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COPYRIGHT © 2017 LOUGHS AGENCY OF THE FOYLE CARLINGFORD AND IRISH LIGHTS COMMISSION
LOUGHS AGENCY OF THE FOYLE CARLINGFORD AND IRISH LIGHTS COMMISSION
Stillwater Status Report:
Lough Finn
Stillwater Fish Stock Survey
Loughs Agency of the Foyle Carlingford and Irish Lights Commission
Art Niven, Jayne Colgan and Fearghail Armstrong
December 2017
A lake fish stock assessment was conducted to record indicative species composition and
abundance of Lough Finn, Co. Donegal during the Autumn of 2017.
COPYRIGHT © 2017 LOUGHS AGENCY OF THE FOYLE CARLINGFORD AND IRISH LIGHTS COMMISSION
Headquarters
22, Victoria Road
Derry~Londonderry
BT47 2AB
Northern Ireland
Tel: +44(0)28 71 342100
Fax: +44(0)28 71 342720
general@loughs-agency.org
www.loughs-agency.org
Regional Office
Dundalk Street
Carlingford
Co Louth
Republic of Ireland
Tel+353(0)42 938 3888
Fax+353(0)42 938 3888
carlingford@loughs-agency.org
www.loughs-agency.org
Report Reference LA/Lake/09/17
CITATION: Niven, A.J., Colgan J. & Armstrong, F. (2017) Stillwater Status
Report: Lough Finn, Co. Donegal. Loughs Agency, 22, Victoria Road,
Derry~Londonderry
Page 2 of 33
COPYRIGHT © 2017 LOUGHS AGENCY OF THE FOYLE CARLINGFORD AND IRISH LIGHTS COMMISSION
DOCUMENT CONTROL
Name of Document Stillwater Status Report: Lough Finn
Author (s): Art Niven, Jayne Colgan and Fearghail Armstrong
Authorised Officer: John McCartney
Description of Content: Stillwater Fish Stock Assessment
Approved by: John McCartney
Date of Approval: December 2017
Assigned review period: 5 Years
Date of next review: September 2022
Document Code LA/LAKE/09/17
No.
TOC Text List of tables Table of Figures
Appendices
This documents comprises
X X X X
Version Control Table
Version No. Status Author (s) Reviewed by Approved by Date of issue
Draft Art Niven, John John December
Version 1 Jayne Colgan McCartney McCartney 2017
& Fearghail
Armstrong
Version 2
Version 3
Page 3 of 33
COPYRIGHT © 2017 LOUGHS AGENCY OF THE FOYLE CARLINGFORD AND IRISH LIGHTS COMMISSION
TABLE OF CONTENTS
TABLE OF CONTENTS ......................................................................................... 4
ACKNOWLEDGEMENTS ...................................................................................... 7
PROJECT STAFF 2017.......................................................................................... 7
EXECUTIVE SUMMARY ....................................................................................... 8
1.0 INTRODUCTION ...................................................................................... 10
Fig 1. Stillwater Fish Survey being carried out on Lough Finn, 2017. ........ 10
2.0 BATHYMETRY SURVEY ............................................................................ 11
Fig 2 . Lough Finn survey underway ......................................................... 11
Fig 3. Bathymetry map of Lough Finn, Co Donegal ................................... 12
3.0 METHODS ............................................................................................... 13
Table 1. Details of survey nets deployed on Lough Finn survey. ............... 13
Fig 5. Nets being prepared before being deployed on Lough Finn............ 13
Fig 6. Lough Finn ...................................................................................... 14
Fig 7. Lough Finn bathymetry map with 50m x 50m grid sqares ............. 15
Fig 8. Net locations ................................................................................... 16
4.0 RESULTS .................................................................................................. 17
4.1 SPECIES RICHNESS ............................................................................ 17
Table 2. Number of each species captured by each gear type during the
survey of Lough Finn, 2017. ..................................................................... 17
4.2 FISH ABUNDANCE ............................................................................. 17
Table 3. Mean (± S.E.) CPUE and BPUE for all fish species recorded on Lough
Finn, 2017. ............................................................................................... 18
Fig 9. Arctic charr and brown trout from Lough Finn ................................ 18
Fig 11. Mean BPUE for all fish species captured in Lough Finn, 2017. ...... 19
4.3 BROWN TROUT STOCK DENSITY & POPULATION STRUCTURE .......... 20
Fig 12. Mean CPUE for all Brown Trout across sampled loughs ................ 21
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COPYRIGHT © 2017 LOUGHS AGENCY OF THE FOYLE CARLINGFORD AND IRISH LIGHTS COMMISSION
Fig 13. Mean BPUE for all Brown Trout captured across sampled loughs . 21
