DISTRIBUTION A N D STATUS OF CRAYFISHES O F THE
G E N E R A CAMBARUS A N D FALLICAMBARUS
(DECAPODA: C A M B A R I D A E ) IN ONTARIO, C A N A D A
Radu
Cornel Guiasu,
D a v i d W. B a r r ,
a n d D a v i d W. D u n h a m
A B S T R A C T
This c o m p r e h e n s i v e update o f the distribution of crayfishes of the genera C a m b a r u s a n d
F a l l i c a m b a r u s in Ontario includes substantial material collected since 1965 and a reexamination
of previous records. Revised provincial range limits are presented for two wide-ranging, openwater species, C. b a r t o n i i b a r t o n i i and C. robustus, as well as for 2 obligate burrowers o f m o r e
restricted distribution, C. diogenes and F. fodiens. Previously unreported locality records represent range extensions, fill in geographic gaps in k n o w n ranges, or confirm the persistence o f
populations for periods o f several decades. Limits to the ranges of the 4 species appear to be
established by patterns o f postglacial migration and habitat preferences. A diagnosis of the
current status o f each of these species suggests the potential impact o f anthropogenic perturbations, such as lake acidification and wetland destruction, for the future o f these crayfishes in
Ontario.
Crayfish species occurring in the province of Ontario are currently grouped in
three genera: Orconectes, Cambarus, and
Fallicambarus. There are three species of
C a m b a r u s in the study area [C. bartonii
bartonii (Fabricius, 1798), C. diogenes Girard, 1852, and C. robustus Girard, 1852]
and one species o f F a l l i c a m b a r u s [F. fodiens (Cottle, 1863)] formerly placed in
Cambarus. Hobbs (1974a, b) revised the
crayfish g e n e r a o f N o r t h A m e r i c a a n d
placed the former C. fodiens in the genus
Fallicambarus. Nevertheless, F. f o d i e n s is
much closer in general habitus to species of
the genus Cambaru.s than to those of other
North American genera such as Orconectes
or P r o c a m b a r u s (see Crocker, 1957; Crocker and Barr, 1968). Thus, we occasionally
refer informally to the four species treated
in this paper as cambariform crayfishes, a
distinction which is useful in northeastern
and north central North America. The four
cambariform species studied here appear to
be long-term residents (since the end of the
Wisconsinan glacial period) of Ontario, and
are found in a variety o f aquatic habitats.
In Ontario, C a m b a r u s b. bartonii and
C a m b a r u s robustus are usually found in
fast-water streams, rivers, and lakes. Camb a r u s diogenes and Fallicambarus fodiens,
however, are semiterrestrial, primary or secondary burrowers (Hobbs, 1974b; Berrill
and Chenoweth, 1982) occurring, for the
most part, in wetlands. The latter species
frequently builds distinctive m u d chimneys
on top o f elaborate tunnels (Crocker and
Barr, 1968; W i l l i a m s e t a i , 1974). Under
extreme conditions, such as drought, C. b.
bartonii and C. robustus, like most northern
crayfishes o f surface waters, can behave as
tertiary burrowers (Berrill and Chenoweth,
1982) and dig very shallow burrows, usually bordered by a rock. In very rare circumstances, C. b. bartonii can also build a
rudimentary chimney out of gravel (McManus, 1960).
The first review o f the distribution of Ontario crayfishes was published by Crocker
and Barr in 1968. In the 30 years since
1965, the last year for which locality records for C a m b a r u s and F a l l i c a m b a r u s
were listed in Crocker and Barr (1968),
many more specimens, belonging to each of
the Ontario species o f these two genera,
have been collected. Some collections reported here were sampled from the field for
this study between 1991 and 1994, while
others have been added to the invertebrate
collections o f the Royal Ontario M u s e u m
(Toronto) and the Canadian M u s e u m of Nature (Ottawa) as a result o f both incidental
collecting trips and specific studies (e.g.,
Judd, 1968).
MATERIALS AND METHODS
All data for this study were obtained by the examination of 2,121 crayfish specimens comprising 457
field collection lots. Those not in the permanent research collections of the Royal Ontario Museum or the
Canadian M u s e u m o f Nature are in the personal collection of the senior author and were collected in the
course of thesis research work between 1991 and 1994.
In addition to all material collected in the last 30 years,
w e also reexamined all specimens reported by Crocker
and Barr in 1968.
