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Management measures for self propagated future recovery of crawfish, Palinurus elephas, in Welsh waters.

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Abstract and Figures

Populations of the crawfish, Palinurus elephas, in Welsh waters have declined significantly since the 1960s and 1970s when changes in fishing practice took place. This large benthic crustacean is a key species in reef features within existing marine Special Areas of Conservation (SACs) and also within the wider context of the Welsh marine ecosystem. Recovery of crawfish populations is considered important in gaining Good Environmental Status (GES) for marine ecosystems under the Marine Framework Strategy Directive (MSFD). This report assesses the potential for both existing and potential management measures to aid in the self-propagated recovery of crawfish populations in Welsh waters and makes some recommendations on future data collection requirements. One of the main difficulties in carrying out an assessment of management measures in facilitating crawfish recovery is a lack of data on both the biology and fishery of this species, which means that analytical stock assessments are not possible. The potential for recovery is therefore assessed based on existing knowledge of the biology of this species from throughout its geographical distribution, and from studies carried out on other spiny lobsters. Fisheries data, in the form of landings per unit effort (LPUE), has been collected for crawfish fisheries in south Wales since the 1980s under a shellfish permit scheme put in place by the South Wales Sea Fisheries Committee (SWSFC). This dataset has been identified as a benchmark to represent recovery towards an interim recovering target heading towards a population with the relevant characteristics to represent GES. Existing management measures include minimum landing sizes (MLS), nature conservation designations, and a non-commercial catch limit. While the catch limits and MLS are specific to crawfish they have not elicited any increase in LPUE since they were introduced. The nature conservation designations currently in place do not have any mandatory management measures specific to crawfish, although there is a voluntary closed area to netting within the Skomer Marine Nature Reserve (NMR) and a voluntary no-take of crawfish by recreational divers. The assessment concluded that none of the management measures currently in place are likely to contribute to the recovery of crawfish in Welsh waters. Of the potential management measures assessed, those which controlled fishing activity were deemed to have the most potential to aid crawfish recovery, as opposed to new nature conservation designations. Both appropriately selected area closures and a prohibition on the landing of crawfish have potential to both reduce fishing mortality and increase the reproductive output of the population. The introduction of appropriate minimum and maximum landing sizes concurrently, and prohibitions on the landing of berried crawfish, both have the potential to increase the reproductive output of the population. Some of the fisheries management measures assessed were deemed to be more suitable for application within a recovering population. These included gear restrictions, prohibitions of individual fishing methods, catch limits, and seasonal closures. Highly Protected Marine Conservation Zones (HPMCZ) in Wales and Marine Conservation Zones (MCZ) in England were also assessed, however, their relatively small size and focus on supporting ecosystem diversity and function may limit their potential to benefit the recovery of crawfish. Further research is required in order to determine which of the management measures would be most effective in facilitating the recovery of crawfish populations in Welsh waters. At present it is not clear if increases in the reproductive output of the population would directly result in increased recruitment to the population. The connectivity of populations within Welsh waters is also important in determining at what level management measures may need to be introduced. Due to the lack of information surrounding recruitment to Welsh crawfish populations, management measures which both reduce removals from the population and increase the potential reproductive output are likely to be most effective in facilitating recovery. Further information is also required to make a determination of whether or not Welsh populations would benefit from management measures implemented at the EU or regional seas level. The legislative framework for implementing fisheries management measures is an important consideration on the effectiveness of management measures and should be taken into consideration during the decision making process.
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1
Management measures for self-propagated
future recovery of crawfish, Palinurus elephas, in
Welsh waters
B. Leslie & R. L. Shelmerdine
CCW Contract Science Report No 989
© CCGC/CCW 2012
You may reproduce this document free of charge in any format or medium, provided that you
do so accurately, acknowledging both the source and Countryside Council for Wales's
copyright, and do not use it in a misleading context.
This is a report of research commissioned by the Countryside Council for Wales. 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.
2
CCW Contract Science Report No 989
i
Recommended citation for this volume:
Leslie, B., & Shelmerdine, R. L. 2012. Management measures for self-propagated future
recovery of crawfish, Palinurus elephas in Welsh waters. CCW Contract Science Report No:
989.
Report series:
CCW Contract Science Report
Report number:
989
Publication date:
May 2012
Contract number:
R002182
Contractor:
NAFC Marine Centre
Contract Manager:
Aethne Cooke
Title:
Management measures for self-propagated future recovery of crawfish,
Palinurus elephas, in Welsh waters.
Author(s):
B. Leslie & R. Shelmerdine
Series editor(s):
None
Restrictions:
No
Distribution list (core):
CCW HQ Library British Library, Document Supply Centre
CCW North Region Library,
Bangor
Welsh Government Library
Scottish Natural Heritage Library
(Electronic)
National Library of Wales
Natural England Library
(Electronic)
Distribution list (others):
UCW Cardiff Library Plymouth Marine Laboratory Library
UCW Swansea Library Marine Biological Association Library
UCW Aberystwyth Natural History Museum London Library
UCW Bangor Library
Catherine Duigan, CCW
Graham Rees, Welsh Government
Aethne Cooke, CCW Phil Coates, Welsh Government
Lucy Kay, CCW Catherine Raymond, Welsh Government
Kirsten Ramsay, CCW Sue Burton, Pembrokeshire Marine SAC Officer
Phil Newman, CCW Alison Hargrave, Pen Llyn a’r Sarnau SAC Officer
Mike Camplin, CCW Jennifer Kelly, Cardigan Bay SAC Officer
Anne Bunker, CCW
Blaise Bullimore, Carmarthen Bay & Estuaries
European Marine Site
Mark Burton, CCW Jennifer Jones, Consultant
Kate Lock, CCW Pembrokeshire LBAP partnership
Lily Pauls, CCW Anglesey LBAP partnership
Rowland Sharp, CCW Gwynedd LBAP partnership
Colin Charman, CCW
Clare Eno, CCW
Andrea Winterton, CCW
Ziggy Otto, CCW
Roger Covey, NE
Rob Enever, NE
Jo Breen, EHS NI
CCW Contract Science Report No 989
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CONTENTS
CONTENTS....................................................................................................................................ii
LIST OF FIGURES......................................................................................................................iv
LIST OF TABLES..........................................................................................................................v
CRYNODEB GWEITHREDOL ...................................................................................................vi
EXECUTIVE SUMMARY..........................................................................................................viii
1
Introduction..........................................................................................................................10
1.1
Biology..........................................................................................................................10
1.1.1
Distribution and Habitat Preferences ........................................................................10
1.1.2
Growth.......................................................................................................................14
1.1.3
Reproductive Biology ...............................................................................................15
1.1.4
Biology Summary .....................................................................................................16
1.2
Fishery..........................................................................................................................19
1.2.1
Fishing Methods........................................................................................................19
1.2.2
Status of the fishery...................................................................................................20
1.3
Legislation....................................................................................................................23
2
Methods.................................................................................................................................24
2.1
Assessment of Management Measures......................................................................24
2.2
Definition of Recovery ................................................................................................24
3
Assessment of management measures.................................................................................26
3.1
Existing Management Measures................................................................................26
3.1.1
Minimum Landing Sizes...........................................................................................26
3.1.2
Marine Special Area of Conservation Management Measures.................................27
3.1.3
Skomer Marine Nature Reserve................................................................................29
3.1.4
Non-Commercial Catch Limit...................................................................................30
3.2
Potential Management Measures...............................................................................30
3.2.1
Maximum Landing Size............................................................................................30
3.2.2
Landing Prohibition...................................................................................................32
3.2.3
Gear Restrictions.......................................................................................................33
3.2.4
Catch Limits..............................................................................................................36
3.2.5
V-notching.................................................................................................................36
3.2.6
Prohibiting the landing of berried females................................................................37
3.2.7
Area Restrictions.......................................................................................................38
3.2.8
Seasonal Restrictions.................................................................................................40
3.2.9
Highly Protected Marine Conservation Zones in Welsh Waters ..............................41
3.2.10
Marine Conservation Zones in England................................................................42
3.3
Potential Recovery Rates............................................................................................44
4
Data Requirements to enable assessment of Welsh Crawfish population(s).....................46
5
Discussion.............................................................................................................................49
5.1
Existing management measures.................................................................................49
5.2
Possible Management Measures................................................................................50
CCW Contract Science Report No 989
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5.3
Conclusions..................................................................................................................55
6
Acknowledgements...............................................................................................................56
7
References.............................................................................................................................57
CCW Contract Science Report No 989
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LIST OF FIGURES
Figure 1.1 Annual residual currents and direction at 50% depth from surface obtained from
Lambkin et al. (2010). This data should be taken when interpreting this data in relation to
Palinurus elephas larval distribution, as discussed in the text.....................................................13
Figure 1.2 Annual Palinurus elephas landings from all fishing gears (not effort related) in the
south Wales shellfish permit area (formerly the South Wales Sea Fisheries Committee Area).
