Rather thin on the ground, these: though there are some interesting reviews in the previous post.
Here's one interesting article: June Dwyer, 'Yann Martel's Life of Pi and the Evolution of the Shipwreck Narrative', Modern Language Studies (35:2, 2005), pp. 9-21
James Mensch, 'The Intertwining of Incommensurables: Martel's Life of Pi', in Corinne Painter and Christian Lotz (eds), Phenomenology and the Non-human Animal: at the Limits of Experience (Volume 56 of Contributions to phenomenology; Springer 2007). This is an interesting essay, but be warned: it's hard philosophy rather than literary criticism (the book's blurb: 'The question of the relation between human and non-human animals in theoretical, ethical and political regards has become a prominent topic within the philosophical debates of the last two decades. This volume explores in substantial ways how phenomenology can contribute to these debates. It offers specific insights into the description and interpretation of the experience of the non-human animal, the relation between phenomenology and anthropology, the relation between phenomenology and psychology, as well as ethical considerations')
Most of Christine Lorre's essay on the novel is available on google books.
You might enjoy Merritt Moseley's overview of 'The Booker Prizes for 2001 and 2002: Cool Young Authors and Old Codgers' The Sewanee Review (111:1 2003), pp. 157-169
Also: I mention in lecture the plagiarism row that flared after Martel won the prize: the accusation being that he had lifted important elements straight from the Brazilian novelist Moacyr Scliar's novel Max and the Cats. You can read more about that here, and here. Scliar's prior novel is about a young boy stranded in a lifeboat with a panther, you know. Martel's own account 'How I Wrote Life of Pi' isn't very forthcoming on this topic. On the other hand, this Library Journal article is rather forgiving to Martel. Some interesting questions about plagiary raised here, I'd say: relevant to the novel (but also to students writing essays and so on)