Size and temperature dependent foraging capacities and metabolism: consequences for winter starvation mortality in fish

Abstract

The foraging related capacities, energy requirements and the ability of individuals to withstand starvation are strongly dependent on body size and temperature. In this study, we estimated size‐dependent foraging rates and critical resource density (CRD) in small Arctic char (Salvelinus alpinus) under winter conditions and compared these with previous observations under summer conditions. We investigated if starvation mortality is size‐dependent in the laboratory, and we assessed the potential for winter growth and the occurrence and size dependency of winter mortality both in a large scale pond experiment and in natural lakes. The efficiency of foraging on macroinvertebrates increased with size but was lower at 4 than 12°C, still CRD was lower at 4 than 12°C as metabolic rates decreased faster than foraging efficiency with temperature. When starved, small char died before large and at rates which suggest that YOY char need to feed during winter to avoid starvation. Results from both our pond experiment and field study indicate that survival of YOY char over winter is high, despite severe winter conditions, because YOY char are able to feed and grow during winter. In seasonal environments with declining resources, the size scaling and temperature dependency of foraging and metabolic demands may provide conditions which can favour either small or large individuals. This size advantage dichotomy relates to that larger individual's by having a higher CRD are more likely to start starving, but once resource levels are below CRD for all size classes, small individuals starve to death at a higher rate. Negative size‐dependent winter mortality from starvation is suggested to be more pronounced in species that are not adapted to feed at low temperatures and in species feeding on zooplankton, since zooplankton abundance, in contrast to macroinvertebrate abundance, is generally low during winter.

Effects of repeated handling and air exposure on the immune response and the disease resistance of gibel carp (Carassius auratus gibelio) over winter

“…synthesis of HSPs may affect the immune functions of organism. Moreover, the metabolic rate and energy depletion of fish in winter is much lower than any other season [31]. Therefore, the present reduced induction of HSP70 expressions in the repeated handled carp post bacterial challenge may also be partially responsible for the increased disease insistence and the improved immune response.…”

Repeated handling compromises the immune suppression and improves the disease resistance in overwintering channel catfish (Ictalurus punctatus)

“…The excess synthesis of HSPs may affect the immune functions of organism. Moreover, the metabolic rate and energy depletion of fish in winter is much lower than any other season [38]. Therefore, the present reduced induction of HSP70 expressions in the repeated handled fish post bacterial challenge may also be partially responsible for the increased disease insistence and the improved immune responses.…”

Climate change and freshwater ecosystems: impacts across multiple levels of organization

“…When differently sized individuals of the same species compete for resources, the smaller individuals may therefore have an advantage (Persson 1985; figure 4f ) if they can grow and sustain themselves at a lower resource level than larger conspecifics (Lundberg & Persson 1993;Persson et al 1998). Mesocosm and in situ experiments have shown that the metabolic demands of Arctic Char increase with temperature at a faster rate than their foraging capacity (Bystrom et al 2006). If warming increases CRD disproportionately for larger individuals, adaptive foraging by exploiting a larger size range of prey might be able to mitigate these energetic requirements (figure 4g).…”

“…The ability to gain energy can be separated into two size-dependent components: the search efficiency (encounter rate, attack rate) and the capacity to process food (handling; Lundberg & Persson 1993;Persson et al 1998): together these make up the foraging capacity of an individual (Bystrom & Andersson 2005;Bystrom et al 2006). The results of recent studies have revealed how complex food webs can arise from simple rules related to FT (Beckerman et al 2006;Petchey et al 2008), but the effects of temperature are yet to be fully incorporated in these new models, despite its strong influence on foraging rates (e.g.…”