Brown trout spawning habitat selection and its effects on egg survival Zo  e Gauthey 1,2 , Margaret Lang 3 , Arturo Elosegi 2 ,C  edric Tentelier 1,4 , Jacques Rives 1,4 , Jacques Labonne 1,4 1 UMR 1224, Ecologie Comportementale et Biologie des Populations de Poissons, INRA, Aquap^ ole, Quartier Ibarron, 64310 Saint-P ee sur Nivelle, France 2 Faculty of Science and Technology, University of the Basque Country UPV/EHU, 48080 Bilbao, Spain 3 Environmental Resource Engineering, Humboldt State University, Arcata 95521, CA, USA 4 UMR 1224, Ecologie Comportementale et Biologie des Populations de Poissons, UFR Sciences et Techniques de la C^ ote Basque, Univ Pau & Pays Adour, All ee du parc Montaury, 64600 Anglet, France Accepted for publication September 25, 2015 Abstract – Salmonid females invest heavily in reproduction, through gamete production, habitat selection and maternal care. Habitat selection and maternal care are expected to provide shelter for eggs against scouring and predators. However, females also tend to produce variable egg sizes, and this trait may interact with habitat quality to influence the survival of offspring. In this study, we aimed at evaluating the role of female habitat selection on egg survival conditional on individual egg size and female body size. We monitored female reproductive activity in two natural rivers for 3 years, in order to relate nest characteristics to female body size. Bigger females dug deeper nests at lower shear stress force. Right after the end of nest construction, we sampled a part of the eggs laid by each female, measured them individually, and placed them back using capsules within their original position in the nest. At time of hatching, the capsules within the nest were collected and individual egg mortality was assessed. Our results indicate that scouring was the main driver for mortality (75%) and that nest burial depth and shear stress force above the nest both influenced scouring. However, subsequent survival was influenced by neither nest characteristics, individual egg size, nor the interaction between both. It is therefore expected that traits or tactics that reduce nest scouring probability should be under strong selection. Key words: phenotype–habitat matching; nest scouring; egg size; shear stress; salmonid Introduction Salmonid females invest heavily in reproduction (Jonsson & Jonsson 1999; Kamler 2008) producing a large number of gametes. They also provide parental care through nest (or redd) building and are thought to lead reproductive habitat selection (DeVries 1997). This particular stage of the salmonid life cycle has for decades received a vast amount of attention from ecologists (Bagenal 1969; Northcote & Lobon-Cervia 2008) because it is thought to strongly affect population dynamics (Elliott 1994). The spawning and incubation life stage also exhibits considerable trait variation at various scales (Berg et al. 2001; Einum & Fleming 2002; Rollinson & Hutchings 2011a). Mortality rates during spawning and incuba- tion can be very variable, due to either the risk of nest scouring or to the variation in the quality of micro-habitat. Thus, this stage might be the most selective phase of the whole life cycle. Salmonid females often exhibit ample phenotypic variation in characteristics such as body size, and they also pre- sent large variation in habitat selection (Ottaway et al. 1981; DeVries 1997; Armstrong et al. 2003; Riedl & Peter 2013). Finally, variation in egg size within and between clutches from the same popula- tion also occurs (Berg et al. 2001; Gregersen et al. 2009). The general expectation is that increased burial depth seems to be less prone to scouring (Mont- gomery et al. 1996), but can only be dug by large females (Ottaway et al. 1981). Large females also produce bigger eggs (Hendry & Day 2003), which seems to increase offspring fitness (Einum & Fleming Correspondence: J. Labonne, UMR 1224, Ecologie Comportementale et Biologie des Populations de Poissons, INRA, Aquap^ ole, Quartier Ibarron, 64310 Saint- P ee sur Nivelle, France. E-mail: labonne@st-pee.inra.fr Salmonid Symposium. doi: 10.1111/eff.12262 1 Ecology of Freshwater Fish 2015 Ó 2015 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd ECOLOGY OF FRESHWATER FISH