Fig 14. Length frequency Brown Trout, Lough Finn 2017 (N=146) ............ 22
Fig 15. Length weight relationship of Brown Trout, Lough Finn 2017 (n=146)
................................................................................................................. 22
4.4 ARCTIC CHARR STOCK DENSITY & POPULATION STRUCTURE............ 23
Fig 16. Mean CPUE for all Arctic Charr captured in Lough Fad East 2017 and
Lough Finn (2017). ................................................................................... 23
Fig 17. Mean BPUE for all Arctic Charr captured in Lough Fad East 2017 and
Lough Finn (2017). ................................................................................... 23
Fig 18. Length frequency of Arctic Charr, Lough Finn 2017 (n=27) ........... 24
Fig 19. Length weight relationship of Arctic Charr, Lough Finn 2017 ........ 24
4.6 EEL STOCK DENSITY AND POPULATION STRUCTURE ......................... 25
Fig 20. Mean CPUE for Eels, Lough Mourne 2010, Carn 2010, Lough Muck
2012, Nambraddan 2014, Camlough 2016, Enagh East 2016, Trusk 2016 and
Lough Finn 2017. ...................................................................................... 25
Fig 21. Mean CPUE for Eels, Lough Mourne 2010, Carn 2010, Lough Muck
2012, Nambraddan 2014, Camlough 2016, Enagh East 2016, Trusk 2016 and
Lough Finn 2017 ....................................................................................... 26
Fig 22. Length frequency for European Eel, Lough Finn 2017 (n=22) ........ 26
Fig 23. Length weight relationship of European Eel, Lough Finn 2017 (n=22)
Table 4. Eel mean length and mean weight comparison for lakes surveyed
2010 – 2017. ............................................................................................ 27
4.5 FISH AGE AND GROWTH ................................................................... 28
Fig 24. Comparison growth curve showing back calculated length at age for
Brown Trout, Lough Muck (2012), Lough Nambraddan (2014), Lough Trusk
(2016), Lough Fad East (2017) and Lough Finn (2017). ............................. 28
Fig 25. Comparison growth curve showing back calculated length at age for
Arctic charr, Lough Fad East (2017) and Lough Finn (2017). ..................... 29
Fig 26. Growth curve showing back calculated length at age comparing
Brown Trout and Arctic Charr, Lough Finn (2017). ................................... 29
5.0 DISCUSSION ............................................................................................ 30
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COPYRIGHT © 2017 LOUGHS AGENCY OF THE FOYLE CARLINGFORD AND IRISH LIGHTS COMMISSION
6.0 INVASIVE SPECIES ................................................................................... 30
7.0 BIOSECURITY........................................................................................... 32
8.0 RECOMMENDATIONS ............................................................................. 32
9.0 REFERENCES ............................................................................................... 33
This document and its contents are copyright of the Loughs Agency ©2017
Page 6 of 33
COPYRIGHT © 2017 LOUGHS AGENCY OF THE FOYLE CARLINGFORD AND IRISH LIGHTS COMMISSION
ACKNOWLEDGEMENTS
The Loughs Agency sponsoring departments, board and staff are gratefully
acknowledged for the funding, support and assistance provided to conduct
stillwater fish stock assessments and status reporting in the Foyle and
Carlingford areas. Land owners and angling associations are also gratefully
acknowledged for their co-operation.
PROJECT STAFF 2017
Fisheries Biologist/Project Manager Art Niven
Fisheries Inspector/Coxswain Roly Wysner
Assistant Scientific Officer Jayne Colgan
Assistant Scientific Officer Paul Doherty
Fisheries Intern Fearghail Armstrong
GIS Manager Marco Tognella/Joe McClelland
For further information contact art.niven@loughs-agency.org
@ArtNiven Loughs Agency TV
© LOUGHS AGENCY OF THE FOYLE CARLINGFORD AND IRISH LIGHTS COMMISSION 2017
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COPYRIGHT © 2017 LOUGHS AGENCY OF THE FOYLE CARLINGFORD AND IRISH LIGHTS COMMISSION
EXECUTIVE SUMMARY
A Water Framework Directive compliant stillwater fish stock assessment was
carried out on Lough Finn in September 2017. The Loughs Agency commenced
a small rolling programme of lake fish surveys in 2010 to gain a better
understanding of fish composition and abundance of the standing waterbodies
within the Foyle and Carlingford areas. The information collected can be used
for many purposes ranging from formal Water Framework Directive
classification, a baseline survey for use in the scrutiny of any future development
proposals and for contributing towards the sustainable development of the
angling amenity.
