The sea lions stop bellowing and slip, one by one, off the jetty into the mocha-brown water of the Fraser River, near Vancouver, British Columbia.
The sea lions stop bellowing and slip, one by one, off the jetty into the mocha-brown water of the Fraser River, near Vancouver, British Columbia. The surface of the water is smooth, except for a line of ripples moving slowly upriver. The sea lions seem to know that the calm surface belies turmoil beneath.
The tide has just turned, and a tongue of salt water is first creeping, then galloping, back into the Fraser just a few hours after being expelled by a strong outflow during the previous ebb. Although the surface appears calm, the underwater intersection of fresh and salt water roils with turbulent eddies as strong as any in the ocean. The confusion of swirling water and suspended sediments disorients homeward-bound salmon, providing an easy feast for the sea lions.
Not all rivers end as dramatically as the Fraser. But the mixing of freshwater streams and rivers with salty ocean tides in a partly enclosed body of water—natural scientists call it an estuary—fuels some of the most productive ecosystems on Earth, and also some of the most vulnerable.
Read more at Woods Hole Oceanographic Institution
Image Credit: Woods Hole Oceanographic Institution