Data from the Welsh Government.................................................................................................20
Figure 1.3 Annual Landings Per Unit Effort (LPUE) from the pot fishery for Palinurus elephas
from the south Wales shellfish permit area (formerly the South Wales Sea Fisheries Committee
Area). Data from the Welsh Government.....................................................................................21
Figure 1.4 Annual UK landings of Palinurus elephas by nationality of vessel (Data from the
Marine Management Organisation)..............................................................................................22
CCW Contract Science Report No 989
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LIST OF TABLES
Table 1.1 Estimated age at size for Palinurus elephas taken from Mercer (1973)
*
. Lengths refer
to carapace lengths (CL)...............................................................................................................14
Table 1.2 Data on size at maturity and fecundity from Palinurus elephas in different areas. The
relationship between number of eggs (E) and carapace length (CL) are shown when available.17
Table 3.1 Examples of Palinurus elephas recovery in other areas, and for other species, with
potential timescales for recovery where the information is available..........................................44
Table 5.1 The potential direct effects for each management measure, if implemented effectively,
to contribute to the recovery of Palinurus elephas in Welsh waters. The capability for increased
reproductive output does not necessarily infer increased recruitment. Increased abundance
refers directly to the management measure reducing removals from the fishery, rather than
through increases in recruitment brought about by the resultant increased reproductive output
(though these may also be possible). Potential combinations of measures refer to the potential
measures set out in this report. .....................................................................................................53
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CRYNODEB GWEITHREDOL
Mae poblogaethau’r cimwch coch, Palinurus elephas, yn nyfroedd Cymru wedi dirywio’n
sylweddol ers yr 1960au a’r 1970au pan ddigwyddodd newid mewn arferion pysgota. Mae’r
cramennog môr-waelodol mawr hwn yn rhywogaeth allweddol mewn nodweddion riffiau yn yr
Ardaloedd Cadwraeth Arbennig (ACA) morol presennol a hefyd yng nghyd-destun ehangach
ecosystem forol Cymru. Ystyrir ei bod yn bwysig adfer poblogaethau’r cimwch coch er mwyn
sicrhau Statws Amgylcheddol Da i ecosystemau morol dan Gyfarwyddeb Fframwaith y
Strategaeth Forol (MSFD). Mae’r adroddiad hwn yn asesu potensial y mesurau rheoli presennol
a darpar fesurau rheoli i gynorthwyo i adfer poblogaethau’r cimwch coch yn nyfroedd Cymru
drwy hunan-luosogi ac yn gwneud argymhellion ar y gofynion o safbwynt casglu data i’r
dyfodol.
Un o’r prif anawsterau wrth wneud asesiad o’r mesurau rheoli i hwyluso adferiad y cimwch coch
yw’r diffyg data ar fioleg a physgodfa’r rhywogaeth hon, ac mae hynny’n golygu nad yw’n
bosibl gwneud asesiadau dadansoddol o’r stoc. Mae’r potensial i’w hadfer felly’n cael ei asesu ar
sail y wybodaeth bresennol am fioleg y rhywogaeth hon o’i holl ddosbarthiadau daearyddol, ac o
astudiaethau a wnaed ar gimychiaid pigog eraill. Bu data pysgodfeydd, ar ffurf glaniadau am bob
uned ymdrech (LPUE), yn cael ei gasglu ar gyfer pysgodfeydd cimwch coch yn ne Cymru ers y
1980au dan gynllun trwydded pysgod cregyn a sefydlwyd gan Bwyllgor Pysgodfeydd Môr De
Cymru (SWSFC). Mae’r set ddata hon wedi’i dynodi fel meincnod i gynrychioli adferiad tuag at
darged adfer interim sy’n anelu at boblogaeth sydd â’r nodweddion perthnasol i gynrychioli
Statws Amgylcheddol Da.
Ymysg y mesurau rheoli presennol y mae maint lleiaf ar gyfer glanio (MLS), dynodiadau
cadwraeth natur, a chyfyngiad ar ddal anfasnachol. Er bod y cyfyngiadau ar ddal a’r MLS yn
benodol i’r cimwch coch, nid ydynt wedi esgor ar ddim cynnydd mewn LPUE ers eu cyflwyno.
Nid oes gan y dynodiadau cadwraeth natur sydd wedi’u sefydlu ar hyn o bryd ddim mesurau
rheoli gorfodol yn benodol i’r cimwch coch, er bod ardal gaeedig i rwydo yn cael ei
gweithredu’n wirfoddol yng ngwarchodfa natur forol (GNF) Skomer ac ymrwymiad gwirfoddol
ymysg deifwyr hamdden i beidio â chymryd dim cimychiaid coch. Mae’r asesiad yn dod i’r
casgliad nad oes dim un o’r mesurau rheoli sydd wedi’u sefydlu ar hyn o bryd yn debygol o
gyfrannu at adfer cimychiaid coch yn nyfroedd Cymru.
O’r mesurau rheoli posibl a aseswyd, ystyriwyd mai’r rheini sy’n rheoli gweithgaredd pysgota
yw’r rhai sydd â’r potensial mwyaf i gynorthwyo adferiad y cimwch coch, yn hytrach na
dynodiadau cadwraeth natur newydd. Wrth gau ardaloedd dethol a gwahardd glanio’r cimwch
coch, fel ei gilydd, ceir y potensial i leihau marwolaethau yn sgil pysgota a chynyddu allbwn
atgenhedlu’r boblogaeth. Wrth gyflwyno maint glanio lleiaf a mwyaf priodol ar y cyd, ceir y
potensial i gynyddu allbwn atgenhedlu’r boblogaeth. Ystyriwyd bod rhai o’r mesurau rheoli
pysgodfeydd y’u haseswyd yn fwy addas i’w defnyddio gyda phoblogaeth sydd yn adfer. Ymysg
y rhain yr oedd cyfyngiadau ar offer, gwaharddiadau ar ddulliau pysgota unigol, cyfyngiad ar
faint dalfeydd, a chyfnodau cau tymhorol. Cafodd Gwarchodfeydd Morol Gwarchodedig Iawn
(HPMCZ) yng Nghymru a Pharthau Cadwraeth Morol (MCZ) yn Lloegr hefyd eu hasesu, fodd
bynnag, gallai eu maint cymharol fychan a’r ffocws ar gefnogi swyddogaeth ac amrywiaeth
ecosystemau gyfyngu ar eu potensial i fod o fudd i adfer y cimwch coch.
Mae ymchwil pellach yn ofynnol er mwyn penderfynu pa rai o’r mesurau rheoli fyddai fwyaf
effeithiol yn hwyluso adferiad poblogaethau’r cimwch coch yn nyfroedd Cymru. Ar hyn o bryd
nid yw’n glir a fyddai cynnydd yn allbwn atgenhedlu’r boblogaeth yn arwain yn uniongyrchol at
gynnydd mewn lefelau recriwtio i’r boblogaeth. Mae’r cysylltiad rhwng poblogaethau yn
nyfroedd Cymru hefyd yn bwysig i benderfynu ar ba lefel y byddai angen cyflwyno mesurau
rheoli o bosibl. Oherwydd diffyg gwybodaeth am recriwtio i boblogaethau’r cimwch coch yng
Nghymru, mesurau rheoli a fydd yn cyfyngu ar dynnu oddi wrth y boblogaeth ac yn cynyddu’r
allbwn atgynhyrchu posibl sy’n debygol o fod yn fwyaf effeithiol i hwyluso eu hadferiad. Mae
CCW Contract Science Report No 989
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gwybodaeth bellach hefyd yn ofynnol i benderfynu a fyddai poblogaethau Cymru yn elwa o
fesurau rheoli a weithredir ar lefel y moroedd rhanbarthol neu’r UE. Mae’r fframwaith
deddfwriaethol ar gyfer gweithredu mesurau rheoli pysgodfeydd yn ystyriaeth bwysig o
safbwynt effeithiolrwydd mesurau rheoli a dylid rhoi ystyriaeth i hwn yn ystod y broses
benderfynu.
