Effect of Temperature and Light on Overwintering Behaviour of Juvenile Atlantic Salmon

Valdimarsson, Sveinn Kari (1997) Effect of Temperature and Light on Overwintering Behaviour of Juvenile Atlantic Salmon. PhD thesis, University of Glasgow.

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This thesis investigated the effect of light, temperature and season on several behaviours of overwintering juvenile Atlantic salmon (Salmo salar L). The sheltering behaviour and the nocturnal activity of the fish was examined in detail since previous work has showed that salmon become more nocturnal as temperature decreases, hiding in streambed crevices during the day. Experiments compared fish with different life history strategies; i.e. resident fish that will spend at least one more winter in fresh water and migratory fish that will leave fresh water in the coming spring. Chapter 2 - Observations of salmon in a semi-natural stream examined how light, temperature and time of year determine activity patterns, I also tested whether the life-history strategy of the fish affected diel activity, comparing fish that would migrate to sea the following spring with those that would be resident in fresh water for at least one additional year. The results showed that light intensity, temperature and time of year can be used to predict whether the fish hide or not: fish tended to hide at high light levels whenever the water was cold but were increasingly likely to emerge as the winter progressed.. There were significant differences between the two groups of fish; the putative migrants sheltered more than the resident group in winter, but this trend was reversed in the spring. Reducing the risk of predation in winter may be one of the reasons for this seasonal change in behaviour. Chapter 3 - Traditionally, behavioural studies on juvenile Atlantic salmon have been conducted during the day in summer. It is known that salmon become nocturnal in winter but very little is known about their behaviour at that time. Furthermore, comparisons between winter and spring are scarce. Therefore, observations in a semi-natural stream were carried out during the day and night, from February to June, comparing diel and seasonal differences in behaviour between the two life-history strategies. The results showed a general trend for more activity in spring than in winter. There were differences in relative feeding rate between the life-history strategies; the migratory fish foraged mostly during the day while the resident fish did more foraging at night. Overall the migratory fish made fewer feeding attempts over the winter which is surprising since they grow faster over that period. This suggests differences in foraging efficiency which could be the underlying mechanism for the separation into these two life-history strategies. Chapter 4 - The function of hiding in daytime refuges in winter has been unclear, but two major types of hypothesis have been proposed. One is that the fish are hiding from something (e.g. a predator) and the other is that the fish are seeking shelter from the water current. These hypotheses were tested by examining the selection by juvenile salmon of refuges that offered different degrees of concealment or shelter. The fish clearly preferred refuges that allowed them to hide (i.e. locations that were dark and opaque) but offered little shelter from the current. Therefore it can be assumed that the primary function of this nocturnal behaviour during winter is most likely to hide from diurnal predators. Chapter 5 - Since the food density (drift in the water column) is correlated with water velocity, the fish should normally choose feeding station in fast flowing water in order to get as much food as possible. However at low light levels the detection range is reduced so the fish will not be able to detect fast-moving items early enough to intercept them before they have been carried away; fish should therefore prefer slower currents on darker nights. Tests were carried out in tapered sections of a stream tank, each of which had a velocity gradient from a mean of 5 cm/s at the upstream end to 45 cm/s at the downstream end. A single fish was placed in each section, and a single record made of the position (and hence velocity) at which it held station under four different night-time light levels (0.00, 0.3, 1.0, 5.0 Ix). The results showed that fish selected slower flowing water as the night-time light intensity decreased. Chapter 6 - The area defended by fish should vary in relation to light level and this variation in territory size should lead to greater aggregations in better foraging areas on dark nights than on bright. Replicate groups of 8 salmon were placed in tanks modified to produce areas of variable flow rates and food supply. Distribution, aggression and feeding rates of the fish were measured in 5 min video samples recorded at even intervals throughout the night and at 4 different light levels (0.00, 0.01, 0.50, 1.00 Ix). The results show that aggression rate, increased with light level. Furthermore, fish aggregated more on darker nights, the minimum distance between fish increasing in relation to light intensity.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Additional Information: Adviser: Neil Metcalfe
Keywords: Zoology, Aquatic sciences, Behavioral sciences
Date of Award: 1997
Depositing User: Enlighten Team
Unique ID: glathesis:1997-75895
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 19 Nov 2019 17:38
Last Modified: 19 Nov 2019 17:38
URI: https://theses.gla.ac.uk/id/eprint/75895

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