THE BIOLOGY, ECOLOGY AND FUTURE
CONSERVATION OF TWAITE SHAD (ALOSA
FALLAX LACÉPÈDE), ALLIS SHAD
(ALOSA ALOSA L.) AND KILLARNEY SHAD
(ALOSA FALLAX KILLARNENSIS TATE
REGAN) IN IRELAND
D. Doherty, N. O’Maoiléidigh and T.K. McCarthy
ABSTRACT
Anadromous twaite shad (Alosa fallax Lacépède) and allis shad (Alosa alosa L.) occur in Irish coastal
waters, although only twaite shad has been confirmed to reproduce in Ireland. A landlocked
subspecies of the twaite shad, known as the Killarney shad (Alosa fallax killarnensis ), occurs in Lough
Leane in south-western Ireland. Relatively little scientific research has been undertaken on the
marine phases of these species in Ireland except for occasional reports of coastal bycatch. The
growth, diet and parasite assemblages of twaite and allis shad sampled from Waterford Estuary and
the upper tidal reaches of the River Barrow have been investigated since 1995. Similarly, aspects of
the Killarney shad have been investigated since 1986. The number of gill rakers or general body size
easily separates these subspecies of shad. The perceived threats to the twaite, Killarney and allis shad
in Ireland, where they have been categorised as ‘vulnerable’ to extinction (twaite shad) and
‘endangered’ (Killarney and allis shad), are listed and discussed.
D. Doherty
(corresponding
author; e-mail:
denis.doherty@
mail.esb.ie),
Electricity Supply
Board, Ardnacrusha,
Co. Clare, (via
Limerick), and
Zoology Department,
National University of
Ireland, Galway;
N. O’Maoiléidigh,
Marine Institute,
Fisheries Research
Centre, Abbotstown,
Dublin 15;
T.K. McCarthy,
Zoology Department,
National University of
Ireland, Galway.
BIOLOGY
AND
INTRODUCTION
The genus Alosa is represented in the British Isles
by twaite shad (Alosa fallax Lacépède) and allis shad
(Alosa alosa L.). In addition, the Killarney twaite
shad or ‘goureen’ occurs in south-western Ireland.
This unique landlocked dwarf twaite shad was
assigned subspecific status in 1911 as Alosa fallax
killarnensis by Regan (1916) from a specimen taken
from Lough Leane, Killarney. Regan was of the
opinion that the specimen must have been part of a
colony of twaite shad that had remained in the lake
and now formed part of a non-migratory lacustrine
group (Regan 1916). Aprahamian et al. (2003)
suggested that the Lough Leane population existed
in isolation due to local tectonic changes. The only
other known European lacustrine twaite shad occur
in several of the northern Italian lakes, i.e. Alosa
fallax gracilis Regan in Lake Garda and A.f. lacustris
Fatio in Lakes Como, Lugano and Maggiore
(Trewavas 1938). Trewavas stated that the
‘goureen’ or lake herring, as they were known
locally, spend their entire life cycle in the lakes
without migrating to the sea. Despite heavy netting
by draft nets in the lower estuary of the Killarney
ENVIRONMENT: PROCEEDINGS
OF THE
lakes system over the past 30 years, there is no
evidence of a contemporary anadromous twaite
shad population in the lakes. In contrast, the
anadromous migratory shads of the Mediterranean
still enter Italian rivers and lakes inhabited by the
lacustrine form (Trewavas 1938).
A map of the current distribution of shad in
Ireland is shown in Fig. 1. There have been
occasional records from locations around the Irish
coast, and these have been referred to in general
accounts of rare and endangered Irish fishes
(Bracken and Kennedy 1967; Whilde 1993;
Maitland 1996). However, many of these records
are historical, and there is no clear knowledge of
their current distribution. Fahy (1982) analysed
variation in bycatch of A. fallax from net fisheries
in Wexford Estuary. O’Maoiléidigh et al. (1988)
examined the two forms of twaite shad using
electrophoretic and multivariate analyses of
their morphometric and meristic character sets.
Doherty and McCarthy (2001) investigated
aspects of the spawning anadromous twaite shad
and transitory non-spawning allis shad from
Waterford Estuary and the River Barrow. The
study involved aspects of the ecology, growth,
parasites, diet and fecundity of both species of
ROYAL IRISH ACADEMY, VOL. 104B, NO. 3, 93 /102 (2004).
#
ROYAL IRISH ACADEMY
93
BIOLOGY
AND
ENVIRONMENT
*
Fig. 1 /The location of twaite shad records in Ireland: 1. River Foyle; 2. Castletown River; 3. River Boyne; 4. Nanny
River; 5. River Liffey; 6. River Slaney; 7. River Barrow; 8. River Nore; 9. River Suir; 10. River Blackwater (Munster);
11. River Lee; 12. River Bandon; 13. River Ilen; 14. River Laune; 15. Lough Leane; 16. Dundalk Bay; 17 East of Lambay
Island; 18. Waterford Harbour; 19. River Eske, and 20. River Feale.