Lough Finn is situated in West Donegal approximately 25km West of Ballybofey
and is the source of the River Finn. The lough is nestled at the base of the
bluestack mountain range. Fintown lies on the Northern shore of Lough Finn.
Previous baseline fisheries and Euopean eel scientific surveys have been
conducted but did not follow Water Framework Directive compliant methods.
Accurate depth (bathymetry) data was available to direct the fish survey.
The 2017 fish stock assessment noted the presence of four fish species in Lough
Finn including Brown trout, Arctic charr, European Eel and Minnow. Brown trout
were the most common fish encountered in the survery. It is notable that a
healthy population of Artic charr is present in the Lough. Water levels can
fluctuate quite quickly on Lough Finn following periods of rainfall. This has been
exacerbated in recent years by unauthorised drainage works which were
conducted at the outflow from Lough Finn. Substrate was added to the outflow
to mitigate the effects of the unauthorised dredging but the lowered bed level
still appears to be having an impact upon water retention within Lough Finn and
potentially upon the Lough Finn and River Finn fisheries.
This lake survey report provides a baseline of species presence and their relative
abundance to resource managers and anglers alike. It is anticipated that this
survey report could contribute towards any future management and sustainable
development of the angling amenity, conservation of the nationally vulnerable
Arctic charr population and wider development of the lough by providing the
basis for an evidence based approach to the management of the lough
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COPYRIGHT © 2017 LOUGHS AGENCY OF THE FOYLE CARLINGFORD AND IRISH LIGHTS COMMISSION
If access to the Fish in Lakes 2 Water Framework Directive classification tool was
available a WFD compliant classification could also be derived for Lough Finn
and provided to the Environmental Protection Agency for national reporting
purposes.
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COPYRIGHT © 2017 LOUGHS AGENCY OF THE FOYLE CARLINGFORD AND IRISH LIGHTS COMMISSION
1.0 INTRODUCTION
Lough Finn is located in West Donegal besdie the town of Fintown, in the Foyle
catchment. The principal dimensions are;
· Length: 4.1km long
· Maximum width: 0.38 km
· Surface area: 115 hectares
· Maximum depth: 24 metres
Fig 1. Stillwater Fish Survey being carried out on Lough Finn, 2017.
Page 10 of 33COPYRIGHT © 2017 LOUGHS AGENCY OF THE FOYLE CARLINGFORD AND IRISH LIGHTS COMMISSION
2.0 BATHYMETRY SURVEY
It is a prerequisite of any WFD compliant lake fish survey to have detailed
bathymetry data, so that the survey can be carried out in accordance with the
standard sampling methods for the assessment of ecological status in
freshwater lakes across the island of Ireland (Eco-region 17). The area of the lake
(ha) and the maximum depth (m) are used to determine the distribution and
number of gill nets required for the survey. A bathymetery survey for Lough Finn
had been previously completed prior to the lake fish survey. This information
was used to direct the fish survey.
Fig 2 . Lough Finn survey underway
Page 11 of 33COPYRIGHT © 2017 LOUGHS AGENCY OF THE FOYLE CARLINGFORD AND IRISH LIGHTS COMMISSION Fig 3. Bathymetry map of Lough Finn, Co Donegal
COPYRIGHT © 2017 LOUGHS AGENCY OF THE FOYLE CARLINGFORD AND IRISH LIGHTS COMMISSION
3.0 METHODS
Nets on Lough Finn were set on the 12th of Spetember 2017 and left overnight
and collected on 13th September according to the methodology described in the
Water Framework Directive compliant NS Share Methods Manual for systematic
surveying of lakes for fish (NSSHARE, 2008). A total of 31 nets were set as
summarised in Table 1 below.
