www.elsevier.nlrlocateraqua-online
An evaluation of the use of triploid Atlantic salmon
ž
Salmo salar L. in minimising the impact of
/
escaped farmed salmon on wild populations
D. Cotter
a,), V. O’Donovan
a, N. O’Maoileidigh
´
b, G. Rogan
a,
N. Roche
c, N.P. Wilkins
ca
Salmon Research Agency of Ireland, Newport, Mayo, Ireland
b
Marine Institute Fisheries Research Centre, Abbotstown, Dublin, Ireland
c
Department of Zoology, National UniÕersity of Ireland, Galway, Ireland
Accepted 18 November 1999
Abstract
The impact of escaped farmed salmon on wild populations may have potentially negative genetic and ecological effects. There is widespread evidence that farmed salmon interact with wild salmon. The use of sterile fish in culture has been proposed as a means of eliminating genetic interaction and minimising the ecological effect of farmed salmon. In this study, the migration behaviour of groups of triploid salmon were investigated through the controlled release of microtagged triploid and diploid stocks on the western coast of Ireland. Mixed-sex and all-female stocks of ranched grilse origin were triploidised using hydrostatic pressure. Smolts were ranched from the hatchery of origin and two groups of post-smolts were released from cages in a marine site. The return of adult salmon from these experimental release groups to coastal and freshwater capture sites was monitored as part of the Irish national coded wire tag recovery programme. The return of triploid salmon from each of the release groups, both to the coast and to fresh water, was significantly reduced compared to diploid salmon. The highest percentage return to fresh water
Ž2.25% was in the ranched mixed-sex diploid group. In contrast, no salmon from the cage release.
groups returned to the hatchery location on the Burrishoole river system and recoveries in other
Ž .
freshwater systems were low -0.01% . The return of a small number of hormonally deficient, sterile triploid female fish suggests that migration to fresh water is not inextricably linked with reproduction. The substantially reduced return of hormonally competent triploid males to the coast and to fresh water, indicates that other factors may have an effect on their marine survival. The
)Corresponding author. Tel.:
q353-98-41112; fax:q353-98-41112.
Ž .
E-mail address: [email protected] D. Cotter .
0044-8486r00r$ - see front matterq2000 Elsevier Science B.V. All rights reserved.
Ž .
reduced return of triploid salmon to the coast and to fresh water, together with their inability to produce viable offspring, demonstrates the potential for triploidy as a means of eliminating genetic interactions between cultured and wild populations, and of reducing the ecological impact of escaped farmed fish.q2000 Elsevier Science B.V. All rights reserved.
Keywords: Triploid; Atlantic salmon; Migration; Escapes
1. Introduction
In recent years, concerns have been expressed about the genetic and ecological
Ž .
consequences of interaction between wild and cultured Atlantic salmon Salmo salar L.
ŽHindar et al., 1991; Saunders, 1991; Heggberget et al., 1993; Ferguson et al., 1995 ..
The escape of cultured salmon and subsequent interaction with wild salmon in rivers
Ž
has been widely reported Gausen and Moen, 1991; Webb et al., 1991; Carr et al.,
.
1997 . Evidence of genetic changes in wild salmon populations has been demonstrated in recent studies, where adult farmed salmon are known to have escaped and interbred
Ž .
with wild salmon in adjacent rivers Crozier, 1993; Clifford et al., 1998 . The ecological and behavioural interactions between cultured and wild salmon were reviewed by
Ž .
Jonsson 1997 , highlighting differences in migration behaviour and reproductive suc-cess.
Commercially farmed salmon are frequently derived from non-indigenous sources that have been selectively bred for production traits, such as rapid growth and late
Ž .
maturity Gjedrem et al., 1991; Friars et al., 1996; Gjoen and Bentsen, 1997 . Escapes of commercial stocks are considered to present a potential genetic threat to wild popula-tions, particularly to small indigenous populations in local rivers, where interbreeding could result in significant genetic change. Where adaptive differences exist between native and cultured salmon, interbreeding may lead to an overall reduction in survival
Ž .
and recruitment in the native population Verspoor, 1997 . Genetic changes can also occur indirectly through competition, which may cause a reduction in the effective
Ž
population size, resulting in inbreeding and loss of genetic variability Hindar et al.,
.
1991 .
