A book or short story about planet colonizing

I remember reading it at school but do not remember if it was in a collection of short stories or a book.
It was the 80's so it would be that time or before the 80's.
What I remember is a new planet the ship I think crashed or had a malfunction and some how some dna got mixed up.
I remember the main character watching what was either a seal hybrid or a dolphin hybrid swimming.It was mixed up with something weird that today we know would not happen.
Its been over 20 years and that's about all I can remember.