D a t a from m u s e u m collection labels were entered in
an electronic database (dBase I I I + - . d b f file format).
At the same time, the specimens were e x a m i n e d for
accurate determination and recognition of sex a n d lifehistory stage.
Crayfish samples in m u s e u m collections are generally collected either by seining, dipnetting, or trapping
(Hobbs, 1991). Thus, by and large, they must be reg a r d e d as qualitative in nature. Field collectors sampling for systematic/biogeographic studies generally
attempt to be exhaustive in their sampling instead o f
quantitative. Thus, it m a y be a s s u m e d that the majority
o f samples contain all but very rare species occurring
in the habitat sampled. O u r analysis, therefore, deals
with an accumulation of species occurrences at particular localities, on a presence/absence basis, giving rise
to broad patterns of species d i s t r i b u t i o n - t h e " r a n g e s "
o f the 3 native species o f Cambaru.s and I o f Fallic a m b a r u s in Ontario. Collection data on habitat type
have also been included in our analysis.
Older m u s e u m collections o f invertebrates seldom
include geocoding in their documentation. All records
for this study have been g e o c o d e d retrospectively (a
posteriori) by assigning geographic coordinates, using
a provincial gazeteer ( A n o n y m o u s , 1988), topographic
m a p s ( 1:50,000 series), and other geographic references. These coordinates (in the degree/minute system)
are stored, along with other elements o f collection
data, in the electronic database file. At the time of
preparing s e c o n d a r y files for the p u r p o s e of m a p p i n g
and analysis, the simple calculations required to convert, for instance, 8 0 ' 3 0 ' W to - 8 0 . 5 0 0 ° , are performed.
Retrospective g e o c o d i n g of traditional m u s e u m collections involves an unavoidable level o f imprecision.
Locality data on labels are s e l d o m given in sufficient
detail to locate the site o f collection accurately on a
topographic m a p sheet (at, for instance, a scale of 1:
50,000). However, a high level of precision (for instance, to the nearest second) is u n n e c e s s a r y for the
preparation o f typical collection-site dot distribution
m a p s of the kind that have b e c o m e standard for systematic accounts o f invertebrates.
Su c h collection-site dots typically have a m a p dia m e t e r in the order o f at least 5 - 1 0 k m at midlatitudes,
corresponding to approximately 3 - 5 m i n or more of
either latitude or longitude. Moreover, since the geographic coordinates must typically be located in a gazeteer, one is limited to the data recorded for standard
m a p objects, such as townsites, river mouths, and the
central point for lakes. S uch objects provide only a
general guide to the precise location o f the collecting
site. Thus, our practice has been to a c k n o w l e d g e the
imprecision inherent in the data and record latitude and
longitude to the nearest minute only. This should be
m o r e than adequate for biogeographic analyses, alt h o u g h for relocating a site to collect a new sample
f r o m the s a m e population, greater precision would be
desirable.
W h e n e v e r higher accuracy in the data can be reliably determined, it should be recorded. It is to be hoped
that the position of all future collecting sites will be
recorded to an accuracy of at least the nearest second
with the use of hand-held GPS (Global Positioning
System). Then the presence or absence of seconds in
the electronic database will clearly distinguish fieldcoded samples from a posteriori geocodes.
For the preparation of distribution maps, records in
the database were sorted by species and province. Data
were imported in MapInfo Version 3.0.2 running under
MS-Windows for visualization and preparation of figures.
RESULTS
The genus C a m b a r u s occurs widely
throughout the southern and eastern portions of the province of Ontario, extending
north and west roughly to a line joining the
mouth of the Moose (Missinaibi) River on
James Bay to Michipicoten Harbor on Lake
Superior. This is an area of approximately
2 9 0 , 0 0 0 km2, r e p r e s e n t i n g the n o r t h e r n
range limit for the species o f Cambarus.
Previously unreported locality records for
crayfish species of the genera Cambarus
and Fallicambaru.r in Ontario fall into three
categories. Some represent range extensions
for given species, others fill geographic
gaps between previously known localities
for certain species, while the remainder
simply confirm the persistence of crayfish
populations at certain locations over periods
o f several decades.