The use of sterile fish in culture has been proposed as a measure to minimise the
Ž
genetic impact of cultured salmon on wild populations Hindar et al., 1991; Anon.,
.
1994; Hansen and Youngson, 1998 . Few published data are available on the behaviour of sterile fish, but a study on the migratory behaviour of hormone-sterilised coho salmon
ŽOncorhynchus kisutch Walbaum found that they remained in the marine environment.
ŽSolar et al., 1986 ..
The most effective method of the sterilisation of Atlantic salmon is high pressure
Ž .
induction of triploidy in newly fertilised eggs Johnstone et al., 1991; Johnstone 1998 .
Ž .
In diploid fish, the cell nucleus contains two sets of chromosomes 2N . However, in
Ž .
triploid fish, a third set of chromosomes 3N is retained in the cell nucleus resulting in functionally sterile fish. Although there are many similarities between triploid and diploid fish, there are basic differences which are addressed in a review by Benfey
The objective of this study was to evaluate the potential use of triploid salmon in minimising the genetic and ecological impact of farmed salmon on wild populations. The return migration to Irish coastal waters and to fresh water of triploid salmon was monitored through a controlled release programme. Triploid cultured salmon and diploid controls, which had been microtagged, were released from freshwater and marine release sites. The retrieval of tag data was made possible by the Irish national coded wire tag recovery programme, which was initiated in 1980 to estimate the marine survival of Irish salmon stocks and exploitation rates by high seas fisheries and home water
Ž .
commercial and recreational fisheries Browne, 1982 .
2. Materials and methods
2.1. Stock origins
Experimental groups were produced in December 1994 at the Salmon Research
Ž .
Agency of Ireland SRAI hatchery facilities located on the Burrishoole river system in
Ž . Ž .
Newport, Co. Mayo, Ireland. Mixed-sex MS and all-female AF salmon stocks were produced using ova from 32 females of ranched Burrishoole grilse origin. This stock has been line-bred in an ongoing experimental ocean ranching programme since the early
Ž .
1970s Piggins and Mills, 1985 . The pooled ova were divided into two groups. The MS stock was produced by fertilising half of the ova with milt from 22 ranched Burrishoole grilse males. The AF stock was produced by fertilising the remaining ova with milt from three sex-inverted ranched Shannon grilse males from the Parteen hatchery located on the river Shannon, Co. Limerick.
2.2. Triploidisation and ploidy assessment
A proportion of the MS and the AF fertilised ova were exposed to hydrostatic
Ž .
pressure to induce triploidy, after Benfey and Sutterlin 1984 . Ova were subjected to
9500 psi for a period of 5 min, 3008min post-fertilisation. Subsequently all four groups
ŽMS and AF diploid 2N and triploid 3N groups were subject to the same husbandryŽ . Ž . .
practices.
Ploidy levels were determined in pre-smolts to assess the success rate of the triploidisation procedure. Blood smears were allowed to air dry on slides and were fixed
Ž .
in methanol for 5 min. The blood smears were stained in 5% Giemsa pH 6.8 for 45 min at room temperature, rinsed in running water and air dried. The slides were then
Ž .
mounted in DPX Gurr . Major cell axis measurements of 10 erythrocytes per sample were made under oil immersion. The validity of using major cell axis measurements to
Ž .
assess triploidy was confirmed by Benfey et al. 1984 . In the case of returns to fresh
Ž
water, where it was impossible to infer ploidy level from gonad status i.e., in the case
.
2.3. Tagging
Diploid and triploid pre-smolts were microtagged and cold branded ‘X’ and ‘O’,
Ž .
respectively in February 1996. Precocious males 2.7% were removed from the MS2N
Ž .
stock. Pre-smolts were microtagged according to the methods of Browne 1982 . Each magnetised microtag had a specific code, which identified the release group, stock and ploidy of the fish. The adipose fin was removed to facilitate identification of these fish in the recovery programme. A quality control check was made on tagged fish to ensure that tags were correctly magnetised. Prior to release or smolt transfer, tag loss was estimated and subsequent analysis was based on numbers of tagged fish migrating.
2.4. Release sites
Ž .
Two release sites on the western coast of Ireland were used in this study Fig. 1 :
Ž X X
. Ž X X
.
Lough Furnace 9855 W, 53835 N , Co. Mayo and Inver Bay 8818 W, 54838 N , Co.
