"Tag them?"
"With a little aluminum button fastened to their tail, just as bad youngsters fasten a tin can to a dog's tail. Every tag has a number, and we use aluminum because it corrodes rapidly in salt water."
"Then I should think," said Colin, "that was the very reason why you shouldn't use it."
"Why not?" asked the professor mildly. "We know that the salmon are not going to stay in the salt water, because they are going up the river to spawn. If, therefore, we catch a fish in the nets higher up stream, with the tag bright and shining, we know that it hasn't been in salt water at all; if dull and just a little worn away, that the fish with that tag has been staying in the brackish water near the mouth of the river; but if it is deeply corroded, that the fish returned to sea for a time. As you see, a good deal of information is gathered that way. But in the morning you will have a chance to see how it is done, and then the results—when they are published—will seem more interesting."
"Have you been associated with the Bureau of Fisheries, Professor Podd?" Colin asked.
"Not directly," the other replied. "I should
have enjoyed it, and it seems to me a work of the first importance, but every man is apt to think that about his own work, or work that is like his own. But I can tell you what decided me, nearly twenty years ago, to give all my spare time to the fishery question."
"What was that?" asked Colin.
"It was a phrase in a lecture that Dr. Baird, the founder of fish culture in America, was giving about the need of the work. He pointed out that there was more actual life in a cubic foot of water than in a cubic foot of land, and closed by saying, 'The work of conserving the Fisheries of the United States will not be finished until every acre of water is farmed as carefully as every acre or land.'"
"I never quite thought of it as farming," said the boy.