As kids, so many of us spent countless hours in streams flipping over rocks in the hopes of finding crayfish. It seemed a tiny ecstatic miracle every time a crayfish appeared, waiting with its menacing claws pointing back up at us. As an adult, the joy of finding crayfish is no less compelling (at least for me). The technology used by astacologists (those who study crayfish) hasn’t progressed much beyond flipping rocks are catching crayfish with nets. But doing so in a systematic way guided by scientific questions can yield some fascinating information about our aquatic ecosystems. Here are a few of the more common ways used by scientists to collect and study crayfish:
Kick Seining: This is a method used by stream ecologists who study macroinvertebrates in general. A pair of people stand downstream holding a wide net (up to 20′ wide) while someone upstream walks down the stream kicking over rocks. Crayfish (and other macroinvertebrates) are dislodged and swept up by the current, tumbling downstream into the net. This works best in streams with higher flow velocity (Video)
Kick Nets: Essentially a kick seine for 1. A smaller net (typically 3’x3′) is attached to two poles and anchored downstream. Just as with a kick seine, someone walks up stream kicking over rocks and sending macroinvertebrates tumbling down into the net. This is easy for one person to do, but covers a smaller area and is more commonly used for insects (Video).
Hand catching: This method works great for catching crayfish. The challenge is that crayfish can be tricky to nab once you find one hiding under a rock or log. Using a dip net (a mesh net attached to a pole), can help capture the crayfish once you locate it (a great how-to video).
Crayfish traps: Crayfish traps are easy to buy online (these are also sold as minnow traps), and typically cost $8 to $15 per trap. If you’re in a particularly productive stream, you can also buy an extension for your trap to hold more crayfish. There are a variety of different types of crayfish traps sold. Using a variety of diameter entrances can help catch smaller traps. Make sure your traps are fully submerged. You can bait them with almost anything, but the fresher the better. There’s some debate about how representative samples collected in these traps actually are (Video 1, Video 2).
Electrofishing: This is the least common method, but is highly efficient for sampling crayfish populations, and results are not sex biased (as they can be with crayfish traps). The biggest drawback of this method is that over a quarter of crayfish, mostly smaller crayfish, lost their chelae as a result. In electrofishing for crayfish, one person operates a battery or gas powered shocker that pulses electricity through a water way. Crayfish are stunned and potentially lose their footing. A person or two people stand downstream with a seine to catch any crayfish dislodged (PDF, Video).