why does the french mate use stubb's visit as a chance to deceive his captain

He does not want to actively deceive his captain, but he does want them to "dump" the whales that he feels are useless. In getting Stubb's help (Stubb has one agenda and the mate has a different agenda), he is able to accomplish his goal of getting os whales that he believes are worthless; he then gives Stubb the chance to get the whales which Stubb will then use to recover the ambergris.

how did ismael survive for one day after the other sailors died?

How did the men feel about the final hunt for Moby Dick?