) found in a winter study that brown trout (Salmo trutta) inhabiting riffle areas moved out of their shelter before nightfall to avoid being trapped by anchor ice. These observations have also been supported in later studies (Brown and Mackay, 1995; Jakober et al., 1998; Stickler et al., 2006) indicating riffle habitats as less preferable and that fish in these locations may be forced to move due to the ice development. However, contrasting results have also been reported. Whalen et al. (1999) and Roussel et al. (2004) made observations of juvenile Atlantic salmon inhabiting riffle habitat during dynamic ice formation. Roussel et al. (2004) concluded that the anchor ice was exploited by the fish as cover from super cooled water. However, these contrasting results indicate that there may be other mechanisms involved. In a previous study by Melanie et al. (2000), invertebrate drift during anchor ice formation was found


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to increase in abundance of up to thirty times. In a study by Cunjak (1988), ice edges was suggested as important habitats. Therefore, it can be expected that ice edges in high gradient locations may act as important feeding habitats due to the proximity to high velocity fields and increased drift densities. The dynamic stream conditions during winter and the variety of findings in winter research on winter refugee and winter behaviour of stream fishes reflects the complexity of the nature. Therefore, more knowledge with a particular focus on the interaction between the physical habitat and behaviour of juvenile stream fishes during winter is needed. This paper relates physical conditions in terms of steep and mild river bed gradients with mobility of Atlantic salmon parr in a small, natural river. The presented study was conducted during freeze up, defined as a period when surface ice starts to form along banks and boulders including events with dynamic ice formation in open leads in high gradient locations. The objective was to look at potential differences in movement of Atlantic salmon parr between mild and steep river gradients in a small, natural river. Also, ice edge as preferable habitats between gradients was investigated.

MATERIALS AND METHODS

Study area and physical conditions Southwest Brook is a small, natural river located in Terra Nova National Park (48 36’ 25’’ N, 53 58’ 50’’ W) on the north-east coast of Newfoundland, Canada (Figure 1). The river has a basin area of 36.7 km2 and an average gradient of 1.3 %. Mean winter discharge is 0.5 m3/s. Two reaches with different gradient were selected as study sites. Section I (low gradient section; LGS) was 100 m long, 14 m in average wetted width and had a mean gradient of 0.3 % favoring static ice formation. Section II (high gradient sections; HGS) consisted of two sub reaches of 100 m long and an average wetted width of 8 m with equal gradient of 1.8 % favoring dynamic ice formation. Substrate size was found to be not significant (Mann Whitney U-test; U = 767, p = 0.75) different between the LGS (mean ± s.e.; 225.4 mm ± 2.2 mm) and the HGS (224.2 mm ± 1.2mm). In both sections substrate had minimal compaction of fine sediments (low embeddedness) providing interstitial spaces for the fish. The study was conducted from 20 January to 26 January 2006. Flow discharge had a mean (± s.e.) of 0.75 ± 0.05 m3/s and a mean (± s.e.) air temperature of -5.8 C ± 0.4 C (Figure 2). On the night of January 23rd, air temperature dropped to -15.6 C causing super cooling and extensive ice formation and ice built up in both sections (Figure 2). In the LGS surface ice formed covering 98 % (Figure 2) of wetted area with a thickness of 2 cm. In the HGS anchor ice formed covering 80% of the river bed with a thickness up to 15 cm. In the latter section, four anchor ice dams with maximum height of 60 cm were established initiating surface ice formation upstream and increased water level by up to 20 cm (Stickler and Alfredsen, 2005).


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Figure 1: Map and location of study area in Newfoundland, Canada.

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Fish tagging From 24 November to 28 November 2005 (TW = 6.0 C) a total of 143 (NLGS = 60, NHGS = 83) Atlantic salmon (Salmo salar L.) parr (mean ± s.e. fork length, LF = 128.4 ± 1.6 mm) were caught using a 24 V backpack electro fisher (Smith Root, Model 12). No significant difference in fish length were found between LGS and HGS (Mann Whitney U-test, U = 2437, p = 0.66). Each individual was measured by fork length (mm) and weight (0.1 g), in addition to that sexual status (precocious or not) was determined. Fish smaller than 84 mm were rejected as suggested by Roussel et al., (2000) to ensure minimal impacts of tagging. Passive Integrated Transponder (PIT) tags (Texas Instruments; length; 23-mm; diameter; 3.9 mm; weight: 0.6 g in air; tag/fish weight ratio (mean ± s.e.); 3.2 % ± 0.1 %) were surgically implanted. Fish were anesthetized by immersion in an aqueous solution of clove oil (100 ppm) and placed dorsal side down on a foam pad during surgery. The tag was inserted through a 10 mm long ventral incision posterior to the pelvic fin. The incision was closed with two sutures of 4-0 Ethicon braided silk. The procedure

