Grey seal distribution and abundance in North Wales, 2002-2003

82 Pages·2004·0.56 MB·English

Grey seal distribution and abundance in
North Wales, 2002-2003
Westcott, S.M. & Stringell, T.B.
Marine Monitoring Report No: 13
This is a report of research commissioned by the Countryside Council for Wales. The Council has a
programme of research in scientific and other areas, which supports the development of policies and
practical work and helps point the way to new countryside legislation. However, the views and
recommendations presented in this report are not necessarily those of the Council and should,
therefore, not be attributed to the Countryside Council for Wales. No part of this report may be
reproduced, stored in a retrieval system, or transmitted, in any form or by any means, electronic,
mechanical, photocopying, recording, or otherwise, without the prior permission of the Countryside
Council for Wales.
i
Report Number: 13
Publication Date: March 2004
Contract Number: FC-73-02-183
Nominated Officer: T.B. Stringell
Title: “Grey seal distribution and abundance in North Wales,
2002-2003”
Authors: Westcott, S.M. & Stringell, T.B.
Series editors: W.G. Sanderson (monitoring) A. McMath (marine mammals)
Restrictions: None
Distribution List
CCW:
T. Stringell CCW HQ x3 M. Baines x1
M.McMath, CCW HQ x1 S. Stansfield, Bardsey Island Bird
B.Sanderson CCW HQ x1 Observatory x1
R. Holt, CCW HQ x1 A. Moralee, RSPB South Stack x1
L. Kay, CCW NWA x1 C. Sharpe, Manx Bird Atlas x1
Mike Camplin, CCW, H'FordW x1 T. Johnston, Exploris, Portaferry, NI x1
Blaise Bullimore, CCW H'fordW x1 C. Liret, Oceanopolis, Brest, Brittany x1
Paul Day, CCW NEA x1 R. Penrose, Marine Env Monitoring x1
Neil Smith, CCW NEA x1 Ivor Rees, Uni. Wales, Bangor x1
CCW HQ Library x1 Peter Hope Jones x1
CCW NWA Library x1 David Mawer, IoS Wildlife Trust x1
CCW Cardiff Library x1 T. Nicholson, Cornwall Wildlife Trust x1
CCW Mold Library x1 Marine Awareness North Wales x1
CCW West Area x1 Ian Bullock x1
CCW Skomer MNR x1 Jim Poole x1
Powell Strong x1
Others: David Thomas x1
JNCC Peterborough, Library x1 Chris Richardson, x1
EN Peterborough Library x1 Hilbre Island Observatory x1
R. Covey, EN Cornwall x1 K. Abt, Wadden Sea, Germany x1
SNH Edinburgh, Library x1 R. Witte, Texel, Netherlands x1
National Library Wales x1 UW Cardiff Library x1
National Assembly for Wales Library x1 UW Swansea Library x1
C. Duck, SMRU x1 UW Aberystwyth Library x1
Joe Breen EHS x1 UW Bangor Library x1
PML, Library, Plymouth x1 British Library, Document Supply Centre,
S. Westcott x5 Boston Spa x1
Recommended citation for this volume:
Westcott, S & Stringell, T.B. 2004. Grey seal distribution and abundance in North
Wales, 2002-2003. Bangor, CCW Marine Monitoring Report No: 13. 80pp.
ii
PREFACE
Under the Council Directive 92/43 EEC on the Conservation of natural habitats and of wild
fauna and flora (the ‘Habitats Directive’), Member States are required to designate and
conserve Special Areas of Conservation (SACs). The purpose of this is to maintain or restore
habitats and species listed in Annex I and Annex II to ‘Favourable Conservation Status’. The
grey seal Halichoerus grypus Fabricus, is a species listed in Annex II of the Habitats
Directive and in Wales they are therefore ‘interest features’ of the Lleyn Peninsula and the
Sarns, Pembrokeshire Marine, and Cardigan Bay candidate SACs.
The work presented in this report is the second study of its type to investigate the abundance
of grey seals as a possible indicator of condition in the ‘Lleyn Peninsula and the Sarns’ SAC.
Overall, the work has contributed to the development of methods and procedures for
monitoring SACs as well as a dataset that will help to inform how targets could be set for the
management of the SAC.
Over the last few years many other reviews, surveys, surveillance and monitoring projects
have been initiated in Wales for Annex I and II habitats and species. Further CCW reports in
this series will be produced as part of this ongoing programme to develop marine monitoring
work that underpins the management of conservation sites.
