Signal Crayfish
(Pacifastacus leniusculus)
Crayfish are freshwater crustaceans that belong to the infraorder Astacidea, that also includes lobsters, which crayfish closely resemble. They date back some 280 million years!
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Not surprisingly, in some areas crayfish are called lobsters. In the USA, the nomenclature varies from Crayfish in the north while in the central and south USA, Crawdad and Crawfish are used, and even Mudbugs and Jabbies.
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According to a number of sources there are between one and three species of crayfish in British Columbia. Here we present the most commonly seen, the Signal Crayfish (Pacifastacus leniusculus).
While the Signal Crayfish populates many of BC’s freshwater lakes and watercourses, documentation of these locations seems to be rather under-reported as few range Canadian maps exist on this subject. This species can be identified by its uniform blue-brown to red-brown colouration and also the unique white or light coloration of the main claw joint as well as the smooth surface of its carapace and claws.
Range
The E-Fauna BC distribution map (above) shows Signal Crayfish distributed in southern B.C., from Vancouver Island, the Lower Mainland and east to the Kootenays, and as far north as Okanagan Lake. Because there are no records of these crayfish on Vancouver Island prior to 1900, it is believed it was introduced there by humans. It is considered endemic to northwestern USA but was introduced to some southern states as well as Japan and numerous countries in Europe where it is now considered invasive.
Anatomy of a Crayfish
Signal Crayfish are organisms that have an exoskeleton, jointed appendages and segmented bodies and as such they belong to the Phylum Arthropoda.
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Signal Crayfish have two main body areas: the cephalothorax, which consists of the head and upper body, and the abdomen, which is flexible and has 6 segments. Colouration is a blue-brown to red-brown. Signal Crayfish have a distinctive white to pale-blue-green patch located near the main joint of its large Cheliped claws.
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Males grow to 16 - 17.5 cm while females reach 12 cm. Typical weight is between 60-110g
Beginning with the head: two long-thin antennae and a smaller set called antennules, are all used to probe the environment.
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Behind these are two compound eyes on stalks which can move independently and provide excellent eyesight. Although these crayfish can regenerate other body parts, they cannot regenerate their eyes.
Located below the eyes is the mouth with two powerful horizontally-opposing mandibles, used for crushing food. Around the mandibles are maxillae used to hold and tear food apart and also three sets of maxillipeds, short appendages used by the crayfish to manipulate their food into their mouths.
The carapace, which projects backwards from the head and covers all of the thorax is a hard shield that protects the upper cephalothorax. The carapace also protects the delicate feather-like gills which branch off from the base of each leg.
Under the cephalothorax are 5 sets of legs. The first set are very large and equipped with large jointed claws called Cheliped used to capture food and for defence. The common name of this species is derived from the white to pale blue-green patch located near the claw hinge.
The rear 4 sets of “walking” legs are thin; the first two sets have very small claws at the tips while the last two have hook-shaped tips. At the top of these legs but usually hidden from view underneath the edge of the carapace are the, greyish, feathery gills. The gills occupy the space between the carapace and a clear section of exoskeleton and water is channelled through the gills to provide oxygen.
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At the rear of the crayfish is the abdomen or tail with its 6 sections. Underneath are 5 pairs of small appendages called “swimerettes”, which as the term suggests, provide some propulsion to swim. The swimerettes can also direct water over the gills and and they also play a role in reproduction; more about this later.
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The rear-most segment of the abdomen is called the Telson, with fan-like fins extending rearward on both sides.
Lifecycle
Age to maturity varies from 2 to 3 years, and a life expectancy of up to 20 years is possible.
It has recently been discovered that mature females release a sex pheromone during the breeding season to stimulate courtship and mating behaviour in males.​
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Mating and egg-laying generally occurs in the autumn when 200 to 400 eggs are laid and carried by the female under her tail through the winter (approximately 7 months).
Hatching is temperature dependant. Usually this is in March-May and the hatchlings, which emerge as miniature crayfish, stay with the mother while they pass through three stages (moults of their exoskeleton). They gradually begin to forage independently, hunting primarily benthic (living on the bottom) insects. After 1-2 months they leave their mother. Juveniles may moult up to 11 times in the first year. Growth is rapid and most males reach sexual maturity during their second summer while females may take longer. In their third year these crayfish moult twice and after 4 years, they moult once a year.
