The Metraxi were a seal-like species.
When they became sterile, the Metraxi believed it was due to contamination on their homeworld Kinneret. They left their planet to find a new one, maintaining their population through cloning during the search. The First Doctor, Susan, Ian and Barbara encountered their ship after radiation leakage was causing Metraxi deaths. They managed to help and discovered that Greneva's sterility had actually been reversed. The Doctor speculated that more Metraxi would become fertile as well. (AUDIO: A Star is Born)