Allis shad have been captured occasionally from the Irish and Celtic Seas (Bracken and Kennedy 1967) and also from
Waterford Estuary (Doherty and McCarthy 2001). A detailed map of the St Mullins area on the River Barrow is also
shown, indicating the area fished during the annual shad fishing competition and the spawning site below the weir.
anadromous shad. In addition, their morphometric
and meristic character sets were also analysed using
multivariate analysis.
According to Whilde (1993), allis shad are
thought to be ‘endangered’, while twaite shad are
‘vulnerable’. Both species are much less common
than formerly over their European range, including
Ireland (Maitland 1996). Due to the decline in
abundance of Alosa spp, the species have been
included in Appendix III of the Bern Convention
and in Annexes II and V of the EU Habitats
Directive (Aprahamian et al. 2003). European
populations of allis and twaite shad are in decline
due to overfishing in estuaries, obstruction of river
migration by pollution, dams and weirs, and habitat
destruction resulting from pollution and
engineering works.
This paper aims to summarise the current
knowledge and status of the Alosa genus (two
species and one subspecies) and to review their
conservation status and discuss possible threats to
the shad species in Irish waters.
DIFFERENTIATION OF THE
THREE SHADS
All of the shads are members of the herring family,
Clupeidae . In general body form they are deepbodied and laterally compressed, with large, easily
detached scales. The number of gill rakers on the
94
first gill arch and the geographical location of the
subspecies effectively separate the two Alosa
species. Twaite shad have 35 /60 gill rakers
(depending upon size) and allis shad have 80 /155
(dependant upon size). Killarney shad have between
43 and 53 gill rakers (Wheeler 1969; Sabatié et al.
2000; Aprahamian et al. 2003). Extensive variation
and hybridisation have been recorded among
European populations (Alexandrio 1996). The
presence of hybrid fish in Ireland is thought to be
doubtful as there is no known Irish spawning site
for allis shad (Doherty 1999).
Apart from the obvious differences in body size
(the allis shad being larger), a combination of shape
differences in the morphometric character sets
allows for differentiation between the two
anadromous shad species on the basis of their
morphometric and meristic character sets
(Doherty and McCarthy 2001). O’Maoiléidigh
et al. (1988), in a comparative study of the two
forms of Irish twaite shad, reported that apart from
the dwarfed appearance of the lacustrine Killarney
shad and the increased number of gill rakers
carried on the first branchial arch, a broad overlap occurred in the meristic character sets.
Furthermore, no consistent shape differences were
observed between the two forms of twaite shad.
O’Maoiléidigh et al. (1988) reported that the
taxonomic position of the Killarney shad was
uncertain in that it differed phenotypically from
other twaite shad but displayed few genetic
BIOLOGY, ECOLOGY
Fig. 2a
*
Fig. 2b
*
/
AND
FUTURE CONSERVATIONS
Allis shad Alosa alosa . Reproduced with the kind permission of Peter Maitland.
/
Twaite shad Alosa fallax . Reproduced with the kind permission of Peter Maitland.
differences. These authors advocated the retention
of a subspecific name for Alosa fallax killarnensis
because it served to focus attention on a unique
Irish lacustrine population. More recently, Kottelat
(1997) suggested reclassifying Alosa fallax killarnensis
(Regan 1916) as a separate species and proposed
‘Alosa killarnensis Regan, 1916’ as the valid
scientific name.
ECOLOGY OF THE SHADS
GROWTH AND LIFESPAN
Twaite shad sampled from the River Barrow in
1996 and 1997 by Doherty and McCarthy (2001)
ranged from 202mm to 429mm in length and
182g to 1178g in weight and were 2 to 7 years old.
Allis shad sampled in 1996 and 1997 were larger
and older, ranging from 386mm to 504mm long
and 988g to 1775g in weight and were 5 to 9 years
old. The growth curves of Irish and European
populations of twaite and allis shad are shown in
Fig. 3. Growth of Irish twaite shad is broadly similar
to other European populations, though Quignard
and Douchement (1991) reported that growth
rates and longevity of both twaite and allis shad
varied with locality. The age and weight of a small
sample of allis shad from Waterford Estuary
indicated that these were the slowest growing and
smallest when compared with other European allis
shad populations as described by Quignard and
Douchement (1991). This may be due to the small
sample size (n /12) or because these were
occurring at the edge of their European range.