Net type No. Deployed Water depth (m)
Dutch fyke nets 6 0 – 2.9
(chain of 3)
Multi-mesh gill nets 4 0 – 2.9
Multi-mesh gill nets 4 3 – 5.9
Multi-mesh gill nets 5 6 – 11.9
Multi-mesh gill nets 4 12 – 19.9
Multi-mesh gill nets 4 >20
Floating gill net 4 18-21
Table 1. Details of survey nets deployed on Lough Finn survey.
Fig 5. Nets being prepared before being deployed on Lough Finn.
Page 13 of 33COPYRIGHT © 2017 LOUGHS AGENCY OF THE FOYLE CARLINGFORD AND IRISH LIGHTS COMMISSION
Survey locations were chosen within randomly selected 50m X 50m grid squares
overlaid on a bathymetric map of the lough (Figure 3). The location and depth
of each net is also shown in figure 4. A handheld Trimble Geo HT GPS was used
to record the precise location of each net as shown in Figure 4 above. Any fish
which were alive and in good condition were measured and released live after
removal from the nets, this included all eels caught in fyke nets. All other fish
were removed from the nets, identified and measured at Loughs Agency
headquarters.
Fig 6. Lough Finn
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Fig 7. Lough Finn bathymetry map with 50m x 50m grid sqares
Page 15 of 33COPYRIGHT © 2017 LOUGHS AGENCY OF THE FOYLE CARLINGFORD AND IRISH LIGHTS COMMISSION
Fig 8. Net locations
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4.0 RESULTS
4.1 SPECIES RICHNESS
A total of 4 fish species were recorded on Lough Finn in September 2017 with a
total of 209 fish captured during the survey. A list of all species captured by each
gear type is presented in Table 2. Arctic charr one of Irelands rarerest native fish
species was recorded with 23 captured during this survey. Brown trout were the
most common fish species encountered in the benthic gill nets. All eels apart
from 1 were captured in the fyke nets. A total of 13 minnows were also captured.
Common Scientific Benthic Fyke Pelagic Total
Name Name Gill Nets Gill Nets
Nets
Brown Salmo trutta 138 8 0 146
trout
Arctic Salvelinus 23 1 4 28
Charr alpinus
European Anguilla 1 21 0 22
Eel anguilla
Minnow Phoxinus 10 3 0 13
phoxinus
Table 2. Number of each species captured by each gear type during the survey of Lough Finn,
2017.
4.2 FISH ABUNDANCE
Fish abundance, mean catch per unit effort (CPUE) was calculated as the mean
number of fish caught per metre of net. Fish biomass, mean biomass per unit
effort (BPUE) was calculated as the mean weight of fish caught per metre of net.
For all fish species CPUE/BPUE is based on all nets including fyke nets. Weights
were not available from those fish which were released alive. In such cases
weights were calculated from the length weight relationship of recorded fish. A
summary of CPUE and BPUE data for each species is shown in Figure 10 and 11
below.
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Brown trout were the dominant fish species in terms of abundance and also in
terms of biomass. Arctic Charr were much lower in terms of abundance and also
in terms of biomass as shown below in Table 3.
Common name Scientific name 2017 CPUE 2017 BPUE
Brown Trout Salmo trutta 0.157 (0.042) 11.741 (3.345)
Arctic Charr Salvelinus alpinus 0.029 (0.010) 1.874 (0.620)
European Eel Anguilla anguilla 0.122 (0.031) 15.767 (4.782)
Minnow Phoxinus phoxinus 0.019 (0.009) 0.019 (0.009)
Table 3. Mean (± S.E.) CPUE and BPUE for all fish species recorded on Lough Finn, 2017.
Fig 9. Arctic charr and brown trout from Lough Finn
Page 18 of 33COPYRIGHT © 2017 LOUGHS AGENCY OF THE FOYLE CARLINGFORD AND IRISH LIGHTS COMMISSION
0.250
0.200
CPUE (number of fish/m of net)
0.150
0.100
0.050
0.000
Brown Trout Arctic Char Eel Minnow
Species
Fig 10. Mean CPUE for all fish species captured in Lough Finn, 2017.
25.000
20.000
BPUE (number of fish/m of net)
15.000
10.000
5.000
0.000
Brown Trout Arctic Char Eel Minnow
Species
Fig 11. Mean BPUE for all fish species captured in Lough Finn, 2017.
