How does Pi end up alone with Richard Parker? How does he keep them both alive?

There is no land in sight and the ocean is shark-infested, so Pi builds a raft which he attaches to the lifeboat, to keep himself at a safer distance from Richard Parker. Eventually, however, life on the raft proves too exhausting, and Pi realizes that if Richard Parker gets hungry enough, he will swim to it and kill Pi. So Pi decides that he must tame Richard Parker. Using a whistle, seasickness, and a turtle-shell shield, Pi manages to assert his authority over Richard Parker and delineate his own territory on the lifeboat, where he is comparatively safe from the tiger.

While at sea, Pi and Richard Parker face many challenges, traumas, tragedies, and miraculous occurrences. They never have sufficient food and fresh water, and the constant exposure is highly painful. A severe storm, which they miraculously survive, destroys the raft. Pi manages to capture and kill a bird. They are almost crushed by an oil tanker, which then passes by without seeing them.

During an especially severe period of starvation, Pi and Richard Parker both go blind. While blind, Pi hears a voice, and realizes that they have drawn near another lifeboat that contains a similarly starving and blind Frenchman. Pi and this man converse for a while, and bring their boats together. The Frenchman climbs onto Pi’s boat, and immediately attacks him, planning to kill and eat him. He doesn’t realize that there is a tiger on the boat, however, and accidentally steps into Richard Parker’s territory. The tiger immediately attacks and kills him. Pi, saved at the cost of his attacker’s life, describes this as the beginning of his true moral suffering.

Pi and Richard Parker come upon a weird island that is made of algae with trees protruding from it, teeming with meerkats but no other life. Pi and Richard Parker stay on the island for weeks, eating the algae and the meerkats, growing stronger, and bathing in and drinking from the fresh water ponds. They never stay on the island at night, however, Pi because he feels safer from the tiger in his delineated territory, and Richard Parker for a reason unknown to Pi. Pi eventually starts to sleep on the island, and while doing so realizes that the island is carnivorous—it emits acid at night that dissolves anything on its surface. Greatly disturbed by this, Pi takes Richard Parker, and they leave the island.