Once returned , they fight for position in a dominance hierarchy to gain closer access to spawning females .
Hooknose males leave their natal rivers at the end of their first year of life , but then return after maturing for 3 to 5 years on average .
Once returned , males fight for position in a dominance hierarchy to gain closer access to spawning females .
Hooknose males leave their natal rivers at the end of their first year of life , but then return after maturing for 3 to 5 years on average .