Behaviors of Fishing Bears

Bears apparently eat spawning fish whenever and wherever they are vulnerable enough to be caught. Both black and brown bears congregate along streams during spawning runs, not only along the Pacific coast, but also under favorable circumstances in some inland areas (as described on this site: currently in Yellowstone National Park and historically in central Idaho).  The popular image of the "fishing bear" is, however, the brown (or grizzly) bear.  The extent to which bears can profit from fishing is clearly linked to how they are built, specifically the extent to which they can manipulate and handle food with their dextrous forearms and paws. No other large terrestrial mammal is as flexible (see Front limbs), which is the main reason they can efficiently capture and land fish.  
 
Selection of a specific fishing spot seems to not only involve knowledge of previous success, but also a complex social interplay among bears and humans based upon dominance and aggression; i.e., subordinate bears and species have to settle for second best, third best, or none at all.  Setting these social factors aside, bears appear to preferentially select the kind of sites where probability of success is higher. Success is not only a function of fish abundance and size, but also stream characteristics such as depth, gradient, bank structure, and streamside debris.  In short, bears orient toward stream reaches where spawner density (i.e., the ratio of spawners to stream volume) is high, the water shallow (optimally, so that the fish's back protrudes), the current high (so that the fish's forward movement and vagility is impeded), and there is enough debris and bank structure to allow either ambush or containment of corralled fish.
 
Conditions at McNeil River Falls in Alaska are clearly favored as a fishing spot by high spawner densities and dramatically retarded forward motion of the fish, and, accordingly, there is consistently a crowd of brown bears trying out their fishing skills.  However, this picture that has been captured by photographers thousands of times, and that we consequently associate with bears fishing for salmon, is atypical. Most fishing occurs along the rapids and shallow riffles of medium-sized to small tributaries, often in forested or brushy reaches, and consequently in areas where log jams can sometimes be exploited for more sophisticated fishing techniques.  Less commonly, bears may even "snorkel" for fish that are spawning along the beaches of inland lakes.  As a consequence, most fishing is characterized by bears scattered up and down streams and rivers, sometimes moderately aggregated in favorable locations, but rarely stacked up like the crowd at McNeil River Falls.
 
Bears use many different fishing techniques that seem to vary not only with site-specific conditions and geographic area, but also idiosyncratically among individuals.  In shallower water bears will bound from the shore, jump from the bank or a log jam, or stand silently in mid-stream waiting for passing fish.  Some bears also herd fish into shallower water or hedge them against piled debris or a cutbank. In deeper water bears add the plunge and submerged scan to their repertoire.  In all cases, bears attempt to take fish by surprise when they are most vulnerable or, conversely, somehow increase that vulnerability.  At the extreme, bears in some areas primarily consume salmon that are already dead from the rigors of spawning, or are so weakened that the demand for fishing technique is minimal. Actual capture involves permutations of mouth and paw holds, ranging from first pinning the fish to the bottom with one or both front paws, to simply grabbing the fish directly with the canines.  Less often, there have been descriptions of bears knocking passing fish out of the water with a broad and powerful sweep of the paw.  In any case, most bears end up on shore, often ensconced in the brush, eating their catch.  Bears are also apparently not fixated upon any given technique and fishing spot, and like any good angler often vary their approach.
 
As with their other prey, bears are not ambivalent to the different parts of a captured fish.  There is a clear pattern to the parts that bears leave uneaten; most often the jaws, gills, opercula, testes, and tail. On the other hand, bears consistently favor the skin and fatty eggs and brains.  There have even been reports of bears selectively keeping and eating unspawned females, which they apparently determine by a combination of olfactory and visual cues, and presumably for the sake of the eggs.  In another case where grizzlies were fishing for spawning suckers (along Witch Cr, tributary to Heart Lake in Yellowstone Park), they pinned their catches against a log to scrape off some of the scales prior to eating; a move not unexpected by anyone who has had the misfortune of eating sucker scales.
 
When all is said and done, bears are capable of eating 20 to 40 kg of fish in a single day. I had the opportunity to take detailed notes on one epsiode of a bear fishing for spawning cutthroat trout. In just 41 minutes the young bear was able to catch 24 roughly 0.6-kg fish, eat roughly 42% of each (plus or minus 32%), and, in the process, consume over 6 kg of trout. During this episode the bear moved roughly 242 m at an average speed of 2.6 km/hr, and spent roughly 44% of its time eating. The conditions were close to ideal; the spawning trout were passing through a particularly shallow stretch of water close to the beach--so shallow, in fact, that the fishes' backs protruded. As a result, the bear merely had to pin the trout to the stream bottom, and then grab them with its canines, or, in some instances, was able grab them directly with its teeth. In any case, it is not too difficult to imagine a series of episodes such as the one described here for a bear to end up ingesting 20-40 kg of fish in a single day, especially if fishing for the larger (4-30 kg each) coastal salmon.