Copyright 2006 Blackwell Munksgaard
Ecology of Freshwater Fish 2007: 16: 41–46
Printed in Singapore Æ All rights reserved
ECOLOGY OF
FRESHWATER FISH
The Coomasaharn char, a morphometrically
highly specialised form of Salvelinus alpinus
in Ireland
Cullen P, McCarthy TK, Doherty D. The Coomasaharn char, a morphometrically highly specialised form of Salvelinus alpinus in Ireland.
Ecology of Freshwater Fish 2007: 16: 41–46. 2006 Blackwell
Munksgaard
Abstract – A reputedly ‘unique’ Irish form of Arctic char, characterised by
its long and numerous gill rakers and referred to as Salvelinus fimbriatus
[Regan, The Annals and Magazine of Natural History 2 (1908) 225], has
long been known to inhabit Coomasaharn Lough in the south-west of
Ireland. However, this species description was based on a single specimen
and, in the intervening period, little research on the unusual gill attributes
of the char population has been published. In 2000, the char population of
the lake was surveyed by gill netting. The morphometrics of the head
region and the gill raker attributes of this population of Irish char were
compared with two other Irish char populations. The results of this analysis
highlighted the specialised morphology of the Coomasaharn char in an
Irish context and demonstrated the planktivorous nature of the
Coomasaharn char.
Introduction
The Arctic char population of Coomasaharn Lough
has been regarded as a separate species by several
authors (Kottelat 1997), since Regan (1908) assigned
it the specific name fimbriatus. The term fimbriatus
(‘fringed’) referred to the long and numerous gill
rakers, thought to be characteristic of Coomasaharn
char, which were noted in the single specimen
described by Regan (1908). Since the first description
in the early 1900s, many other references to the char of
this lake are in the form of capture records (Went
1945, 1971; Twomey 1960; Fitzmaurice 1977). The
unusual number of gill rakers was again noted by
Ferguson (1981), who included information on the
average number of gill rakers recorded in a sample of
15 char from the lake which he included in a study of
the systematics of Irish char as indicated by electrophoretic analysis. Finally, Quigley & Flannery (1997)
described a single specimen from the lake and some
ecological data were presented by Igoe & Hammar
doi: 10.1111/j.1600-0633.2006.00163.x
P. Cullen, T. K. McCarthy,
D. Doherty
Zoology Department, National University of
Ireland, Galway, University Road, Galway, Ireland
Key words: geometric morphometric analysis;
phenotypic variation; ecological specialisation
P. Cullen, Zoology Department, National University of Ireland, Galway, University Road, Galway,
Ireland; e-mail: paula@dspsrv.ch
Accepted for publication March 3, 2006
(2004). However, despite the unusual number of gill
rakers, no further scientific studies were carried out on
the gill morphology of the char of this lake. With these
facts in mind, this study investigates not only the
number but also the relative length of the gill rakers of
the Coomasaharn char by comparison with two other
populations of Irish char, and published data on other
Irish char populations. Differences in the morphology
of the three char populations are investigated by means
of geometric morphometric analyses.
Study area
Char were obtained from three Irish lakes as part of
this study. Coomasaharn Lough, a near pristine
oligotrophic corrie lake, is located in a sparsely
populated mountain valley in the Iveragh Peninsula
in Co. Kerry (Irish National Grid V6384). The lake,
along with other smaller loughs and oligo-dystrophic
pools, discharges via the small River Behy system to
Dingle Bay, about 9 km to the north. A bathymetric
41
Cullen et al.
survey of the lake, undertaken in September 2002
(McCarthy, unpublished data), revealed that the deeper
inner basin has a maximum depth of 62.6 m and that a
trough of just over 40 m was a feature of the outer
basin. Water clarity is extremely high, with Secchi disk
readings of about 10 m being typical. The lake
stratifies in summer with the deeper areas exhibiting
partial oxygen depletion. A hydroacoustic survey of
the fish stocks of the Coomasaharn Lough indicated
that the char are the dominant species in the lake,
which is also inhabited by brown trout Salmo trutta L.
and eel Anguilla anguilla L. (McCarthy, unpublished
data).
