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13 THE BIOLOGY OF CRAYFISHES Worldwide the freshwater crayfishes (superfamily Astacoidea) are divided into three groups; the Astacidae, Cambaridae, and Parastacidae. The Astacidae are found in Europe and the west coast of North America. The Cambaridae are found in eastern North America and parts of China. The Parastacidae are found in the South Pacific (particularly Australia and New Zealand) as well as Chile and Argentina in South America. Africa and Antarctica have no crayfishes. The Astacoidea has some 393 species worldwide of which over 340 are restricted to the United States and Canada. Within the Cambaridae of North America, the subfamily Cambarinae includes the three most successful genera, Cambarus, Procambarus, and Orconcectes with 333 species and subspecies 234 . Of these, only five are native to Nebraska including one species of Cambarus, one species of Procambarus, and three species of Orconectes. HABITATS At it's very simplest, crayfish need to be wet or, at least, their gills and bodies need to be damp. Like all living organisms, they need to eat and they need refuges from predation, dessication, or freezing. We usually think of crayfishes as living in streams or lakes. But many species will also burrow and a crayfish's propensity to burrow is rated as primary, secondary, and tertiary. We have five native species of crayfish in Nebraska and each of these three burrowing types is represented by one or more of our species. Primary burrowers spend most of their adult lives living in a burrow. The Grassland crayfish, Procambarus gracilis, is a primary burrower and may spend 95% of its life in a burrow. The Devil crayfish, Cambarus diogenes, is also a primary burrower spending 80-90% of its life in the burrow though adults or young can occasionally be found in open waters. Burrows don't have to be very near open water, either. While the burrows of the Devil crayfish will often be found on stream banks or in wet meadows, those of the Grassland crayfish can be found in grasslands or road ditches a considerable distance from open water. But, in either case, the burrow has to reach ground water which can be several meters down. Burrow water is often very low in oxygen so these crayfishes tend to live in the damp air just above the water. Secondary burrowers dig burrows to escape drying waterbodies or freezing weather. The Calico crayfish, Orconectes immunis, is a secondary burrower. It spends most of its life in open waters but, in the fall or when a waterbody begins to dry, they dig a deep burrow. These can be a couple of meters deep. Tertiary burrowers are crayfish that dig a burrow as a last resort and, even then, it is not an extensive or deep burrow. The Northern crayfish, Orconectes virilis, is a tertiary burrower which often digs a shallow burrow beneath a rock during winter or during drought. The Ringed crayfish, Orconectes neglectus, is also classified as a tertiary burrower but my observations are that it is a non-burrower. I have found them in dry streams under rocks or logs where