A gill-netting survey of Lough Leane carried
out in 1985 and 1986 captured Killarney shad from
3 to 5 years old. Back-calculated growth data
obtained from the 1985 and 1986 surveys of
Lough Leane are given in Table 1.
SPAWNING AND LIFE HISTORY
In Ireland, the only known spawning population of
anadromous twaite shad occurs in the upper tidal
limit of the River Barrow as shown in Fig. 1.
According to Doherty and McCarthy (2001), it is
doubtful that a spawning allis shad population
occurs within the Nore, Suir or Barrow rivers
discharging into Waterford Harbour because only
immature allis shad were captured in their study and
there is neither documented nor anecdotal evidence
95
of spawning. These allis shad probably represent
transitory non-spawning migrant fish. The nearest
known reproducing population is in northern and
western France (Quignard and Douchement 1991).
The spawning habits of both species of shad are
broadly similar, although there are some differences
in timing and location (Boisneau et al. 1992;
Alexandrio 1996). Both species enter the upper
reaches of large European rivers during the spring
months after reaching sexual maturity at 3/7 years
old (Boisneau et al. 1992; Assis 1990). In Ireland,
where only twaite shad are known to spawn,
mature fish enter the River Barrow from April
to June, with peak spawning activity occurring in
late May. Considerable variation in activity may
occur depending upon water temperature, tidal
strength and river flow. Mature males were
younger and significantly smaller than females
(Doherty and McCarthy 2001). Doherty (1999)
found that gravid female twaite shad on the
spawning site at St Mullins on the River Barrow
had a mean age of 5.6 years, compared to younger
males that were 2.95 years old. Sexual dimorphism
also occurred in the two shad species, the females
being significantly larger in size.
According to Quignard and Douchement
(1991) spawning usually occurred near a confluence, but may be anywhere along a river
where the current is fast enough and where the
bed is mainly gravel with a water depth of less than
1.5m. During the spawning period, adults moved to
the spawning grounds at night and left at the break
of day. According to Aprahamian et al. (2003)
water temperature ( /128C) is the most important
environmental factor moderating spawning
migratory behaviour. The description of French
spawning sites is similar to the River Barrow
spawning site as shown in Fig. 1. On
the River Barrow, spawning occurs immediately
downstream of the last navigation weir located
at the uppermost tidal limit (Doherty 1999).
Spawning usually begins at dusk and occurs
where the water depth generally ranges from
one to two metres. Eggs are released directly into
the water column, where they sink into the
gravel bed of the river, hatching 4 /8 days later.
The fry, which are approximately 10mm in length
upon hatching, grow rapidly and reach 14 /18cm
after one year (Maitland and Campbell 1992).
Adults return to the sea almost immediately after
spawning, whereas the young fish move
downstream to the estuary in the autumn
(Wheeler 1969; Claridge and Gardiner 1978;
Aprahamian 1988).
In 1996 and 1997, River Barrow twaite shad
congregating at the spawning site had gonad:
somatic index (GSI) values (mean9/standard
deviation) of 16.59/7.3 (18.89/7.5 for females
and 11.49/2.9 for males) (Doherty 1999). This
96
ENVIRONMENT
500
(a)
450
400
350
Length (mm)
AND
300
250
200
150
100
50
France (Loire)
France (Garonne)
France (Adour)
Ireland (R. Barrow)
0
1
2
3
4
5
6
7
Age (years)
500
(b)
450
400
350
Length (mm)
BIOLOGY
300
250
200
150
100
50
France (Loire)
France (Garonne)
France (Adour)
Ireland (R. Barrow)
0
1
2
3
4
5
Age (Years)
*
Fig. 3 /The growth in length of some European
populations (Quignard and Douchement 1991) of (a)
female and (b) male twaite shad along with twaite shad
sampled from Waterford Estuary and the River Barrow
(after O’Maoiléidigh 1990; Doherty and McCarthy 2001).
6
7
BIOLOGY, ECOLOGY
AND
700
600
Length (mm)
500
400
300
200
100
0
1
2
3
4
5
6
7
8
9
Age (years)
Loire, France
Duoro, Spain
Garonne, France
Waterford estuary, Ireland
Adour, France
*
Fig. 4 /The growth in length (mm) of some European
populations (Quignard and Douchement 1991) of allis
shad including a sample from Waterford Estuary (Doherty
and McCarthy 2001).
compares to 3.19/4.2 (3.69/4.5 for females and
0.49/0.0 for males) for a post-spawned estuarine
sample captured from Waterford Estuary in the
same years (Doherty 1999). According to Quignard
and Douchement (1991) the GSI of French and
Portuguese twaite shad populations increased
rapidly one or two months prior to spawning,
with high values reported at spawning time due to
the loss of somatic weight. However, Quignard and
Douchement (1991) stated that twaite shad GSI
values may differ from year to year and from site to
site, e.g. males (and females) of the Loire River had
GSI values of 7.8 (12.2); the Ardour River, 9.1
(16.4); and the Rhône River, 7.7 (18.7).
