Acid episodes and the behavioural ecology of Atlantic salmon Salmo salar L

Bale, Claire 2007. Acid episodes and the behavioural ecology of Atlantic salmon Salmo salar L. PhD Thesis, Cardiff University.

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Abstract

Although the impacts of surface water acidification on Atlantic salmon (Salmo salar L.) and brown trout (Salmo trutta L.) are well described, factors affecting recovery following pollution abatement are poorly understood. Paradoxically, despite increasing average pH over the last two decades, stocking efforts to rehabilitate damaged populations have not been successful. One possible explanation is that average pH measurements mask the effects of episodic fluctuations during high flow when pH is transiently reduced, metal concentrations are elevated and some organisms are affected adversely. However, because salmonid fish (i) avoid acid water and (ii) shelter within stream bed interstices, assessing the effects of acid episodes on their populations requires some understanding of how refuge use, refuge availability and refuge conditions affect recolonisation opportunities. This project therefore examined the effects of acid episodes on the behaviour of Atlantic salmon at different life stages as a possible explanation for the limited recovery of re-stocked populations. Sampling in acid sensitive-streams at low and high (episodic) flow revealed that the stream hyporheos was less acid than surface water in the same streams, with temperature and conductivity also more favourable in interstices. Laboratory experiments were then used to examine (i) the behaviour of Atlantic salmon alevins during a simulated episode in a vertical substrate-filled tank (Chapter 3) (ii) the behaviour of Atlantic salmon parr during a simulated episode in a shelter choice tank (Chapter 4) and (iii) if differences resulting from rearing environment affected the behaviour of Atlantic salmon parr during a simulated acid episode (Chapter 5). Hatchery-reared alevins avoided episodically acid conditions by moving into an area of more neutral pH opercular rate and mortality were both greater in acid water. Hatchery-reared pan- preferentially used a neutral shelter acid exposure also resulted in increased activity and opercular rate. Fish reared in a simulated wild environment were better able to avoid acid pulses (i.e. they showed greater use of neutral refuges) than hatchery-reared fish, but other behavioural responses (activity and opercular rate) were similar. These results illustrate the potential importance of the streambed during acid episodes as chemical refuges to salmonids, which both alevins and parr are able to exploit. However, at least for hatchery-reared fish, the success of re-stocking programmes could be improved by subjecting fish to acid stress- conditioning regimes prior to release.

Item Type:	Thesis (PhD)
Status:	Unpublished
Schools:	Biosciences
Subjects:	Q Science > QH Natural history > QH301 Biology
ISBN:	9781303209758
Date of First Compliant Deposit:	30 March 2016
Last Modified:	09 Jan 2018 20:21
URI:	https://orca.cardiff.ac.uk/id/eprint/54634

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