RHAGAIR
Dan Gyfarwyddeb y Cyngor 92/43 EEC ar warchod cynefinoedd naturiol a fflora a ffawna
gwyllt (y ‘Gyfarwyddeb Cynefinoedd’), mae’n ofynnol i aelod-wladwriaethau ddynodi a
gwarchod Ardaloedd Cadwraeth Arbennig (ACA). Diben hyn yw cynnal neu adfer
cynefinoedd a rhywogaethau a restrir yn Atodiad I ac Atodiad II yr adran sy’n ymwneud ag
elfennau sydd â statws cadwraethol ffafriol (‘Favourable Conservation Status’). Fe restrir y
morlo llwyd Halichoerus grypus Fabricus yn Atodiad II y Gyfarwyddeb, ac yng Nghymru
maent felly yn ‘nodweddion o ddiddordeb’ o fewn ymgeisydd am ACA Pen Llyn a’r Sarnau,
ACA Morol Sir Benfro, o fewn ymgeisydd am ac o fewn ymgeisydd am ACA Bae
Ceredigion.
Yr ail astudiaeth o’i bath gyda’r nod o archwilio faint o forloi llwyd a geir fel arwydd o
gyflwr ACA Pen Llyn a’r Sarnau - dyma yw’r gwaith a gyflwynir yn yr adroddiad yma. Yn
gyffredinol, mae’r gwaith wedi cyfrannu at ddatblygu dulliau a gweithdrefnau ar gyfer
monitro ACA yn ogystal â set ddata a fydd yn ein cynorthwyo i weld sut y gellir gosod
targedau yn ymwneud â rheoli ACA.
Yn ystod y blynyddoedd diwethaf, mae nifer o adolygiadau, arolygon, a phrosiectau
goruchwylio a monitro eraill wedi cael eu rhoi ar y gweill yng Nghymru, sef rhai yn
ymwneud â chynefinoedd a rhywogaethau Atodiad I ac Atodiad II. Felly, fe fydd
adroddiadau pellach yn perthyn i’r gyfres hon yn cael eu llunio gan y Cyngor Cefn Gwlad yn
seiliedig ar ganlyniadau’r rhaglen barhaus yma i ddatblygu gwaith monitro morol sy’n sail i
ddulliau rheoli safleoedd cadwraethol.
1
SUMMARY
The results of a full census of grey seal distribution and abundance for the period 29 July
2002 to 17 April 2003 are presented here. Occasional winter counts of seals on Ynys
Enlli/Bardsey Island are also included. Where possible, female and well-marked male seals
were photographed, in order to initiate a detailed study examining the fidelity of seals to
North Wales assembly sites. However, in this survey the main purpose of site visits was to
count the seals, as far as possible without disturbing them.
In North Wales, grey seal distribution at haul-out sites was almost entirely confined to three
districts: 1) Ynys Enlli/Bardsey Island and Penrhyn Llyn/Lleyn Peninsula, 2) the West Hoyle
Sandbank at the mouth of the Dee Estuary, adjacent to Hilbre Island, 3) a cluster of localities
in Ynys Môn/Anglesey: Ynys Arw/North Stack, Ynysoedd y Moelrhoniaid/The Skerries,
Trwyn y Gader/Carmel Head, Ynys Dulas and Ynys Seiriol/Puffin Island.
The sites used by grey seals in North Wales are usually remote from human access and
adjacent to tide races; most consist of rocky island shores or sea cave sites. However, the site
where the largest number of seals have been recorded, the West Hoyle Sandbank, is the one
exception in that it consists exclusively of fine sand and offers immediate access to strongly
tidal water.
As in 2001 (Westcott, 2002), counts were highest in summer at the north-east (West Hoyle
Sandbank) and west (Ynys Enlli/Bardsey Island) extremes of the seals’ range in North Wales.
Highest winter counts were lower than highest summer counts for the region as a whole, and
the apparent distribution of the seals also varied between summer and winter. Highest counts
for single sites in winter were most often made in the central sector of their range, at the east
Ynys Môn/Anglesey islands of Ynys Dulas and Ynys Seiriol/Puffin Island and in the far
eastern sector, at West Hoyle Sandbank. Nevertheless, Ynys Enlli/Bardsey Island remained
important at this time.
At all sites, counts made on consecutive days sometimes showed considerable fluctuation due
to weather and sea conditions, or as an aftermath to human disturbance.
The number of seals using haul-out sites varied through the year, with the largest number and
variety of sites being used during the peak weeks of the breeding season, in September and
October.
