Crayfish Habitat Use in Ozark Streams
Extracting crayfish from stomach of goggle-eye.
Capturing crayfish with 1 square-meter quadrat sampler in a vegetation patch
Backwater pool habitat on Big Piney River
Backwater pool habitat on Jacks Fork River
The spothanded crayfish (Orconectes punctimanus)
The Ozark crayfish (Orconectes ozarkae)
The golden crayfish (Orconectes luteus)
Most of us have heard the story about the country mouse and his cousin the city mouse. For whatever reasons, some of us "mice" feel more comfortable living in a country habitat, whereas others become panicked if they leave the bustle of the city. And then there are those that can call just about any habitat a home as long as they can find a way to rustle up three meals a day. As it turns out, we see the same types of differences in habitat use or preference within many groups of animals. A recently completed study by MDC fisheries research biologists found that Missouri's crayfishes are no exception.
Crayfish are an important food for more than 200 species of fish and wildlife in and around Missouri streams. Fisheries biologists have found that crayfish make up two-thirds of the diet of some popular sport fish such as smallmouth bass and goggle-eye, and they are also found on the menus of largemouth bass, spotted bass, flathead catfish, blue catfish, and several species of sunfish. Crayfish are important to the maintenance of stream ecosystems, so biologists need to learn everything they can about them so they can better manage them. Knowledge of their habitat needs is critical to that management.
We recently completed a study of crayfish habitat use in the Jacks Fork and Big Piney rivers. Many Ozarks streams contain 2 or more species of crayfish, so we wanted to examine their habitat use on three levels. First, we looked at the entire crayfish "community" in those streams to determine which habitats were or were not being used. Second, we studied how individual species used (or not) the habitats that were available to them. Finally, we were interested in whether or not juvenile crayfish require different habitats than adults.
Our study showed that no Ozarks stream habitats are being "wasted"; the crayfish community is using them all. Yet surprisingly, some of the least common habitats held the most crayfish. We identified two very important habitat types; vegetation patches and backwater pools. Vegetation patches are those shallow plant beds (called water willow) that are usually found along the edge of stream banks or gravel bars.
Backwater pools are small, shallow pools that often appear to extend up into the upper or lower ends of gravel bars or are completely separated from the mainstream by decreasing water levels.
We calculated that these two habitats together make up only about 10 % of the area in a typical Ozarks stream. Yet, they held numbers of crayfish that were as high as any reported anywhere in the world! Typically, in an area about half the size of your kitchen table (a square meter), we caught an average of 30 to 35 crayfish.
Despite the fact that the crayfish community used the entire stream, we learned that some species are more fussy than others when choosing where to hang out. One of the species we studied, the spothanded crayfish, was a habitat "specialist".
Nearly all that we found were in those vegetation patches, although some of the largest spothanded crayfish laid claim to the largest rocks around the bluff walls that are common to our Ozarks streams. We found at least a few individuals of a second species, the Ozark crayfish, scattered throughout the stream, but most chose to use vegetation patches, backwater pools, and the deep, main pools that make up much of those streams.
The golden crayfish was what we call a habitat "generalist", meaning that they were scattered everywhere.
These crayfishes also told us that what's good for adults may not be good for junior. In at least two of the three species, we saw that adults and juveniles used different habitats. Very few juvenile crayfish were found in the fast-flowing riffle habitats. The juveniles seemed to prefer life in the lazy, shallow, vegetation patches and backwater pools. Young crayfish are a much-desired meal for many fish, and it is likely that these juveniles found refuge from predators and abundant food in these shallow and slow-flowing habitats.
The natural world is typically quite variable, so it was interesting for us to note that the habitat use patterns we observed were generally consistent across five years, among four sites on two rivers, and in two seasons (summer and fall). Documentation of these consistent patterns will provide fisheries managers with increased understanding of important sportfish prey populations. In addition, our data may help biologists with future conservation efforts on some of Missouri's rare crayfishes.
Our study yielded interesting and important information, but like most research studies, it also brought to light more questions and concerns. As resource managers should we be concerned that such high numbers of juvenile crayfish concentrate in two of the least common habitats? The phrase "placing all your eggs in one basket" comes to mind; especially because vegetation patches and backwater pools typically exist in portions of streams that are most threatened by some land use practices, such as poor gravel mining methods, channelization, and clearing of streamside trees. Gravel mining often takes place right in or around these streamside habitats and could eliminate important crayfish nursery areas. Other land use practices that contribute sediment and silt to streams could degrade these habitats because silt and sediment often settles out in these quiet, low-flow areas of streams, and can clog and bury shelters and food of young crayfish. Less habitat for young crayfish translates into fewer overall numbers in their population. Ultimately this means less food to support fish and wildlife in and around Missouri streams.
Our study was the most comprehensive research ever conducted on stream crayfish habitat use. We invested so much time and effort in this research because crayfish are such an important link in the food chains of so many fish and wildlife species in and around Missouri streams. Destruction or loss of crayfish habitat could potentially lead to a "domino effect" whereby many animals are negatively affected. We noted that crayfish, like many animals, use a variety of habitats, but some of those habitats were especially important as nursery areas and are also susceptible to habitat degradation. Additional data collected in this study will be featured in future reports discussing:
1. the specific physical factors that make certain habitats preferable to crayfish,
2. how crayfish populations behave over the long term, and
3. the importance of crayfish in the diets of smallmouth bass and goggle-eye.