When Crayfish moult, they are able to regenerate any lost limbs (claws or legs) however they cannot regenerate their eyes.
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Water temperatures between 18-25°C are considered best for good growth although they can survive over a much wider range. Once water temperatures dip below 15°C crayfish become less active and do not feed well and are less likely to become attracted to the bait in traps. Cold weather does not present a major mortality issue for crayfish. They do not hibernate but seek deeper water; alternatively, in some areas, they are also known to dig burrows. They spend their winters eating minimally and slowly depleting energy stores.
Do They Walk or Swim?
They generally walk slowly forward, backward or sideways using their legs. When they wish to escape, they swim backwards with astonishing speed while keeping their eyes focused on the threat. They achieve this backwards motion by rapidly and repeatedly folding their jointed abdomen under them.
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An entertaining way to appreciate their mobilty is this short video from England.
Habitat
Signal Crayfish are found in small streams, rivers and lakes, including subalpine lakes. They are hardy and tolerant of cool or brackish water. As with most crayfish species, calcium levels above 5 mg/L are needed in the water for re-calcification of the exoskeleton following moulting. Adults prefer sandy, silty areas in deeper water, while juveniles prefer boulder and gravel areas.
Foraging and Food
Crayfish can eat fish and other invertebrates like crabs and shrimp. They are generally carnivorous and can harm fish in a fish tank if you try to keep them as pets. The interesting thing about their mandibles is that unlike human jaws, the powerful jaws of the crayfish open from side to side.
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Crayfish are benthic, meaning bottom dwellers and so most of their food is obtained at the sediment/water interface (mud) in the bottom of ponds, lakes, swamps, or streams. To a degree, they can tolerate warm temperatures but prefer cooler water.
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They feed on animals and plants, either living or dead or on decomposing detritus. Detritus consists of fine particulate organic materials such as dead phytoplankton, zooplankton and the outer walls of diatoms and coccolithophores, dead skin and scales of fish, fecal pellets, bacteria, fungi, micro-algae, meiofauna, and mucus. The mucus or "slime" is biofilm that can be felt on the surface of submerged leaves and branches.
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They are omnivorous scavengers, known to leave the water to graze on nutrient poor material such as grass and leaves. Their need for a balanced diet requires that they be highly selective.
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Analyses of crayfish reveal their guts contain mud or detritus, fine particulate organic matter (FPOM) mixed particles of lignin and plant cellulose such as roots, leaves, bark and wood. While some animal material can also be found in the gut this is, by volume, just a tiny portion of their diet.
They are highly restricted in the ability to catch large living animals but are able to feed on small organisms if they can be grasped in their small feeding claws. Also crayfish have been shown to be coprophagic - eating their own faeces, they also eat their own exuviae (moulted carapace) and each other.
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Crayfish may graze and eat for many hours but when consuming detritus, (black organic mud, in the end phase of decomposition), they injest that quickly, taking just a few minutes. Injested material is sorted by size and mixed with digestive fluids for elimination in 10-26 hours.
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Crayfish do not stray far and usually have limited home range. When feeding, the crayfish is exposed to predators such as large fish, otters, raccoons, mink, and great blue herons. The primary predators of crayfish young and eggs are other crayfish and fish. To minimize risk from predators, crayfish feeding behaviour is often a rapid choreographed process of eat, then hide, then process and eliminate. They tend to eat to satiation and then take many hours to rest, digest, and eliminate their waste.
In BC, is Signal Crayfish an Endangered or Invasive species?
The BC government has a pamphlet on the Red Swamp Crayfish which are prevalent in the neighbouring states of Washington and Oregon. However, reports of that species existing in BC are not mentioned.
The BC government also has a pamphlet on the Rusty Crayfish even though they are not in BC. We are told however that they have invaded Ontario.
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We did find a 2015 study that states: “there are two invasive species already present in BC; the Asian clam (Corbicula fluminea) and the New Zealand mudsnail (Potamopyrgus antipodarum)."
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As far as we can see, the government of BC has not published information or a pamphlet about Signal Crayfish.