CCW Contract Science Report No 989
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EXECUTIVE SUMMARY
Populations of the crawfish, Palinurus elephas, in Welsh waters have declined significantly
since the 1960s and 1970s when changes in fishing practice took place. This large benthic
crustacean is a key species in reef features within existing marine Special Areas of Conservation
(SACs) and also within the wider context of the Welsh marine ecosystem. Recovery of crawfish
populations is considered important in gaining Good Environmental Status (GES) for marine
ecosystems under the Marine Strategy Framework Directive (MSFD). This report assesses the
potential for both existing and potential management measures to aid in the self-propagated
recovery of crawfish populations in Welsh waters and makes some recommendations on future
data collection requirements.
One of the main difficulties in carrying out an assessment of management measures in
facilitating crawfish recovery is a lack of data on both the biology and fishery of this species,
which means that analytical stock assessments are not possible. The potential for recovery is
therefore assessed based on existing knowledge of the biology of this species from throughout its
geographical distribution, and from studies carried out on other spiny lobsters. Fisheries data, in
the form of landings per unit effort (LPUE), has been collected for crawfish fisheries in south
Wales since the 1980s under a shellfish permit scheme put in place by the South Wales Sea
Fisheries Committee (SWSFC). This dataset has been identified as a benchmark to represent
recovery towards an interim recovering target heading towards a population with the relevant
characteristics to represent GES.
Existing management measures include minimum landing sizes (MLS), nature conservation
designations, and a non-commercial catch limit. While the catch limits and MLS are specific to
crawfish they have not elicited any increase in LPUE since they were introduced. The nature
conservation designations currently in place do not have any mandatory management measures
specific to crawfish, although there is a voluntary closed area to netting within the Skomer
Marine Nature Reserve (MNR) and a voluntary no-take of crawfish by recreational divers. The
assessment concluded that none of the management measures currently in place are likely to
contribute to the recovery of crawfish in Welsh waters.
Of the potential management measures assessed, those which controlled fishing activity were
deemed to have the most potential to aid crawfish recovery, as opposed to new nature
conservation designations. Both appropriately selected area closures and a prohibition on the
landing of crawfish have potential to both reduce fishing mortality and increase the reproductive
output of the population. The introduction of appropriate minimum and maximum landing sizes
concurrently, and prohibitions on the landing of berried crawfish, both have the potential to
increase the reproductive output of the population. Some of the fisheries management measures
assessed were deemed to be more suitable for application within a recovering population. These
included gear restrictions, prohibitions of individual fishing methods, catch limits, and seasonal
closures. Highly Protected Marine Conservation Zones (HPMCZ) in Wales and Marine
Conservation Zones (MCZ) in England were also assessed, however, their relatively small size
and focus on supporting ecosystem diversity and function may limit their potential to benefit the
recovery of crawfish.
Further research is required in order to determine which of the management measures would be
most effective in facilitating the recovery of crawfish populations in Welsh waters. At present it
is not clear if increases in the reproductive output of the population would directly result in
increased recruitment to the population. The connectivity of populations within Welsh waters is
also important in determining at what level management measures may need to be introduced.
Due to the lack of information surrounding recruitment to Welsh crawfish populations,
management measures which both reduce removals from the population and increase the
potential reproductive output are likely to be most effective in facilitating recovery. Further
information is also required to make a determination of whether or not Welsh populations would
CCW Contract Science Report No 989
ix
benefit from management measures implemented at the EU or regional seas level. The
legislative framework for implementing fisheries management measures is an important
consideration on the effectiveness of management measures and should be taken into
consideration during the decision making process.
CCW Contract Science Report No 989
10
1 INTRODUCTION
The crawfish, Palinurus elephas, is a large benthic crustacean found mainly on rocky seabeds
from the Azores in the south to Norway in the North and throughout the Mediterranean. This
species is commercially valuable and has been targeted by fisheries for over a century; however,
fisheries in Wales and beyond have seen a steep decline in landings since the 1960s which
coincided with the introduction of net fisheries for this species.
The crawfish is a priority species for the UK Biodiversity Action Plan and is also an important
component of Special Areas of Conservation (SACs) designated for rocky reefs. It has been
identified by the National Assembly for Wales as one of the species of ‘principle importance for
the purpose of conserving biodiversity’ in Wales and is listed in the Natural Environment Rural
Communities (NERC) Act 2006. This act requires that steps be taken that are ‘reasonably
practicable to further the conservation of the living organisms’ listed and to ‘promote the taking
by others of such steps’. It is therefore important to understand the potential impact of fisheries
management measures, and other management measures, on the recovery of this species both in
designated areas and within the wider context of Welsh waters as a whole, including the
potential impact of regulations or management measures in adjacent waters.
The aim of this report is to establish the potential effectiveness of existing and possible
management measures (both fishery and nature conservation based) to enable self-propagated
recovery of P. elephas populations in Welsh waters, within the context of their declined status.
This is to be carried out through a review of relevant literature on this and other crustacean
species to determine, using the best available data and information, the potential benefit of the
different management measures.
1.1 Biology
Two reviews have been carried out presenting the body of information on the biology of
Palinurus elephas (Hunter, 1999, Goñi and Latrouite, 2005). The following sections focus on
the aspects of biology which are most relevant to the self-propagated recovery of crawfish in
Welsh waters.
1.1.1 Distribution and Habitat Preferences
The European spiny lobster, or crawfish (Palinurus elephas, Fabricius, 1787), is widely
distributed from its southern limit in west Africa to its northern limit off western Norway
(Mercer, 1973) but also includes the Mediterranean, Azores, and the Adriatic and Aegean Seas
(Goñi and Latrouite, 2005, Jackson et al., 2009). Around the British Isles, P. elephas, has been
found to occur mainly along the west coast although some historical records have recorded
sightings of P. elephas on the Scottish east coast (Ansell and Robb, 1977). The authors also
noted the occurrence of P. elephas larvae in this area.
Palinurus elephas show a preference for exposed areas of reef with strong currents and often
steep topography with crevices. Mercer (1973) reported that P. elephas preferred reef areas
close to relatively deep water of at least 30 m. All P. elephas collected by Ansell and Robb
(1977), using SCUBA divers, were from areas of strong tidal currents on shallow inshore reefs
which were interspersed with steep vertical rock faces. The authors noted that the majority of
specimens were found on rocky surfaces in the open or among weed but occasionally some were
found in crevices. This has particularly been noted for juveniles which can be found grouped
together, although in separate crevices within a gully (Jones, in prep). Ansell and Robb (1977)
noted a varying depth of capture from 5 to 20 m. Hayward and Ryland (2004) reported a depth
distribution of between 20 and 70 m. However, information cited in Goñi and Latrouite (2005)
suggest that their distribution extends down to 200 m.
CCW Contract Science Report No 989
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There is no known published information available on the depth distribution and habitat
preference of P. elephas within Welsh waters. Underwater SCUBA diving between 1960 and
2006 documented 62 records of P. elephas (records held by Marine Recorder and supplied to the
authors by CCW). Of these, only 24 had a biotope code assigned to the location and these
consisted of either Infralittoral Rock (IR) or Circalittoral Rock (CR). Where the classification
extended beyond this, both rock habitats were classed as either high energy or moderate energy
sites. A large amount of habitat data for the southern Irish Sea is available through the
HABMAP project (see Robinson et al., 2009a; Robinson et al., 2009b; Robinson et al., 2011).
The majority of the area presented utilises predictive habitat mapping based on existing data, but
some sub-areas were intensively surveyed with a higher degree of confidence closer to shore.
The results do show that, based on the biotope classification, suitable habitat for P. elephas is
present within Welsh waters, including within the existing SACs of Pembrokeshire Marine and
Pen Llŷn a’r Sarnau. Due to the predictive nature of the HABMAP data it is not possible to
utilise it to make any precise estimates of the actual extent and distribution of available crawfish
habitat within Welsh waters.
