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  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.
LOUGHS AGENCY OF THE FOYLE CARLINGFORD AND IRISH LIGHTS COMMISSION
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

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                             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

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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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      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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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

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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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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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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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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.

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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

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Fig 3. Bathymetry map of Lough Finn, Co Donegal
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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.

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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
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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

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                                       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.
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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).

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                                              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

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                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)

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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).

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                  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)

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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.

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Frequency                                                                                                                                                                                                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, Nambraddan
COPYRIGHT © 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 33
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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 33
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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).

                                                                              Page 29 of 33
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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
                                                                     Page 30 of 33
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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

                                                                     Page 31 of 33
COPYRIGHT © 2017 LOUGHS AGENCY OF THE FOYLE CARLINGFORD AND IRISH LIGHTS COMMISSION

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

                                                                     Page 32 of 33
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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).

                                                                     Page 33 of 33
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