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took no longer than 1.5 min, and during this time, tepid water was poured over the fish’s gills to prevent freezing. After surgery, tagged fish were held in a bucket for several minutes to recover before they were brought to cages located in the river. Fish were held for 24 hours before releasing them into their respective habitats.

Data and tracking procedure Fish movement was monitored implementing PIT technology and using tracking procedures similar as Linnansaari et al. (2006). Manual tracking was conducted twice a day (0900 and 1300) and once a night (2100) using a hand-held antenna with a detection range of 60 cm. During anchor ice formation an additional night tracking was conducted (0100). Two of the gates were bed antennae to retain stability during flood events and ice break-ups. To ensure temporal comparability of fish movement between the two study sites, two sets of manual tracking devices were used. Each fish position was geo-referenced using a Sokkia SET 600 total station. Further, four double PIT “gates” were installed upstream and downstream of each section to record movement and direction of movement between sections. From 20 to 26 of January 51 % (n = 71) of the previous tagged fish were found and tracked. No fish mortality was observed, however, tracks of mink (Mustela vison) and otter (Lutra canadensis) were found on two occasions in December and later in March. Information on meteorological conditions was collected by a weather station located 1 km from the study site (Canada Environment, Campbell Scientific; 1 hour resolution). Water level and discharge corrected for ice build up were monitored by a gauging station 100 m upstream (pressure sensor, Campbell Scientific). Data on ice thickness and ice growth were collected using 1) a total station; geo-referencing on distribution and thickness of ice during surveys and 2) time lapse (every 30 minutes) video cameras. Water temperature was monitored using high accuracy data loggers (SeaBird Electronics, SBE39; accuracy ± 0.002 C), which allowed detecting super cooled water and thus periods with dynamic ice formation.

Statistical analysis Fish movement was defined as radial movement calculated by the Pythagorean theorem in a similar procedure as Roussel et al. (2004). In contrast to latter study median position instead of mean position was used to decrease the effect of “sallies” (Worton, 1995). In addition, individuals moving between sections (2.8 %, nfish = 2) were excluded in order to explicitly investigate fish inhabiting LGS and HGS, and to avoid artificially enlarged home ranges. Home range calculations were based on Minimum Convex Polygon (MCP) method (Worton, 1995). Arc Editor (ESRI Inc., ArcMap 9.1) with the Spatial analyst extension was used to plot and analyze fish positions and movement. Statistical analyses were performed using SPSS 14.0. Assumptions of normality and homogeneity of variance were tested in each case using the Anderson test and Levene’s test, respectively. When deviations were detected, non-parametric Mann-Whitney U-test and Kruskal-Wallis test were conducted. All statistical analysis was considered significant at the p = 0.05α level.


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RESULTS

Movement Parr in the LGS had significantly longer mean movement compared to fish in the HGS (Mann-Whitney U-test; U = 19508.0, p < 0.001; LGS0∀SE: 2.6 ± 0.3 m; HGS0∀SE: 1.6 ± 0.2 m; Figure 3). In the HGS a significant difference in movement was found between consecutive days from 20 January to 26 January (Kruskal-Wallis; χ2 = 17.75, df = 6, p < 0.01). Parr on 24 January moved significant less compared to 25 January (Mann Whitney U-test; U = 421, p = 0.01). In the LGS no difference were found (Kruskal-Wallis; χ2 = 5.44, df = 6, p = 0.49), but an increase in movement variability on 23 January was revealed (Figure 3).

