![[Cambarus robustus]](crobustus.jpg)
Cambarus robustus
Robust Crayfish
DESCRIPTION
The Robust Crayfish is also
known as Ecrevisse robust. It is a large
crayfish with strong chelae and colour is
basically greenish-brown. It is distinguished
from similar species the Appalachian Brook
Crayfish by larger adult size, more elongate
rostrum and double row of tubercles on
inner border of palm of chelipeds.
HABITAT
Appears to be tolerant of pollution. The species can survive in acidic lakes and in polluted
urban streams with heavy sediment input. It is found is most of the streams flowing into
Lake Ontario from Toronto to Niagara.
DISTRBUTION
Canada/Ontario
Canada/Ontario Ð This
species is found in Ontario and Quebec. In
Ontario, where its distribution has been
well documented, it is found from Lake
Temagami in the north, westward to the
eastern shore of Georgian Bay, south to the
western end of Lake Erie and east to the
upper Trent River drainage (Crocker and
Barr, 1968; Berrill, 1978; David et al., 1997;
Guiasu et al. 1996; Hamr and Berrill, 1985). In
Quebec it has been recorded only in
the following two southeast
locations: Ruisseau
Kennedy in Papineau
county and Rapides des
Cedres on the Riviere du
Lievre (Dube and Provost, 1990).
These populations are well
established but it is not
certain whether they are an
extension of the natural
distribution or the result of
an introduction.
North America
This species' range
centers on the Great Lakes-Ohio River
drainages and is found in Quebec, Ontario,
New York, Connecticut, Pennsylvania,
Michigan, Ohio, Kentucky, Tennessee,
Indiana, Virginia, West Virginia and
North Carolina.
ECOLOGY
The Robust
Crayfish often occurs in or adjacent to
areas of high flow such as rapids and
waterfalls (Crocker and Barr, 1968; Bousfield,
1969; Berrill, 1978; Hamr, 1983; Dube and
Provost, 1990; Guiasu et al., 1996) and
studies have shown that it can hold on to
substrate in current speeds of 50 cm/sec Ð
a value significantly higher than that for
any other crayfish species found in Ontario
(Maude and Williams, 1983). The Robust
Crayfish usually constructs shallow burrows
under larger stones on rocky and gravelly
substrates but it can also be found on
silt and mud (Crocker and Barr,
1968; Hamr, 1983). The species
appears to be tolerant of
pollution as it can survive in
acidic (Taylor et al., 1995)lakes and
in polluted urban streams with
heavy sediment input.
Despite its larger size, the presence of
predatory fish affects the activity and
trapability but not the density of this
species (Collins et al., 1983). The Robust
Crayfish is a large and aggressive species
which has been shown to be clearly
dominant in aggressive interactions with
the Appalachian Brook Crayfish which in
turn is generally more aggressive than the
Canadian orconectids (Guiasu and Dunham,
1997). In Canada, the Robust Crayfish has
been found together with the Appalachian
Brook Crayfish, the Northern Clearwater
Crayfish, the Virile Crayfish, the Obscure
Crayfish, the Papershell Crayfish and the
Rusty Crayfish (Berrill, 1978; Hamr 1983;
David et al., 1997).
LIFE HISTORY
In Ontario, reproduction
appears to take place in the summer.
Mature females show strong glair gland
development from May to August while
copulation has been observed in June in
the field and June to early July in captivity
(Hamr and Berrill, 1985). Females with eggs
are found from June to July and with
young from July to September. Most
females lay their eggs by mid-July and the
peak of hatching occurred in early August
after about 30 days. The young undergo
two moults in their metamorphosis,
spending about 22 days attached to their
mothers and then become free-living in
mid to late August. In some central
Ontario populations, females with stage 3
young were collected in September,
October and April suggesting that young
may be carried over winter and released in
the following spring (Corey, 1990).
Moulting occurs from May to September
and immature crayfish reach 17-26 mm
(0.66-1.0 in.) CPL by the end of the
second summer. Most individuals mature
at 2 years of age. However some may not
reach maturity until 3 years of age which
is the average life-span of the species
(Hamr and Berrill, 1985). Adults of both
sexes moult in September. Form I and
Form II individuals are present throughout
the year (Berrill, 1978; Hamr and Berrill,
1985; Corey, 1990). The maximum life span
is 4 years and the maximum recorded size
is 57 mm (2.22 in.) CPL.
In Ontario, reproduction
appears to take place from spring to fall.
Mature females show strong glair gland
development from April to August.
Copulation has been observed in October in
the wild and late April to early June in
captivity. Females with eggs are found from
June to August and with young from July to
September. Eggs and young are therefore
carried into autumn and there is evidence
that some females may over winter with
attached eggs or young and release them
(and then moult) the following summer
(MacManus, 1960b; Hamr, 1983). Hatching
occurs between July and August and the
young undergo two moults in their
metamorphosis, spending about 15 days
attached to their mothers. Free-living young
measuring about 5 mm (0.195 in.) CPL are
first found in August (Hamr, and Berrill, 1985).
Moulting in immature crayfishes take place
form May to early October and maturity is
reached at about 2 years of age. Adult males
moult in July and September. Moulting into
both Form I and Form II at the same time of
year has been observed (Hamr and Berrill,
1985). Mature females moult once following
the reproductive season but the timing of
moult is variable (September or the
following June-July) depending on local
conditions. The average life-span appears to
be 3 years old and the maximum life-span is
4 years. The maximum recorded size is 39
mm (1.52 in.) CPL from a male collected in
Rawdon, Quebec. Sexual dimorphism with
respect to chela length between sexes and
Form I and From II males is present but not
as pronounced as in the Orconectid
crayfishes (Hamr and Berrill, 1985).
CONSERVATION STATUS
The Robust
Crayfish appears to tolerate pollution as its
distribution overlaps highly industrialized
areas of southern Ontario where it survives
in urban streams with high sediment and
pollutant loadings (Jain and Hamr, 1996). It
is also among the most acid-tolerant of the
freshwater crayfishes tested, which explains
its presence in acid stressed lakes of north-
central Ontario (Taylor et al., 1995).
Juveniles of this species are able to survive
in water with pH as low as 4.0 (Berrill et al.,
1985). The Robust Crayfish is a large and
aggressive species and, given its apparent
expansion in Ontario and Quebec during
the past 30 years, it appears that this
species has the potential to competitively
exclude other species when competing for
limited resources (Guiasu and Dunham,
1997). It is not clear whether the
introduced and rapidly expanding Rusty
Crayfish can successfully compete with or
eliminate the Robust Crayfish from its
habitat, but regardless of the outcome of
the interaction between the two, the
Robust Crayfish should be able to survive
in the more acidic waters of the Canadian
Shield where the Rusty Crayfish appears to
be excluded. Due to its abundance and its
ability to cope with various pollutants as
well as competitors, the Robust Crayfish
remains common within its range and must
therefore be considered to have a
"Currently Stable" status in Canada.
(Used by permission: text by Premek Hamr, modified from "Baitfish of North America"2007
painting by Aleta Karstad)
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