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There is only one crayfish that is native to Oregon: the Signal Crayfish, which has a characteristic white spot on the claw pivot. There are at least three other crayfish that are invasive to Oregon waters. (Read DFW report on crayfish in Oregon). To our knowledge, all of the crayfish pictured here are natives.
Signal crayfish mate in autumn, and the female carries 200-400 eggs on her abdomen until they hatch in the spring. Juveniles hatch from these eggs and stay with their mother until after they molt three times. Crayfish, like all creatures with exoskeletons, have to shed their shell in order to grow. Signal crayfish typically reach sexual maturity after their second year, and may have a lifespan of twenty years.
Hatchling crayfish are tiny; no larger than #16 mayfly nymphs. Many of the trout we have caught on dull, tannish-brown nymphs may have mistaken them for baby crayfish. The tiny crayfish pictured above is not as long as a joint in my finger, yet I have seen crayfish that were smaller. (If you check out the second picture in Utilizing Crayfish Patterns, you will see one that is half this size). You can bet that many of these small crayfish get eaten by fish and possibly larger aquatic insects. Diving birds, such as ouzels and mergansers are sure to get their share. As crayfish grow larger, so do the predators that eat them, such as raccoons, and even humans.
The way crayfish grow in size is to grow a new skin under their hard shell. Then they discard the hard shell and expand the new shell before it hardens. During this period they tend to hide, because they are vulnerable. In the soft-shell phase, Signal crayfish are dark olive with a bluish tinge. These dark colored vulnerable crayfish are considered to be delicacies by most trout and char that are large enough to eat them.
Crayfish are native to nearly all freshwater in North America where game fish live. They are a large part of the diet of many trout and bass. In many lakes in Oregon, crayfish supply much of the protein for trout over 14" long, and even many trout under 9". The first time I fished the Deschutes River in Oregon in 1966, the guy who took me fishing was an expert at finding crayfish and using them for bait. He had his 15 fish limit in no time. When the fish were butchered, stomach autopsies revealed that every redband trout over 14" had recently eaten at least one crayfish. Now of course, these trout are catch-and-release, but their diet probably hasn't changed significantly.
In the late 1980's I was involved in a research project which caught 78 Eastern brook trout from one of the natural high lakes in the Mount Hood National Forest in Oregon. Most of these trout were under 11" long, but most had at least one crayfish in their stomach. Many seemingly barren lakes have big crayfish populations, and these crayfish become the major food source for trout. Crayfish are omnivorous. Our experiment with the gill net study proved that as soon as trout were caught in the net, crayfish climbed up the net and started to eat them. The fish were feeding on crayfish, and the crayfish were feeding on fish, forming a complete food chain between them.
Even though there are more insects in weedy lakes, crayfish are at the top of the menu in these places too. Many crayfish live in rivers also. Crayfish don't only inhabit the calm water parts of our rivers. There are also crayfish in some of the fastest water as well. Fishing techniques using crayfish fly patterns vary with depth and water speed.
Given the variability of sizes of crayfish available, and the range of aquatic habitats they inhabit, crayfish are worth studying by fly fishers. All types of fly tackle and fly presentations work, depending on the water being fished. Nymph fishing with floating lines and long leaders, as well as full sinking lines and various retrieves, and two-hand rods and deep swinging presentations with Skagit line and sinking tips are all in the mix. Be sure to read our blog post "Utilizing Crayfish Patterns" by Jacob Noteboom.