Dunlewy Lough (Irish National Grid B9019) is a
small (1.1 km2) lake, situated at 60 m.a.s.l. and about
15 km from the sea, in a relatively isolated river basin
in northwest Donegal. The lake, which is impounded
as part of a hydroelectric scheme, is classified as ultraoligotrophic or oligotrophic (McGarrigle et al. 2002).
The nutrient-poor, low ionic (conductivity generally
less than 60 lSÆm)1) waters and somewhat dystrophic
conditions are generally unproductive, resulting in low
algal densities. Likewise, aquatic macrophytes and
littoral/benthic macroinvertebrates only occur in low
numbers and biomass in the lake. The inner section of
the lake includes a deep area, which extends to 45 m
depth in places. In addition to char, this lake also holds
good stocks of trout and eel and salmon (Salmo salar
L.) are known to pass through its waters as they
migrate to and from upstream spawning and nursery
areas.
Eske Lough is situated in the north-west of Ireland
in Co. Donegal. It is an oligotrophic lake with a
surface area of 3.64 km2 and a maximum depth of
21 m. The major outflow from the lake is the Eske
River which flows in a south-west direction for a
distance of approximately 8 km before reaching the
sea in Donegal Bay. There is angling for small brown
trout, sea trout (anadromous S. trutta L.) and Atlantic
salmon on this lake and it is also one of the only lakes
in Ireland on which there is a tradition of angling for
Arctic char, which occurs in November when the fish
come inshore to spawn.
frozen prior to further analysis. Samples of 30 fish
from both Coomasaharn Lough and Dunlewy lake and
13 from Eske Lough were subsequently thawed,
length and weight measurements were taken and to
provide data for the geometric morphometric analyses,
the head region of the fish were then photographed
using an Olympus Camedia 3030C digital camera
(Olympus Ltd, London, UK) under natural light
conditions. The first gill arch was dissected out from
the left side of each fish, and counts made of both the
total numbers of gill rakers and the numbers present on
the lower gill arch alone. In addition, the length of the
lower gill arch and of the gill rakers attached to this
arch was measured with the aid of a dissecting
microscope. Comparison of measurements was carried
out using analysis of variance (anova).
For the geometric morphometric analysis, the
photographs of the bodies of the fish were first
compiled using the computer program tpsUtil (Rohlf
2002). The program tpsDig (Rohlf 2001) was then
used to digitally set the scale on each image and
digitise the set of 12 landmarks highlighted in Fig. 1.
To carry out a Procrustes analyses, the landmarked file
was imported in the computer program imp: CoordGen6 (Sheets 2002a). This program translated, rotated
and scaled the images to generate a series of Bookstein
coordinates for each fish. These coordinates were then
analysed by means of a canonical variates analysis
(CVA) using imp: CVAGen6 (Sheets 2002b). The
results were interpreted with the help of a vector
diagram which was generated using the same program
following a regression analysis of shape on the CVA
axis and which showed all the changes in shape that
were correlated with the CVA axis scores.
Results
The length–frequency distributions of the fish analyses
(Fig. 2) indicated that the sampled Coomasaharn fish
were slightly smaller in size (mean length 15.9 cm)
than those captured on the two other lakes, which held
similarly sized fish (Dunlewy Lough mean char
length 17.7 cm, Eske Lough mean char length
Materials and methods
As part of a survey on the char stocks of six Irish
loughs (McCarthy et al. 2004), the char of Coomasaharn were sampled in late August 2000 by benthic
variable mesh gill nets (mesh size ranging from 8 to
50 mm knot to knot, 60 m long · 1.5 m deep).
Subsequent to capture, char samples were individually
wrapped in plastic and frozen prior to further examination. Char populations in Eske Lough and Dunlewy
Lough were sampled by means of benthic set fyke
nets in late November 2002. These fish were also
42
Fig. 1. Location of the 12 morphometric landmarks on the body of
the char which were used in the morphometric analyses.
The Coomasaharn char
40
% Frequency
35
30
25
20
15
10
5
0
130–139 140–149 150–159 160–169 170–179 180–189 190–199 200–210 210–220
Length (mm)
Dunlewy L. (n=30)
L. Eske (n =13)
Fig. 2. Length–frequency distributions of the char samples from
Coomasaharn Lough, Dunlewy Lough and Eske Lough.