However, looking elsewhere, there is much to be learned. In Europe , starting in 1960’s, Signal Crayfish began to be introduced in Sweden and Finland. Today Signal Crayfish is the most widespread alien crayfish in Europe, occurring in 25 countries, from Finland to Great Britain and from Spain to Greece. It was first introduced to Great Britain in 1976. In Britain for example they were introduced to be farmed and marketed as a fashionable seafood. While the Signal Crayfish was intended to be kept in commercial fisheries for export to European markets, it quickly escaped into the ecosystem and began to outcompete the remaining native crayfish for both habitat and food causing an unfortunate decline in numbers of docile White-Clawed Crayfish such that they are now a protected species.
The invasive Signal Crayfish quickly became a significant problem throughout Europe, and huge efforts have since been made to control their spread. The impact that Signal Crayfish had on European ecosystems is the subject of continued study. A citizen science approach emerged to tackle these species and anglers have been encouraged to kill any invasive crayfish that they encounter. Despite all efforts, they continue to cause havoc throughout Europe, where Signal Crayfish not only prey on native crayfish and out-compete them for food and habitat but can also wipe out native fish stocks.
In light of the above you may wonder if either Canada or British Columbia are heeding the lessons learned in Europe. Are we being proactive or not? Why is there no information being provided by the BC Government?
Instead, what we can see is, a 2013 Fisheries Canada project conducted to demonstrate and develop new aquaculture techniques in the production of Signal Crayfish in British Columbia.
Here is a summary from that report: “During this project, individuals hatched from wild brood stock, fertilized in the laboratory, were successfully raised for an entire year with minimal mortalities. The system of vertical incubators used for hatching and rearing juvenile crayfish provided an effective means of intensively producing juveniles that could be used for out planting to culture ponds for grow-out. Three different artificial-feed formulations were developed for Signal Crayfish and shown to provide good growth rates.” This project appears to be a primary planning tool for anyone interested in the development of crayfish farming operations.
It is customary that the government of BC publishes information about wildlife in the province. However, currently, there is very little information about Signal Crayfish being published by the government of BC.
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This is strange considering that Signal Crayfish are included in a joint Canada-BC government, Pacific Freshwater/Land-Based Aquaculture Application which specifically includes Signal Crayfish as a licenceable farming opportunity. In 2018 a commercial farming of Signal Crayfish was opened on Malahat Lake north of Victoria.
So if you wonder why the BC government is silent on Signal Crayfish while commercial farming is being authorized, you might be interested to read what Ontario has to say about Signal Crayfish:
What is Ontario Doing?
Quote: "To prevent these unwanted invaders from coming into the province, Ontario has regulated the Pacifastacus genus as prohibited under the Invasive Species Act, 2015.
Background: The Genus Pacifastacus includes six crayfish species native to western North America. The signal crayfish, Pacifastacus leniusculus, native to the Columbia river basin, is at risk of being introduced to Ontario, where it is invasive. Signal crayfish can be introduced to Ontario from anglers bringing the crayfishes from their native range to use as bait or can be released from aquarists.
Range: Signal crayfish is native to the northwestern United States within the Columbia river basin. Their northern distribution includes Washington, Oregon, Idaho and southern British Columbia, their southern range includes Oregon’s coast.
For an up to date distribution of signal crayfish in Ontario, visit EDDMapS.org/distribution.
Impacts of Signal Crayfish
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May act as a vector of spread for diseases to native crayfish, such as the crayfish fungus plague.
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By eating large quantities of aquatic vegetation, they reduce spawning and nursery habitat for native fish.
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Crayfish are known to eat fish eggs and larvae, which can lead to decreased populations of desired sport fish.
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Can exploit a variety of freshwater ecosystems and compete with native crayfishes and other aquatic species.” End of quote from province of Ontario.
In the absence of any risk assessment by the Province of BC we have searched for a credible source elsewhere and found it in: Quote: “Signal Crayfish (Pacifastacus leniusculus), Ecological Risk Screening Summary”, published by the US Fish and Wildlife Service:
“Summary of Risk to the Continental United States
Native to the Pacific Northwest, P. leniusculus has established itself in new areas of the US, Europe, and Japan. Its invasion has led to the decline of native crayfish species, both through competition and as a vector of crayfish plague. This crayfish also alters native habitats, reduces abundances of macroinvertebrates and macrophytes, and influences the behavior of native fish.