C a m b a r u s bartonii bartonii
Cambaru.s b. bartonii has an extensive
distribution along the east coast of North
America, from Georgia to Nova Scotia, and
inland to the Ohio River and Great Lakes
drainages (Crocker and Barr, 1968). Based
on the 159 collections examined, it has the
most extensive distribution in Ontario (approximately 245,000 km2) of the four cambariform species considered here (Fig. 1). It
has a northern limit in our records o f the
Kapuskasing River (part of the Moose River watershed) (approximately 50°N) and a
w e s t e r n l i m i t at M i c h i p i c o t e n H a r b o r
(85°W). In the south, it is restricted largely
to eastern Ontario, with only a single locality known as far west as the Niagara Escarpment. The most common habitats for
this species are rocky lake margins and
streams on the Precambrian (Canadian)
S h i e l d , a l t h o u g h it o c c u r s in s c a t t e r e d
streams farther south, almost to the northern
shore of Lake Ontario. It is a relatively
Fig. 1.
Distribution of Cambaru.s b. b a r t o n i i in Ontario, Canada.
common crayfish along the southern margin
o f the shield.
New locality records of C. b. bartonii
from the Moira River (44°18'N, 77°20'W;
Hastings County) and Glenora and Yorkshire Shoal (43°56'N, 76°35'W; Prince Edward County) are the first for this species
from these counties, both o f which are located in eastern Ontario. These records fill
a gap between the previously recorded localities of Ganaraska River tributaries (Durham Region) to the southwest and the Ottawa River and Jock River (Ottawa-Carleton County) to the northeast. In central Ontario, there are new records for this species
from the Nipissing District (Kakasamic
Creek [46°00'N, 79°03'W], Bastien Creek
[46°19'N, 78°42'W] and Emerald Lake
[46°48'N, 79°18'W]), Parry Sound District
(Cashman Creek [45°37'N, 79°10'W]) and
Haliburton County (Clayton Lake [45°21'N,
78°45'W]). All these records are from the
general vicinity o f Algonquin Provincial
Park, an area where C. b. bartonii seems to
be fairly abundant and widespread. Farther
north, there are new records o f C. b. bartonii from the Sudbury District ( M a k w a
Lake [47°32'N, 81°44'W]), Timiskaming
District
(Montreal
River
[47°30'N,
79°40'W]), and Algoma District (Beaver
Falls near Searchmont [46°44'N, 84°08'W],
Crystal Creek near Sault Sainte Marie
[46°34'N, 84°13'W], and within the boundaries of Lake Superior Provincial Park
[47°35'N, 84°45'W]).
A previously reported (Crocker and Barr,
1968) record of C. b. bartonii from Hespeler (Waterloo County) would have been
the southwesternmost Ontario record for
this species. However, upon careful reexamination during this study, this specimen
actually is C. robustus, well within the
known range o f that species in Ontario.
Thus, in Ontario, C. b. bartonii is restricted,
for the most part, to the Ottawa River, Lake
Ontario, Georgian Bay, and Lake Superior
drainages.
The isolated, northernmost Ontario record o f C. b. bartonii from the Moose River
watershed (Cochrane District) means that
this species also has access to the remote
James Bay drainage area. This is an old collection (1919) and the locality is given only
as the Moose (Kaibushkasing) River. As a
Fig. 2.
Distribution o f Cambaru,s robustu,s in Ontario, Canada.
result, the precise site of the collection is in
doubt and is estimated conservatively at
49°49'N, 82°00'W, the point where the
Kapuskasing River joins the Mattagami
River, a major tributary of the Moose River.
Nevertheless, this location is much farther
north than that for any other species in this
study, although it is not clear at present exactly how much farther north in this watershed the range may extend. C a m b a r u s b.
bartonii also has the easternmost range limits of all o f these species in Ontario. Within
Canada, the distributions o f C. robustu.s, C.
diogenes, and F. fodien.s are restricted to the
province o f Ontario, whereas the distribution o f C. b. bartonii extends eastward into
the provinces o f Quebec and New Brunswick (Faxon, 1885).
