He had fired upon the beast in the first instance, not through the lust of killing but because he was prompted to do so by the instinct of the hunter who lives upon the product of his weapons.

In this far northern land it is the instinct of self-preservation to kill, for here if man would live he must kill.
In Labrador they butcher wild animals for food just as we butcher steers and sheep and hogs for food, and the only difference is that the wild creature, matching its instincts and fleetness and strength against the hunter's skill, has a reasonable chance of escape, while our domestic animals, deprived of liberty, are driven helpless to the slaughter.
In our kindlier clime the rich soil, too, produces vegetables and fruits upon which we might do very well, if necessary, without ever eating meat; but in the bleak land where Bobby and Jimmy lived the summer is short and the soil is barren, and there are no vegetables, and no fruits save scattered berries on the inland hillsides.

And so it is that here men must depend upon flesh and fish for their existence and they must kill if they would live.
Every lad on The Labrador, therefore, is taught from earliest youth to take pride in his profession of hunter and trapper and fisherman--for on The Labrador every man is a professional hunter and trapper and fisherman--and to strive for skill and the praise of his elders, and Bobby was no exception to the rule.
And so it came about that Bobby at the age of thirteen proved himself a bold and brave hunter, and standing now over the carcass of his victim he felt a vast and consistent pride in his success; for it was no small achievement for a lad of his years to have killed, single-handed and poorly armed, a full grown polar bear.

It was an accomplishment, indeed, in which a grown man and a more experienced hunter than Bobby might have taken pride; and a grown man could scarcely have employed better tactics, or shown greater skill and courage, after the first foolhardy shot had been fired.
But this was Bobby's way.

It was an exhibition of his old trait of getting himself and Jimmy into a scrape and then by quick action and practical methods getting them safely out of it again.
Skipper Ed and Abel had heard the reports of Bobby's gun, and they knew that something unusual was on foot.