Tuesday, July 30, 2013

The Crayfish: An Adirondack Crustacean

CrayfishAdirondack waterways serve as home to a wealth of invertebrates that range in size from microscopic to those that are several inches in length. Among the giants of this complex and diverse group of organisms are the crayfish, which are larger, more robust and meaty than many vertebrate forms of life in our region.

Because of their size and abundance, crayfish are an important component of all fresh water environments; however these fierce-looking entities have not been as thoroughly researched and studied as have other creatures that reside in the same general surroundings. While the basics of their biology and natural history are known, much still remains to be learned regarding the individual species that populate the many bodies of water throughout the Adirondacks.

Like lobsters and shrimp, crayfish are classified as crustaceans and have two primary body segments, a cephalothorax and an abdomen. Protruding from the cephalothorax are four sets of walking legs and one very conspicuous set of claws. These pinchers are used for grabbing parts of a plant that a crayfish wants to pull into its mouth, attacking a smaller animal on which it may also want to feed, fighting with a rival that is infringing on its space, and defending itself against the numerous forms of wildlife that enjoy dining on its tasty meat.

Along the middle of its top shell or the back of its exoskeleton is a grooved line known as the areola. The shape of this indented space and the design and features of its claws are two basic characteristics used by naturalists to distinguish between the many different species of crayfish.

Each species of crayfish prefers to inhabit a specific aquatic setting with many favoring flowing water in larger streams and rivers. Yet regardless of the body of water, all crayfish confine their activities to sections along the bottom where rocks, submerged stumps and logs, and other sunken debris exist. Places in which there is an abundance of vegetation are also inhabited by crayfish.

The crayfish is primarily nocturnal but is known to forage late in the day if a layer of heavy overcast limits light intensity. When inactive, crayfish burrow under an object big enough to prevent it from being easily grabbed by a predator. Any person that wades into a stream, river, or lake can usually uncover a crayfish or two in a matter of minutes by turning over softball-size rocks on the bottom. The burrowing skill of the crayfish is well developed, as its ability to seek refuge beneath objects that are not easily moved allows this arthropod to rest during the day without being attacked.

Like other crustaceans, crayfish have two sets of feelers on their head which they use to gather information about their immediate surroundings. The crayfish has two large eyes, each set on a short stalk, but rather than using sight, this animal relies primarily on its feelers to locate food and detect danger.

When it comes time to forage, the crayfish has the ability to ingest and derive nourishment from a wide array of objects. Many forms of living and dead vegetation, bugs, small fish, tadpoles, young salamanders, and the partially rotted remains of larger dead creatures all serve as food to the opportunistic omnivore/scavenger.

Many species of crayfish enter into a breeding period as the water begins to significantly cool toward the end of August or during the first weeks of September in the Adirondacks. Males that have sexually matured locate females and mate with them. Most females store sperm and use it to fertilize their eggs months later after the ice has completely melted in spring and the water is again warming. Eventually the female’s mass of fertilized eggs are released from her body, but are held on the underside of her abdomen until they hatch in mid spring. The babies may remain tucked into the folds of the underside of her abdomen for another few days before finally wandering off and settling into a patch of rocky gravel or dense weeds. It takes about two years before a crayfish matures and begins the cycle again.

Under normal conditions, crayfish do not travel far during the course of their life. This tends to restrict one species that has developed in a particular river drainage system from spreading into nearby river systems. Since these creatures are occasionally collected by anglers to serve as bait, and periodically escape during a fishing trip, the distribution of various species has greatly expanded over the past century. It is now difficult to say what species are native to an area, and which ones have been introduced. While such information is significant to aquatic ecologists, any species encountered by a mink, great blue heron, smallmouth bass or pike tastes just as good as any other species of crayfish.

 


Tom Kalinowski

Tom Kalinowski is an avid outdoor enthusiast who taught field biology and ecology at Saranac Lake High School for 33 years. He has written numerous articles on natural history for Adirondack Life, The Conservationist, and Adirondack Explorer magazines and a weekly nature column for the Lake Placid News. In addition, Tom’s books, An Adirondack Almanac, and his most recent work entitled Adirondack Nature Notes, focuses on various events that occur among the region’s flora and fauna during very specific times of the calendar year. He also spends time photographing wildlife. Tom’s pictures have appeared in various publications across the New York State.




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