Winnie's initial talk with Angus was essentially an initial warning against immortality. Angus knows that Winnie is thinking about it. He also knows what would result if many people knew about the spring water. He fervently explains the downsides to Winnie about living forever. His most powerful argument is when he says that he wishes that he could die again. He longs for the ability to die, because he says that is how a person truly lives.
"You can't have living without dying. So you can't call it living, what we got. We just are, we just be, like rocks beside the road."
Miles's conversation with Winnie the next morning reiterates the warning to Winnie. Winnie flat out asks Miles why he didn't give his wife and kids the spring water. She believes that he could have kept his family in tact had he done that. Miles flat out denies that possibility.
"No, it'd all have been so mixed up and peculiar, it just wouldn't have worked. Then Pa, he was dead-set against it, anyway. The fewer people know about the spring, he says, the fewer there are to tell about it."
Winnie still isn't convinced though. She can't bear the thought of death. She believes the world would be better off if nothing had to die. I love Miles's response, because it is so scientific. He responds with a simple overpopulation argument.
"If you think on it, you come to see there'd be so many creatures, including people, we'd all be squeezed in right up next to each other before long."
At the end of the boat ride, Winnie pleads to Miles that he throw the fish back into the water to let it live. He does, but he calmly explains that living and dying is normal and natural.
"People got to be meat-eaters sometimes, though. It's the natural way. And that means killing things."
All in all, Winnie's second boat ride is a reiteration of the importance of the natural living and dying cycle. Disney said the same thing with the "Circle of Life" song from The Lion King.