Page 19 of 33COPYRIGHT © 2017 LOUGHS AGENCY OF THE FOYLE CARLINGFORD AND IRISH LIGHTS COMMISSION
4.3 BROWN TROUT STOCK DENSITY & POPULATION STRUCTURE
The relative density (CPUE & BPUE) and length frequency distribution of Brown
trout is presented below in Figures 12, 13, 14 & 15. Values are also compared
with other lakes which have been surveyed within the Foyle and Carlingford
areas. A total of 146 Brown trout were recorded during the Lough Finn survey,
lengths ranged from 60mm to 299mm (mean length 186mm). The abundance of
Brown trout in Lough Finn is significantly higher than many other surveyed
loughs. Eight Brown trout were recorded in Lough Fad East (2017), lengths
ranged from 170mm to 450mm (mean length 277mm). Forty four Brown trout
were recorded in Lough Muck (Donegal) 2012, lengths ranged from 69mm to
212mm (mean length 168mm). Eighteen Brown trout were recorded in Lough
Alaan 2013, lengths ranged from 134mm to 314mm (mean length 234mm).
Three Brown trout were recorded in Lough Carn 2010, lengths ranged from
389mm to 422mm (mean length 406mm). Twenty five Brown trout were
recorded in Lough Ash 2011, lengths ranged from 297mm to 421mm (mean
length 343mm). Two Brown trout were recorded in Lough Mourne 2010, lengths
ranged from 205mm to 220mm (mean length 213mm). Fifety nine Brown trout
were recorded in Lough Nambradden 2014, lengths ranged from 55mm to
240mm (mean length 147mm).
Page 20 of 33COPYRIGHT © 2017 LOUGHS AGENCY OF THE FOYLE CARLINGFORD AND IRISH LIGHTS COMMISSION
0.25
0.2
CPUE (Number of fish/m net)
0.15
0.1
0.05
0
Nambraddan 2014
Alaan 2013
Trusk 2016
Muck 2012
Carn 2010
Mourne 2010
Fad 2017
Finn 2017
Ash 2011
Site
Fig 12. Mean CPUE for all Brown Trout across sampled loughs
50
45
BPUE (Mean biomass (g) of fish/m net)
40
35
30
25
20
15
10
5
0
Nambraddan 2014
Mourne 2010
Alaan 2013
Trusk 2016
Muck 2012
Carn 2010
Fad 2017
Finn 2017
Ash 2011
(Donegal)
Site
Fig 13. Mean BPUE for all Brown Trout captured across sampled loughs
Page 21 of 33COPYRIGHT © 2017 LOUGHS AGENCY OF THE FOYLE CARLINGFORD AND IRISH LIGHTS COMMISSION
25
20
15
Frequency
10
5
0
130 - 139
140 - 149
110 -119
150 -159
230- 239
100 - 109
120 - 129
160 - 169
170 - 179
180 - 189
190 - 199
200 - 209
210 - 219
220 - 229
240 - 249
250 - 259
260 - 269
270 - 279
280 - 289
290 - 299
300 - 309
10 - 19
20 - 29
30 - 39
40 - 49
50 - 59
60 - 69
70 - 79
80 - 89
90 - 99
0-9
Length (mm)
Fig 14. Length frequency Brown Trout, Lough Finn 2017 (N=146)
350
y = 3E-05x2.795
300 R² = 0.9178
250
200
Weight (g)
150
100
50
0 3.6
0 50 100 150 200 250 300 350
Length (mm)
Fig 15. Length weight relationship of Brown Trout, Lough Finn 2017 (n=146)
Page 22 of 33COPYRIGHT © 2017 LOUGHS AGENCY OF THE FOYLE CARLINGFORD AND IRISH LIGHTS COMMISSION
4.4 ARCTIC CHARR STOCK DENSITY & POPULATION STRUCTURE
The relative density (CPUE & BPUE) and length frequency distribution of Arctic
Charr is presented below in Figures 16, 17, 18 & 19. A total of 28 Arctic Charr
were recorded in Lough Finn, lengths ranged from 60mm to 214mm (mean
length 175mm). Values for Arctic Charr are compared with results from Lough
Fad East which was also sampled in 2017 and contained Charr.
0.045
0.040
0.035
CPUE (Number of fish/m net)
0.030
0.025
0.020
0.015
0.010
0.005
0.000
Lough Fad 2017 Lough Finn 2017
Fig 16. Mean CPUE for all Arctic Charr captured in Lough Fad East 2017 and Lough Finn (2017).