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CRYNODEB
Yma, cyflwynir canlyniadau cyfrifiad llawn sydd wedi ceisio darganfod dosbarthiad a
niferoedd morloi llwyd rhwng 29 Gorffennaf 2002 ac 17 Ebrill 2003. Hefyd, caiff y morloi a
gafodd eu cyfrif o dro i dro ar Ynys Enlli yn ystod y gaeaf eu cynnwys. Fe orwedd yr
arfordir a’r ynysoedd a arolygwyd rhwng Aberystwyth yn y de ac Aber Afon Dyfrdwy yn y
gogledd-ddwyrain, gan gynnwys Ynys Môn.
Yng Ngogledd Cymru, roedd dosbarthiad morloi llwyd ar safleoedd a ddefnyddid fel
safleoedd gorffwyso wedi eu cyfyngu bron yn gyfan gwbl i dair ardal: 1) Ynys Enlli a Phen
Llyn, 2) Banc Tywod West Hoyle yng ngheg Aber Afon Dyfrdwy, ger Ynys Hilbre, 3)
clwstwr o lecynnau yn Ynys Môn: Ynys Arw, Ynysoedd y Moelrhoniaid, Trwyn y Gader,
Ynys Dulas ac Ynys Seiriol.
Fel arfer, mae’r ynysoedd a gaiff eu defnyddio gan forloi llwyd yng Ngogledd Cymru yn bell
o fannau y gall y cyhoedd fynd arnynt, ac yn ymyl cerhyntau cryfion. Mae’r rhan fwyaf yn
cynnwys glannau creigiog neu ogofâu môr. Fodd bynnag, y safle pwysicaf un, sef Banc
Tywod West Hoyle, yw’r unig eithriad o ran ei fod yn cynnwys dim byd ond tywod mân, ac o
ran y gellir mynd at ddwr llanwol cryf yn syth o’r safle.
Fel yn 2001 (Westcott, 2002), fe welwyd y rhan fwyaf yn ystod yr haf ym mhegynau
gogledd-ddwyreiniol (Banc Tywod West Hoyle) a gorllewinol (Ynys Enlli) cwmpas y morloi
yng Ngogledd Cymru.
Roedd y niferoedd mwyaf a gafodd eu cyfrif yn ystod y gaeaf yn llai na’r niferoedd mwyaf a
gafodd eu cyfrif yn ystod yr haf wrth ystyried y rhanbarth yn ei gyfanrwydd, a hefyd fe
welwyd gwahaniaeth yn nosbarthiad y morloi rhwng yr haf a’r gaeaf. Gan amlaf, mewn
mannau tua chanol y rhanbarth y cafodd y nifer fwyaf o forloi eu cyfrif ar safleoedd unigol yn
ystod y gaeaf, yn ynysoedd dwyreiniol Ynys Môn, sef Ynys Dulas ac Ynys Seiriol, ac ym
mhen dwyreiniol pellaf y rhanbarth ym Manc Tywod West Hoyle. Er hynny, roedd Ynys
Enlli yn dal i fod yn bwysig yn ystod y cyfnod yma.
Ym mhob safle, roedd y nifer a gafodd eu cyfrif ar ddyddiau dilynol weithiau yn amrywio’n
sylweddol yn sgîl y tywydd â’r môr, neu o ganlyniad i’r ffaith fod pobl wedi tarfu arnynt.
Drwy gydol y flwyddyn, fe amrywiai’r niferoedd o forloi a ddefnyddiai safleoedd gorffwyso,
gyda’r niferoedd a’r amrywiaeth mwyaf o safleoedd yn cael eu defnyddio yn ystod wythnosau
prysuraf y tymor bridio, sef ym mis Medi a mis Hydref.
Pan oedd modd, fe dynnwyd lluniau o forloi benywaidd a morloi gwrywaidd amlwg, a hynny
er mwyn rhoi astudiaeth fanwl ar y gweill i weld pa mor ffyddlon yw morloi i safleoedd
ymgynnull yng Ngogledd Cymru. Dim ond trwy barhau â’r gwaith yma dros gyfnod o bum
mlynedd o leiaf y gellir datblygu gwerth yr wybodaeth yma. Fodd bynnag, prif ddiben yr
arfer o ymweld â safleoedd yn yr arolwg yma oedd cyfrif y morloi, gan darfu cyn lleied â
phosibl arnynt.