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Home range and habitat use Parr had a mean (± s.e.) home range size of 18.5 ± 40.0 m2. 95 % of the parr utilized home ranges below 58 m2 while the remaining 5 % had homeranges up to 260 m2 ( Figure 4). No significant differences in home range size was found between fish in LGS and HGS (Mann-Whitney U-test; U = 386, p = 0.06). Parr in the LGS had a mean (± s.e.) homerange of 22.8 ± 8.6 m2 while the homerange of parr inhabiting the HGS was 14.2 ± 5.1 m2. 2.8 % (n = 2) of the tracked fish made movements from the HGS to the LGS, whereas one was precocious. During the study period surface ice had no coverage to 98 % and 80% coverage in the LGS and HGS, respectively (see Figure 2). In both sections, 77% and 67% of the parr inhabited ice-free locations during ice formation, day and night, respectively. No significant difference in distance to ice edge between day and night was found (Mann Whitney U-test; U = 20596, p = 0.58). However, parr in the HGS inhabited areas significant (Mann-Whitney U-test, U = 12712, p < 0.01) closer to the edge compare to parr in the LGS ( Figure 4).


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DISCUSSION AND CONCLUSION In this study Atlantic salmon parr made significantly larger movements and had larger size of home range in the LGS compared to the HGS. Further, a change in movement was observed on an extensive ice formation event. Here, parr in the LGS became more active while, in contrast, parr in the HGS decreased their activity. As suggested by Cunjak and Power (1986) and Valdimarsson and Metcalfe (1998) surface ice is a significant source of cover during winter as the predation risk reduces. In relation to this it can be hypothesized that the decrease of amount of light due to surface ice nocturnal behaviour can be trigged even during day time and thus further increases the feeding behaviour and finally the fish activity. As this study indicate parr increase their activity in ice covered areas probably due to cover and altered light conditions and potentially explained by latter hypothesis. On the night 24 January surface ice formed and covered 98 % of the reach. Here, the parr increased their movement indicating a shift in activity pattern. Next day the parr decreased their movement and remain stable throughout the period. Latter observation might be explained by change in the physical conditions in which potentially stresses the fish and forces them to increase their movement and energy expenditure. In the HGS parr made significantly smaller movements compared to LGS. On the night 24 January anchor ice formed within the reach covering 80 % of the river bed. Then, at day time, anchor ice ceased and no anchor formation was further observed throughout the period. Through the study period parr made no shift in movement until anchor ice release on the 25th. Here, a small, but significant change in movement was observed. In the study by Whalen et al. (2004) and Roussel et al. (2004) parr was observed to stay during anchor ice formation. In the present study similar observations were made. Only 2.8 % of observed individuals emigrated from high to low gradient section indicating suitable conditions within the study reach. In the study by Roussel et al. (2004) on Atlantic salmon parr the author hypothesized that fish used anchor ice as cover against super cooled water. In this study this hypothesis was tested in which super cooled water was detected underneath the anchor ice suggesting other factors. One potentially explanation can be that fish are using the ice as cover, not against super cooled water, but in