3.000
Bpue (Mean biomass (g) of fish/m net
2.500
2.000
1.500
1.000
0.500
0.000
Lough Fad 2017 Lough Finn 2017
Fig 17. Mean BPUE for all Arctic Charr captured in Lough Fad East 2017 and Lough Finn (2017).
Page 23 of 33COPYRIGHT © 2017 LOUGHS AGENCY OF THE FOYLE CARLINGFORD AND IRISH LIGHTS COMMISSION
10
9
8
7
6
Frequency
5
4
3
2
1
0 100 - 109
120 - 129
160 - 169
170 - 179
180 - 189
190 - 199
200 - 209
210 - 219
130 - 139
140 - 149
10 - 19
20 - 29
30 - 39
40 - 49
50 - 59
60 - 69
70 - 79
80 - 89
90 - 99
110 -119
150 -159
0-9
220-229
Length (mm)
Fig 18. Length frequency of Arctic Charr, Lough Finn 2017 (n=27)
140
120 y = 2E-06x3.3602
R² = 0.9617
100
80
Weight (g)
60
40
20
0
0 50 100 150 200 250
Length (mm)
Fig 19. Length weight relationship of Arctic Charr, Lough Finn 2017 (n=27)
Page 24 of 33COPYRIGHT © 2017 LOUGHS AGENCY OF THE FOYLE CARLINGFORD AND IRISH LIGHTS COMMISSION
4.6 EEL STOCK DENSITY AND POPULATION STRUCTURE
The relative density (CPUE & BPUE) and length frequency distribution of Eels is
presented below. A total of 23 Eels were recorded in Lough Finn, lengths ranged
from 32.5cm – 53.5cm. Values are also compared with other lakes which have
been surveyed within the Foyle and Carlingford areas.
0.5
0.4
CPUE (Number of fish/m net)
0.3
0.2
0.1
0
Muck 2012 (Donegal)
Lough Finn 2017
Enagh East 2016
Nambraddan 2014
Mourne 2010
Camlough 2016
Carn 2010
Trusk 2016
Site
Fig 20. Mean CPUE for Eels, Lough Mourne 2010, Carn 2010, Lough Muck 2012, Nambraddan
2014, Camlough 2016, Enagh East 2016, Trusk 2016 and Lough Finn 2017.
Page 25 of 33Frequency BPUE (Mean biomass (g) of fish/m net)
0
1
2
0
25
50
75
100
125
150
175
200
0-9
20 - 29
40 - 49 Mourne
2010
60 - 69
80 - 89
100 - 109
Carn 2010
120 - 129
140 - 149
160 - 169
Muck 2012
180 - 189 (Donegal)
200 - 209
220 - 229
240 - 249
Nambraddan
2014
260 - 269
Site
280 - 289
Length (mm)
300 - 309 Camlough
320-329 2016
340-349
360-369 Enagh East
Fig 22. Length frequency for European Eel, Lough Finn 2017 (n=22)
380-389 2016
400-409
420-429
2014, Camlough 2016, Enagh East 2016, Trusk 2016 and Lough Finn 2017.
440-449 Trusk 2016
460-469
480-489
500-509 Lough Finn
520-529 2017
540-549
COPYRIGHT © 2017 LOUGHS AGENCY OF THE FOYLE CARLINGFORD AND IRISH LIGHTS COMMISSION
Page 26 of 33
Fig 21. Mean CPUE for Eels, Lough Mourne 2010, Carn 2010, Lough Muck 2012, NambraddanCOPYRIGHT © 2017 LOUGHS AGENCY OF THE FOYLE CARLINGFORD AND IRISH LIGHTS COMMISSION
350
300 y = 0.0016x3.0023
R² = 0.9642
250
Weight (g)
200
150
100
50
0
0 10 20 30 40 50 60
Length (cm)
Fig 23. Length weight relationship of European Eel, Lough Finn 2017 (n=22)
Lake Number of Eels Mean Length Mean Weight
Lough Mourne 13 465 mm 231 g
2010
Lough Carn 1 605 mm 420 g
2010
Lough Muck 10 380 mm 123 g
2012 (Donegal)
Nambraddan 12 409 mm 130 g
2014
Camlough 2016 25 529 mm 764 g
Enagh Lough 1 529 mm 720 g
East 2016
Lough Trusk 31 442 mm 230 g
2016
Lough Finn 22 424mm 137g
2017
Table 4. Eel mean length and mean weight comparison for lakes surveyed 2010 – 2017.
