![[Orconectes rusticus]](orusticus.jpg)
Orconectes rusticus
Rusty Crayfish
DESCRIPTION
A medium to large crayfish.
It has a brown cephalothorax and abdomen,
green claws with dark black bands near tip,
green legs, prominent (dorso-lateral) rusty
spots on each side of the carapace and small
rusty spots also present on abdominal
segments. A blue morph of this species has
been recorded in Ontario (Hamr, unpublished
data). It can be distinguished from the
similar Northern Clearwater Crayfish by
absence of rostral carina and presence of
rusty markings on exoskeleton. The other
similar native species, the Virile Crayfish, is
generally more blue in colour (without rust
markings) with broader shorter chelae
bearing distinct yellow tubercles, whereas
the Rusty Crayfish has larger more elongated
fingers of claws without tubercles.
HABITAT
Occurs in lakes, rivers, streams and ponds. The Rusty Crayfish prefers areas that offer rocks,
logs, or other debris as cover but substrate types may also include clay, silt, sand and gravel.
It can inhabit slower, deeper pools as well as shallow fast water areas of streams.
DISTRBUTION
Canada/Ontario Ð This
species has been introduced to
various locations in
southern and
northwestern Ontario.
Since it is established in
the Lake of the Woods and
the Ottawa River drainage
(Momot, 1992; Schueler, 1988),
it is likely that it has or will in
the near future also invade
Manitoba and Quebec. Its
distribution within Ontario
appears to be spreading continuously
though more introductions as well as the
through the spread of current populations.
Ontario drainages/regions which have been
colonized by this species include; the
Magnetawan River between Emsdale and
Kearney (Lloyd Ð Gottinger, pers. com.), Lake
of the Woods, Quetico Provincial Park
(Basswood Lake), Lake Superior and its
tributaries near Thunder Bay (Needing-
MacIntyre, Pigeon Lake, Portage Little Pine,
Kaministiquia and Jackfish Rivers; lakes
Pounsford, Lenore and Wiswell), Eramosa
River (near Guelph), Berford Lake (on the
Bruce Penisnula); the region from the east
edge of Toronto (Rouge River and Duffin
Creek) to Plevna in eastern Ontario (Shaw
and Plevna Lakes) north through the
Kawartha Lakes (from Rice Lake north to
Balsam Lake) into Haliburton (Head,
Kashagawigamog and Drag Lakes) and east
to the Jock and Rideau rivers confluence
(Crocker and Barr, 1968; Berrill, 1978;
Corey, 1988; Maude, 1988; Schueler,
1988; David et al., 1994; Karstad,
1995; Hamr, 1997; Momot, 1992;
Momot, 1997). It is also now
widespread in the upper Mississippi
drainage in Lanark and Frontenac
counties, the lower Trent system
(Schueler, pers.comm., 1988) and Rouge
River(Hamr, unpublished).
North America
The Rusty Crayfish is
thought to be native to the Ohio River
Basin and the state of Ohio, Kentucky,
Michigan and Indiana. However, this
species has been widely introduced in
North America and is now found in
Ontario, Illinois, Tennessee, Missouri, West
Virginia, Iowa, Minnesota, New York, New
Jersey, Pennsylvania, Wisconsin, Vermont,
Massachusetts, Connecticut, Maine, New
Hampshire and New Mexico (Gunderson,
1995; Page 1985; Taylor et al., 1996).
ECOLOGY
Rusty Crayfish
generally do not dig burrows (except for
shallow excavations under rock and stones)
but have been observed to construct
extensive and quite deep burrows in a clay
bottomed Ontario stream (Hamr, 1997a).
This species appears to need permanent
lakes or streams that provide suitable water
quality year round. Rusty Crayfish,
especially juveniles, feed heavily on
benthic invertebrates and it has been
estimated that this species can consume
twice as much food as similarly sized Virile
Crayfish because of a higher metabolic rate
(Momot, 1992; Jones and Momot, 1983).
Rusty Crayfish are therefore more likely to
compete with juvenile game fish and forage
species for benthic invertebrates than are
native crayfish species.
LIFE HISTORY
In southern Ontario, the
species has been shown to breed very early
in spring (March-April) when water
temperatures rise above 4¡C (39¡F). Eggs are
laid 11-12 days after copulation and are
carried for 6-8 weeks. The fecundity ranges
from 35-351 and eggs are about 2.4 mm
(0.094 in.) in diameter (Berrill and Arsenault,
1982; Corey, 1987, 1988). The average
fecundity and egg volume of this species is
greater than that of the native Virile
Crayfish and Northern Clearwater Crayfish
(Corey, 1987). Males moult for Form I to
Form II in May and then back into Form I in
June-July (Corey, 1988; Momot, 1991).
The Rusty Crayfish grows rapidly with
maturity being reached early in both sexes,
in some cases at the end of the first summer
of life and young Rusty Crayfish then may
participate in mating within less than a year
of hatching. Maturity is attained between
14-23 mm (0.63-0.9 in.) CPL and the
maximum life span is 3-4 years at a
carapace length of 40-45 mm/1.6-1.8 in.
(Berrill, 1978; Corey, 1988; Momot, 1991;
Hamr, 1997a). Maximum size measured to
date is 54 mm CPL (Momot, 1997).
In southern Ontario densities may reach
very high numbers Ð average densities of
6-64 crayfish per m2(1.2 yards2) have been
counted in rivers draining into Rice Lake
(maximum counts as high as 113/m2or
371/ft2). The sex ratio is about 1:1 but
adult males are generally more active
throughout and therefore make up the
majority of hand samples and trap catches
(88% of total) (Hamr, 1997a).