Ansell and Robb (1977) suggested that P. elephas may have a seasonal migratory pattern in
Scottish waters as there is an increased catch in shallow waters during spring and summer,
moving to deeper waters in the winter. Although the authors note this pattern may be due to a
seasonal variation in the fishing pattern rather than an actual seasonal migration, the findings are
corroborated by Mercer (1973). Mercer (1973) also recorded smaller scale movements of
P. elephas moving to deeper water, during moulting, for shelter from swell and strong currents.
Mercer (1973) defined seven different types of movement carried out by P. elephas in Irish
waters. These movement types were:
Type A Regular onshore/offshore migrations of seasonal occurrence
Type B Large-scale migrations involving a major proportion of the population moving either
in single files or ‘en masse’
Type C Reproductive migrations and movements
Type D Relatively small local movements for feeding and moulting
Type E Migrations due to weather conditions
Type F Isolatory movements of animals of the same sex or juveniles
Type G Random wanderings
The author noted that although other studies did not record all of the above movement types, this
was most probably due to the methodology used rather than the lack of movement type within a
particular population. Movement Type G was considered a source of natural repopulation of reef
systems which had experienced heavy fishing pressure with repopulation estimated to take
between a week and ten days (Mercer, 1973). However, this would only apply if there was a
thriving, widespread P. elephas population in the near vicinity. Goñi and Latrouite (2005)
reported on tag-recapture studies which suggested a maximum movement of P. elephas of 20 km
after one to eight years at large, although most animals were found to move less than 5 km (see
also Follesa et al., 2009). The authors also noted some additional studies in the Mediterranean
which report movements of 50 and 70 km. Follesa et al. (2009) reported on a total of 389
recaptured, tagged animals and showed that 60% of recaptures moved less than 2 km from the
release site (nearly 80% were found <5 km from the release site) and only 2.3% of crawfish
moved further than 20 km. The greatest movement was made by an 80 mm CL female which
covered a distance of 134 km over 712 days. However, these results should be treated with a
degree of caution as all animals were initially released in the centre of a protected area
irrespective of their initial catch location. This may have had a corresponding effect on the
distance travelled with regard to potential disorientation effects.
CCW Contract Science Report No 989
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Tagging of Panulirus argus has shown that juveniles appeared to be more mobile than mature
individuals, which were more residential in nature (Davis, 1977). Goñi et al. (2001) suggested
that juvenile Palinurus elephas settled in shallow water but then underwent a migration to deeper
water at between two and three years of age. The authors suggested that this migration took
place during winter or spring.
1.1.1.1 Distribution of larval and post-larval stages
Palinurus elephas hatch from the egg into a planktonic larval stage, termed a phyllosoma.
Phyllosoma go through several stages of development within the plankton before
metamorphosing into the puerulus stage. The puerulus stage is a transitional stage to a benthic
existence prior to becoming an adult (see section 1.1.3 for further information).
There are no free-swimming larval stages in P. elephas (Mercer, 1973). The author reports
phyllosoma larval Stages I and II as common in inshore waters, close to shore off west Ireland,
from May to early July. Stage III larvae were rare and only found in July and August off Ireland
with a possible Stage IV recorded in mid-August (Mercer, 1973). The author noted no
recordings of further larval stages or of the puerulus stage off Ireland. The later stage larvae are
not found in near-shore environments but are found at variable distances, possibly 100 miles or
more, offshore (Mercer, 1973). The phyllosoma larval stages are poor horizontal swimmers but
are competent in making vertical movements within the water column (Goñi and Latrouite,
2005). Several studies were cited by Mercer (1973) with regard to larval distribution and
corresponding interconnectivity. All the studies cited were from exposed areas such as
California, Hawaii, and South Africa with all studies suggesting an initial offshore movement of
larvae followed by a corresponding onshore movement driven by eddies potentially operating off
the main current system. The author also noted that a lack of information on currents would
make predictions of larval distribution very hard. It is not clear whether such a system would
function in a more enclosed area such as that off Wales. It has been suggested that larvae
produced in south Wales could be taken offshore by the Carnsore current and then return to
Welsh waters via the Lands End Corner current (Davies, 1999).
Lambkin et al. (2010) carried out an in-depth analysis of residual currents around British and
Irish coasts extending out into the Atlantic. The work carried out by Lambkin et al. (2010) had
several caveats, two of which were in regard to; proximity to shore, and vertical movements.
Confidence in the model produced by Lambkin et al. (2010) is reduced in areas close to shore, at
and around headlands, and when depth of the animal or particle does not remain constant.
Overall there seemed to be very little residual currents at 50% depth in Welsh waters off the
Cardigan Bay/south Irish Sea area for all four seasons (Lambkin et al., 2010) suggesting
phyllosoma larvae may remain within the area for a substantial period. Annual residual current
and direction for 50% depth reported by Lambkin et al. (2010) are shown in Figure 1.1. As
mentioned previously, the phyllosoma stages exhibit an initial close correlation with inshore
waters before being carried offshore where they are able to undertake vertical migrations in the
water column (Mercer, 1973). Based on the data from Lambkin et al. (2010) connectivity in
terms of larval supply to other P. elephas populations may be possible via a southerly
distribution out of the Irish Sea along the south Irish coast to the Atlantic and also north along
the west of England coastline into Scottish waters. Incoming residual currents would, in the
south, come from the southwest of England and from the north along the Northern Ireland coast.
This is based on residual currents at 50% depth and assumes no vertical movements. Detailed
information on localised currents would have to be applied to the larval biology in the area while
considering natural variation of larva release due to climatic conditions (see Section 1.1.3).
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Figure 1.1 Annual residual currents and direction at 50% depth from surface obtained from Lambkin et al. (2010).
This data should be taken when interpreting this data in relation to Palinurus elephas larval distribution, as
discussed in the text.
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1.1.2 Growth
Growth, of no more than four millimetres carapace length, has been recorded at the moult for P.
elephas, although in some cases change in length was non-existent but weight increases, in some
cases of over 50%, were observed (Ansell and Robb, 1977). Such small growth increments,
sometimes negligible, were also reported by Mercer (1973) who also noted that such small
increases were not uncommon in captive animals. Hepper (1977), studying 46 recaptured
animals off Cornwall, recorded a range of growth increments of one to eight millimetres and
calculated a mean growth increment of 1.96 ± 1.38 mm. The mean annual length increase of an
Irish P elephas population, measured in their natural habitat, was calculated as 12.2 mm CL
(30.5 mm total length, n = 7) for males and 12.0 mm CL (35.1 mm TL, n = 8) for females
(Mercer, 1973). A larger growth study was conducted off Corsica but these results should be
treated with caution when comparing to the colder climes of the Atlantic (cited in Hunter, 1999)
as it is well known that temperature has an effect on growth rates. Age at length data was
estimated by Mercer (1973) but extreme caution should be taken when applying the estimates
(see Table 1.1). The author estimated males of 111 mm CL and females of 110 mm CL both to
be about four to five years old.
Table 1.1 Estimated age at size for Palinurus elephas taken from Mercer (1973)
*
. Lengths refer to carapace
lengths (CL).
Male
Female
CL (mm) Age (years) CL (mm) Age (years)
87 2-3 86 2-3
99 3-4 98 3-4
111 4-5 110 4-5
123 5-6 122 5-6
136 6-7 134 6-7
148 7-8 146 7-8
160 8-9 158 8-9
172 9-10
* The author attached a cautionary warning to the data and recommended that if used, the lower
age estimates should be considered.
Males are larger than females (Ansell and Robb, 1977, Hepper, 1977, Goñi and Latrouite, 2005)
throughout their geographic distribution. The largest animals caught off the west coast of
Scotland were measured as 170 mm carapace length (CL) in males and 158 mm CL in females
(Ansell and Robb, 1977). The authors noted a similarity from studies in other geographic areas,
namely an Irish population (males: 165 mm CL; females: 151 mm CL) and one from Cornwall
(males: 182 mm CL; females: 152 mm CL).
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1.1.3 Reproductive Biology
The reproductive biology of an Irish population of Panulirus elephas was extensively examined
by Mercer (1973) with several additional studies reporting on the reproduction of P. elephas
from various geographic locations. Much of this information has been summarised in two
reviews (see Hunter, 1999, Goñi and Latrouite, 2005).
In UK waters female P. elephas moult in the summer months from July to September, (Mercer,
1973, Ansell and Robb, 1977, Hepper, 1977, Hunter, 1999) and the moult is completed in ten to
15 minutes (Mercer, 1973, and see Hunter, 1999 for a review). In Irish waters, P. elephas, move
to deeper water to moult (Mercer, 1973) but on the Scottish west coast, moulting was observed
to occur in inshore areas (Ansell and Robb, 1977). After moulting, the new shell hardens within
seven to 19 days (see Hunter, 1999 for a review). Mating has been observed to take place within
two weeks of the female moult (Ansell and Robb, 1977) with egg laying occurring five to ten
days after this. The positioning of the spermatophore during mating is important and therefore
the male and female must be of a similar size (Davies, 1999). The female then carries the eggs
throughout the winter before they hatch in the following spring (Ansell and Robb, 1977).