Annual variation of a twaite shad population is
evident in records of the annual twaite shad angling
competition on the River Barrow, which is
operated on a catch-and-release basis. The records
of the competitions, together with those of the Irish
Specimen Fish Committee (ISFC), may give an
indication of the annual variation in numbers
of spawning twaite shad in the River Barrow.
The ISFC maintains records of large rod-caught fish
referred to as ‘specimen’ (/0.964kg) twaite
shad. There was considerable interannual variation
Table 1
Range
n
FUTURE CONSERVATIONS
(Fig. 5) in the number of specimen twaite shad
reported by anglers from the River Barrow
between 1980 and 2001 (n /305, mean9/SD/
13.59/13.96, range 0 /41). Over 99% of these
shad were caught between March and June.
Catches are influenced by tidal cycles. No
specimen allis shad (/1.814kg) have been
recorded in Irish waters by the ISFC within the
past 46 years (ISFC 2001). The weight frequency
distributions of these specimen twaite shad are
shown in Fig. 6.
Lough Leane shad are reported to spawn on
gravel bars and gravelled shallows surrounding the
larger islands in the lake between June and early
July. However, the exact location of these sites is
unknown (O’Maoiléidigh 1990). The length of
Killarney shad sampled by gill nets of variable mesh
size in 1985 and 1986 was between 17.0cm and
22.4cm (Table 1). In both years the mean size of the
females was considerably larger than that of the
males. An examination of the scales of Killarney
shad showed a predominance of four-year-old fish.
Only one fish over five years was taken, and it is
likely that the life span of Killarney shad is quite
short. However, the population age structure was
not apparent for the 1985 or 1986 sampling
programmes, as the gill nets did not sample
the lower age groups. In contrast to the
anadromous twaite shad from the River Barrow,
the Killarney shad scales did not display the same
degree of spawning erosion on the scale edges. This
probably reflects the shorter migration and the less
exhaustive spawning activity of the Killarney shad
compared to the anadromous spawning run
(O’Maoiléidigh 1990).
The sex ratio of the Killarney shad did not
differ from a 1:1 ratio (Chi2 /3.4, P /0.063).
However, the sex ratios changed considerably
during the 1986 sampling period. Prior to
spawning, male fish dominated the samples;
subsequent to spawning, there was almost an
equal ratio of spent male and female fish.
DIET AND PARASITOLOGY
The variation in feeding intensity of spawning
French populations of twaite and allis shad
recorded by Quignard and Douchement (1991)
has also been noted in River Barrow twaite shad
(O’Maoiléidigh 1990; Doherty and McCarthy
* A comparison of back-calculated length at age of Killarney shad sampled during
1985 /6 (O’Maoiléidigh 1990).
/
L1 (cm)
L2 (cm)
L3 (cm)
L4 (cm)
L5 (cm)
2.5 /6.2
93
8.3 /15.0
93
14.5 /19.5
91
17.2/22.0
29
20.5
1
97
2001). Both of these studies reported that feeding
ceased during the spawning period. Doherty and
McCarthy (2001) reported that post-spawned
estuarine twaite shad sampled from Waterford
Estuary fed to a large extent on invertebrates,
although piscivory appeared to be particularly
important for the larger specimens of both shad
species. Adult twaite shad actively fed on marine
mysids Praunus neglectus (G.O. Sars), which formed
99.9% by number and 96.8% by weight of stomach
contents. The remainder of the diet was made up of
small sprats, Sprattus sprattus (L.). The relatively
larger allis shad, although fewer in number, also fed
extensively upon the marine mysid P. neglectus .
Three marine fish species*/whiting (Merlangus
merlangus (L.)), sprats and European smelt (Osmerus
eperlanus (L.)) were recorded in allis shad stomachs,
fish making up a significant proportion by weight of
the diet. A small number of shrimps, Crangon
allmani Kinahan, were also recorded (Doherty and
McCarthy 2001). In the River Severn, twaite shad
were found to feed upon a range of prey, with
preferential items being fish and secondary
items including mysids, shrimps, isopods, detritus
and other aquatic insects (Aprahamian 1988).
According to Quignard and Douchement (1991)
large allis shad are plankton feeders, with the main
food being copepods (Calanus sp.), decapods
(Pandalus sp.), euphausids (Meganyctiphanes sp.)
and young fish. Bracken and Kennedy (1967)
reported that the diet of adult twaite and allis shad
captured in the Irish Sea consisted of zooplankton
and small euphausids.