Donegal. Lough Furnace is a tidal lake adjacent to the SRAI’s hatchery installations, at the lower end of the Burrishoole river system. Inver Bay, Co. Donegal, is the site of a
Ž .
Fig. 1. Map of Ireland showing: ' the ranched release site at Lough Furnace, Co. Mayo on the Burrishoole
Ž .
commercial aquaculture operation located approximately 150 km northeast of the Burrishoole system. Cage structures are situated 1 km from the shore in Inver Bay within Donegal Bay.
2.5. Release groups
Diploid and triploid fish were released as three groups in 1996. These were categorised as ranched release, cage release I and cage release II groups. The release
programme is outlined in Table 1. Ranched release groups were released as 1qyear-old
smolts into Lough Furnace. Cage release groups were transferred as smolts to Inver Bay in April 1996 and released as post-smolts in May and June.
2.6. Coded wire tag recoÕery
Information on capture location and return data of the experimental groups was gathered as part of an ongoing Irish national coded wire tag recovery programme.
Ž .
Catches from coastal commercial fisheries drift nets, draft nets, etc. were monitored at 15 major salmon landing ports in Ireland. These fisheries operate between May and July inclusive and catches were scanned consistently during this period. Marine fishery areas from which coded wire tags were recovered are shown in Fig. 1. Declared landings in each of the corresponding areas were collected by seven regional fisheries boards and compiled into a national data set by the Marine Institute. Landings were also monitored by the Foyle Fisheries Commission and tag recovery information was supplied by the
Ž .
Department of Agriculture for Northern Ireland DANI . During the course of this study, no microtags were reported at Faroes or Greenland where limited sampling programmes were implemented. Over 50% of the catch landed in Ireland is sampled for tags each
Ž .
year. The number of tagged salmon taken in these fisheries ‘‘raised’’ data was
estimated by multiplying the actual number of tagged salmon in each area by the ratio of the total declared salmon landings in these areas to the sample size examined. An
Table 1
The release date, release location, stock–ploidy combination and the number of fish migrating for each release group
AFsall-female, MSsmixed-sex.
Ž .
Release group Date Location Stock Ploidy n
Ranched release 25 April 1996 Lough Furnace, Co. Mayo MS 2N 4897
MS 3N 4867
AF 2N 4860
AF 3N 4801
Cage release I 30 May 1996 Inver Bay, Co. Donegal MS 2N 1061
MS 3N 1084
AF 2N 1065
AF 3N 1086
Cage release II 30 June 1996 Inver Bay, Co. Donegal AF 2N 1632
adjustment for non-catch fishing mortality due to losses from nets and non-reporting of catches was also applied.
Complete upstream and downstream trapping facilities of the SRAI, situated on the Burrishoole river system in Co. Mayo, ensured an accurate count of the numbers of tagged adult salmon returning to the hatchery location. The number of fish entering the river was derived from total trap data and angling for the Burrishoole system. In addition to the Burrishoole system, the trap and angling catches from 13 other rivers systems were monitored for the presence of tagged salmon to indicate the prevalence of straying. For fresh water, the percentage return was calculated using the actual number of tags recovered divided by the number of fish migrating.
Ž .
The total number of one sea-winter 1 SW salmon returning to the Irish coast is the sum of all fish taken by the coastal commercial nets, the non-catch fishing mortality, the
Ž .
number surviving to enter fresh water angling and trap data , and finally, the number of tagged fish which may have strayed into other rivers. It was assumed that the tags were randomly distributed throughout the fishery and that non-recognition or non-detection of tags was minimal. The percentage return of tagged fish to the coast is then expressed in relation to the number of tagged smolts that migrated.
2.7. Data collection and analysis
Ž . Ž .
Length cm , weight kg , and sex were recorded for a subsample of the returned fish. Gonad weight was recorded for all triploid and a proportion of diploid returns to the
Ž .
Burrishoole traps from July to 24 September 1997. The gonadosomatic index % was
Ž .
calculated as: gonad weightrbody weight =100. Condition factor was calculated as
Ž .3
W=100r L , where W is body weight converted to grams and L is the fork length in
centimetres. Data on all the tags recovered for each microtag code, e.g., the recovery location, date of capture and size, were reported through the national coded wire tag recovery programme.
