Lamprey pileup

Lampreys at Bonneville

Sometimes when reviewing the video of salmon passing through our Vaki Riverwatcher, we notice a weird phenomenon on the skin of some fish. Every so often, fish will have small, round wounds on them, circles of damage with a bunch of small puncture marks surrounding one larger puncture mark in the middle. These fish have fallen prey to one of the largest bloodsuckers on the planet: the Pacific lamprey. Lampreys are parasitic fish that cruise the coastlines of the Pacific Ocean and have evolved to latch onto other animals and drink their blood. The adults can be as large as 3 feet. The lamprey attaches onto its prey with its fearsome-looking sucker mouth, then hooks its teeth in to stay on. The fish do not have tongues – instead, they have a boney appendage called a radula that is used to scrape and scratch. But these hungry creatures do not start off so bloodthirsty.

The Pacific lamprey is anadromous just like salmon: is it is born in rivers then swims to the ocean to live its life. Then it returns to rivers and streams to reproduce before dying. Juvenile lamprey are nothing like their adult versions. They are actually filter feeders that bury themselves into the mud at the bottom of streams. Once there, they poke their heads out and filter nutrients and food out of the water. It is not until they become adults that they develop their taste for blood. Our staff recently took a trip to Bonneville Dam and saw this pile of lampreys trying to make their way up the fish ladder. Traveling by mouth is hard work – the fish use their suckers to latch on as they travel upstream in fast moving water, but if they encounter a corner of any kind, the fish lose their grip and slip off. The fish weren’t successfully making their way up the traditional ladders installed for salmon, so a few years ago, Bonneville installed a smooth chute designed for lamprey passage. We never seem to tire of writing about these fascinating first fish, whether it’s their unusual life cycle or terror-inspiring mouthparts.