In the rising tide of the afternoon, Piya starts seeing less of the dolphins. She wonders if the dolphins weren't migrating, as she initially thought. The narrator explains that some Orcaella dolphins like coastal saltwater, while others like fresh rivers. The freshwater ones tend to be territorial and return to the same spots year after year. Piya came to the Sundarbans expecting coastal Orcaella, which don't behave like the dolphins she spent the morning observing—though the water is too salty for freshwater ones as well. She wonders if the Sundarbans Orcaella migrate daily instead of twice per year, a hypothesis with profound implications for conservation.
Piya's background in science means that she's been raised knowing that part of science is being willing to rethink hypotheses in light of new data, something that she's also doing as she learns to humanize Fokir. This shows that science is also yet another form of communication.
Piya thinks about the unique water quality of the Sundarbans: the mix of salt and freshwater creates microenvironments of differing salinity. She thinks about all the questions she has and all she'd need to do to properly study the dolphins of the Sundarbans. It would be decades' worth of work. Piya thinks of her own lack of ambition and the fact that she was drawn to field biology for the untethered lifestyle. This discovery won't change that, but she feels strangely satisfied to feel as though her future is resolved.
While Nirmal and Nilima represent two ends of a spectrum between inaction and action, Piya shows here that she sits in the middle: though unambitious by nature, Piya is perfectly happy to take the difficult path when it presents itself. However, it's also worth noting that in Piya's case, science naturally combines theory and practicality, while Nirmal's pursuits made that far more difficult.