Friday, March 6, 2009

BROWN BEARS: HANDLING AND INGESTING FISH PREY

A large boar gives its salmon prey a hug before "processing" it for ingestion.

Grizzlies use a number of different handling techniques when feeding on salmon. In most cases, the savvy “fisherbear” will grasp its prize in its jaws and carry it from the waterway to the shore, a gravel bar or surrounding grassy meadow/woodland (subordinate grizzlies, in the presence of conspecifics, are often more likely to move farther from the capture site than larger, more dominant bears). They then place their catch on the ground and stand on it with the fore paws. How the prey fish is processed may vary from one individual to the next or from one location to another. In many cases the first thing a bear will do is bite down on the posterior region of the fish and remove the tail section. Another body tissue targeted early in the handling process is the skin. To skin its quarry, the bear will grasp the skin with the incisors and pull upward, peeling the integument from the salmon’s body.

If food is in short supply (e.g., it is early in the salmon run or if fish numbers are down) the bear will consume the entire fish. If food is abundant, the bruin may select the choicest parts of the fish and leave much of its behind for scavenging birds, other mammals or even other bears (e.g., subordinate individuals or those that are poor at fishing). As mentioned in other posts, the skin is preferred as are the brains, but rather than ingesting the entire head, the bear often bites through the top of the cranium and laps out the brain or plucks them out with its incisors (see video footage below).

Not all bears take the time to leave the stream to eat their prize. It is not uncommon to see a bear, standing in knee deep water, clamping the fish against the front foreleg with the opposite paw (some bears employ this technique when eating fish on shore). The bear then rips the fish apart, one bite at a time. If the water where a fish is captured is shallow enough, some bears will pin the fish to the stream bed, while in a state of repose, and then stick their head underwater and rip pieces from their piscine prize (the bear will raise its head to masticate and then submerge to take another bite).

I have noticed that in many cases the fish rarely struggle much after being trapped in the bear’s jaws. They seem to go limp. They may flop about if the bear should drop them on the shore before pinning them down to eat, but otherwise they resist very little while in the jaws of the bruin. (I did see occasions where they fish would struggle if a bear bit down on the upper back.)

In the video featured below, you will see various fishing methods and some of these handling methods employed by a number of different Katmai brown bears. A few things to look for: there is a sequence of video that shows a big brown bear deftly removing the brain from a fish. There is a scarred, big boar diving into a deep river pool from the shoreline and submerging in an attempt to capture its slippery quarry (he finally succeeds in capturing a "spent" fish in the video and stands on its hind feet as it tears the fish apart). Toward the end of the video, you will see a large boar launching some of its great bulk from the river and plunging back into the water with fore legs outstretched. At one point, it has herded a big school of salmon along the river bank and appears to be trying to push some of the fish onto the shoreline. Turn up the sound and enjoy!

video

© Scott W. Michael

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