Journal of Fish Biology (2012) 80, 2384–2389 doi:10.1111/j.1095-8649.2012.03284.x, available online at wileyonlinelibrary.com Visibility conditions and diel period affect small-scale spatio-temporal behaviour of pike Esox lucius in the absence of prey and conspecifics P. A. Nilsson*, H. Baktoft, M. Boel, K. Meier, L. Jacobsen, E. M. Rokkjær, T. Clausen and C. Skov National Institute of Aquatic Resources (DTU-Aqua), Technical University of Denmark, Vejlsøvej 39, DK-8600 Silkeborg, Denmark (Received 21 October 2011, Accepted 22 February 2012) Pike Esox lucius in the absence of prey and conspecifics were shown to have the highest habitat- change activity during dusk and to decrease preference for complex habitats in turbid water. As the behaviours indicate routine responses in the absence of behavioural interactions, E. lucius spatio- temporal distributions should be directly affected and thereby more easily assessed and avoided by prey, with potential consequences for encounter rates.  2012 The Authors Journal of Fish Biology  2012 The Fisheries Society of the British Isles Key words: activity; habitat choice; piscivore; predator; turbidity. The spatio-temporal distribution of piscivores can influence encounter probabilities with prey, and thereby also incur effects on and of predation rates (Nilsson, 2001; Skov et al., 2002; Nilsson, 2006). Piscivore activity and habitat-choice behaviours should affect distribution patterns and can vary between diel periods and environmen- tal conditions (Diana, 1980; Jepsen et al., 2001; Turesson & Br¨ onmark, 2007). Such piscivore behaviours may be directly determined by diel period or environmental conditions, with prey responding to piscivore distribution to avoid risk of predation. Alternatively, diel period and environmental conditions may act only indirectly on piscivore distribution, if piscivores adjust behaviours according to risks and prey behaviours that are directly driven by these factors. Both scenarios pose spatio- temporal games between piscivores and prey but with different opportunities for prey to assess piscivore distributions. The pike Esox lucius L. 1758 is an important piscivore in many temperate sys- tems, and is described as an ambush predator hiding in, for instance, dense vegetation (Craig, 1996). Different indications of the diel periodicity of E. lucius activity are found in the literature, but an overall assumption is that E. lucius are primarily active during daytime and at moderate light intensities during dawn and dusk (Dobler, 1977; *Author to whom correspondence should be addressed at present address: Department of Biology – Aquatic Ecology, Ecology Building, Lund University, SE-22362 Lund, Sweden. Tel.: +46 46 2228365; email: anders.nilsson@biol.lu.se 2384  2012 The Authors Journal of Fish Biology  2012 The Fisheries Society of the British Isles