Male salmon appear to have a clever way to get ahead of their breeding rivals.

A Canterbury University study has found chinook salmon can adjust their sperm's swimming speed, when competing with a rival to reproduce.

PhD student Michael Bartlett says the adjustment of sperm velocity alters male reproductive success and therefore fitness.

He said it's probably not a conscious decision by the fish.

"It's a physiological response by the fish in response to those cute signals from various things."

Bartlett is continuing the study in an effort to try to learn more about human fertility.

LISTEN ABOVE AS MICHAEL BARTLETT SPEAKS WITH MIKE HOSKING