Hirsch's The Physical Impossibility of Death in the Mind of Someone Living is another work that reminds me a lot about philosophy. Martin Heidegger, an existentialist philosopher said that death is the only experience in life which we truly experience all on our own, anything otherwise is inherently interactive or social in some way. We cannot experience anyone else's death, and they cannot experience ours. Therefore, it is in some ways impossible to physically experience death in our mind when we are still living. Even the though of the process is somewhat impossible because we have never experienced it, and when we do it will only happen once.
I'm not sure that this is what Hirsch was going for exactly, but it does play a role in how I would view the art if I were to see it today. Much like Rachel Whiteread's casts, The shark is a symbol of something past. It no longer lives and interacts with its environment. As a result, the only interaction which it can be present in is up to us as viewers to create and manipulate.
In my research on the piece, I found that the original shark had actually begun to deteriorate, and was eventually replaced by another. It is interesting that the shark was actually replaced, as it seems to say in its own way that nothing lasts forever (the shark), except the social and cultural concepts we construct and choose to continue.