INTRODUCTION STATUS
The Rusty
Crayfish is thought to have been introduced
into Ontario in the early 1960s presumably
by anglers from Ohio (Crocker and Barr,
1968). The probable introduction point is
in the Kawartha Lakes where it has been
first reported Ð its densities are the highest
documented (up to 113/m2or 371/ft.2) and
it is the dominant or sole occupant of many
watersheds (Hamr, 1997a). It is an aggressive
species and a prolific breeder which, as a
result, has spread significantly in Ontario,
and has displaced resident native species
(Virile Crayfish, Northern Clearwater
Crayfish and Appalachian Brook Crayfish)
in numerous lakes and waterways in the
south and north of the province of Ontario
(Berrill, 1978; Corey, 1988; Momot, 1992;
Hamr, 1997a; Hamr, 1997). Barr (1996)noted
that when the available records for Rusty
Crayfish in southern Ontario are mapped it
is more likely that the south-most of the
two points of introduction identified by
Crocker and Barr in 1968 has given rise to
the currently observed range by a process
of gradual outward diffusion. During the
same time period, the species has been
observed to extend its range in Ohio,
Illinois (Page, 1985) and Wisconsin(Capelli,
1982), and thus appears to be in an
expansive phase throughout its range.
Similarly, Momot (1997) documented the
rapid and continued spread of this species
in the Thunder Bay region since 1991 and
estimated its rate of expansion at about 1
km/year (0.62 mi./year). Given its presence
and continued expansion in Lake of the
Woods in the northwest and the Jock,
Rideau and Mississippi drainages in the
southeast, it is only a matter of time before
the species enter the provinces of Manitoba
and Quebec. In fact, specimens thought to
be hybrids of Rusty Crayfish and Northern
Clearwater Crayfish have been collected
from Lake Heney near Gracefield, Quebec
in 1980 (National Museum of Nature
unpublished record).
There appear to be few constraints on the
ultimate range of the Rusty Crayfish in
Ontario Ð the only barrier may be the
Canadian Shield, whose physical and
chemical character and/or harsh
environmental conditions may prove
limiting. Water ranging in pH from 5.4-6.1
was shown to be toxic to juvenile Rusty
Crayfish in the laboratory (Berrill et al.,
1985). Beaver dams, weirs and waterfalls can
also prevent or slow down the expansion
within rivers (Momot, 1997). Additionally,
water temperatures play an important role in
the rate of expansion as crayfishes are less
active at cold temperatures (< 10¡C/5¡F). The
southern warmer regions of Canada, where
water temperatures are warmer for longer
periods of the year, are therefore the most
vulnerable to rapid invasion of the Rusty
Crayfish. Laboratory studies have shown this
species to have superior streamlining
capabilities and station holding capability
(40 cm/sec or 15.6 in./sec) which enables it
to colonize the upstream portions of even
fast-flowing rivers and streams (Maude and
Williams, 1983).
Where it has established itself, this species
is an effective competitor and has often
eliminated native species such as the
Northern Clearwater Crayfish and the Virile
Crayfish (Momot et al., 1978; Capelli 1982;
Lodge et al., 1986; Olsen et al., 1991; Hamr,
1997a; Momot, 1997). Larger size, earlier
breeding season, higher fecundity, faster
egg, larval and juvenile development appear
to be some of the factors contributing to its
dominance. In addition, the species may be
able to better compete for food, withstand
pressure from fish predation, and hybridize
with closely related species such as the
Northern Clearwater Crayfish (Capelli and
Capelli, 1980; Smith, 1981; Berrill, 1985;
DiDonato and Lodge, 1993; Gunderson 1995;
Lodge, 1997). It is not clear whether the
Rusty Crayfish can successfully compete
with or eliminate the Appalachian Brook
Crayfish, the Robust Crayfish, the Northern
Clearwater Crayfish, the Virile Crayfish, the
Papershell Crayfish and the Obscure
Crayfish. This shows that itÕs a potential
threat to all species living in open water
habitats in Ontario.
Therfore, the expanding dense populations
of this species not only poses a threat to
the biodiversity of the native crayfishes, but
also potentially endangers other aquatic
invertebrate fauna, aquatic vegetation as
well as sport fish (in terms of competition
for aquatic prey as well as predation upon
fish eggs). Many of these effects have been
well documented in the United States where
the species has aggressively displaced
native crayfishes and had a significant
impact on aquatic ecosystems (Capelli,
1982; Lodge et al., 1985; Olsen et al., 1991;
Momot, 1992; Gunderson, 1995). One of the
most serious impacts is the destruction of
aquatic plant beds. Rusty Crayfish have
been shown to reduce aquatic macrophyte
abundance and diversity (Lodge and Lorman,
1987; Olsen et al., 1991). This can be
especially damaging in relatively
unproductive northern lakes, where beds of
aquatic plants are not abundant.
It will be difficult to control the spread of
this species in Canada. None of the
available chemical poisons can selectively
kill the Rusty Crayfish without killing other
crayfish species (Gunderson, 1995). Intensive
harvest will probably not eradicate this
species, but may help reduce adult
populations and minimize some impacts
(Hamr, 1997a). The most effective method of
control is to prevent further introductions.
Education of the general public (anglers,
crayfish trappers, bait dealers and
educators) about the threats posed by the
Rusty Crayfish should help reduce the risk
of spreading it to new areas within the
country. It is very important to note that it
is not necessary to introduce both a male
and female crayfish to begin a new
infestation. One female carrying viable
sperm could begin a new population if
released into a suitable environment
(Gunderson, 1995).
(Used by permission: text by Premek Hamr, modified from "Baitfish of North America"2007
painting by Aleta Karstad)
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