Mercer (1973) found egg hatching to have occurred by mid-May, although the author noted that
this can vary depending on seasonal temperature fluctuations. In the Atlantic, incubation lasts
around nine months and hatching takes two to eight days (Hunter, 1999). In the Atlantic, post
hatching P. elephas spend up to a year in the water column as a larva (see also Section 1.1.1.1),
termed phyllosoma (see Hunter, 1999, and Goñi and Latrouite, 2005 for reviews). There is very
little observed information from post larva, termed puerulus, through to adulthood (Hunter,
1999).
Goñi et al. (2003a) found that there was considerable variation in egg production between
females of similar size. The number of eggs per clutch was found to increase linearly with
increasing body size, however the maximum reproductive yield, in terms of eggs per unit weight,
occurred in females from 100 to 110 mm CL (Goñi et al., 2003a). Hunter (1999) stated that, “as
a general rule, fecundity in P. elephas is three to five times smaller than in spiny lobsters of the
genera Jasus and Panulirus”. Egg loss during incubation under laboratory conditions has been
shown to vary from 10 to 30% (Mercer, 1973, and see Hunter, 1999 for a review) but this may
not be representative of conditions in the wild.
The smallest berried female varied geographically, ranging from 67 mm CL to 121 mm CL with
the smaller animals recorded in warmer waters (see Hunter, 1999 for a review). Hunter et al.
(1996) reported the smallest berried female in southwest England measuring 90 mm CL and 121
mm CL in Wales while the smallest berried female in Scotland, measured by Ansell and Robb
(1977), was 98 mm CL. Sexual maturity in an Irish population was estimated between 70 and 94
mm CL, with 50% maturity at 82 mm CL (Mercer, 1973). An assessment of the female
reproductive biology of P. elephas in the Spanish Mediterranean indicated that females reached
physiological and functional maturity at 76 to 77 mm CL, although individuals with ripe ovaries
were observed as small as 69 mm CL (Goñi et al., 2003a). Information on particular size at 50%
maturity is summarised in Table 1.2. Males were slightly larger, reaching physiological maturity
at 82.5 mm CL (Goñi et al., 2003a). When looking at the female size where 50% of individuals
are mature this varied from 95 mm CL in Brittany (Goñi and Latrouite, 2005) to 139.9 mm CL in
Wales (Hunter et al., 1996), as shown in Table 1.2.
There is a difference in reproductive behaviour relative to female size with larger females mating
and laying eggs early in the breeding season and smaller females laying eggs later in the season.
Male P. elephas have been shown to mate repeatedly throughout the breeding season (Goñi et
al., 2003a).
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1.1.4 Biology Summary
The biology of Palinurus elephas has been studied in several geographic locations within its
distribution. On a large geographic scale, two distinct areas of investigation were identified from
the literature; the cooler Atlantic and the warmer Mediterranean. In the context of Welsh
populations, studies from the latter region should always be treated with a degree of caution as
temperature is a known variable affecting growth rates and the reproductive cycle. Interpretation
of data collected from other species should also be carried out with caution, as aspects of their
biology and location will be different to populations of P. elephas in Welsh waters.
Many studies have examined the reproductive biology of P. elephas in different geographic areas
(see Section 1.1.3). There is a substantial amount of information available, although some data
is deficient or scarce (e.g. information on male maturity and female fecundity in Welsh waters,
see Table 1.2). The reproductive cycle from the female moult through to egg hatching, larval
phase, to puerulus stage can range from around 21 to 22 months, based on the findings in Section
1.1.3, with the puerulus stage probably occurring from around April through to July, based on a
moulting period of July to September. There is very little information in the literature regarding
the puerulus stage to adulthood. It was suggested by Mercer (1973) from in situ observations
that this stage may “prefer low salinity environments” but little to no data is available regarding
aspects such as; time spent in low salinity environments, growth rates, and ecology to name but a
few. Larval connectivity is one of the main areas of data deficiency with regards to the biology
of P. elephas in Welsh waters (see Section 1.1.1.1). Further work would have to be conducted in
order to investigate this fully.
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Table 1.2 Data on size at maturity and fecundity from Palinurus elephas in different areas. The relationship between number of eggs (E) and carapace length (CL) are shown when
available.
Location size at 50%
maturity
(mm CL)
Smallest ovigerous
(mm)
(n=total females sampled)
fecundity size at
maturity
Reference
Wales 139.8 (mean size
of berried )
121 (n=135) Hunter et al. (1996)
SW England 135.0 (mean size
of berried )
90 (n=1592) Hunter et al. (1996)
East Cornwall 65 000 to 184 000 Hepper (1977)
Ireland 82 70-90 E = 2553CL – 165602
40 560 to 214 128
84.5 Mercer (1973), cited in Hunter et
al. (1996)
NW Ireland 119 (mean size of
berried )
85 (n=232) Robinson et al. (2008)
Scotland 98 Ansell and Robb (1977)
Bay of Biscay 100 000 Valenciennes (1858)
Brittany 95 (mean size of
berried )
92 cited in Goñi and Latrouite
(2005)
Portugal 110 84 E = 3355CL – 283832
Galhardo et al. (2006)
Portugal
Portugal
82 000 to 209 000
E = 2520CL – 196225
as reported by Hunter (1999)
cited in Galhardo et al. (2006)
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Spanish Mediterranean 76.5 (n=192)
69 23 483 to 201 549
E = 2428CL – 148998
82.7 (n=94)
Goñi et al. (2003a)
Corsica 70 20 000 to 210 000 Campillo and Amadei (1978)
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1.2 Fishery
Palinurus elephas command a high market price and have been subject to fishing activity for
centuries, with fisheries in the UK and Ireland developing in the early 1900s. These fisheries
were mainly carried out using pots until the introduction of trammel (and tangle) nets in the
1960s and 1970s (Groeneveld et al., 2006). This resulted in increased fishing effort and greater
efficiency of gear, and stocks declined. More recently there have been reported declines in
Palinurus spp (P. elephas and P. mauritanicus) throughout all European and African countries
between 1988 and 1996 (e.g. Galhardo et al., 2006). It is generally accepted that that
modernisation of fishing fleets and changes in fishing gear have resulted in over-fishing of
crawfish stocks during these periods. However, in some cases, there is a lack of fisheries data
with which to scientifically corroborate this.
1.2.1 Fishing Methods
The three main methods for catching P. elephas are netting (tangle and trammel), potting, and
dive fisheries. Historically fisheries began by potting for crawfish and this was followed by the
introduction of more efficient dive and net fisheries. Crawfish caught in pots in Welsh waters
are a bycatch of fisheries for lobsters and crabs, there is no targeted pot fishery. Traditional rush
traps have been used to catch crawfish in the Mediterranean. However, as the skills required to
produce them are lost, modern plastic traps have been looked at as an alternative to trammel nets
which are considered to be unsustainable due to high catch rates. A study by Gristina and
Gagliano (2004) showed, under experimental conditions, that there was not a difference in catch
rates between traditional rush traps and modern plastic traps. The efficiency of targeted trap
fisheries is affected by soak time with the catch rate falling after two nights fishing (Robinson
and Dimitriou, 1963). Potting activity for lobsters and crabs around the Welsh coast is
widespread and there are several different kinds of pots in use (CCW, 2010).
Netting is a more effective method of fishing for crawfish than potting (Hepper, 1977, Gristina
and Gagliano, 2004). In Welsh waters crawfish are caught as a bycatch in spider crab fisheries.
A comparison of percentage catch rates between tangle nets and pots in south Wales during
1997, showed that nets represented 37,850% of the pot catch (Davies, 1999). Goñi et al.(2003b)
have reported that there are differences in the catchability of male and female crawfish in both
pot and trammel net fisheries. This showed that the pot fishery did not accurately represent the
size structure of the population and preferentially caught females.
Net fisheries are carried out all along the Welsh coast although tangle netting appears generally
to be concentrated along the Pembrokeshire coast and the Llŷn peninsula and along the north
coast of Wales to the east of Anglesey (CCW, 2010). Within what was the South Wales Sea
Fisheries Committee area net fisheries for crustaceans peaked in 1993 when 33 vessels were
actively working and 90% of the ten to 12 tonne catch was taken using tangle nets. By 2001
only four vessels were registered to take crustaceans by net with a further six vessels registered
to use pots and nets (as reported in Thomas, 2003). Less than one tonne of crawfish was landed
in 2001, with net fisheries landing over 260 tonnes of spider crabs.
Scuba diving has been identified as a cause of the population decline in crawfish in parts of
Wales in the late 1970s where a dive fishery around the Llŷn peninsula led to a rapid decline in
numbers in that area such that within two years, diving for crawfish was no longer economically
viable (R. Sharp pers. comm.). In dive fisheries from the south of Wales it has been reported
that they preferentially removed females from an area leaving males behind, this would then
attract more females into the area which could be fished again a few weeks later (P. Coates pers.
comm.). Preferential removal of females like this could affect the potential for recovery by
reducing the reproductive output of the population.
