True "bony" fishes belong to a modern class, called Osteichthyes. Lampreys are not true fishes, and they actually belong to an ancient class of vertebrates, called Agnatha. Although these primitive fish lived for millions of years, the only survivors found today are hagfishes and lampreys. Lampreys are lacking many of the features that true fishes have, such as bones, scales, and paired fins. Their skeleton is formed completely from cartilage, and their bodies are eel-like and slimy. Pacific lampreys can grow up to two feet in length.
Adult lampreys spawn from late spring to late summer. They generally spawn in stream riffles, where they use their specialized mouths to dig a depression among the rocks that will be used as a nest. Females lay up to 200,000 eggs. The eggs hatch and become larva, called ammocetes. The larval stage is what zoologists find most intriguing because by studying this stage they are able to make important evolutionary links between the ancient invertebrates and modern vertebrates. Ammocetes are blind, and they spend most of the larval stage buried in the stream bottom with only their mouths exposed to protect themselves from predators. During this stage of their life they are filter-feeders, meaning they feed on microscopic organisms in the water. Ammocetes may take between five and seven years to finally metamorphose into adults. As adults, lampreys have a very unique lifestyle.
Lampreys do not have jaws like our modern fishes. During metamorphosis their filter-feeding mouth is reformed into a circular mouth, called an oral disc. Their tongue is also unique, having small teeth on the surface. These mouthparts serve a very important purpose. Adult lampreys are parasites, meaning they attach themselves to another species (called the host) and take the nutrients they need from it. After metamorphosis adult lampreys migrate to the ocean and attach themselves to large fish using their mouths. The teeth on the specialized tongue are used to penetrate the host fish, which allows the lamprey to feed on the host's fluids. When the lamprey is no longer receiving enough fluids, it releases itself from the host and finds a new one. Most of the host fish survive, but some will die from loss of fluids and/or infection in the open wound. Salmon, a popular host fish, are commonly found with scars from lampreys.
After one to two years in the sea, the adults will return to the stream where they were born to stream to spawn. This migration back to fresh water begins in fall, and it takes the lampreys up to five months to complete their journey. Species that are born in freshwatee, then migrate to the ocean as adults, and return to freshwater to spawn are called "anadramous." They will excavate their nests in stream riffles, lay eggs, and die shortly after.
In 2007, BLM partner agencies like the U.S. Forest Service and the Freshwater Trust began fixing decades of human river manipulation, returning the ecosystem to its more natural state. This included removing two dams in the Sandy Basin, demolishing river berms and putting log jams at strategic points to increase water flow to vital side channels, where steelhead like to lay eggs.
For several years now, Bruce Zoellick—fish biologist for the Bureau of Land Management—has been doing practically everything he could to restore habitat for the threatened steelhead. That even means snorkeling underwater to count juvenile fish. The results have been encouraging, to say the least.
“I’m so excited about steelhead because it’s a great response — but it’s also my favorite fish,” said Zoellick after a river survey last month. Since 2012, Zoellick has been closely monitoring a particular 2-mile stretch of the Salmon River, a primary tributary for the Sandy, maneuvering all the side channels to count steelhead redds, or nests in the gravel where fish lay eggs. “We reconnected those side channels and got a really good response from the fish,” said Zoellick, who added that numbers for coho salmon and lamprey are also positive.
To learn more about the BLM's fisheries program head on over to: http://www.blm.gov/or/programs/fisheries/index.php
Footage shot on the Sandy River in spring 2016.
Video: Bruce Zoellick
Music: Ukelele Parade by Fernando Oyaguez Reyes