3
Grey Seal Distribution and Abundance in North Wales, 2002-2003
Westcott, S.1 & Stringell, T.B.2
1 Nancherrow Cottage, Nancherrow, St Just-in-Penwith, Cornwall, TR19 7PW
2 Countryside Council for Wales HQ, Plas Penrhos, Ffordd Penrhos, Bangor, LL57 2LQ, UK
Contents
1 INTRODUCTION 6
1.1 Objectives............................................................................................................6
2 METHODS 8
2.1 Study area............................................................................................................8
2.2 Abundance and distribution data collection............................................................8
2.3 Seal assemblage composition..............................................................................10
2.4 Methods of site access........................................................................................10
2.5 Observatory observations....................................................................................11
2.6 Weather conditions and survey considerations......................................................13
2.7 Recording condition............................................................................................13
2.8 Minimising disturbance.......................................................................................13
2.9 Data storage.......................................................................................................14
3 RESULTS 15
3.1 Overall seal distribution and abundance in North Wales, 2002-2003......................15
Porth Bribys to Ynys Fydlyn.............................................................................15
Carreg Ddû......................................................................................................15
Carreg y Trai (North)........................................................................................16
Carreg y Trai (South)........................................................................................17
Glanllynnau Skerries........................................................................................18
Gwylans Coast.................................................................................................18
Ynys Arw/North Stack Coast............................................................................19
Porth Widlin Coast...........................................................................................20
Rhosgor...........................................................................................................20
4
Trwyn Cilan.....................................................................................................21
Trwyn y Gader/Carmel Head.............................................................................22
Tudwals (composite)........................................................................................23
West Hoyle Sandbank (using standard methods).................................................23
Ynys Dulas......................................................................................................24
Ynys Seiriol/Priestholm/Puffin Island................................................................25
Ynys Enlli/Bardsey Island (using standard methods)...........................................25
Ynys Tudwal East............................................................................................26
Ynys Tudwal West...........................................................................................27
Ynysoedd y Moelrhoniaid/The Skerries.............................................................28
Other sites........................................................................................................28
3.2 Winter seal counts at Ynys Enlli/Bardsey Island and West Hoyle Sandbank (using
observatory observations)............................................................................................29
3.3 Seal assemblage composition..............................................................................32
4 DISCUSSION 34
4.1 The distribution and abundance of grey seals at haul-out sites in North Wales........34
4.2 Use of haul-out sites / seal assemblage composition..............................................36
4.3 Recommendations..............................................................................................37
5 ACKNOWLEDGEMENTS 39
6 REFERENCES 40
7 APPENDICES 41
Appendices 1-19 Seal counts made for each site visit. 41
Appendix 20 Site specific notes 65
Appendix 21 Risk Assessment 71
Appendix 22 Environmental influences on survey effort 75
5
1 INTRODUCTION
The UK population of grey seals represent about 40% of the world population and 95% of the
EU population (SCOS, 2003). At the start of the 2000 breeding season, Great Britain held
some 124,000 grey seals with a further 300-400 around the Isle of Man and Northern Ireland
(SCOS 2000). The grey seal colonies of Wales represent over 2% of annual UK pup
production (SCOS 2000).
A survey of grey seals in North Wales was conducted in 2001 for the Countryside Council for
Wales (CCW). It provided baseline data on seal distribution at haul-out sites and on pup
production (Westcott, 2002). In 2001, seals were found to be present at all surveyed sites
throughout the year, albeit in varying numbers, with highest counts for a single site in summer
being made at the West Hoyle Sandbank, Ynys Enlli/Bardsey Island and, to a lesser extent, at
the Tudwal Islands (East and West). Highest winter counts were made at the two east Ynys
Môn/Anglesey islands of Ynys Dulas and Ynys Seiriol/Puffin Island, with generally lesser but
still substantial assemblies of seals counted at West Hoyle Sandbank and Ynys Enlli/Bardsey
Island.
The most similar study to this survey was carried out in the Molène archipelago, off the west
coast of Brittany, where the southernmost breeding sites of the grey seal in the east Atlantic,
are found (Vincent, 2001). Boat-based censuses of haul-out assemblies were carried out once
every two weeks from December 1997 to August 2000. A previous examination of grey seal
distribution and abundance in North Wales (Swarbrick, 2000) proposed a summer population
size of about 2000, a figure based mainly on a review of records held at Ynys Enlli/Bardsey
Island Bird Observatory, Hilbre Bird Observatory and the Ynysoedd y Moelrhoniaid/Skerries
Bird Observatory, but also on site visits for which no methodology is given.