C a m b a r u s robustus
Cambaru.s robustus is a species o f the
Ohio River and Great Lakes drainages
(Crocker and Barr, 1968), with a distribution in Ontario (Fig. 2) that is concentrated
along the Niagara Escarpment and along
the southeastern shore o f Georgian Bay,
and then, less commonly, on the plain that
slopes westward to Sarnia (Chapman and
Putnam, 1966). It ranges from Lambton
County, at the southwestern tip of the province, to Lake Temagami to the north (approximately 47.5°N) and from the eastern
shore o f Lake Huron to the west to the Gull
River and Koshlong Lake to the east. Data
from the 186 collections examined for this
study indicate that this species occurs in
near-shore areas o f Lakes Ontario and Huron and also Georgian Bay, as well as in
scattered shield lakes to the northwest of
Georgian Bay. The total Ontario range is
approximately 81,000 km2.
Within the previously established general
range for C. robustus in southwestern Ontario, there are many new records from several locations along the Speed and Eramosa
Rivers (Wellington County). The presence of
this crayfish in the Eramosa-Speed river system o f southwestern Ontario, near Guelph
(43°35'N, 80°16'W), was reported by Corey
(1990), who found that C. robustus was
more common in the upper regions o f these
streams and became increasingly uncommon
farther downstream. Another previously unreported locality record for this species is the
Conestogo River (43°40'N, 80°43'W; also in
Wellington County), within the Conestogo
Conservation Area, near Drayton. A new
r e c o r d f r o m the Nith R i v e r ( 4 3 ° 1 2 ' N ,
80°28'W) is only the second known location
for this species from Oxford County, in
southern Ontario. There is also a new record
of C. robustus from Halton County (Bronte
Creek [43°30'N, 79°57'W]).
Crocker and Barr (1968) reported the
presence of C. robustus at several locations
on the southwestern side of the Bruce Peninsula, along the eastern shore o f Lake Huron. In this study, we include new Georgian
Bay records from the eastern side of the
Bruce Peninsula (Lion's Head [45°00'N,
81°15'W] and White Cloud Island [44°50'N,
81°00'W]). P r e v i o u s l y r e p o r t e d localities
(Crocker and Barr, 1968) from the Muskoka
District bordered the southeastern shore o f
Georgian Bay. New records from this district
are now reported from locations farther inland, east of Georgian Bay, such as Moon
River (45°06'N, 79°57'W), Severn River
(44°50'N, 79°40'W), and Lake Muskoka,
near Gravenhurst (45°00'N, 79°25'W).
Farther east, there are new records of C.
r o b u s t u s f r o m Elliot Falls ( 4 4 ° 4 5 ' N ,
78°50'W), on the Gull River (Victoria County), and Koshlong Lake ([44°58'N, 78°30'W]
Haliburton County). These records, which
represent eastward extensions o f the range
known for this species in Ontario, confirm
a previous report o f the presence o f this
species in the Gull River and Koshlong
Lake by Berrill (1978). Although that author also reported finding C. b. bartonii at
the Elliot Falls location, during four years
(1991-1994) o f extensive field work at Elliot Falls, we were not able to confirm the
presence of the second species. New records from the Nipissing District (Duchesnay Creek [46°19'N, 79°30'W] and Temagami [47°02'N, 79°47'W]) confirm similar,
nearby records reported by Crocker and
Barr (1968), and represent the northernmost
locations for C. robustus in Ontario.
The range o f C. b. bartonii and C. robustus, two species so similar that they
were formerly considered subspecies of C.
b. bartonii (see Crocker and Barr, 1968),
appear to be largely nonoverlapping in Ontario. The main areas o f potential contact
appear to be in a broad zone east o f Georgian Bay and in one locality on the Niagara
Escarpment.
Cambaru.s diogenes
The two remaining species considered in
this study, C a m b a r u s diogenes and Falli-
c a m b a r u s fodiens, appear to be obligate
burrowers in Ontario. They may fabricate
m u d chimneys above an underground burrow in moist terrestrial (wetland) habitats.
C a m b a r u s diogenes is locally rare in Ontario, being restricted to a handful of sites
within a few kilometers o f the northern
shore o f Lake Erie (Carolinian Zone) and
one locality in the northwest (11 collections
examined). It has an extensive distribution
farther south and to the west in the Mississippi drainage basin, and a large portion of
the east coast, from Georgia to New Jersey.
The total range o f the species in southern
Ontario (Fig. 3) covers an area o f approximately 4,500 km2, an area some 300 km
long (from Point Pelee to Wainfleet) but
only 10-30 km wide. The m a x i m u m northern boundary of this portion o f the range is
about 43°N. The habitat is usually mud flats
with little vegetation. Chimneys are not always constructed where the ground is very
soft and moist.