High climate matches in a good portion of the US increase the risk. Overall risk for this species is high.
Assessment Elements:
History of Invasiveness: High
Climate Match: High
Certainty of Assessment: High
Overall Risk Assessment Category: High”. End of quote.
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Can Signal Crayfish Cause Harm to Humans?​
These solitary bottom-dwellers tend to try and escape confrontations and seem unlikely to cause physical harm to humans. ​
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While crayfish can be a delightful addition to a meal, it is essential to understand the potential dangers associated with their consumption. Allergies, bacterial contamination, parasites, toxins, and handling hazards should be taken seriously to safeguard one's health. By following proper handling, cooking, and consumption practices, individuals can enjoy crayfish safely and minimize the risks involved. It is crucial to stay informed, make informed choices, and prioritize food safety when it comes to eating crayfish or any seafood.
Fishing for Crayfish? Do You Need a licence?
In order to catch crawfish in non-tidal waterways in BC, you must be 16 years old or older and have a valid basic freshwater fishing licence. You'll also need to get the necessary supplemental licences and stamps. Regulations also stipulate limits and may also request the release of any crawfish that are less than 9 cm in total length as well as those bearing eggs or young.
Of course, on line there are no end of tips and information on how to lure crayfish into traps with an array of baits from dog biscuits, fish heads, meat, etc. And just as easy to find are the many recipes with which you can convert your crayfish-catch into a culinary masterpiece.
Are they Endangered or Invasive
​They have been around for some 280 million years, it seems that Signal Crayfish have a pretty good track record of survival. Are they endangered? No! Are they Invasive? The answer is a well-documented YES. So they must be watched closely because: “This crayfish also alters native habitats, reduces abundances of macroinvertebrates and macrophytes, and influences the behavior of native fish”.
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The Signal Crayfish has already been implicated in a 2010 study of Stickleback in Enos Lake, BC. The title of the study speaks speaks volumes.
For a broad perspective on crayfish here is an entertaining video for you : America's Crayfish: Crawling In Troubled Waters
References:
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E-FAUNA BC: ELECTRONIC ATLAS OF THE WILDLIFE OF BRITISH COLUMBIA: https://linnet.geog.ubc.ca/efauna/Atlas/Atlas.aspx?sciname=Pacifastacus leniusculus​
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Fisheris and Oceans, Aquaculture Collaborative Research and Development Program (ACRDP) Fact Sheet, March, 2013, Signal Crayfish: Improving Culture Techniques and Diets in British Columbia: https://waves-vagues.dfo-mpo.gc.ca/library-bibliotheque/354367.pdf
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Vaeßen, S., Hollert, H. Impacts of the North American signal crayfish (Pacifastacus leniusculus) on European ecosystems. Environ Sci Eur 27, 33 (2015). https://doi.org/10.1186/s12302-015-0065-2: https://rdcu.be/dXxn8 or https://enveurope.springeropen.com/articles/10.1186/s12302-015-0065-2
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Signal Crayfish (Pacifastacus leniusculus), Ecological Risk Screening Summary - 2015: https://www.fws.gov/sites/default/files/documents/Ecological-Risk-Screening-Summary-Signal-Crayfish.pdf
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A joint Canada-BC government, Pacific Freshwater/Land-Based Aquaculture Application which specifically includes Signal Crayfish farming: https://www2.gov.bc.ca/assets/gov/farming-natural-resources-and-industry/natural-resource-use/land-water-use/crown-land/crown-land-uses/aquaculture/pacific_freshwater_land-based_amendment_application.pdf
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Science Direct, various studies concerning Signal Crayfish and associated diseases: https://www.sciencedirect.com/topics/agricultural-and-biological-sciences/signal-crayfish#chapters-articles
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Oregon State pamphlet on four different species of crayfish, Aquatic Invasions! A Menace to the West • SPECIES GUIDE
https://seagrant.oregonstate.edu/sites/seagrant.oregonstate.edu/files/cr-species-guide_0.pdf
Crow's Path has been connecting people to wildness since 2010:https://crowspath.org/natural-history/crayfish/life-history/