Westcott (2002) tentatively estimated the total number of grey seals at North Wales sites as
365. This was calculated by multiplying the pup production estimate from the 2001 survey
by a factor of 3.5 (one pup to three and a half adults) that was derived from a life table
devised by Hewer (1974), in which it is assumed that the population is stable. The authors
assert that applying a population number to the seals in North Wales should be viewed with
caution.
During this survey, an east Atlantic phocine distemper epizootic progressed from the Danish
island of Anholt, in May, around the North Sea basin and as far as the north Irish Sea coast.
Although principally causing heavy mortality among common (harbour) seals, some grey
seals also died on British coasts (SMRU, 2002). Concern that the phocine distemper virus
might affect seals using the North Wales coast meant that close attention was given to the
physical condition of the seals, with any abnormalities being noted.
Work on the current project began on 29 July 2002, although data from Hilbre Bird
Observatory covers the period January to December 2002.
1.1 Objectives
Distribution and abundance
To record grey seal distribution and abundance on Pen Llyn/Lleyn Peninsula Ynys
Enlli/Bardsey Island, Ynys Môn/Anglesey and the West Hoyle Sandbank in the Dee Estuary
for the 2002-2003 season, while recognising that there is a conflict inherent in going on site to
record numbers of seals and going on site to photograph individuals. At the same time, visits
6
to sites not previously identified as being used by seals were made, to check for any signs of
expansion of known range.
A comparison is made of abundance and distribution data collected in North Wales in 2000-
2001(Westcott, 2002) and data collected from the present survey.
The development of site based Standard Operating Procedures for future monitoring of
distribution and abundance of grey seals in North Wales are reported separately (Westcott &
Stringell,in prep).
Observatory/opportunistic data (seal numbers and calibration of methods)
Historically, data on grey seal numbers in North Wales have been collected by Hilbre Island
Bird Observatory, RSPB (at Ynysoedd y Moelrhoniaid/The Skerries) and Ynys Enlli/Bardsey
Island Bird Observatory (Westcott, 2002). In this survey, effort was made to report seal
numbers and calibrate the different survey methods carried out by these organisations so that
in future they will be comparable.
Guidelines for using observatory data in estimating seal numbers are reported separately as
site based Standard Operating Procedures (Westcott & Stringell, in prep).
Photo-ID
The present work aimed to generate images for a site- and time-specific photographic
identification catalogue for all seals photographed or filmed at nursery sites during the
project. The work is reported in Westcott & Stringell (in prep). The catalogue will provide a
basis for future work in the evaluation of breeding population size, the estimation of
abundance using mark:recapture techniques, seal distribution, site fidelity and movement
between sites.
The evaluation of methods for generating images for photographic identification of grey seals
in North Wales is reported in Westcott & Stringell (in prep).
7
2 METHODS
2.1 Study area
The study area can be regarded as falling into three districts:
1. Penrhyn Llyn/Lleyn Peninsula, consisting mainly of sites on the south coast of the
peninsula, west of Pwllheli, and Ynys Enlli/Bardsey Island
2. Ynys Môn/Anglesey: Ynysoedd y Moelrhoniaid/The Skerries, Ynys Cybi/Holy Island
(consisting of sites between Ynys Lawd/South Stack and the harbour at Holyhead),
Trwyn y Gader/Carmel Head (consisting of sites between Cemlyn Bay and Church
Bay), and islands on the east coast, Ynys Dulas and Ynys Seiriol/Puffin Island.
3. West Hoyle Sandbank.
Ynysoedd y
Moelrhoniaid/The Skerries Middle
Mouse West Hoyle Sandbank
East Mouse
Trwyn y
Gader/Carmel Head
C
Porth Bribys to Ynys Dulas
Ynys Fydlyn
B
Ynys Arw/North
Stack coast Ynys
Seiriol/Puffin
Ynys
Island
Llanddwyn
Carreg Ddu
Rhosgor
Glanllynnau Skerries
Porth Gwylan
A
Tudwals and
Porth Widlin Carreg y Trai
Trwyn Cilan
Ynys
Enlli/Bardsey
Sarn Badrig
Island*
Porth Meudwy Gwylans Coast
Map 1. Grey seal haul out sites in 2002-2003. The three districts are: (A) Pen
Llyn/Lleyn Peninsula including Ynys Enlli/Bardsey Island, (B) Ynys Môn/Anglesey, and
(C) West Hoyle Sandbank. * For an enlargement of Bardsey Island see Map 2.
2.2 Abundance and distribution data collection
A haul-out site denotes a place ashore where seals are found. Consequently, nursery sites are
also classified as haul-out sites in the context of the distribution and abundance survey.
8