Page 27 of 33COPYRIGHT © 2017 LOUGHS AGENCY OF THE FOYLE CARLINGFORD AND IRISH LIGHTS COMMISSION
4.5 FISH AGE AND GROWTH
Scales were taken from 77 Brown trout and 26 Arctic charr caught during this
survey. A sub sample of 32 Brown trout scales and 15 Arctic charr scales were
read for fish aging and back calculated growth analysis. Figure 23 below outlines
the average length at age for Brown trout caught during the survey and
compares them to Brown trout caught in Lough Muck (2012), Lough
Nambraddan (2014), Lough Trusk (2016) and Lough Fad East (2017). A range of
age classes were present in Lough Finn with the oldest Trout found to be in the
6+ age class.
50
Lough Muck
45
Lough
Nambraddan
40
Lough Trusk
35
Lough Fad
(East)
30
Lough Finn
Length (cm)
25
20
15
10
5
0
L1
L2
L3
L4
L5
L6
Length at age
Fig 24. Comparison growth curve showing back calculated length at age for Brown Trout,
Lough Muck (2012), Lough Nambraddan (2014), Lough Trusk (2016), Lough Fad East (2017)
and Lough Finn (2017).
Page 28 of 33COPYRIGHT © 2017 LOUGHS AGENCY OF THE FOYLE CARLINGFORD AND IRISH LIGHTS COMMISSION
Figure 25 below shows the average length at age for Arctic Charr caught during
the survey. The oldest Arctic charr was found to be in the 4+ age class.
18
16
14
12
Length (cm)
10
Lough Fad
8
Lough Finn
6
4
2
0
1 2 3 4
Length at age
Fig 25. Comparison growth curve showing back calculated length at age for Arctic charr, Lough
Fad East (2017) and Lough Finn (2017).
30
25
20
Length (cm)
15
Brown Trout
Arctic Charr
10
5
0
L1 L2 L3 L4 L5 L6
Length at age
Fig 26. Growth curve showing back calculated length at age comparing Brown Trout and Arctic
Charr, Lough Finn (2017).
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5.0 DISCUSSION
Additional information collected during survey but not reported on here
includes water quality data on Dissolved Oxygen, pH, temperature, Total
Phophorous and fish stomach content analysis. This information has been
retained for future analysis if and when time and resources become available.
Lough Finn is an extremely important lough. It holds a population of nationally
rare Arctic charr which as evidenced during the 2017 survey had multiple
cohorts present including young of the year. This population appears to be in
reasonable condition but further assessment against favourable condition
standards would need to be made in order to derive a formal condition
assessment.
The population of Brown trout and European eel also appears to be in
reasonable condition. A large population of small Brown trout was recorded. No
larger specimens were encountered during this survey and a general decline in
larger Brown trout caught by local anglers was commented on by local contacts.
Larger salmonids have been observed locally at the outflow to Lough Finn at
spawning time. It is not known if these fish were Salmon or Trout.
Lough Finn has a small geographical area draining into it and water levels
historically where stable. The outflow was dredged a number of years ago and
reinstated to a lower level. The reducytion in bed level at the outflow results in
water levels running off the lough much faster than previously. This has added
to the spate nature of the Finn catchment minimising the natural buffering
caopacity offered by Lough Finn on both water chemistry and water levels.
Arctic charr may be spawning in the littoral areas and any fluctuations in water
levels at sensitive incubation periods have the potential to impact negatively on
this population.
6.0 INVASIVE SPECIES
Invasive non-native species are those which have been transported outside of
their natural range. They are capable of spreading rapidly and colonising a wide
range of habitats. They also exhibit competitive dominance by out-competing
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native flora and fauna for light, oxygen and food. There is growing evidence to
suggest that invasive riparian plants are having an adverse effect on aquatic
habitats and species by altering both in-stream processes and terrestrial-aquatic
linkages. Invasive species threaten native species as direct predators or
competitors, as vectors of disease, and by modifying the native habitats.
Invasive species are considered the second biggest threat after habitat loss to
biodiversity worldwide by the Millennium Ecosystem Assessment in 2005.
