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Title: The effect of light and temperature on the behaviour of juvenile Atlantic salmon (Salmo salar L.)
Author: Fraser, Neil Hugh Campbell
Awarding Body: University of Glasgow
Current Institution: University of Glasgow
Date of Award: 1994
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The overall aim of this thesis was to investigate behaviour exhibited by juvenile Atlantic salmon at certain key times in their life, that might predominantly be controlled by either light or temperature. Two key times chosen were: movements away from the redd and the first winter. The overall result was a series of studies in controlled environments on a variety of behaviour patterns which are known to occur in the natural environment. Salmonids move away from the redd predominantly at night-time. Light level would therefore appear to be the controlling factor releasing activity. However, the exact relationship between light level and alevin activity is not known and so the first part of the thesis centred around this behaviour. To begin with a series of artificial redds were used to monitor salmon alevin movements under various night-time incident light levels. A single redd was subjected to a single light level only on alternate nights. In all six experimental redds were run during the three years. Combining the results together gave a significant negative correlation between the numbers of salmon alevins moving away from a redd on a light night and light level. This behaviour was interpreted as a negative photokinesis since the frequency of movement was dependent on the intensity of the stimulation. There were two possible functional explanations as to why alevins may react in this way to light level. Firstly, the reaction could have been a simple photoresponse which has evolved to ensure that alevins only move away from the redd when they are least likely to be caught by a predator. Secondly, retinal developmental differences between alevins (less developed alevins becoming temporarily disorientated and move away from the redd because the ambient night-time incident light is still below their threshold level) could have led to the observed negative photokinesis (Ali, 1961; Manteifel, 1978). To investigate the exact underlying mechanism behind this behaviour, fine scale patterns of behaviour during movement were needed. Fortunately, in most of the artificial redds used in the above experiments some additional trapping and filming had been done already so these results were presented as evidence for the fine scale patterns of behaviour during movement. A recent study on alevin movements away from the redd indicated that a large proportion of alevins might disperse tlirough the gravel away from the redd so a series of undergravel traps were used to monitor movement of alevins in the artificial redds. The trapping results, presented in Chapter 3, revealed that there was a small proportion of alevins moving through the gravel. In addition, the filmed behaviour of alevin movement revealed that fish were moving away from the redd at two different levels in the water column; close to the substrate and in midwater. Filmed alevin movements were also temporally clumped and the peak dispersal time was in the first half of the night which is in agreement with other studies. In both cases alevins were moving in close association with the gravel which suggested that they are able to control the timing and method of movement away from the redd by using the gravel as an orienting factor and a medium for movement. This goes against the traditional view that movements away from the redd are purely the result of displacement due to a temporary disorientation (Bardonnet et al., 1993). Therefore, it was concluded that alevins are able to control their movement away from the redd by means of visual and tactile stimuli. The overwintering behaviour studied centred around the diumal-noctumal shift in behaviour which was recently found for stream resident trout in Norway. In this thesis the sheltering behaviour, during the day and the night, of individuals and groups of salmon subjected to manipulated water temperatures was monitored. This showed that there was an increasing tendency for fish to remain in refuges (without access to food) during the day as water temperature dropped below 10°C. However, they would emerge with the onset of darkness, and so the proportion of the daily active period occurring in darkness increased markedly as temperature decreased. This was matched by changes in feeding patterns. Total daily food intake in salmonids (as with all poikilotherms) declines at low temperatures, but this decline was far greater in daytime intake than in food obtained by night, so that the proportion of the daily total that was obtained at night increased to almost 100% in both experiments. Thus at 'summer' temperatures feeding rates were higher during the day than at night while this was reversed at 'winter' temperatures. This was a consequence of the tendency of fish to retreat into refuges by day but re-emerge at night as the temperature dropped. The social behaviour of the fish kept in a group changed with light intensity: fish were more aggressive at higher temperatures, but at any given temperature aggression rates per fish were on average six times higher by day than by night. By day the fish kept in a group tended to be well spaced, with some individuals defending territories whilst at night fish were often within a few centimetres of one another. The results of the two experiments indicate that overwintering noctumalism exhibited by salmonids occurs independently of season and it appears to be the first demonstration of a temperature controlled inversion of daily activity patterns. A possible functional explanation for this shift in foraging pattern may well to reduce predation risk in winter since salmon are relatively more vulnerable to endothermic predators when temperatures are cold due to their much slower escape responses (Chapter 6).
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available