Consumption choice by bears feeding on salmon

Abstract

Consumption choice by brown (Ursus arctos) and black bears (U. americanus) feeding on salmon was recorded for over 20,000 bear-killed fish from 1994 to 1999 in Bristol Bay (sockeye salmon, Oncorhynchus nerka) and southeastern Alaska (pink, O. gorbuscha and chum salmon O. keta). These data revealed striking patterns of partial and selective consumption that varied with relative availability and attributes of the fish. As the availability of salmon decreased, bears consumed a larger proportion of each fish among both years and habitats. When availability was high (absolute number and density of salmon), bears consumed less biomass per captured fish, targeting energy-rich fish (those that had not spawned) or energy-rich body parts (eggs in females; brain in males). In contrast, individual fish were consumed to a much greater extent, regardless of sex or spawning status, in habitats or years of low salmon availability. The proportion of biomass consumed per fish was similar for males and females, when spawning status was statistically controlled, but bears targeted different body parts: the body flesh, brain and dorsal hump in males and the roe in females. Bears thus appeared to maximize energy intake by modifying the amount and body parts consumed, based on availability and attributes of spawning salmon.

Evaluating the potential for grey seal predation to explain elevated natural mortality in three fish species in the southern Gulf of St. Lawrence

“…For large prey, these behaviours are consistent with optimal foraging theory, whereby seals may maximise their net rate of energy acquisition by differentially feeding on the most energy-rich or easiest-to-process portions of individual prey items, leaving a prey partially consumed when it is more profitable to search for another intact prey item (e.g. Sih 1980, Gende et al 2001.…”

Bacterioplankton niche partitioning in the use of phytoplankton-derived dissolved organic carbon: quantity is more important than quality

“…Optimal foraging models for consumer-prey interactions predict higher specialization in highly productive systems, and more generalist diets in low-resource regimes (for example, Werner and Hall, 1974;Gende et al, 2001). However, this applies only at the individual or population level.…”

Eco-evolutionary dynamics in Pacific salmon

“…When salmon are sufficiently abundant and easy to catch, bears kill salmon selectively on the basis of size (for example, Quinn and Kinnison, 1999;Ruggerone et al, 2000;Quinn and Buck, 2001) ); and they also target energy-rich (that is, newly arrived) fish (Gende et al, 2004), as well as energy-rich body parts such as the eggs of females (Gende et al, 2001). Body size selection based on stranding at the creek mouth could therefore have bioenergetic consequences for the bears, as the per-fish energetic reward is less for small fish than large fish.…”

“…Thus, in years when this selection at the creek mouth is intense, it might increase the chances of energy limitation for bears. For example, bears might have to increase their foraging effort, change their selectivity for energy-rich fish (Gende et al, 2004) or change their selectivity for energy-rich tissues (Gende et al, 2001). These effects are unlikely, however, to be particularly important when the overall salmon population is large and bears can easily catch the fish.…”