Observed vs. expected return rates were compared using the x2 statistic. A one-way
ANOVA was used to detect the differences between ploidy levels and also between
stock types with respect to weight, length, and condition factor. Hartley’s Fmaxtest was
used to test for homogeneity of variance. In cases where the assumption was violated a
non-parametric Mann–Whitney U-test was used. A significance level of P(0.05 was
adopted.
3. Results
3.1. Tag recoÕery
The number of 1 SW tagged fish recovered in coastal commercial fisheries for each
Ž .
experimental group is shown as actual and ‘raised’ data Table 2 .
Table 2
Ž .
The actual and raised numbers of one sea-winter Atlantic salmon 1 SW coded wire tag recoveries from Irish coastal commercial nets and fresh water
The tag recoveries in fresh water were all from the Burrishoole trap with two exceptions. See Table 1 for abbreviations.
Release group No. migrating Coastal commercial Fresh water Total 1 SW tag recovery tag recovery recovery
a
Actual Raised Rod and trap Raisedqrod and trap
Ranched release
MS2N 4897 109 224 110 334
MS3N 4867 25 51 28 79
AF2N 4860 140 281 45 326
AF3N 4801 35 71 10 81
Estimated number of tagged salmon taken in fisheries see text .
b Ž .
River Eany, Co. Donegal rod caught July 1997 .
c Ž .
River Erne Trap, Co. Donegal July 1997 .
mainly in the summer season from May to September. In the vicinity of the release sites at Lough Furnace, Co. Mayo and Inver Bay, Co. Donegal, traps were monitored for the entire run on the Burrishoole system, and on the Erne river, which flows into Donegal
Ž .
Bay, respectively Table 2 .
3.2. Percentage returns
In each of the three release groups, the percentage return of triploid MS and AF
Ž .
stocks was significantly lower than diploid MS and AF stocks Table 3 . Returns of
Ž 2
ranched release triploid groups were significantly lower x s21.97, dfs1, P-0.001
2 .
for AF salmon and x s46.55, dfs1, P-0.001 for MS salmon than ranched release
diploid groups. The relative proportions of triploid to diploid ranched release returns
Ž .
were of similar magnitude to the coast and to the river Table 3 . The percentage return
Ž 2
of ranched release AF2N stock to fresh water was significantly lower x s27.22,
.
dfs1, P-0.001 than the percentage of ranched release MS2N returning. Ranched AF
groups were more heavily exploited in coastal waters by commercial nets than ranched
Ž .
Table 3
The return of one sea-winter Atlantic salmon to Irish coastal waters and the Burrishoole river expressed as a percentage for each release group
Ž .
Release group Return to coast % Return to
Ž .
Cage release I and cage release II groups show a similar pattern in percentage returns to coastal waters where triploid returns were four- to six-fold lower than those of their
Ž 2 2
diploid counterparts x s29.71, dfs1, P-0.0001 and x s74.19, dfs1, P
-. Ž .
0.0001 Table 3 . None of these groups returned to the hatchery location on the
Burrishoole river system and only two triploid salmon were recovered in other rivers. Both of these were in the Donegal region: one MS3N in the River Erne and one AF3N
Ž .
in the River Eany Table 2 .
3.3. Growth performance
Mean length, weight and condition factor of coastal and freshwater returns are shown in Table 5. Although triploid fish tended to be lighter than diploid fish and the condition factor was lower, there were no significant differences in weight, length or condition factor between triploid and diploid coastal returns, within stocks. However, there was a
Table 4
The percentage of the total one sea-winter ranched release recovery, which was exploited in Irish coastal waters by commercial nets and in the Burrishoole river by freshwater angling and traps
See raw data in Table 2.
Ž .
Release group Total 1 SW Coastal commercial Fresh water %
Table 5
Ž . Ž . Ž .
Mean length cm , weight kg and condition factor "SE of one sea-winter Atlantic salmon recovered for each release group, in coastal waters and fresh water from the commercial drift net catch and the SRAI upstream traps on the Burrishoole system, respectively
See Table 1 for abbreviations.
Ž . Ž .
Different letters superscript denote significant differences ANOVA at P-0.05 .
Ž . Ž .
Release group n Length cm Weight kg Condition factor
Mean"SE Mean"SE Mean"SE
( )
Coastal net catch 1 June to 31 July 1997
Ranched release
Freshwater SRAI upstream traps June to September 1997
Ranched release
significant difference between ranched diploid MS and AF stocks returning to the coast;
Ž
AF2N salmon were significantly heavier and longer than MS2N salmon ANOVA, df 1,
.
