Thermal and digestive constraints to foraging behaviour in marine mammals

Abstract

While foraging models of terrestrial mammals are concerned primarily with optimizing time/energy budgets, models of foraging behaviour in marine mammals have been primarily concerned with physiological constraints. This has historically centred on calculations of aerobic dive limits. However, other physiological limits are key to forming foraging behaviour, including digestive limitations to food intake and thermoregulation. The ability of an animal to consume sufficient prey to meet its energy requirements is partly determined by its ability to acquire prey (limited by available foraging time, diving capabilities and thermoregulatory costs) and process that prey (limited by maximum digestion capacity and the time devoted to digestion). Failure to consume sufficient prey will have feedback effects on foraging, thermoregulation and digestive capacity through several interacting avenues. Energy deficits will be met through catabolism of tissues, principally the hypodermal lipid layer. Depletion of this blubber layer can affect both buoyancy and gait, increasing the costs and decreasing the efficiency of subsequent foraging attempts. Depletion of the insulative blubber layer may also increase thermoregulatory costs, which will decrease the foraging abilities through higher metabolic overheads. Thus, an energy deficit may lead to a downward spiral of increased tissue catabolism to pay for increased energy costs. Conversely, the heat generated through digestion and foraging activity may help to offset thermoregulatory costs. Finally, the circulatory demands of diving, thermoregulation and digestion may be mutually incompatible. This may force animals to alter time budgets to balance these exclusive demands. Analysis of these interacting processes will lead to a greater understanding of the physiological constraints within which the foraging behaviour must operate.

Comparative analysis of methods for inferring successful foraging areas from Argos and GPS tracking data

“…This minimal lag is in the range of values mentioned for post-breeding females in the literature and seems biologically coherent for mammals (Rosen et al 2007, Thums et al 2008. Although empirical descriptors presented high Fig.…”

In cold blood: evidence of Pacific sleeper shark (Somniosus pacificus) predation on Steller sea lions (Eumetopias jubatus) in the Gulf of Alaska

“…2). Many processes that lead to death are associated with the reduced ability of marine mammals to thermoregulate (Dierauf and Gulland, 2001;Rosen et al, 2007;Stoskopf, 2005). Inflammation and infection often lead to pyrexia (fever).…”

“…The normal abdominal temperature of healthy pinnipeds-although not well studied-is thought to range from 36°C to 38°C (Whittow, 1987). Antemortem temperature patterns may reveal hypothermia or pyrexia (fever), the former indicative of chronic energetic imbalance and starvation (Rosen et al, 2007), the latter indicative of inflammatory responses to immune challenges (Stoskopf, 2005).…”

Environmental constraints upon locomotion and predator–prey interactions in aquatic organisms: an introduction

“…This now requires direct validation on instrumented animals to investigate the extent to which this behaviour contributes to diving patterns in the wild. Rosen et al (2007) argue that, despite being the focus of much research, the ADL is only one factor among the physiological constraints within which foraging behaviour must operate in marine birds and mammals. Citing work on pinnipeds and cetaceans, the authors explore how foraging activity can also depend upon the ability to capture and process (digest) prey items.…”

“…(b) Differential effects on predators and prey An important issue that needs further attention is the ecological implications of how factors such as temperature (Farrell 2007;Lovvorn 2007;Rome 2007;Rosen et al 2007) and oxygen (Abrahams et al 2007;Domenici et al 2007) can exert different constraints on the physiology of different animal groups; for example, upon ectotherms versus endotherms or water breathers versus air breathers. Most aquatic ectotherms are also water breathers, therefore these effects may be additive.…”