Why young salmon leap

This 11 October 2012 video from North America says about itself:

Pacific Sockeye Salmon – Oncorhynchus nerka

Fall is the time of the Sockeye Salmon as they return to the same river beds they originated from to spawn and die, finishing their life cycle.

The sockeye eggs hatch in winter and the young salmon make their way down to the sea, sometimes hundreds of kilometers away. In the ocean they grow, if they can evade their predators which include everything from birds when they are smaller to whales, seals and fishermen as they grow into a prized commercial and sport game fish.

Then 4 years into their short life they return to the rivers, retracing their journey just 4 years earlier back to the same riverbed where they started life, spawning and dying afterwards, the cycle of the Pacific Sockeye Salmon continues.

From Simon Fraser University in Canada:

Young salmon may leap to ‘oust the louse’

August 13, 2018

A study by Simon Fraser University aquatic ecologists Emma Atkinson and John Reynolds reveals that young salmon may jump out of water to remove sea lice.

“Ideas about why fish leap include getting over obstacles during their upstream migration as adults, catching food and avoiding predators”, says Atkinson.

“However, these reasons may not apply to young salmon since their diet is composed almost exclusively of underwater zooplankton and their tendency is to scatter rather than leap when escaping from predators.”

Atkinson hypothesized that the leaping behaviour could be the fish’s way of removing parasitic sea lice, which is a common condition for wild and penned salmon off the B.C. [British Columbia] coast. Heavy sea-louse infestation is correlated with reduced growth, impaired swimming and competitive foraging ability for young salmon.

To test her hypothesis, Atkinson and her team caught wild juvenile sockeye salmon during their coastal migration away from the Fraser River. They held the fish in flow-through net-pen enclosures, half of which were covered with netting to prevent leaping and the other half were left uncovered to allow leaping. After three days, the team counted the lice on each fish.

The researchers found that, on average, the salmon that were allowed to leap in the uncovered pen had 22 per cent fewer sea lice compared to those that weren’t allowed to leap in the covered pen.

The researchers also found that it may take more than 50 leaps for a young salmon to dislodge a sea louse, which Atkinson acknowledges is a substantial amount of energy to expend. She says these costs may be offset by the benefits of successfully removing sea lice, but will have to be investigated in another study.

In a 20-year study, researchers have found that nearly 600,000 pounds of sockeye salmon carcasses tossed to the left side of a small, remote stream in southwest Alaska, helped trees on that side of the stream grow faster than their counterparts on the other side: here.

1 thought on “Why young salmon leap

  1. Pingback: Rare Madagascar ducks back in the wild | Dear Kitty. Some blog

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