Although according to Hobbs and Jass
(1988), C. diogenes is one of the three most
widely ranging crayfishes in North America, this species was considered by Crocker
and Barr (1968) to be the rarest Ontario
crayfish. P r e v i o u s l y , this s p e c i e s w a s
known in southern Ontario only from Point
Pelee (Essex County) and Long Point and
Turkey Point (Haldimand-Norfolk County),
along the northern shore o f Lake Erie
(Crocker and Barr, 1968). Although new locality records from the Wainfleet Marsh
(42°54'N, 79°20'W), near Welland (Niagara
County), and Binbrook (43°08'N, 79°41'W;
Hamilton-Wentworth County) represent
eastward and northward extensions o f the
k n o w n range, this species remains extremely rare in the province.
The one atypical record o f C. diogenes
from northwestern Ontario (48°45'N,
91°40'W; Rainy River District, near Atikokan) is valid, but its location could not be
explained by Crocker and Barr (1968). Updated knowledge of the North American
distribution o f this species (Hobbs and Jass,
1988) shows, however, that C. diogenes is
also found in northeastern Minnesota, just
south o f the Rainy River District o f Ontario. Therefore, it is possible that the northern
Ontario location for this crayfish species is
due to an extension o f its range northward,
from Minnesota and Wisconsin.
Fig. 3. Distribution o f Cambaru.s diogenes in Ontario, Canada. Inset shows the provincially disjunct record
from the northwest.
F a l l i c a m b a r u s fodiens
Fallicambaru.c fodiens is a specialized
burrower and the only species o f its genus
occurring in Ontario, at the extreme northern end o f its range. The main range for the
species is the Mississippi Valley. In this
province we have 93 collection records,
scattered broadly across southwestern Ontario (Fig. 4), covering an area o f approximately 25,000 kM2. To the north and east,
F. f o d i e n s extends no farther than approximately the position of Lake Simcoe (44°N,
79°W). Burrows m a y be found not only in
moist clay among rooted semiaquatic plants
such as Typha and Scirpus, but also in relatively hard, dry ground where the water
table is far below the surface and the vegetation primarily terrestrial.
We report new records for this species
from Lambton County (Thedford [43°11'N,
81°55'W], Wallaceburg [42°36'N, 82°23'W],
a n d W a r w i c k [ 4 3 ° 0 0 ' N , 8 1 ° 5 6 ' W ] ) , in
southwestern Ontario, and Wellington
County (Aberfoyle [43°28'N, 80°09'W] and
Oustic [43°43'N, 80°15'W]) in southern
Ontario. The several new records from the
Peel Regional Municipality, southwest o f
Toronto, are the first for F. fodien.s from this
region.
To summarize, F. fodiens, is represented
by populations that are marginal in terms o f
the entire range, scattered over a wide geographic area but never locally common, and
restricted to isolated patches. Fallicambaru.s fodiens has never been found together
with C. diogenes at the same locality in this
province.
DISCUSSION
Postglacial Migration
All crayfishes o f the genera C a m b a r u s
and F a l l i c a m b a r u s of Ontario have invaded
the aquatic habitats o f this province from
glacial refugia located in central and eastern
areas of the United States (Crocker and
Barr, 1968). These invasions took place in
the period o f time following the end of the
Wisconsinan glacial period, which took
place 80,000-10,000 years before the present (BP) (Mandrak and Crossman, 1992).
In order to determine the glacial refugia and
the possible dispersal routes into Ontario
used by these four species, we have relied
on current distributions in Ontario and
Fig. 4.
Distribution o f Fallicamharu.s fodien.s in Ontario, Canada.
North America (Hobbs, 1974b; Hobbs and
Jass, 1988), as well as on recent information on the glacial refugia and dispersal
routes presumably used by naturally occurring fresh-water fishes of Ontario (Mandrak
and Crossman, 1992, fig. 3). Crayfish species are presumably restricted largely to the
use o f the same aquatic dispersal routes as
fresh-water fishes, even though semiterrestrial crayfishes, such as C. diogenes and F.
fodiens, probably also travel across short
stretches of moist land.
