We'll assume for the purposes of this thought experiment that the shark just wants a nibble - he'll be satisfied for sure with either one.
Also an older scientist might be past his prime and have lower expected utility for the rest of his career while still expecting high pay.
Yes, I realized this after it was too late to edit (well, I still could edit, but people have already replied, so it wouldn't be fair) - I probably should have made the doctor younger.
But in any case, it brings up the question: how young is "young enough" to prefer throwing a baby overboard to throwing a highly promising child/teenager/adult? Is there a "young enough" age for you, or would you always toss the older person, no matter how likely they were to be exceptional for the rest of their life?
Meh. Then cut off your arm and give it to him. The problem with these philosophical experiments is controlling external variables. It just can't be done.
Does utilitarianism demand total knowledge? Can't you posit a baby exception wired into your brain (by evolution, $deity, whatever), obey it, and still be an orthodox utilitarian?