The parasite species assemblages, as recorded
by Doherty and McCarthy (2001) and listed
in Table 2, were found to be similar for both
anadromous Alosa species. All of the parasite
species were new Irish host records, although
they all had been previously reported from
other European twaite and allis shad populations
(Aprahamian 1985; Quignard and Douchement
1991). Differences noted in parasite species
infection levels of the two shad species may be
due to the specificity of the parasite or aspects of the
host fishes such as dietary preferences or
movements at sea.
Dietary analysis of Lough Leane Killarney shad
(n /32), sampled in a gill-netting survey in June
1985, demonstrated that stomach contents were
almost exclusively composed of zooplankton
(Table 3). Daphnia longispina Müller was found in
all stomachs that contained food. D. longispina
represented 93% of the total numerical abundance
of all food items (Table 3). The next most
important food items were copepods, which were
found in 82% of stomachs. Numerically they were
less important than the Daphnia spp (4.8%). The
pupating chironomids and ceratopogonids also
found were probably migrating through the water
98
ENVIRONMENT
45
40
35
No. of specimens
AND
30
25
20
15
10
5
0
1980
*
1982
1984
1986
1988
1990
1992
1994
1996
1998
2000
Year
Fig. 5 /A histogram showing the number of specimen
(/0.964kg) twaite shad recorded in Irish waters during
the period 1980 /2001. A total of 305 specimens were
captured on the River Barrow at St Mullins, while one
specimen was captured on the River Suir in 1992 (Irish
Specimen Fish Committee 2001).
45
40
35
Frequency (no. of f ish)
BIOLOGY
30
25
20
15
10
5
0
0.85 0.89 0.93 0.97 1.01 1.05 1.09 1.13 1.17 1.21 1.25 1.29 1.33 1.37 1.41 1.45 1.49 1.53
*
Weight (kg)
Fig. 6 /A histogram showing the weight frequency
distribution of all specimen twaite shad (n/305)
recorded in Ireland from 1980 /2001 (Irish Specimen
Fish Committee 2001).
column when eaten by the shad. Water mites and
Argulus spp also formed a small portion of the diet,
but whether they were deliberately selected or
ingested accidentally while feeding on plankton is
not clear.
The Italian lacustrine form of twaite shad
(Alosa fallax lacustris) was also found to feed
primarily on Daphnia (in this case Daphnia hyalina
Leydig) during the summer months (Berg and
Grimaldi 1966). However, from autumn to
spring, the diet was found to consist almost
entirely of copepods.
While evidence of piscivory has been noted
for Italian lacustrine shad and anadromous Irish
BIOLOGY, ECOLOGY
AND
FUTURE CONSERVATIONS
twaite shad, dietary analysis found no fish
eaten by Killarney shad (O’Maoiléidigh 1990).
Nevertheless, anglers using small spinning lures
often catch Killarney shad.
THE CURRENT STATUS, PERCEIVED
THREATS AND CONSERVATION OF
SHAD IN IRELAND
During the first half of the twentieth century,
twaite and allis shad were the main commercial riverine clupeids in Europe, with high
catches, greater than 100 metric tons, in the
North and Baltic Sea basins. Nowadays they have
declined or disappeared from many areas of Europe
(Assis 1990; Bervoets et al. 1990; Maitland and
Lyle 1990; Alexandrio 1996; Nicola et al. 1996;
Elvira et al. 1998; Aprahamian et al. 2003). The
general decline of the shads throughout their
Table 2
*
/
European range has been attributed to overfishing
in estuaries, obstruction of river migration and
habitat destruction by pollution and engineering
works. In Portugal, Assis (1990) recommended
remedial actions for twaite and allis shad on the
River Tagus, such as promotion of detailed studies
of the bioecology of the migrant populations under
threat, reduction of pollution levels, maintenance
of functional and efficient fishways, protection
(full and partial) of the spawning grounds,
creation of closed fishing seasons and recognition
of the need to establish fish hatcheries for restocking
purposes.
In Ireland, twaite and allis shad are not, like
many other rare and endangered fish species,
protected under any specific national legislation.
Such legislation is largely aimed at the conservation
of fish as an exploitable resource rather than as an
element of the native fauna (Doherty and
McCarthy 2004). Whilde (1993) designated twaite
Infection parameters of each parasite species recorded from samples of twaite and allis
shad sampled from the River Barrow and Waterford Estuary (Doherty and McCarthy
2001). The intermediate host of each parasite species is also indicated where
applicable.
