LitCharts assigns a color and icon to each theme in The Hungry Tide, which you can use to track the themes throughout the work.
Language
Man vs. Nature
The Human Cost of Environmental Conservation
Idealism and Theory vs. Practicality and Action
Summary
Analysis
Within four hours of arriving at the Forest Department office, Piya has the necessary permits to conduct her survey. Her triumph feels less sweet when she learns that she'll be forced to accept the accompaniment of an armed forest guard. After they leave the office, the guard becomes very brisk and self-important. He leads her to a man he calls Mejda, and translators explain that Mejda knows the waterways well. The cost for Mejda's boat is exorbitant, but Piya feels she has no choice but to agree. She feels it's worth a shot to show him her flashcards of the Gangetic dolphin and the Irrawaddy dolphin to see what he knows.
It's worth noting that after this point, Piya overwhelmingly refers to the Irrawaddy dolphins by their Latin name, Orcaella. The fact that she uses both names suggests that she does have some familiarity switching between languages to use one that works better, though in a very different way than Kanai does. The flashcards also represent another way of communicating, and one that doesn't require a shared written or spoken language to understand.
Active
Themes
Usually, fishermen are able to figure out what Piya wants when confronted with the flashcard. However, Mejda's response is strange: in English, he asks if the creature is a bird. Perplexed, Piya decides that the dolphin could look like a bird and smiles. Her optimism fades when they reach Mejda's boat. It's a large diesel steamer that reeks, and he orders all his helpers but the guard off the boat. He then enacts a strange pantomime that ends with motioning to Piya's mouth and his own crotch, which puts Piya on edge. Piya seldom feels vulnerable on her surveys; people usually leave her alone because she's foreign.
Mejda's response suggests that communicating with him and the forest guard won't be an easy task, and his gesturing to his crotch casts a distinctly predatory glow to their interactions. This begins to show how the lack of a common spoken language can be used to control and intimidate, given how vulnerable this makes Piya feel.