About five million years ago, the North American Pacific Northwest was teeming with some pretty big fish that would have made the continent’s biggest salmon runs look small. An eight to 10-feet-long prehistoric salmon species called Oncorhynchus rastrosus stalked the seas and streams of the Miocene. It weighed upwards of 400 pounds and was almost twice as long and three times heavier than today’s largest salmon species–the Chinook/king salmon.