Parasite species
Authority
Intermediate host
Monogenea
Mazocraes alosae
Hermann
Direct lifecycle
Digenea
Pronoprymna ventricosa
Diplostomum gasterostei
Rudolphii
Williams
Amphipods
Bivalves, molluscs,
gastropods
Bivalves, molluscs,
gastropods
Copepods
Diplostomum spathaceum
Rudolphii
Hemiurus appendiculateus
Rudolphii
Nematoda
Hysterthylacium osculatum
Rudolphii
Hysterthylacium aduncum
Rudolphii
Crutaceans, other
fish species
Crutaceans, other
fish species
Spawning
freshwater
twaite shad
(n /60)
Post-spawned
estuarine
twaite shad
(n/6)
Allis shad
(n /12)
Abundance
Abundance
Abundance
43.4
58.2
83.7
353.1
1.3
76.2
7.2
2.7
0.5
10.5
8.0
0.8
5.6
5.0
27.9
7.6
2.2
2.8
36.9
9.2
30.9
Absent
Cestoda
Eubothrium fragile
Rudolphii
Copepods
1.1
0.5
Crustacea
Clavellisa emarginata
Kroyer
Direct lifecycle
2.6
2.5
0.1
99
BIOLOGY
AND
shad as ‘vulnerable’ and the Killarney and allis shad
as ‘endangered’ in the Red Data Book of Irish
vertebrates. The incorporation of Alosa populations
into the EU Habitats Directive places an obligation
on members of the European Union to assess
numbers and exploitation of the populations and
to designate Special Areas of Conservation (SACs)/
Sites of Community Interest (SCIs) to safeguard
populations (Aprahamian et al. 2003).
At sea both Alosa alosa and Alosa fallax are
coastal in habit and are clumped in aggregations
around the major catchments for reproduction
(Aprahamian et al. 2003). Twaite and allis shad
are occasionally captured by commercial salmon
drift-net fishermen during March /July within
Waterford Estuary and for the most part are
returned unharmed to the estuary. A relatively
large annual catch (0.4 tonnes) of twaite shad was
reported by Fahy (1982) on the River Slaney in
County Wexford. Though adequate information is
not available, it appears that the bycatch is not as
great in Waterford Estuary (Doherty and McCarthy
2001). In the River Slaney, twaite shad are captured
by ring and snap nets, which use smaller mesh
sizes (44 /125mm) compared to the drift nets
(119 /125mm) used within Waterford Estuary
(Fahy 1982; Doherty and McCarthy 2001). In
Ireland the capture of either shad species as
bycatch by netsmen is not usually reported. Thus
the extent of the migrant estuarine twaite and allis
shad elsewhere is unknown and the significance of
bycatch levels for both species of shad within Irish
estuaries and in adjacent coastal waters is difficult to
quantify, as no reliable records are kept. However,
anecdotal evidence of bycatch from the salmon
(Salmo salar L.) drift- and snap-netting fisheries of
Waterford Estuary and the Munster Blackwater
Table
3
*
Food Group
Stomach content analysis of
Killarney shad (n /32) captured
in June 1985 (O’Maoiléidigh
1990).
/
No. of
food
items
Daphnia spp
29,904
Copepoda
1529
Argulus spp
7
Water mites
10
Dipteran pupae
8
Ceratopogonids
2
Shad scales
5
Pupating chironomids
19
100
%
%
occurrence number
100.0
82.1
14.3
25.0
14.3
7.1
17.8
35.7
93.20
4.76
0.02
0.03
0.03
0.01
0.02
0.06
ENVIRONMENT
indicate that the levels of bycatch are very low
(M. Doherty and M. O’Keefe, pers. comm.).
Threats to the shad species in Ireland are similar
to those described for Irish populations of European
smelt (Doherty and McCarthy 2004) and include
deteriorating water quality and habitat degradation.
These threats apply especially to the localised River
Barrow twaite shad spawning population and the
freshwater population of Killarney shad in Lough
Leane. The reversal of long-term nutrient
enrichment on Lough Leane is a priority to
protect the population of Killarney shad. The
presence of excessive filamentous algal growths
overlying littoral gravel areas may impede
spawning shad or inhibit intragaseous exchange in
the developing eggs, and recently hatched juveniles
may become enmeshed in the material and may
die as a result. The presence of such excessive
algal growth as an overlay is due to Lough Leane
being moderately eutrophic (Lucey et al. 1999).
The clear identification of spawning sites within
Lough Leane and the protection of such sites from
the effects of possible development works and
factors such as declining water quality are
priorities to ensure the long-term survival of the
Killarney shad.
According to de Groot (1990) the possible
restocking of the River Rhine with A. fallax was
being reviewed. If needed, this same approach
could be implemented for the Lough Leane and
River Barrow spawning populations of twaite shad.