Water is an excellent transport medium for the dispersion of many of these
species. Rivers and loughs with their banks and shorelines are amongst the most
vulnerable areas to their introduction, spread and impact. The focus for the
Loughs Agency is predominantly on aquatic and riparian invasive species as
these are a serious threat to our sensitive aquatic habitats. The spread of
invasive species can also further threaten already endangered native species. In
freshwater habitats the introduction of invasive species is considered the
second leading cause of species extinctions. Invasive species are a global
problem and once they are established eradication is often costly and extremely
difficult. Previous studies suggest that early intervention is a more successful
and cost-effective way of preventing the spread of invasive species.
There are a multitude of invasive non-native species across the UK and Ireland
at present, many of them with the potential to cause serious environmental
harm. Three species in particular, Japanese Knotweed (Fallopia japonica),
Himalayan Balsam (Impatiens grandulifera) and Giant Hogweed (Heracleum
mantegazzianum) have become an established threat to the streams and rivers
of the Foyle and Carlingford areas. Rivers are an excellent means of transporting,
dispersing and spreading invasive species, therefore it is no great surprise to see
a proliferation along our river corridors.
There is a growing body of evidence demonstrating the damaging impacts of
(INNS) invasive non-native species. The problem of excessive soil erosion along
the riparian zone can have grave consequences for freshwater fish species.
Atlantic salmon (Salmo salar) and Trout (Salmo trutta) are reliant upon finding
appropriately sized spawning gravel to complete their life cycle. However,
Himalayan Balsam will die back in winter time, leaving behind exposed river
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banks devoid of any natural vegetation. The lack of vegetation on the riparian
zone leaves the bank highly susceptible to soil erosion at times of increases flows
and floods. Excessive soil erosion will increase the sediment load into the stream
reach and can potentially smother the eggs buried in the spawning gravel,
starving them of oxygen. Atlantic salmon stocks are at unprecedented low levels
and they are also experiencing very high mortality rates during the marine phase
of their life cycle. Increased sediment being introduced to rivers and streams has
the potential to diminish juvenile abundance even further and merely
exacerbates the problem still further.
7.0 BIOSECURITY
Good biosecurity exists on Lough Finn with boat launching access limited and
controlled. A fleet of angling boats are available for rent minimising the pressure
to transport boats from other areas which may host invasive species. Additional
biosecurity measures should also be encouraged to prevent the spread of
invasive non nantive species.
Invasive species are an ever present threat in our aquatic and riparian systems
and it is imperative that none of our field operations exacerbate the risks to the
environment and to the economy that are posed by these species. Fish parasites,
pathogens and diseases also represent a significant threat to the health status
of our watercourses. The introduction or transfer of such pathogens or diseases
has the potential to wipe out large populations of fish in affected waters or
catchments. Loughs Agency staff are required to be vigilant to help prevent the
spread of fish diseases and invasive species. The agency has incorporated
biosecurity protocols into its freshwater fisheries monitoring programme and
these guidelines are also adhered to by fishery officers and field staff alike. The
Loughs Agency biosecurity protocol for field operations was fully implemented
during the Lough Finn fish survey.
8.0 RECOMMENDATIONS
· Repeat survey every 5 years.
· Conduct fisheries assessments on the inflowing tributaries to Lough Finn
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· Conduct spawning survey/camera deployment/trapping exercise at the
outflow to Lough Finn at spawning time
· Investigate the potential for raising the outflow to Lough Finn to align with
original bed levels.
· Compare results against any future surveys in the Foyle area to ascertain
comparative growth rates across and within a range of stillwaters of the
Foyle and Carlingford areas.
· Communicate findings internally to colleagues and externally to
stakeholders
· Continue to conduct stillwater fish surveys temporally and spatially within
the Foyle and Carlingford areas.
· Promote Biosecurity awareness with angling community
· Liaise with angling associations to develop best practice management
advice
9.0 REFERENCES
Kelly, FL (2008) WFD Surveillance Monitoring Fish in Lakes (2007) Central and
Regional Fisheries Board report.
Kelly, F.L., Connor, L., Wightman, G., Matson, R., Morrissey, E O’Callaghan, R.,
Feeney, R., Hanna, G. and Rocks, K., (2009) Sampling fish for the Water
Framework Directive – Summary Report 2008. Central and Regional Fisheries
Board report.
North South Share Aquatic Resource (NS Share). Methods Manual V Fish (2008)
European CEN Standard. Water quality-Sampling of fish with multi-mesh gill
nets (2005).
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