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similar matter as with surface ice. However, it has also been observed in other winter studies that juveniles seek shelter from locations with dynamic ice formation. E.g. Heggenes et al. (1993) observed juvenile brown trout seeking out of their shelter before night fall suggestion avoidance of dynamic ice formation. Stickler et al. (2006) and Whalen et al. (1999) made similar observations where Atlantic salmon parr increased their movement in anchor ice exposed areas and made habitat shift from riffles and closer to river bank with surface ice. It has also been suggested in previous studies that juvenile steam fish rather seek shelter in deeper parts of the river system with stable conditions (Bremset and Berg, 1999; Cunjak, 1988) instead of high gradient locations with unstable conditions. These contradictory findings suggest other additionally mechanisms behind such behaviour. In a recent field study by Stickler and Alfredsen (2005) on anchor ice growth, observations of ice filling interstitial spaces within the substrate were made. Ice formation within the substrate is potentially excluding important habitats. In contrast, Roussel et al. (2004) observed that anchor ice was forming on top of the substrate as a carpet and not between the substrate which might explain the differences. Other explanations of fish seeking out of such locations can be that the fish are being trapped underneath the anchor ice. Anchor ice forms during night (Carstens, 1970) potentially covering the whole river bed (Tesaker, 1994). As the fish has reached its winter state and become nocturnal (Heggenes et al., 1993; Valdimarsson and Metcalfe, 1998) the ice may reduce the escape possibilities. Although anchor ice normally cease during day time (Ashton, 1986) the fish is most likely not to move due to its new winter state by sheltering in the substrate on this time of the day. As the recent studies and our observations indicate physical conditions may be vital for fish behaviour and choice of habitat. In previous studies ice edges have been suggested as important habitats for juvenile stream fishes due to cover from predation and as hydraulic shelter (Cunjak, 1988; Whalen et al., 1999). Further, ice and stream edges in general may also provide important feeding habitat due to its close proximity to higher velocity fields thus potentially increased drift densities. In this study parr in the HGS were located in areas closer to the ice edge compared to parr in the LGS. Further, there were found no difference in distance to ice edge between night and day and in average 80 % of the parr inhabited areas with no surface ice. Based on previous results it may seem that there may be other important or additional factors. Size of substrate in LGS and the HGS was not found to be different, although substrate in the HGS was larger. However, both sections had coarse substrate with low embeddedness providing interstitial spaces and thus suitable habitats. Observations and results from this study show how potentially complex and dynamic in-stream conditions may be during freeze up events in small, steep rivers. Different river gradients will lead to different ice regimes and flow conditions, and thus potentially influence on the fish behavior and habitat choice. However, studies of tagged fish also may be affected by other factors. In a study by Heggenes et al. (1996) movement of Atlantic salmon parr was found to be positive correlated with fish size. However, parr in this study parr movement was significantly not affected by their size, probably due to the narrow range in fish size distribution. According literature winter predation on juvenile stream fish by mink (Mustella vision) and otter (Lutra canadensis) can be significant (Hiscock et al., 2002a; Valdimarsson and Metcalfe, 1998). In the present study 51 % of total parr tagged were found and tracked during the period. Here, no single tags or mortality among tagged fish was found. However, tracks of mink and otter were seen on


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two occasions, and thus predation can not be disregarded. Effects of surgically implanted tags on behavior and survival of juvenile stream fish have also been discussed. Roussel et al. (2000) suggested using Atlantic salmon parr < 84 mm in PIT experiments. In our study the smallest parr was 105 mm and within the suggested limits. In a study by Winter (1996) the author recommended a tag/body weight ratio in air less than 2 %. However, this “2 % rule of thumb” was tested by Brown et al. (1999) who evidently found that swimming performance was not affected by implantation of transmitters weighing up to 12 % of the fish body mass, although behaviour was not tested. This 2% general rule of thumb has also been criticized by Jepsen et al. (2004) who concluded that there is no generally applicably rule, but rather defined by other factors such as e.g. study objectives, tagging method and species/life stage. During the present study no visual marks/exterior wounds were found among the tagged parr indicating small or no effects. However, the tag/body ratio exceeded 2 % (mean ± s.e.; 3.2 g ± 0.1 g) and should be considered. In light of our results it may seem that substrate is a predominant factor for habitat selection. In general, low gradient rivers and river sections are normally providing less coarse substrate as a result of low flow velocity. However, in small, natural rivers this might not always be true as flood events can be large and devastating through all seasons. In this study observations of fish movement have been related to gradient and thus physical conditions during winter, i.e. ice formation. The results indicate that surface ice is an important factor in relation to cover and potentially increase the fish activity and feeding behaviour. However, this type of behaviour also demand more energy expenditure for the fish and might be a strategic “trade of”. Further, the presented results indicate that high gradient sections provide good habitats, but have to be considered with physical conditions, i.e degree of dynamic ice formation. Finally, our results indicate that ice edges as preferable habitats are more important in high gradient areas compared to low gradient areas.

ACKNOWLEDGES Special thanks are given to Craig Kelly and Neil Ollerhead for their assistance in the field. The project was funded by Natural Resources Canada's (NRCan) Panel for Energy Research and Development (PERD). Visiting Travel grants from the Norwegian University of Science and Technology (NTNU) and Fisheries and Oceans Canada were given to Morten Stickler and Eva Enders was funded by a Visiting Fellowship in Canadian Government Laboratories from the Natural Sciences and Engineering Research Council of Canada (NSERC).

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GRADIENT RELATED MOVEMENT OF ATLANTIC SALMON PARR DURING A FREEZE UP EVENT IN A SMALL, NATURAL RIVER

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