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Size mat­ters in the sex life of sal­mon

Source: helsinki.fi

For Atlantic salmon, size matters when it comes to love. Larger males and females that may spend up to four years at sea produce many more babies, but they are very rare compared to younger fish.

Every summer, tens of thousands of Atlantic salmon migrate from the Barents Sea to the Teno River, Finland, to spawn in the streams where they were born. This journey is a feat of endurance: salmon stop feeding and must navigate fast flowing water, leap over obstacles, and avoid predators, hooks, and fishing nets to arrive at their spawning grounds.

The marathon doesn’t stop there though: once they arrive at their spawning grounds, they must fight for the possibility to mate with members of the opposite sex. Who are the winners of this evolutionary competition? It turns out that the largest fish produce the most offspring, but there are far fewer of these fish on the spawning ground battling for reproductive success than their younger – and smaller – competitors, according to researchers at the University of Helsinki and the Natural Resources Institute Finland (Luke). MORE

Header image: a large male is sampled and released unharmed in the Teno River, northern Finland. Credit: Mikko Ellmen.