According to our data, C. b. bartonii entered Ontario from the southeast, most likely from the Atlantic Coastal Refugium, using the Champlain Sea and St. Lawrence
River dispersal route. Given its current Ontario distribution, C. robustus could have
entered the province either from the Atlantic Coastal Refugium, using the M o h a w k
dispersal route from the southeast, or from
the Mississipian Refugium using, most likely, the Lower Peninsula o f Michigan dispersal route from the southwest. Based on
the overall North American distribution of
this species, we propose the latter alternative as the more plausible. Our records suggest that intensive survey efforts in the
western half o f Essex County might further
clarify the provincial distribution o f C. robustus.
Cambarus diogenes probably entered
Ontario from the southwest, from the Mississipian Refugium, perhaps using the Fort
Wayne dispersal route. Given the presentday Ontario and North American distributions o f this species, however, including
western New York State (Pickett et al.,
1982; Hobbs and Jass, 1988), dispersal into
Ontario from the southeast also remains a
possibility. The considerable number of additional sites now known for C. diogenes in
New York State (W. Gall, personal communication) suggest that intensive survey
e f f o r t s in O n t a r i o ' s N i a g a r a P e n i n s u l a
might produce additional records of the
species.
Cambaru.s diogenes also entered Ontario,
perhaps more recently and possibly through
human intervention, at another, separate,
northern location (Rainy River District, approximately 50 km north o f the Minnesota
b o r d e r ) , e x p a n d i n g its r a n g e n o r t h w a r d
from Minnesota and Wisconsin. Fallicamb a r u s f o d i e n s apparently entered Ontario
from the southwestern tip o f the province,
using the Fort Wayne dispersal route f r o m
the Mississipian Refugium.
Constraints on Distribution
Physical habitat factors appear to exert a
strong influence on the range limits o f che
species considered in this study.
In Ontario, C. b. bartonii inhabits rapids,
cool fast-flowing streams, and many Precambrian Shield lakes (Berrill, 1978; Hamr
and Berrill, 1985). This species is never
found in large Ontario rivers south o f the
P r e c a m b r i a n S h i e l d ( C r o c k e r and Barr,
1968). Berrill (1978) reported collecting C.
b. bartonii in very shallow rapids below
certain dams in the Kawartha region of
southern Ontario. We have also collected
this species in rapids and near waterfalls in
the Oxtongue River-Ragged Falls area, near
the southwestern border of Algonquin Provincial Park.
In the United States, C. b. bartonii is restricted, for the most part, to cold mountain
streams with a rocky substrate (Crocker,
1957; DiStefano et al., 1991). Maude and
Williams (1983) showed that C. b. bartonii
can hold station in fast currents of up to 39
cm/s, thus confirming the adaptation of this
crayfish for fast-water habitats. The same
authors also found that C. b. bartonii was
the only one among eight Ontario crayfish
species tested (including C. robustus) that
clearly preferred a gravel substrate to a mud
substrate. We have collected this species
only on rocky, gravel-boulder substrates.
Burgess and Bider (1980) showed that the
modification of a section of stream, through
the addition of small dams made o f rocks,
led, after two years, to a 220% increase in
the biomass of C. b. bartonii in that area.
These environmental factors help explain
the current range limits o f C. b. bartonii in
Ontario. This species is c o m m o n in the fastwater streams and cool lakes found in and
around the Algonquin Provincial Park area,
but relatively rare south o f the Precambrian
Shield. At the southern edge o f its Ontario
range, we collected C. b. bartonii in small
numbers, only in the very cold, clear waters
o f the upper regions of two small tributaries
o f the Ganaraska River, near Kendal and
Garden Hill, respectively. C a m b a r u s b. bartonii was not found farther downstream in
this river system.
We have collected C. robustus in fastflowing sections o f large rivers (Conestogo
River, Credit River, H u m b e r River, M a d
River, and Speed River) as well as in smaller, fast streams (Duffin Creek and Centreville Creek), and, as in the case of C. b.
bartonii, in rapids and waterfalls downstream from dams (Elliot Falls on the Gull
River). In fact, Maude and Williams (1983)
showed that C. robustus is able to maintain
station at a current speed of 49.7 cm/s, a
value significantly higher than those for any
other crayfish species in Ontario, including
C. b. bartonii. Thus, C. robustus is ideally
suited for withstanding the rigors o f life in
fast-water streams and rapids.