F ratios5.34, P-0.05 for weight and df 1, F ratios4.58, P-0.05 for length . Mean weights for coastal returns were 2.9 and 3.1 kg for MS2N and AF2N groups,
Ž .
respectively Table 5 .
There was a significant difference between ranched release triploid and diploid MS
Ž
salmon returning to fresh water with respect to mean weight ANOVA, df 1, F
.
ratios4.61, P-0.05 but not for length. MS3N salmon returning to fresh water had a
mean weight of 2.4"0.13 kg compared to 2.8 "0.08 kg for MS2N returns.
Conse-Ž
quently, there was also a significant difference between condition factors ANOVA, df
.
1, F ratios4.44, P-0.05 for the two groups. When the male and female components
of both diploid and triploid MS stock were examined, although females were smaller than males, the difference between males and females within each ploidy level was not significant.
3.4. Sexual maturity
Gonadosomatic indices were measured in returns from July until September 1997.
Ž .
Develop-Table 6
Ž .
Mean gonadosomatic index GSI of triploid and diploid one sea-winter Atlantic salmon sampled in August and September 1997, from SRAI upstream traps on the Burrishoole system
Ploidy Sex Gonadosomatic index
August September
Ž .n Mean"SD Ž .n Mean"SD
Triploid Male 3 0.279"0.071 4 4.08"0.90
Diploid Male 3 0.224"0.027 4 3.65"0.80
Triploid Female 3 0.08"0.025 5 0.16"0.08
Diploid Female 3 3.35"0.650 4 12.43"1.70
ment in males was similar for triploid and diploid salmon with mean gonadosomatic
Ž .
indices GSI of 4.08"0.89 and 3.65"0.80, respectively. In triploid females, however,
gonad development was very much reduced, resulting in a low mean GSI of 0.158"
0.083 compared to 12.44"1.68 for diploid females. The sex ratios of MS ranched
returns examined in fresh water were 62 F:43 M and 12 F:14 M for diploid and triploid salmon, respectively.
Ž . Ž . Ž . Ž .
Fig. 2. The distribution of diploid 2N and triploid 3N mixed-sex MS and all-female AF tag returns, from the ranched release group, cage release I group, and cage release II group of Atlantic salmon. The tag
Ž .
Table 7
The number, length, and weight of two sea-winter ranched release returns to the Burrishoole system from each release group of Atlantic salmon in 1998
See Table 1 for abbreviations.
Ž . Ž . Ž .
Release group No. of returns n Sex Length cm Weight kg
a
MS2N 1 – – –
MS3N 2 F 83.0 5.5
F 74.0 3.5
AF2N 2 F 79.8 5.5
F 79.0 3.7
AF3N 2 F 80.1 4.7
F 74.7 4.2
a
Rod caught fish, no data available.
In view of the observed gonad development in triploid males, milt was stripped from a triploid male in December 1997 and was used to fertilise ova from a diploid female. Only 1.6% of the resulting fry survived to first feeding compared to 92.7% of fry from diploid parents reared as controls. Yolk sac absorption was poor and survivors were weak with no prospect of survival.
3.5. Distribution of coastal tag recoÕeries
The distributions of tag recoveries from the three release groups are shown by area in Fig. 2. Ranched release tag recoveries were distributed from Donegal to west Cork. The recoveries occurred with greatest abundance from Donegal to Galway with a peak in the Mayo fishery area.
Tag recoveries from cage release groups I and II extended from Donegal to Kerry and from Donegal to the south coast, respectively. In both triploid and diploid groups, recoveries were predominantly made in the Donegal and Mayo areas. In isolated cases the numbers of recoveries can sometimes be distorted due to the raising factor; specifically where the number of fish sampled is low compared to the total reported commercial catch, resulting in a high raising factor. The percentage of AF3N recoveries
Ž .
made in the south coast was a manifestation of this Fig. 2 . The actual number of tags recovered in that area was one vs. five actual recoveries in the Mayo fishery area for the AF3N group.
3.6. Two sea-winter returns
In 1998, three diploid and four triploid 2 SW salmon were recovered in the
Ž .
Burrishoole river system from the ranched release group Table 7 .
