The porpoise is a symbol of dirtiness, shame and unpleasant experiences. The dream suggests to keep yourself out of problem. Sometimes the porpoise have a pleasant meaning which brings domestic happiness, great wealth and health.
Dream dictionary: Porpoise dream meanings
To see a porpoise in your dreams, denotes enemies are thrusting your interest aside, through your own inability to keep people interested in you.
Please see the interpretation of the dolphins.