While both C. b. bartonii and C. robustus
remain fairly c o m m o n in certain parts o f
Ontario, we have collected these species
mostly within protected areas inside provincial parks and conservation areas. In these
regions, by and large, riparian vegetation
surrounding the streams is well preserved
and the level o f water pollution and human
interference is generally lower than in other
areas of the province. At some of these
more sheltered locations, there is evidence
that healthy populations o f C. b. bartonii
and C. robustus have persisted over several
decades. For example, we have found C.
robustus, between 1992 and 1994, at the
Forks o f the Credit River at the same location where it had been previously found
in 1935, in Duffin Creek at the same location as in 1944, and in the Mad River, near
Singhampton, at the same location as in
1927. Similarly, a healthy population of C.
b. bartonii was found between 1992 and
1994 in the Oxtongue River, where this species had previously been recorded in 1963.
While the continuing success o f these crayfish populations over long periods of time
is encouraging, there are potential anthropogenic dangers to some o f the populations
of C. b. bartonii and C. robustus of Ontario.
These dangers will be discussed in more detail in the following section.
Crocker and Barr (1968) suggested that
the very limited distribution of C. diogenes
in Ontario may be due, in part, to competition with the ecologically similar F. fodlens. Norrocky (1991) found, however, that
the two species can coexist and share the
same burrows in north central Ohio. Thus,
while competition between the two species
remains a possibility, the very limited Ontario distribution of C. diogene.s could also
be due to other, as yet unidentified, environmental constraints.
Fallicambarus fodiens lives in woodland
ponds (Bovbjerg, 1952), wet meadows,
marshes (Crocker and Barr, 1968), and
drainage ditches. While this species prefers
stagnant waters, it can also be found in temporary streams in southern Ontario (Will i a m s e t al., 1974). F a l l i c a m b a r u s fodiens
is prevented from colonizing faster streams,
however, by its inability to maintain station
in currents faster than 26.7 cm/s, a relatively low mean slip-speed value (Maude and
Williams, 1983; Bovbjerg, 1952).
F a l l i c a m b a r u s fodien.s needs primarily
clay soils in order to burrow and build shelters (Crocker and Barr, 1968). Since most
o f Ontario, starting just north o f Lake Simcoe, is occupied by the hard rocks o f the
Precambrian (Canadian) Shield (Davidson,
1989), this species is probably unable to
find suitable habitats and expand its range
farther north.
Not surprisingly, given its natural habitat,
F. fodiens, which has a laterally compressed cephalothorax, an adaptation for
burrowing, prefers a m u d substrate to a
gravel one (Maude and Williams, 1983).
Crocker and Barr (1968) suggested that this
species is the c o m m o n burrowing crayfish
of southern Ontario and that the species
could actually be more widespread than its
known locality records would indicate,
since it is easy to overlook crayfish species
located in less traditional aquatic habitats,
such as drainage ditches or wet meadows.
That prediction is borne out by the current
study.
Anthropogenic Pressures
One o f the more serious potential pressures on crayfish species is the gradual
acidification o f certain lakes and streams
due to acid rain, particularly in southeastern
Ontario (DiStefano et al., 1991). Mature C.
b. bartonii and C. robustus are among the
most acid-tolerant of the fresh-water organisms tested. These two species are certainly
much more tolerant o f low pH values than
crayfishes of the genus Orconectes, fishes,
and aquatic insects (Berrill et al., 1985;
B e n d e l l - Y o u n g and H a r v e y , 1991; DiStefano et al., 1991). This suggests that, if
populations o f C. b. bartonii and C. robustus begin to be affected negatively by the
increasing
acidification of lakes and
streams, it may already be too late to save
most other fresh-water species in these habitats.
Juvenile and molting crayfish may be
more vulnerable to the acidification process
than larger, i n t e r m o l t i n d i v i d u a l s (DiStefano et al., 1991). In spite of its relatively high tolerance for acidic waters, C.
b. hartonii can be affected negatively by
low pH values. L o w pH values and p H
shifts from higher to lower values can impair the chemoreception o f food and also
lead to food avoidance in this species (Allison et al., 1992; Uiska et al., 1994). In
addition, the acid tolerance of crayfish is
higher at low water temperatures. Increasing water temperatures, over time, could
therefore, render these species more vulnerable to the effects of acid rain in the future (DiStefano et al., 1991).