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Dive fisheries can also affect the behaviour of spiny lobsters. A study in Florida observing
Panulirus argus showed that there was increased dispersal of individuals following a period of
fishing in an area that had been previously closed to fishing (Davis, 1977). It was suggested that
this dispersal may be as much related to perturbation by divers as reduction in numbers and
indicated that increased dispersion could have impacts in terms of exposure to predators, and
disruption of social structure.
1.2.2 Status of the fishery
A shellfish permit scheme introduced in the South Wales Sea Fisheries Committee (SWSFC)
area in 1980 has resulted in the collection of catch and effort data for the crawfish fishery in this
area. The annual landings data, broken down by fishing type, are shown in Figure 1.2. A report
on data collected via this scheme was produced by Davies (1999) for the period 1980 to 1997.
This showed that landings were under two tonnes per year with the exception of the period from
1990 to 1993 which saw a peak to 12 tonnes in 1992 (Davies, 1999). The peak in landings
observed around 1992, which can be attributed to three boats, was due to the identification of an
area of inshore reef where crawfish were carrying out a migration and nets were specifically set
between two areas of kelp (P. Coates, pers. comm.); however, the fishery became uneconomic by
1993. Landings from the pot fishery have shown a general pattern of decline since 1980 when
annual landings were around 1.2 tonnes, to recent years where landings have remained largely
below 0.5 tonnes since 1993 (Figure 1.2). That is with the exception of 2007 which saw the
highest annual landings from the pot fishery during the data collection period at 1.4 tonnes. The
dive fishery landed around 0.4 tonnes in 1980 and 1981 but no commercial dive fishing has been
recorded in the south Wales area since 1986. Data from the Marine Management Organisation
for the period 2000 to 2011, show that some commercial diving took place in 2010 but that it
made up a small proportion of the total catch (<10 kg). Total annual landings of crawfish since
the peak in 1992 have remained relatively low and landings from Welsh vessels have remained
at less than two tonnes per year since 2000 (Marine Management Organisation). Although the
volume of catch remains low and it is not a targeted fishery, it is of significant value to fishermen
with the two tonnes landed by nine vessels in 2007 having a value of £56,000.
Figure 1.2 Annual Palinurus elephas landings from all fishing gears (not effort related) in the south Wales shellfish
permit area (formerly the South Wales Sea Fisheries Committee Area). Data from the Welsh Government.
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Landings per unit effort (LPUE) calculated from the pot fishery (Figure 1.3) have also shown a
pattern of decline from a high of 0.65 kg per 100 pot hauls in 1980 to below 0.1 kg per pot haul
since 1988, with lows of around 0.003 kg per pot haul in 2003 and 2010 (Figure 1.3). Again the
exception to this was in 2007 when LPUE increased to 0.15 kg per pot haul. The reason for the
observed increase in both landings and LPUE from the pot fishery in 2007 is not clear. Mean
monthly LPUE for the period 1980 to 1997 showed a peak in June, this coincided with the peak
activity in the fishery whereby the landings between May and September represented between 77
and 90.5% of the total for the year (Davies, 1999). The lowest catch rates were recorded in the
period from October to March. LPUE from tangle nets were also calculated (1991 to 1997) and
ranged from 0.93 to 1.37 kg per100 meters of net between 1991 and 1993 followed by a sharp
decline in 1994 to a low of <0.13 kg per100 m net in 1996. This increased slightly to 0.52 kg per
100m net in 1997. During this period the total number of shellfish permits issued by SWSFC,
and the number of full time fishermen in the area, both increased as did the total number of pots
fished (Davies, 1999). This increase is not specific to crawfish fisheries however, and
interpretation in this context should be taken with care. Given the decrease in pot LPUE
alongside the introduction and decline of a tangle net fishery, it is probable that there was over-
fishing of crawfish in this area during this period.
Figure 1.3 Annual Landings Per Unit Effort (LPUE) from the pot fishery for Palinurus elephas from the south
Wales shellfish permit area (formerly the South Wales Sea Fisheries Committee Area). Data from the Welsh
Government.
A shellfish permit scheme also applies to the North West and North Wales Sea Fisheries
Committee area which also collects data on catch and effort from the fishery (P. Coates pers.
comm.). Although more detailed analysis of this data set is not currently available it should be
possible to compare this with information from the south.
Data from the Marine Management Organisation show that Welsh registered vessels fishing for
crawfish have landed just under five tonnes since 2000 which is a relatively small amount when
compared to landings from other areas of the UK (Figure 1.4)
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Figure 1.4 Annual UK landings of Palinurus elephas by nationality of vessel (Data from the Marine Management
Organisation).
In addition to the fishery for crawfish in Wales there have also been targeted crawfish fisheries
around Cornwall. These were mainly carried out using pots until the introduction of diver
fishing in the 1960s. However, dive fishing was considered to be uneconomical by the end of
the 1960s (Hunter et al., 1996). The introduction of net fisheries in the 1970s gradually replaced
pot fisheries and landings have reduced considerably since that time. There has also been a
change in the length frequency distribution of crawfish from the Cornish fishery, whereby the
distribution has skewed to a higher proportion of smaller individuals (Hunter et al., 1996).
Hunter (1999) reported landings of P. elephas in Scottish waters from 1983 up to 1997. All
landings up to, and including, 1991 were below five tonnes per year. Landings increased in 1992
to more than 40 tonnes per year and remained high (above 30 tonnes per year) until a peak in
1995 of about 54 tonnes per year. The peak landings between 1992 and 1995 corresponded with
the introduction of tangle netting. Landings for the years following the peak in 1995 were of a
similar size to those prior to the increase: less than about six tonnes per year. Landings data for
2000 to 2011 are presented in Figure 1.4 and show a continuing trend of yearly landings less
than 7.2 tonnes.
The Irish fishery for crawfish in the late 1960s, was a pot fishery which targeted both lobsters
and crawfish simultaneously (Molloy, 1970). Although the extent and location of the fishery
was not thought to have varied much at this time, the annual catch was shown to fluctuate
considerably and there was an overall decline in landings. It was also reported that the mean
length of crawfish was lowered in some areas (Molloy, 1970), although it was not possible to
determine if this was caused by over-fishing. More recently fisheries in Ireland have been
carried out using trammel nets, with a bycatch of crawfish taken in other set nets (Goñi and
Latrouite, 2005). This change from pot to net fishing is reported to have resulted in depletion of
the stocks and a reduction in the mean size of individuals (Goñi and Latrouite, 2005).
A recurring trend in the literature on crawfish fisheries, as reviewed by Goñi and Latrouite
(2005), is the decline in population levels due to changes in fishing practice from the use of
relatively inefficient pot and trap fisheries to much more efficient net fisheries from the 1960s to
1980s. Stocks of P. elephas are depleted over much of its European range, including Wales.
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1.3 Legislation
This section outlines fisheries legislation that is relevant to crawfish fisheries, although this
report is not intended to provide a full review of fisheries legislation. Definition of the
geographical boundaries at which relevant legislation applies is also pertinent to the assessment
of management measures. The fisheries legislation that applies to Welsh waters is listed in the
Sea Fishing Atlas of Wales (CCW, 2010) and this includes regulations from the European
Union, the United Kingdom, and the Welsh Government. The Marine Management
Organisation also produces a Blue Book
1
which consolidates UK and EU legislation.
Within six nautical miles, only vessels registered in the UK may fish. Crawfish fisheries are
regulated through bylaws which were implemented by the Sea Fisheries Committees (now the
Welsh Government) and have been transferred to Statutory Instruments which apply within the 6
nm limit. These specify a 95 mm carapace length (CL) minimum landing size (MLS) in the
north and a 110 mm CL MLS in the south. Between 6 nm and 12nm historical fishing rights
permit vessels from outside the UK to fish. These include vessels from France, Belgium, and
Ireland and the distribution of these rights is reported in CCW (2010). Welsh Statutory
Instruments, such as the Lobsters and Crawfish (Prohibition of Fishing and Landing) (Wales)
Order 2002, SI2002/676, apply within the 12 nm limit but only to UK vessels. In order to extend
management measures within the 12 nm limit to include all vessels it is possible to obtain
derogations for the conservation and management of fisheries resources under Article 9 of
Council Regulation 2371/2002 on the conservation and sustainable exploitation of fisheries
resources under the Common Fisheries Policy.