The effects of exotic freshwater fish
introductions on native Spanish species have been
reported by Elvira and Almodóvar (2001). They
reported that competition between exotic and
native species was certain to occur, at least to
some degree, but that there was little quantitative
information about these interactions. Similarly, the
effects of exotic freshwater fish introductions in
Ireland and the subsequent spread through
freshwater catchments are very difficult to
determine. Information, education and public
awareness are critical components of any effort to
prevent the spread of introduced fish species
(Elvira and Almodóvar 2001). Three species of
fish were numerically predominant in the 1985 and
1986 gill-netting surveys of Lough Leane. These
were brown trout Salmo trutta L., Killarney shad
and perch, Perca fluviatilis L. (O’Maoiléidigh 1990).
More recently, cyprinids such as roach,
Rutilus rutilus L., and roach /bream hybrids
(Abramis brama L.) are known to be present
within Lough Leane (D. O’Teangeanna, pers.
comm.), and these may represent a threat to
the planktonivorous population of Killarney shad.
Likewise, the competitive effect of introduced
non-indigenous freshwater fish species such as
roach on endangered fish species such as Arctic
char, Salvelinus alpinus L., may be linked to the
BIOLOGY, ECOLOGY
AND
extinction of some char populations, such as those
of Lough Corrib (Doherty and McCarthy 2000). A
similar situation may also occur for other
endangered Irish freshwater species such as the
pollan Coregonus autumnalis Pallas (Harrod et al.
2001), which occurs in Lough Neagh.
ACKNOWLEDGEMENTS
The assistance of the zoology staff of the National
University of Ireland, Galway, the Central Fisheries
Board and South-Western Fisheries Board, the
Cheekpoint drift-net fishermen and St Mullins
anglers is gratefully acknowledged. Details of the
specimen twaite shad were provided by the Irish
Specimen Fish Committee (ISFC).
REFERENCES
Alexandrio, P. 1996 Genetic and morphological
differentiation among some Portuguese populations of allis Alosa alosa (L. 1758) and twaite shad
Alosa fallax (Lacépède, 1803). Publication Especiale
Institute Espana Oceanography 21, 15 /24.
Lucey, J, Bowman, J.J., Clabby, K.J., Cunningham, P.,
Lehane, M., MacCarthaigh, M., McGarrigle, M.L.
and Toner, P.F. 1999 Water quality in Ireland
1995 /1997. Environmental Protection Agency,
Wexford, Ireland.
Aprahamian, M.W. 1985 The effect of the migration
of Alosa fallax fallax (Lacépède), into freshwater, on
branchial and gut parasites. Journal of Fish Biology 27,
521 /32.
Aprahamian, M.W. 1988 The biology of the twaite
shad Alosa fallox fallax (Lacépède), in the Severn
Estuary. Journal of Fish Biology 33A, 141 /52.
Aprahamian, M.W. 1989 The biology of the twaite
shad Alosa fallax fallax (Lacépède), in the Severn
Estuary. Journal of Fish Biology 33A, 141 /52.
Aprahamian, M.W., Aprahamian, C.D., Baglinière, J.L.,
Sabatié, R. and Alexandrino, P. 2003 Alosa alosa
and Alosa fallax spp. Literature Review and
Bibliography. R&D Technical Report W1 /
014/TR. Bristol. Environment Agency.
Assis, C.A. 1990 Threats to the survival of
anadromous fishes in the River Tagus, Portugal.
Journal of Fish Biology 37A, 225 /6.
Berg, A. and Grimaldi, E. 1966 Biologia del agone
(Alosa finta lacustris ) del Lago Maggiore. Memorie
dell’Instituto Italiano di Idrobiologia 20, 41 /83.
Bervoets, L., Coeck, J. and Verheyen, R.F. 1990 The
value of lowland rivers for the conservation of
rare fish in Flanders. Journal of Fish Biology 37A,
223 /4.
Boisneau, P., Mennesson-Biosneau, C. and Guyomard,
R. 1992 Electrophoretic identity between allis
shad, Alosa alosa (L.) and twaite shad, A. fallax
(Lacèpéde). Journal of Fish Biology 40, 731 /8.
FUTURE CONSERVATIONS
Bracken, J. and Kennedy, M. 1967 Notes on some
Irish estuarine and inshore fishes. Irish Fisheries
Investigations, Series B 3, 1 /28.
Claridge P.N. and Gardiner, D.C. 1978 The growth
and movements of the twaite shad, Alosa fallax
(Lacépède), in the Severn Estuary. Journal of Fish
Biology 12, 203 /11.
de Groot, S.J. 1990 The former allis and twaite shad
fisheries of the Lower Rhine, the Netherlands.
Journal of Applied Ichthyology 6, 252 /6.
Doherty, D. 1999 Studies on the parasite assemblages
and general biology of some rare and endangered
Irish fishes. Unpublished PhD thesis, National
University of Ireland, Galway.
