Winter feeding, growth and condition of brown troutSalmo truttain a groundwater-dominated stream

Abstract

Winter can be a stressful period for stream-dwelling salmonid populations, often resulting in reduced growth and survival. Stream water temperatures have been identified as a primary mechanism driving reductions in fitness during winter. However, groundwater inputs can moderate water temperature and may reduce winter severity. Additionally, seasonal reductions in prey availability may contribute to decreased growth and survival, although few studies have examined food webs supporting salmonids under winter conditions. This study employed diet, stable isotope, and markrecapture techniques to examine winter (November through March) feeding, growth, and condition of brown trout Salmo trutta in a groundwater-dominated stream (Badger Creek, Minnesota, USA). Growth was greater for fish 150 mm (mean ¼ 4.1 mg g À1 day À1 ) than for those 151-276 mm (mean ¼ 1.0 mg g À1 day À1) during the winter season. Overall condition from early winter to late winter did not vary for fish 150 mm (mean relative weight (Wr) ¼ 89.5) and increased for those 151-276 mm (mean Wr ¼ 85.8 early and 89.4 late). Although composition varied both temporally and by individual, brown trout diets were dominated by aquatic invertebrates, primarily Amphipods, Dipterans, and Trichopterans. Stable isotope analysis supported the observations of the dominant prey taxa in stomach contents and indicated the winter food web was supported by a combination of allochthonous inputs and aquatic macrophytes. Brown trout in Badger Creek likely benefited from the thermal regime and increased prey abundance present in this groundwater-dominated stream during winter.

Seasonal feeding selectivity of brown trout Salmo trutta in five groundwater-dominated streams

“…This pattern was also evident in other winter studies of brown trout diet in southeastern Minnesota (Anderson et al 2016;French 2014;French et al 2014), and for salmonids in other regions where nocturnal benthic feeding in winter was attributed to lower capture efficiency of drift because of reduced light from ice cover, elevated turbidity, lower drift rates, and avoidance of predators (Tippets and Moyle 1978;Cunjak and Power 1986;Jørgensen and Jobling 1992;Heggenes et al 1993;Fraser and Metcalfe 1997;Johansen et al 2010).…”

“…Overall, Gammarus was a favored drifting macroinvertebrate taxon in our study; however, availability varied among streams and seasons. Low water temperature in winter does not correlate with a reduction in Gammarus, and brown trout demonstrated selection for this taxon in winter in Minnesota (Newman and Waters 1984;French et al 2014;Anderson et al 2016) and in other regions (Bridcut and Giller 1995). In the present study, brown trout ingested Gammarus from the benthos and drift during winter in streams where this taxon occurred, but positive selection toward Gammarus was only significant during spring and summer.…”

“…Reduced temperature, light, and macroinvertebrate productivity have been linked with low or negative growth in many streams (Metcalfe and Thorpe 1992); however, in southeastern Minnesota, there is considerable spatial and seasonal variation relative to maximum growth rates of brown trout (Dieterman et al 2004;Dieterman et al 2012;French et al 2014). Groundwater-dominated streams in this region support highly productive populations of brown trout, but demonstrate variation in production and diversity of aquatic macroinvertebrates (Troelstrup and Perry 1989;Waters 2000).…”

“…Finally, studies of growth of brown trout and prey availability in groundwater-dominated streams of southeastern Minnesota are limited. Recent work examined winter diet and growth (French 2014;French et al 2014), and winter prey selectivity (Anderson et al 2016) in southeastern Minnesota; however, no study has simultaneously addressed brown trout growth and prey selectivity of both benthic and drifting macroinvertebrates, and spanned multiple seasons, years, and streams. Thus, variation in the diet and growth of brown trout in southeastern Minnesota may reflect differences in prey assemblages and selectivity on a seasonal and spatial scale.…”

Brown trout growth in Minnesota streams as related to landscape and local factors

“…This supports conclusions reached by Dieterman et al (2012), who noted that limestone bedrock geology and agricultural watersheds promote high productivity in southeast Minnesota streams such that typical brown trout growth factors like prey availability, intraspecific density, social dominance are less important than in other regions (Bohlin et al 2002;Kaspersson & Hojeso 2009). Although thermal sensitivity did not explain spatial variation in an annual index of growth (MBLAA), previous research indicated late-winter brown trout condition (relative weight; Neumann et al 2013) was positively associated with groundwater input and negatively associated with thermal sensitivity in southeast Minnesota streams (French 2014;French et al 2014). Thus, the effect of thermal sensitivity on growth may be the strongest in cold winter conditions.…”