How much is a dolphin worth?

This is the question being asked in the US as BP gets ready to cough up compensation for the Gulf oil spill. The Guardian report seems to think this is a hypothetical question, but its not. Its an increasingly common way of assessing damage to human health and the environment. There are a lot of ways of estimating it including working out how much it would cost to provide the same 'ecosystem services' that nature provides and asking how much people would be prepared to pay to save a habitat or species or to see them survive.

For example, I've never seen a dolphin when surfing and would be prepared to pay £5/surf to do so. The massive problem with this is that a government or corporation can now argue that if it compensates me and every other surfer £5 / surf they can argue they can destroy the dolphin and massively underestimates the intrinsic value of a dolphin or any other organism that has taken millions of years to evolve but seconds to destroy.