Fish in space: local variations of home range and habitat use of a stream-dwelling fish in relation to predator density M. C. Lucas & D. H. Bubb School of Biological and Biomedical Sciences, Durham University, Durham, UK Keywords predation risk; habitat use; home range; telemetry; individual variation; Thymallus thymallus. Correspondence Martyn C. Lucas, School of Biological and Biomedical Sciences, Durham University, South Road, Durham DH1 3LE, UK. Tel: +44(191) 3341345, Fax: +44(191) 3341201 Email: m.c.lucas@durham.ac.uk Editor: Jean-Nicolas Volff Received 8 August 2013; revised 27 December 2013; accepted 30 January 2014 doi:10.1111/jzo.12129 Abstract A key response of animals to local environmental variation is altered use of space, but studies simultaneously examining local variation in habitat use and space use are uncommon. We predicted that elevated abundance of avian predators would result in grayling Thymallus thymallus, a stream-dwelling fish, using mesohabitats containing more cover, superimposed on seasonal changes in use of key resources (and hence space use) for functions such as reproduction. Using radio-telemetry, the pattern of space and habitat use by 40 wild grayling was determined in neighbouring stream sections in relation to season and predator density. Grayling used different habitats between seasons, but displayed similar patterns of habitat use in adjacent sections. Although patterns of habitat use were stable between stream sections, space use was not. In two winter periods, grayling ranged signifi- cantly more widely where there were significantly greater densities of avian preda- tors, especially cormorant, Phalacrocorax carbo. No such differences were apparent in summer when cormorants were absent, but experimental manipula- tion of predator densities was not possible, so results are correlative. Support for a predator effect is provided from significantly greater rates of injury, associated with avian beak scar marks, present on grayling from the section with highest avian predator densities, compared with adjacent sections with lower levels of avian predators. Unlike many studies of fish behaviour to elevated predation risk, in which fish make greater use of ‘refuge’ habitat, grayling exhibited wide-ranging behaviour and high activity, possibly reflecting avoidance behaviour. Introduction One of the key responses of animals to variation in their environment is to alter their use of space. This plasticity in spatial behaviour has been recognized in laboratory and field studies of animals in response to variations in factors, such as population density (Schradin et al., 2010), food availabil- ity (Brashares & Arcese, 2002; Brodersen et al., 2008; Schradin et al., 2010), sex (Perry & Garland, 2002), preferred physical habitat (Twiss, Thomas & Pomeroy, 2001), repro- ductive condition (Dahle & Swenson, 2003) and predation risk (Lima & Dill, 1990; Werner, 1991; Eklov & Persson, 1996; Yunger, 2004; Heithaus & Dill, 2006; Willems & Hill, 2009). Reported effects of predation risk on behaviour include alterations of levels and timing of foraging activity (Werner, 1991; Railsback et al., 2005; Ross et al., 2013), increased vigi- lance behaviour and grouping (Shulz & Noe, 2002) and increased use of refuge habitat (Grand & Dill, 1997; Krause et al., 1998; Rangeley & Kramer, 1998; Brodersen et al., 2008; Skov et al., 2013). Fewer studies have sought to examine how the extent of space use and habitat choice vary simultaneously under natural conditions of varying predation risk (e.g. Frair et al., 2005; Willems & Hill, 2009; Chapman et al., 2013). Frair et al. (2005) showed the effects of wolves, Canis lupus, on elk, Cervus elaphus, movements and space use, while Willems & Hill (2009) demonstrated, for vervet monkeys, Cercopithecus aethiops, the interplay between relative avoid- ance of areas with high predator threat and elevated use of resource-dense habitat. Chapman et al. (2013) provide evi- dence for a predation/growth-potential tradeoff determining winter migration to refuge habitat by cyprinid fishes. There remains a need for a better understanding, through such natural environment experimental approaches, of the spatial behavioural responses of mobile prey in relation to predators and vice versa (Lima, 2002). In this study, space and habitat use were measured for a stream-dwelling fish, grayling, Thymallus thymallus, in adja- cent river reaches, where avian predator abundance varied within and across seasons. There has been substantial debate as to the impacts of avian predators, especially cormorant, Phalacrocorax carbo, on grayling populations (Suter, 1995; Staub et al., 1998). We predicted that elevated predator density would be associated with grayling spending more time in habitats containing more cover and that home range size and daily movement would be unaffected by predator density, Journal of Zoology Journal of Zoology. Print ISSN 0952-8369 126 Journal of Zoology 293 (2014) 126–133 © 2014 The Zoological Society of London