17.0 cm). Although the capture methods differed
between lakes, it was felt that the char captured during
the present study were typical of the adult populations
of the lakes studied. Previous sampling on Dunlewy
Lough by means of gill netting captured fish similar in
size to those recorded in this survey (mean length
17.6 cm; McCarthy et al. in press) and Doherty (1999)
recorded adult char from Eske Lough of similar size to
those recorded in this study (mean length 17.7 cm).
No discernable difference was noted in the length–
weight relationships of the fish from all three lakes
indicating similar condition factors in all three lakes.
Both gill raker number and measurements differed
significantly between the Coomasaharn char and the
other two populations measured (anova, P < 0.001).
In the case of the Coomasaharn char, a total of 27–30
gill rakers were counted. On the lower gill arch, 17–20
gill rakers were counted, with an average gill raker
length of 1.98 mm. In the case of the Dunlewy and
Eske char, 12–14 gill rakers were counted on the lower
gill arch (total 21–25) with mean lengths of 1.34 and
1.18 mm, respectively. When the lengths of the lower
gill arch were compared, there were no significant
differences between the three different populations,
indicating that the differences in gill raker numbers are
not an artefact of differences in length of the gill arch.
As can be seen in the graphical representation in
Fig. 3, the gill rakers of the Coomasaharn char appear
longer than those recorded in either the Dunlewy or
Eske char, although this difference is not significant.
Canonical variates analysis of the Bookstein coordinates of the three populations of char identified two
significant CVA axes (Fig. 4). A Mahalanobis distance-based approach was then used to determine the
predicted group membership of each of the individual
char based on the CVA scores. The predicted group
membership is determined by assigning each char
specimen to the group whose mean is closest (under
the Mahalanobis distance) to the specimen. This
Fig. 3. Graphic representation of the average length of the gill
rakers on the lower gill arch of Coomasaharn char (gill raker
number ¼ 17–20) and Dunlewy and Eske char (gill raker number ¼ 12–14).
0.02
0.015
0.01
CVA axis 2
Coomasaharn L. (n=30)
0.005
0
–0.02
–0.015
–0.01
–0.005
0
0.005
0.01
0.015
0.02
–0.005
–0.01
–0.015
–0.02
CVA axis 1
Coomasaharn L.
Dunlewy L.
L. Eske
Fig. 4. Results of the canonical variates analysis of the three char
populations. For each population, the average shape of an
individual within the sampled population is highlighted by a larger
open symbol.
analysis indicated that not only all of the char were
assigned to the correct groups by the CVA, but
significant differences in morphology also occur
between all three populations. In Fig. 5, a vector
diagram illustrates the deformation in shape implied
by the first main CVA axis, the axis that clearly
differentiates between the Coomasaharn char and the
Dunlewy and Eske char populations. Most of these
deformations in shape relate to the head and abdominal regions of the fish, with the greatest morphological differences noted in head shape. The
Coomasaharn char were shown to possess a much
more pointed head shape than either Dunlewy or Eske
char, which possessed more rounded blunt head
shapes.
43
Cullen et al.
Table 1. Details on the gill raker counts recorded during some studies on
Irish char populations.
0.3
No. gill rakers
0.2
0.1
0
–0.1
–0.2
–0.3
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
Fig. 5. Vector diagram highlighting the differences in morphology
of the char populations along the first major canonical variates
analysis axes.
Discussion
Although the ‘unique’ nature of the Coomasaharn char
was first noted in the early 1900s, little further
evidence was produced since that time to indicate
whether the differences in gill raker number and, in
particular, length noted by Regan (1908) were indeed
typical of the Coomasaharn char population. However,
it is clear from the present study that the Coomasaharn
char do indeed have longer and more numerous gill
rakers than the other Irish char populations studied.
When the results of gill raker number are compared
with the results of studies on Irish populations
(Table 1), it is clear that there is a clear distinction
between the char of Coomasaharn Lough and other
Irish populations. There is no overlap between the
number of gill rakers recorded in the Coomasaharn
char and the values recorded in any of the other
populations studied.
Differences in gill morphology linked to differences
in feeding ecology (Gerking 1994). Preliminary
stomach content analysis indicated that the Coomasaharn char were feeding exclusively on zooplankton
(McCarthy & Cullen, unpublished data), which was
also indicated in a study by Igoe & Hammar (2004).
