The functional relationship between peak spring floods and survival and growth of juvenile Atlantic Salmon (Salmo salar) and Brown Trout (Salmo trutta)

Abstract

Summary1. The effects of high spring floods on survival and growth of juvenile Atlantic Salmon, Salmo salar, and Brown Trout, Salmo trutta, are explored, using data from a long-term study in the River Saltdalselv, northern Norway. The flow regime in this river is typical for northern rivers. 2. There was considerable variation in year class strength of both species. 3. Mortality of Atlantic Salmon increased significantly in years with high discharge during the alevin stage as well as the first week after emergence. High discharge during the egg stage and more than 1 week after emergence seemed to be of minor importance. Water temperature at emergence was rather high (average 10·5°C) and did not significantly affect year class strength. 4. Brown Trout emerged earlier than Atlantic Salmon at an average water temperature of 8·2°C. Highest mortality was observed in years with low water temperatures at emergence as well as high discharge during the alevin stage. 5. For 1-year-old fish or older, the size of the spring peak flood did not influence mortality significantly. 6. Growth of Atlantic Salmon parr was diminished in years with a high peak spring flood. A similar effect on Brown Trout was not detected. 779Floods and survival of juvenile salmonids stages, but little is known about the relative susceptibility of different life stages and the functional relation between discharges and mortality. A washout effect from abrupt increases in stream discharge has been observed for young fish with limited swimming ability (Heggenes & Traaen 1988). However, the susceptibility to washout may decrease rapidly with increasing fish size (Heggenes & Traaen 1988). Obviously, moderate flows at a particularly sensitive stage may cause higher mortality than considerably higher flows at less sensitive stages.In the present study we quantify the effects of spring peak floods on the same populations over many years, using data from a long-term study of Atlantic Salmon and anadromous Brown Trout from a river in northern Norway. In the River Saltdalselv, we estimated densities of Atlantic Salmon and Brown Trout parr in a systematic way for 22 years . For each year, we also estimated the time when eggs hatched, and the swim-up time of fry. From these data, we analysed the effects of maximum discharge on survival and growth of fish, elucidating the stages that are most sensitive to high discharge. Materials and methodsThe River Saltdalselv in northern Norway (67°N, 15°E) has a catchment area of 1550 km 2 (Fig. 1). The mean annual water discharge is 12·1 m 3 s -1 at our sampling station (Station D), increasing to 55·4 m 3 s -1at the outlet to the sea. The flow regime is typical for northern rivers (Fig. 2). Water quality, including pH, is favourable for salmonids (Koksvik 1977). Atlantic Salmon and anadromous Brown Trout are the dominant fish species in the river. There are no predatory fish present (except a few eels and cannibalistic trout and salmon). Also, predatory birds are few. Both species typically stay 4 or 5 years (range 3-7 yea...

Movement and Mortality of Adult Brown Trout in the Motupiko River, New Zealand: Effects of Water Temperature, Flow, and Flooding

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“…In hydropeaking rivers, the density and growth rate of juveniles was found to be reduced, and the mesohabitat was disturbed (Jensen and Johnsen 1999;Flodmark et al 2006;Korman and Campana 2009). Juveniles are most endangered by displacement or stranding because of their inability to find appropriate shelter, particularly in channelized rivers.…”

Climate change, forests, fire, water, and fish: Building resilient landscapes, streams, and managers

“…An important element that may be facilitating coexistence at higher latitudes is that brown trout tend to be found in larger streams at lower elevations and do not occupy many tributaries used by cutthroat trout for spawning, reducing interactions between brown trout and juvenile cutthroat trout. This downstream-upstream partitioning of stream habitats by brown trout and other salmonids (Weigel and Sorensen 2001) and their absence from small, high-elevation streams in the central Rocky Mountains (Bozek and Hubert 1992;Rahel and Nibbelink 1999) is thought to be related to their poor recruitment at low water temperatures (Jensen and Johnsen 1999;. Because brown trout eggs and fry are also vulnerable to high flows during the latter part of incubation through the early stages of emergence (Lobón-Cerviá and Mortensen 2005), the timing of peak discharge in these environments may also present an obstacle to more-upstream invasions.…”