4. Discussion
In ranched release groups, 1 SW recaptures were made both in Irish coastal waters and in the Burrishoole river system from which they were released as smolts. The percentage return of triploid salmon was some four-fold lower than diploid salmon.
Ž .
Diploid AF salmon were significantly bigger and were more heavily exploited )86%
Ž .
in coastal fisheries than diploid MS salmon 67% . This may have contributed to the lower return rate of AF stock to fresh water. Normally the distribution of ranched stocks from the Burrishoole system is most abundant in the fishery operating closest to the
river, in the MayorDonegal region. Recovery of this stock in the GalwayrLimerick nets
also tends to be high and it is not unusual for a few recoveries to be made further south. Tag recovery by area for the ranched group was as anticipated, with the highest recovery occurring in the Mayo area. Both triploid and diploid 2 SW returns to the Burrishoole system were extremely low, thus, dispelling the possibility that sterile triploid stocks might return to fresh water later than their maturing counterparts.
In cage release groups, which simulated an escape of salmon post-smolts from sea-cages, the majority of recaptures were made in coastal waters and again the percentage return of triploid salmon was significantly lower. There were no recaptures of adult salmon in the Burrishoole system, where the smolts had been reared. This is not unexpected, however, since cage release groups did not migrate from this system and
Ž .
were therefore deprived of the sequential imprinting Harden Jones, 1968 considered necessary for precise homing.
The exploitation of diploid cage release groups was highest in the Donegal and Mayo regions, indicating that homing was directed to the cage release location. Smolts and post-smolts released in coastal waters have been shown to return as adults to the area of
Ž .
release Heggberget et al., 1991; Hansen et al., 1993 . Tag recoveries for triploid cage release groups were low; however, the majority of recoveries were made in the Donegal and Mayo fishery areas.
Only two tags were recovered in fresh water from the cage release groups. Both tags were from triploid groups and were recovered in the rivers Eany and Erne close to the release site. The River Eany flows into Inver Bay and was monitored through angling returns from June to September. Any fish entering the River Eany later in the season would therefore have been undetected. On the River Erne, located only 15 km south of the release site, upstream fish movements were monitored throughout the year. For cage release groups, the highest percentage return in coastal waters was observed for AF2N salmon. The absence of any recoveries of the diploid cage release groups in the River Erne is notable given the observed magnitude of the returns to coastal waters, and given that adult returns from coastal releases have been shown, by others, to enter rivers in the
Ž .
vicinity of the release location Hansen et al., 1993 . However, having homed to the release location, cage release groups may have been available to the commercial fishery for a longer period and therefore more heavily exploited in coastal waters. This potential increase in exposure to commercial fishing pressure and to predation, may explain in part the absence of recoveries in the river.
undergoing the normal physical changes associated with sexual maturity, whereas triploid females had severely retarded ovarian development. The ovaries of triploid females remained in the primary growth phase whereas ovarian development in diploid
Ž .
females was in advanced oogenesis by September Murphy et al., in press . These observations confirm the differences in gonadal development between male and female
Ž .
triploid salmon, already reported by Benfey 1991 . The milt from triploid males in this study, failed to produce viable progeny. Returning triploid males, in spite of their sterility, had normal gonadal steroid and gonadotropin hormone profiles and underwent
Ž .
physiological maturation, in contrast to triploid females Cotter et al., in press . The return of sterile triploid females, albeit at significantly reduced levels, suggests that the return of fish to fresh water is not inextricably linked with reproduction. Despite having similar hormonal profiles, triploid males return at significantly lower levels than diploid males. It is likely, therefore, that factors other than differences in reproductive physiology may be important in determining the return rate of triploid salmon.
The controlled release of tagged triploid and diploid smolts and post-smolts of ranched grilse origin has shown that triploidisation of salmon stocks results in a significant reduction in the return rate to home water fisheries and more importantly to fresh water. The use of triploid salmon stocks in cage culture can therefore reduce the environmental impact of escaped farmed salmon on wild salmon populations both in terms of their reduced rate of return and inability to interbreed successfully among themselves or with indigenous populations.
Acknowledgements
This research was funded by the EU under the AIR programme contract number CT94 2216. We would like to acknowledge all those who contributed to the national coded wire tag recovery programme, particularly Anne Cullen and Tom McDermott of the Marine Institute Fisheries Research Centre.
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