Doherty, D. and McCarthy, T.K. 2000 The
metazoan parasites, diets and general biology of
arctic char, Salvelinus alpinus L., in two Irish Lakes.
Archives für Hydrobiology: Special Advances in
Limnology 27, 1056 /61.
Doherty, D. and McCarthy, T.K. 2001 Aspects of the
ecology, parasites and future conservation of twaite
shad (Alosa fallax Lacépède) and allis shad (Alosa
alosa L.) in south-eastern Ireland. In M. Jungwith,
S. Schmutz and S. Weiss (eds), Freshwater fish
conservation */options for the future, 98 /112.
Vienna. Fishing News Books.
Doherty, D. and McCarthy, T.K. 2004 The ecology
and conservation of European smelt (Osmerus
eperlanus L.) from waterford estuary, in southeastern Ireland. Biology and Environment: Proceedings
of the Royal Irish Academy 104B, 125 /30.
Elvira, B., Nicola, G.G. and Almodóvar, A. 1998 A
catalogue of fish passes at dams in Spain.
In M.J. Collares-Pereira, M.M. Coelho and
I.G. Cowx (eds), Fish migration and fish bypasses ,
203 /7. Vienna. Fishing News Books.
Elvira, B. and Almodóvar, A. 2001 Freshwater fish
introductions in Spain: facts and figures at the
beginning of the 21st century. Journal of Fish
Biology 59A, 323 /31.
Fahy, E. 1982 A commercial net fishery taking twaite
shad Alosa fallax (Lacépède), in the estuary of
the River Slaney. Irish Naturalists’ Journal 20 (11),
498 /500.
Harrod, C., Griffiths, D., McCarthy, T.K. and
Rosell, R.S. 2001 The Irish Pollan, Coregonus
autumnalis: options for its conservation. Journal of
Fish Biology 59A, 339 /55.
Irish Specimen Fish Committee 2001 Irish Specimen
Fish 2000. Annual report of the Irish Specimen Fish
Committee. Central Fisheries Board, Dublin.
Kottelat, M. 1997 European Freshwater Fishes.
Biologia Bratislavia 52, 1 /271.
Maitland, P.S. 1996 Threatened fishes of the British Isles,
with special reference to Ireland . Dublin. Royal Irish
Academy.
Maitland, P.S. and Campbell, R.N. 1992 Freshwater
Fishes. London. Harper Collins.
Maitland, P.S. and Lyle, A.A. 1990 Practical
conservation of British fishes: current action on
six declining species. Journal of Fish Biology 37A,
255 /6.
Nicola, G.G., Elvira, B., and Almodóvar, A. 1996
Dams and fish passage facilities in the large rivers of
101
BIOLOGY
AND
Spain: effects on migratory species. Archive für
Hydrobiology Supplement 113 (1 /4), 375 /9.
O’Maoiléidigh, N. 1990 A study of fish populations
in the Killarney lakes. Unpublished PhD thesis,
University College, Dublin.
O’Maoiléidigh, N., Cawdrey, S., Bracken, J.J. and
Ferguson, A. 1988 Morphometric, meristic
character and electrophoretic analyses of two Irish
populations of twaite shad, Alosa fallax Lacépède.
Journal of Fish Biology 32, 355 /66.
Quignard, J.P. and Douchement, C.L. 1991
The freshwater fishes of Europe volume 2 Clupeidea,
Anguillidae . H. Hoestlandt (ed.), 89 /126, 25 /53.
Wiesbaden, Germany. AULA /Verlag GmbH.
Regan, C.T. 1916 The British fishes of the subfamily Clupeidae and related species in other seas.
102
ENVIRONMENT
Annual Magazine of the Natural History Service 18,
1 /18.
Sabatié, M.R., Boisneau, P. and Alexandrino,
P. 2000 Variabilité Morphologique. In J.L.
Baglinére and P. Eloe (eds), Les Aloses (Alosa alosa
et Alosa fallax spp.). Ecobiologie et variabilite des
populations , 137 /78. Paris. INRA-CEMAGREF.
Trewavas,
E. 1938 The
Killarney
shad
or
‘Goureen’ (Alosa fallax killarnensis, Regan
1916). Proceedings of the Linnaen Society 150 (2),
110 /12.
Wheeler, A. 1969 The fishes of the British Isles and north
west Europe . London. Macmillan.
Whilde, T 1993 Threatened mammals, birds, amphibians
and fish in Ireland. Irish Red Data Book 2:
Vertebrates. Belfast. HMSO.
The subvention
granted by the
National University of
Ireland, Galway,
towards the cost of
publication of papers
by members of its
staff is gratefully
acknowledged by
the Royal Irish
Academy.