This is because wide rivers, whitewater rapids, and so on, aren't all that common. Or at least, they don't form the majority of bear habitat. We watch and photograph bears feeding in such places because it looks dramatic and, more importantly, it's relatively easy to do. It's the same with other predators. We know a fair amount about the hunting habits of wolves and lions because we can watch them in Yellowstone Park or the Serengeti, where the terrain is wide open. That allows us to safely observe their behaviour from a distance, so, understandably, we'd prefer it where possible.
Bears do, of course, catch salmon in large rivers, or we wouldn't have those photographs. But, more commonly, they are using small streams, where they can catch them as they spawn, not as they migrate. That's partly because there are more small streams than large rivers, but also because such places tend to be more remote from human activity, which has to be a plus.
Salmon are well-known for spending most of their lives at sea but swimming upstream into rivers to spawn. In order to watch bears fishing for them, we'd need either to hide and hope they don't notice us or, which is probably better with modern technology, leave video camera traps to, as some researchers put it, "watch the unwatchable".
A study using this latter technique was recently published, observing brown bears fishing for salmon in small streams away from normal human activity. The streams in question feed Lake Aleknagik, in southwestern Alaska. "Small", in this context, means less than 6 metres (20 feet) wide and, on average, they are also all less than 26 cm (10 inches) deep. They are too small to be useful to human fishermen and there are virtually no human structures along the lake, aside from a small village at the far end, and certainly nothing as far from the lake shore as these streams.
"Salmon", under the strict scientific definition, can refer to any of seven different species, of which the largest is the Atlantic salmon familiar from Britain, other parts of northern Europe, and the east coasts of Canada and Maine. The other six species all live in the north Pacific, with some considerable overlap as to where they can be found.
In the case of Aleknagik, however, the vast majority belong to one species: the sockeye salmon (Oncorynchus nerka). At 58 cm (1'11") and 7.7 kg (17 lbs), this is quite small for a salmon, although still larger than most other fish you would find in rivers. They spawn from mid-July to late August, so it was at this time of year that the researchers placed their video cameras to watch the bears try to catch them. (It also helps that this isn't the legal hunting season, which further reduces the chances of humans being about).
As always, the researchers went into the study with some expectations as to what they would find - and, as is often also the case, at least some of their guesses failed to pan out. For instance, they had expected male bears to be more successful at catching fish than females. That's not because they would be inherently better at it, but because, being larger and socially dominant, they should be able to control access to the very best patches of the river. But they proved no better than females, so either they don't try to do this, or there are enough good fishing stretches to go around, or they are just not good at finding them.
They had also thought that bears might be more successful at catching fish at night, since we already know they like to do this. But again, this wasn't the case; bears have good night vision, so it doesn't make things any worse, but it didn't seem to help.
Overall, the bears used four different tactics to catch fish. This is not counting methods such as scavenging on dead fish, pinching fish off smaller bears, and (for young bears) "hoping mum will catch them for you". Perhaps surprisingly, the most successful tactic was the one that required the least effort: standing around in the stream and hoping a fish comes past close enough that you can grab it. This worked about 70% of the time, but the bears don't do it very often, presumably because, while you may get lucky in the end (the stream not being very wide), you may also have quite a wait. Perhaps it's a good tactic for when you aren't especially hungry and don't fancy a lot of exercise.
The second tactic is to actively look out for fish, and when you spot one, lunge for it and chase it until you catch it. This only works about half the time, as the fish has more of a head start, but it has the advantage of speed. This turned out to be the most popular tactic, as it will probably get you more fish in the long run than just sitting about and hoping. A mixed tactic, where the bear wanders about slowly but does not actually pursue fish, was also popular, but doesn't seem very successful, perhaps because bears engaged in it were focusing on something else.
The fourth tactic was only used by the youngest bears, most of which could still be described as "cubs". It consists of dashing into the stream and flailing about randomly in the hope that something happens. Which it usually doesn't.
Therefore, it seems that the best predictor of fishing success for brown bears is basically being old enough to know what they're doing. It evidently takes time to develop skill, something that, unsurprisingly, has also been seen in other species with well-developed foraging tactics.
The authors of the study also note that scavenging dead fish - often those half-eaten by another bear but then left behind - was particularly common. This has the advantage of requiring very little energy and, by definition, having a 100% success rate when the opportunity arises.
If you don't have to put the effort in, why bother?
[Photo by Richard A. Weaver, from Wikimedia Commons.]
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