The diets of the Eske Lough and Dunlewey Lough
char have been previously shown to be predominantly
planktonic while also feeding on benthic prey
(McCarthy, Cullen & Doherty, unpublished data).
Differences in the head shape of char have been well
documented in relation to feeding ecology, with a
blunt snout commonly associated with benthivorous
char and a pointed snout with planktivorous feeding
(Skúlason et al. 1999). Gill morphology also indicates
specialist planktivorous feeding in the Coomasaharn
char. The morphometric analyses indicated that
there are differences in the head region of the fish
44
Lake
No. fish Lower arch Total
Anscaul
Cloonasnacta
Coomasaharn
Coomasaharn
Coomasaharn
Conn
Conn
Corrib
Dunlewy
Eske
Eske
Finn
Inchiquin
Kindrum
Mask
Melvin
Melvin
Naback
Nacung
1
6
30
1
15
1
25
9
30
13
35
33
2
1
61
3
25
10
17
13
14.00
17–20
18
18.21
13
13.96
14.89
12–14
12–14
–
13.03
10–12
13
–
10–11
14.12
13.90
–
Reference
–
23.71
27–30
–
29.07
–
23.84
24.67
21–25
21–25
21–26
22.45
–
–
22–26
Quigley & Flannery (1997)
Ferguson (1981)
This paper
Quigley & Flannery (1997)
Ferguson (1981)
Twomey (1960)
Ferguson (1981)
Ferguson (1981)
This paper
This paper
Doherty & McCarthy (2000)
Ferguson (1981)
Twomey (1960)
Quigley & Flannery (1997)
Doherty & McCarthy (2000)
Twomey (1960)
23.20 Ferguson (1981)
23.90 Ferguson (1981)
21–25 McCarthy, Cullen & Doherty
(unpublished data)
Only mean values were given for these populations.
populations examined here, with the Coomasaharn
char tending towards the more pointed snout shape,
considered typical of planktivorous feeding (Skúlason
et al. 1999). When combined, the results of analyses
on gill attributes, the available information on feeding
ecology and the morphometric analysis of head shape
show that the Coomasaharn char can be considered to
be typical of the planktivorous feeding dwarf form of
char. Although differences in the morphology of the
abdominal region of the fish were recorded, these are
most likely due to the more advanced reproductive
state of the Dunlewy and Eske fish.
The Coomasaharn char appear to be highly specialised population of char in Ireland in respect of their
gill raker morphology, the feature that led to them
being original named Salvelinus fimbriatus. In this
respect, the Coomasaharn char are more similar to the
populations found in the Alpine regions of Europe and
those of the Kara Sea–Taimyr Peninsula (Behnke
1980). Behnke (1972) suggested that while the
Coomasaharn char may be derived from the same
ancestral char as all other Irish char and may have
developed its higher number of gill rakers while
inhabiting Coomasaharn Lough, it is more likely that it
represents a relict population of a distinct stock
differentiated in preglacial time in another region.
Arctic char populations, especially those at the
southern edge of the species range, are threatened by
environmental change of a variety of kinds, and in
several countries, the species is listed as vulnerable or
endangered (Whilde 1993; Keith & Allardi 1996;
Kirchofer & Hefti 1996; Maitland & Lyle 1996;
The Coomasaharn char
Alekseev & Pichugin 1998). In a number of regions,
char appear to be decreasing under the influence of
eutrophication (Johnson 1980). According to Johnson
(1980), the evidence indicates that the Arctic char is
the northern freshwater fish species most susceptible
to the results of eutrophication and consequently its
range is decreasing. In Ireland, despite the recent
additions of some newly reported populations, there
are generally large gaps in the knowledge of the
current status of char populations with many populations already extinct (Doherty & McCarthy 2000;
McCarthy et al. 2001; Igoe et al. 2003). Ferguson
(1981) advocated conservation of char stock in both
Ireland and Britain on the grounds of their having
persisted as glacial relicts for at least 10,000 years and,
as such, they represented excellent models for the
study of genetic changes in isolation. Bearing these
facts in mind, it is important, for conservation reasons,
that every effort be made to understand and protect
char stocks in general and the environment in which
they live, and especially such unusual populations as
the Coomasaharn char, isolated since their postglacial
colonisation of the lake as a pioneering anadromous
stock.
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