There is some evidence suggesting that
the number o f available Ontario habitats for
F. f o d i e n s is shrinking. The species range
is also the most urbanized and industrialized part o f the province, as well as being
the center of most o f Ontario's agricultural
production. There is insufficient evidence to
suggest that the species is "threatened" in
Ontario. However, it may be termed a "vulnerable" species, one where the probability
of habitat destruction, and thus o f local extinctions, is high.
Reid (1989) estimated that as much as
7 0 - 8 0 % of the 2 - 2 . 4 million hectares o f
wetlands originally found in southern Ontario have been severely altered or destroyed altogether. This trend continues today, thus seriously reducing the available
habitat for all wetland fauna, including F.
fodiens and C. diogenes, in southern Ontario. Several o f the Toronto locations reported
by Crocker and Barr (1968), which used to
have colonies o f F. fodiens in the early and
mid-1960s, have since been developed for
industrial or commercial purposes. At the
same time, some areas within the jurisdiction of the Metropolitan Toronto and Region Conservation Authority, which formerly supported populations o f F. fodiens,
have now become unsuitable for these crayfishes, due to development (Lionel Normand, Environmental Technician, M T R C A ,
personal communication).
Furthermore, since the burrow o f each
a d u l t F. f o d i e n s a n d C. d i o g e n e s c a n h a v e
several
entrances
( C r o c k e r a n d Barr,
and
mud
chimneys
1 9 6 8 ; W i l l i a m s e t al.,
1 9 7 4 ) , it is d i f f i c u l t t o e s t i m a t e d i r e c t l y t h e
number
simply
of adults
present
counting
chimneys.
the
in a c o l o n y ,
number
W i l l i a m s e t al.
of
by
available
(1974)
reported
t h a t a l a r g e p e r c e n t a g e o f j u v e n i l e F. f o d i e n s p r e s e n t in a t e m p o r a r y s t r e a m in s o u t h ern Ontario failed to dig b u r r o w s into the
m u d as the w a t e r retreated b e l o w the surface.
As
a result,
all
these juveniles
per-
i s h e d . I f t h i s is a g e n e r a l t r e n d f o r p o p u l a tions o f F. f o d i e n s in Ontario, t h e n recruitment
for
this
species
is
fairly
low.
This
w o u l d l i m i t t h e a b i l i t y o f c o l o n i e s o f F . foodiens to recover quickly after severe envir o n m e n t a l d i s t u r b a n c e s . A s a r e s u l t o f all
the
aforementioned
factors,
the
long-term
f u t u r e o f b u r r o w i n g crayfishes in s o u t h e r n
Ontario
may
be
in d o u b t
unless
steps
are
t a k e n to identify a n d p r e s e r v e m o r e o f the
habitat around their colonies.
ACKNOWLEDGEMENTS
Julie Ray, Tuhin Giri (from 1 9 9 2 - 1 9 9 4 ) , and Erin
Uiska (in 1991) offered valuable assistance during
m a n y crayfish collecting trips and John Prideaux provided substantial assistance in recording collection
data in electronic form. Fieldwork was partially funded
by grants from the Environmental Youth Corps program, administered by the M i n i s t r y o f Natural Resources o f Ontario, to D W D . D. A. Jackson, H. H.
Harvey, and K. Ciruna generously m a d e several crayfish specimens from Clayton Lake available to us, and
K. M. S o m e r s of the Ontario M i n i s t r y o f the Environm e n t provided a suite o f recent samples from central
Ontario. W. Gall kindly discussed details o f his studies
of C. dio,qene.c in western N e w York State, and J.-M.
G a g n o n generously loaned specimens f r o m the Canadian M u s e u m of Nature. Dale Calder provided helpful
c o m m e n t s on an interim draft o f the manuscript. Funding during this study was provided by University o f
Toronto O p e n Doctoral Fellowships to R C G , by National Sciences and Engineering Research Council o f
C a n a d a grants to D W D and through Royal Ontario
M u s e u m operating funds to D W B .
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RECEIVED: 13 June 1995.
AccePTED: 25 A u g u s t 1995.
Addresses: (RCG, D W D ) D e p a r t m e n t o f Zoology,
University o f Toronto, 25 Harbord Street, Toronto, Ontario, C a n a d a M 5 S 1 Al ; ( D W B ) D e p a r t m e n t of Invertebrate Zoology, Royal Ontario M u s e u m , 100 Q u e e n ' s
Park, Toronto, Ontario, C a n a d a M 5 S 2C6.