Within the six nautical mile limit all fisheries management powers are devolved to the Welsh
Government. In 2010 the area of responsibility for fisheries policy, management, and marine
enforcement was extended to the median line border with the Republic of Ireland, Isle of Man,
and England via The Welsh Zone (Boundaries and Transfer of Functions Order) 2010. Under
this legislation Welsh Statutory Instruments could be extended to the median line border but
would still remain applicable only to UK vessels. EU legislation, including a MLS of 95 mm CL
for crawfish, applies to all Welsh waters.
The Habitats Directive has resulted in the designation of marine Special Areas of Conservation
(SAC) in Welsh waters. The scope of the sites relevant to crawfish is set out in Section 3.1.2.
The Sea Fishing Atlas of Wales (CCW, 2010) lists Competent Authorities for different fishing
techniques and the relevant fisheries legislation which applies within Welsh marine SACs. The
Skomer Marine Nature Reserve was designated under the Wildlife and Countryside Act and its
relevance is set out in Section 3.1.3.
1
http://www.marinemanagement.org.uk/fisheries/monitoring/regulations_bluebook.htm
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2 METHODS
For the purposes of this report the term “crawfish” is used to represent Palinurus elephas and
both terms are used interchangeably throughout. Where necessary, in order to provide the most
complete assessment of potential management measures, examples have been drawn from
studies on other Palinurid species, and other exploited crustacean species.
2.1 Assessment of Management Measures
In order to assess the potential effectiveness of existing and potential management measures for
the recovery of Welsh populations of P elephas a review of available information has been
carried out in the form of a literature review, including grey literature, and through liaison with
persons with specific relevant expertise. Where possible direct examples of recovery attributed
to different management measures are reported including timescales (see also Table 3.1). Where
direct examples are not available, comparisons are drawn and aspects of the biology of
P. elephas are interpreted with regards to the specific management measure in question. Where
relevant management measures are applied in adjacent areas with the potential to aid recovery in
Welsh waters, these are also included. The limitations of each management measure in aiding
the potential recovery of crawfish populations in Welsh waters are also discussed.
The assessment provided in this report is not intended to provide recommendations on future
management of crawfish in Welsh waters or to review the socio-economic implications of each
management measure, nor does the scope of the project include any proactive recovery measures
such as husbandry techniques.
2.2 Definition of Recovery
The Marine Strategy Framework Directive (MSFD) sets out in its quantitative descriptors for
determining good environmental status that; “Populations of all commercially exploited fish
and shellfish are within safe biological limits, exhibiting a population age and size
distribution that is indicative of a healthy stock”, thus setting a mandate for recovery of
crawfish populations in Welsh (and UK waters). For the purpose of the MSFD “within safe
biological limits” is defined as being exploited sustainably consistent with high long-term
yields and to have full reproductive capacity (Piet et al., 2010). The authors also add that in
assessing these attributes a precautionary approach be taken in setting target levels of fishing
effort and spawning stock biomass. The age and size distribution of a healthy stock is
considered to consist of greater numbers of older and larger individuals. Achieving these targets
would result in good environmental status (GES) for the stock.
Currently there is no information available on the historical, or current, stocks of P. elephas from
Welsh waters, or indeed from the UK with which to define “safe biological limits”, nor with
which to compare a population size distribution that is indicative of a healthy stock. It is not
possible therefore to make any formal analytical fisheries assessment on the stocks of crawfish
around the Welsh coast, nor to determine what population size and structure would represent
GES. Neither is it possible to draw direct comparisons with other spiny lobster fisheries, as in
most cases it has not been attempted to calculate the absolute abundance. Where the relative
abundance has been estimated from catch rate in fished populations the differing gear used in
each fishery precludes any comparison between species (Morgan, 1980).
In addition to the identified areas of data deficiency with regards to the fishery which prohibit
the use of formal assessment techniques, there are also biological knowledge gaps with respect to
the behaviour and reproduction of crawfish in Welsh waters. It is nevertheless important to
utilise the available information to make reasoned judgments on the potential for different
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management measures, alone or in combination, to contribute to the recovery of crawfish
populations.
A demarcation of what constitutes ‘recovery’ is needed to undertake this review of management
measures for their effectiveness in enabling self-procreated recovery of crawfish. The MSFD
target is an acceptable descriptive recovery target for crawfish, but these targets are not, and can
not be, defined numerically. However, it is important to know what the status of the crawfish
population in Welsh waters currently is, what the desired population status is and hence the
magnitude of recovery that the various management measures need to redress.
Landings Per Unit Effort (LPUE) data are available for the South Wales Sea Fishery Committee
area since 1980 when declines in crawfish had already become evident. In 1980 when the
population was already being exploited LPUE was recorded at 0.7 kg per 100 pots, while current
LPUE is much lower and has remained at around 0.05 kg per 100 pots as recorded in 1997
(Davies, 1999). It is recognised that data from a pot-hauled method is not an accurate
representation of a crawfish population as it is a relatively inefficient fishing method and has
been shown to be selective for females (Goñi et al., 2003b). LPUE does, however, provide a
relative index of abundance in the crawfish population.
This data from south Wales can be used to indicate the status of crawfish populations in Wales
historically and to indicate the magnitude of recovery that is desired (bearing in mind that
declines in crawfish were already evident during the period for which this data exists). Use of
this data as a benchmark does not facilitate numerical modelling of effectiveness of management
measures, but serves as a context in which logical judgements can be made about the
effectiveness of the management measures in enabling recovery. This will be based on an
appreciation of their declined status in Welsh, UK, and European waters, and using knowledge
of crawfish biology and ecology, of Palinuridae/lobster population dynamics and the effects of
fishing on populations.
LPUE data does not represent all attributes of crawfish recovery, for example it does not
encompass the age and size distribution in a population. Therefore, historical Welsh LPUE data
from the 1980s can be viewed as only an interim ‘recovering’ target heading towards a
population with a density, size distribution and geographical distribution that would represent the
achievement of GES and recovery of crawfish. LPUE data should also be considered as an
interim target because crawfish have been fished for several decades before the 1980s and LPUE
data from this period is unlikely to represent a ‘recovered’ state.
This report assesses the potential effectiveness of each management measure with respect to their
ability to reduce or restrict fishing effort, increase reproductive output or reduce catch rates, and
provides indications on the potential scale of recovery and time implications where possible.
The future implementation of any management measures may be assessed through the collection
of new LPUE data and comparisons made with the historical data that is available. The aim
being to reach a population level where LPUE values are greater than those observed in the early
1980s and are able to be maintained within prescribed limits in order to maintain GES.
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3 ASSESSMENT OF MANAGEMENT MEASURES
Management measures for the protection of Palinurus elephas populations include those affected
both through fisheries legislation and through nature conservation legislation as set out in
Section 1.3. Potential recovery rates, relating to the different management measures, reported
from different areas or with regards to other species are summarised in Section 3.3.
3.1 Existing Management Measures
3.1.1 Minimum Landing Sizes
The main function of a minimum landing size (MLS) is to allow individuals to reach sexual
maturity and to reproduce prior to entering the fishery. The aim of this is to prevent recruitment
over-fishing, by which the individuals remaining in the population do not have a sufficient
reproductive output to replace those removed by fishing. It is important therefore that the MLS
set for a fishery is greater than the size at first maturity of the target species within the area of the
fishery. Two separate MLS are currently in force within Welsh waters. This is as a result of
differing management measures put in place by the two Sea Fisheries Committees whose role
has now been taken over by the Welsh Government. The EU minimum landing size of 95 mm
carapace length (CL) is in force in the North West and North Wales Sea Fisheries Committee
(NW&NWSFC) area, while in 1997 the South Wales Sea Fisheries Committee (SWSFC)
adopted a more conservative MLS of 110 mm CL. As this bylaw only extends to the six nautical
mile limit, it does not provide protection for crawfish caught further offshore which would be
subject to the EU limit.
The mean size at maturity (SOM) of crawfish has been shown to vary regionally (Goñi and
Latrouite, 2005) and examples from the literature are presented in Table 1.2. Research on Jasus
edwardsii has also shown that SOM can vary with depth (Linnane et al., 2009). The size at
maturity is often taken to be the size of the smallest berried female and this varied from 69 mm
CL in the Spanish Mediterranean to 121 mm CL in south Wales. These data provide an
indication of the possible individual SOM; however this value may not be representative of the
population as a whole. A study in Portugal showed that 50% of females were mature at a
carapace length of 110 mm (Galhardo et al., 2006), although the smallest ovigerous female was
84 mm CL. The authors showed that an increase in MLS from 80 to 95 mm CL had little
potential to increase reproductive output as less than 20% of females under 95 mm were mature
(Galhardo et al., 2006). Goñi and Latrouite (2005) also report that MLS in fisheries from
Croatia (80 mm CL) and Brittany (> mean SOM) were not sufficient to protect stocks from over-
fishing or to elicit recovery of stocks.
