Evidence of concealment behavior by adult rainbow trout and brook trout in winter

Abstract

– There has been little investigation of the winter ecology of adult trout during winter, especially in regard to concealment behavior. We compared day vs night underwater counts of adult rainbow trout and brook trout from four streams. At water temperatures between 1°C and 9°C, daytime counts accounted for 44% and 16% of nighttime snorkeling counts for rainbow trout and brook trout adults, respectively. As winter progressed, nighttime counts declined more so for brook trout than rainbow trout, but the decline was not significant for either species. Nocturnalism of both species was higher in streams with colder water temperatures. We observed few fish within concealment structure; however, by electrofishing concealment habitat during the day, we captured 10 times more adult trout than we counted immediately beforehand by snorkeling. Adult trout were concealed in cobble‐boulder substrate and woody debris during the day.Note

Accuracy of Removal Electrofishing Estimates of Trout Abundance in Rocky Mountain Streams

“…Channel complexity in our study influenced removal estimate bias, and this was especially true for the percentage of boulder substrate, which appeared in all but one of the most plausible regression models and positively influenced removal estimate bias for both size-classes (i.e., more boulder substrate resulted in more bias in the removal estimates). Both juvenile and adult salmonids are often concentrated near boulder substrate (e.g., Baltz et al 1991;Gries and Juanes 1998;Meyer and Gregory 2000). Moreover, stream temperatures in our study averaged 10 • C during our surveys, which is near the threshold at which juvenile and adult trout conceal more regularly within boulder substrate (Chapman and Bjornn 1969;Griffith and Smith 1993;Meyer and Gregory 2000) and adopt a winter-type behavior.…”

Seasonal changes in stream salmonid population densities in two tributaries of a boreal river in northern Japan

“…Because these depressed densities increased again in the spring before the recruitment of newly emerged fry, emigration provides a more plausible explanation than mortality for the winter density decrease. However, low detectability in the winter because of concealment behaviors (e.g., Thurow 1997;Meyer and Gregory 2000) should not be ruled out. Nevertheless, we do not know where white-spotted charr overwintered.…”

“…In general, overwintering salmonids move downstream, form aggregations (e.g., Jakober et al 1998;Brown 1999), and show concealment behaviors (e.g., Thurow 1997;Meyer and Gregory 2000). As with other salmonids, juvenile masu salmon often move to low water velocity areas with shelter as water temperature decreases (Miyakoshi et al 2002(Miyakoshi et al , 2007Watanabe et al 2006;Nagayama and Nakamura 2007).…”

Ontogenetic and diel variation in stream habitat use by brook trout (Salvelinus fontinalis) in a headwater stream

“…Although several studies have examined ontogenetic (Griffith 1972;Johnson and Dropkin 1996) and seasonal differences (Cunjak and Green 1983;Johnson 2008), little information exists on diel habitat use by brook trout (Meyer and Gregory 2000). This is surprising since differences in the diurnal versus nocturnal habitat use of other species of stream salmonids are well documented (Bonneau and Scarnecchia 1998;Roussel and Bardonnet 1999;Jakober et al 2000).…”

“…Because preferred habitat can vary by fish size (Johnson and Dropkin 1996), season (Meyer and Gregory 2000), and time of day (Jakober et al 2000), assessment of preferred habitat must account for all these variables. Failure to understand these differences can adversely impact habitat suitability models for stream salmonids (Jakober et al 2000) and may greatly reduce the efficacy of habitat modifications designed to enhance stream populations (Bradford et al 1995).…”