A study carried out in south Wales (Hunter et al., 1996) between Strumble Head in the north and
St Govan’s Head in the south reported that the mean size of males was 155.5 mm CL (range 89
to 182 mm CL) and the mean size of berried females was 138.7 mm CL (range 121 to 150 mm
CL, see Table 1.2). The smallest unberried female recorded was 113 mm CL. The results of this
study would indicate that the current EU MLS is not appropriate for crawfish in this area and that
even the higher MLS introduced by the SWSFC of 110 mm CL would do little to increase the
reproductive output of the population as all reproductively active females, and the majority of
males, were larger than the MLS. The sample sizes in this study were relatively small however
and the smallest ovigerous females found in Cornwall, Ireland, and Scotland were smaller than
that reported for south Wales (see Table 1.2). It may be that there are smaller individuals within
the Welsh population, but for some reason, they were not captured during this particular study.
Hunter et al. (1996) also examined physiological maturity in 40 females (including the smallest
individuals from the Cornish fishery) and surmised that the majority of crawfish from around the
UK would be sexually mature before they entered the fishery (i.e. at 95 mm carapace length).
As data from Mediterranean populations of crawfish indicates that females become both
CCW Contract Science Report No 989
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physiologically and functionally mature at the same time (Goñi et al., 2003a) this would indicate
that the SOM in Welsh populations could be smaller than the size range of berried females
described by Hunter (1996), but further data collection is required to affirm this.
Given the disparity between the existing MLS and somewhat contradictory length frequency and
SOM data presented by Hunter et al. (1996), it is possible that a substantially higher MLS would
be required to increase the reproductive potential of crawfish populations in Wales. The scale of
any recovery of crawfish populations through increased MLS is difficult to predict for several
reasons. It is not clear what the current length frequency distribution of the population is and
therefore what proportion of individuals would be removed from the fishery. Length frequency
data, along with information on SOM, are also required to determine the potential gains with
respect to egg production. Should increased egg production occur and result in enhanced
recruitment in Welsh populations it would be expected to take a minimum of four to five years
before any upturn was observed in the fishery, as this is the predicted length of time it would
take for both males and females to reach a carapace length similar to the current MLS (see Table
1.1). Should populations in Wales be clearly linked to larval production from a population
outside UK waters then an increased MLS set at the European level, or another appropriate sea
area, may be considered appropriate in order to facilitate recovery in Welsh waters.
A further consideration with regards to the recovery of crawfish populations is the attainment of
an age and length structure that is indicative of a healthy stock, which is considered to consist of
greater numbers of larger and older individuals (Piet et al., 2010). The use of MLS alone may
not provide a means by which GES, with regards to length frequency, could be attained or
maintained, as larger individuals would be the focus of the fishery. This could be particularly
important should any recovery in terms of abundance attract greater fishing effort.
3.1.2 Marine Special Area of Conservation Management Measures
Marine Special Areas of Conservation were designated under the European Habitats Directive,
which has been transposed by The Conservation of Habitats and Species Regulations 2010 in
England and Wales. The legislative process requires the Secretary of State to propose a list of
sites which are important for habitats and/or species (listed in Annexes I and II of the Habitats
Directive respectively) to the European Commission. Sites are then identified as Sites of
Community Importance (SCI) and must then be designated as a Special Area of Conservation
(SAC) within six years (JNCC; http://jncc.defra.gov.uk/page-1379). Features of the
Pembrokeshire Marine SAC include eight habitat types listed in Annex I of the Habitats
Directive, one of which is ‘reefs’, and seven species groups listed in Annex II of the Habitats
Directive (www.pembrokeshiremarinesac.org.uk). Features of the Pen Llŷn a’r Sarnau SAC
include eight habitat types listed in Annex I of the Habitats Directive, one of which is ‘reefs’,
and four species groups listed in Annex II of the Habitats Directive
(www.penllynarsarnau.co.uk). Reefs form important habitats for Palinurus elephas (see Section
1.1.1) and, although P. elephas are not listed in Annex II of the Habitats Directive, they are one
of the largest benthic predators in Welsh waters and as such having a healthy crawfish
population would contribute to attaining favourable conservation status for the reef habitat.
3.1.2.1 Pembrokeshire Marine SAC
The management scheme for Pembrokeshire Marine SAC identifies that net fishing (fixed, gill,
tangle, and trammel) is increasing within the site. The report also indicates that there is the
potential for this to have an effect on the designated features of interest, but that at present there
is not sufficient data to determine if any adverse effects are actually occurring. This is also the
case with continuing potting activity, which is widespread throughout the site (CCW, 2010). It
CCW Contract Science Report No 989
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should be noted that any fishing activity within the site which removed crawfish would be
affecting the status of the features of interest as crawfish are part of the reef feature.
There are no fisheries specific management measures within the SAC management scheme
which would enable crawfish recovery. There are aspects of the management of the site which
have potential benefits for the local population but which are unlikely to contribute to any
recovery. These include the possible introduction of biodegradable latches in pots. This might
benefit crawfish through the reduced potential for mortality of individuals by ghost fishing of
lost gear. The extent to which this occurs within the site is unclear, and pot fishing for crawfish
is not as efficient as other methods so it is likely that the impacts of this management measure
would be relatively minimal. Management measures which protect the water quality within the
area may well have a beneficial effect with regard to the planktonic life stages of crawfish,
however, the sensitivity of this species to contamination in the water column, including
eutrophication, is not well described (Jackson et al., 2009).
The management scheme action plan does include an action to “establish sustainable limits for
each species/stock and a range of appropriate management measures to maintain catches within
those limits”. With regards to the recovery of crawfish, the setting of sustainable limits would
need to be applied within the context of Good Environmental Status as required by the Marine
Strategy Framework Directive, as it is possible that a sustained fishery can be carried out on a
depleted population. A further proposed item listed in the management scheme is the
establishment of unexploited scientific “control” sites, although the plan, timescale, and
likelihood of their introduction is not clear. These could potentially provide refuges for
populations of P. elephas, and would also provide the ideal situation to assess potential recovery
of populations. Site selection specifically for crawfish study would be desirable in order to gain
the greatest possible benefit from such a management measure (see also Section 3.2.7). The
management scheme includes actions on the collection of fisheries data including spatial
distribution and effort within the site, and specifically in the Skomer Marine Nature Reserve
(MNR), to inform SAC management. Whilst this could provide a valuable source of baseline
data on which future assessments could be based, these actions do not relate to direct
management action and would not contribute to recovery. A permit scheme exists for shellfish
fisheries in the south Wales area. This was implemented by the SWSFC (now the Welsh
Government) and although it is not implemented through the SAC management scheme, it would
mean that annual licence applications could be considered a plan or project and would therefore
trigger an appropriate assessment.
3.1.2.2 Pen Llŷn a’r Sarnau Marine SAC
Potting for crustaceans and tangle netting for fish and crustaceans is carried out within the Pen
Llŷn marine SAC. Fishing activity around the Llŷn Peninsula is reported as being
predominantly part-time (Thomas, 2003), with potting carried out during the summer months
and netting in spring and autumn. Diving is carried out within the site and recreational catch
limits apply, with permits required for any proposed collection activity greater than the limits
would allow. A shellfish permit system was also put in place by the NW&NWSFC (now the
Welsh Government) as in the south. Although these permit systems are not implemented
through the SAC management plan, applications for permits could constitute a plan or project
and therefore be subject to appropriate assessment.
The management plan for this SAC states that there is no evidence at present to suggest that
either netting or diving is having an adverse effect on either the features of interest within the site
or the wider coastal ecosystem through the removal of target species. It should be noted,
however, that as fishing with both pots and nets is carried out within the site, there is the
potential for crawfish populations to be reduced. As crawfish are a component of the reef this
could be considered to be detrimental to the features of interest.
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With regards to the self-propagated recovery of crawfish there are no management actions within
the SAC management plan which specifically relate to crawfish or which would confer any
benefits to recovery of this species within the site boundary, or beyond.
3.1.3 Skomer Marine Nature Reserve
Fishing activity within the Skomer Marine Nature Reserve (MNR) is regulated through two
fisheries byelaws. These are Byelaw 27 which prohibits the use of dredges and beam trawls
within the Skomer area; and Byelaw 28 which prohibits the removal of any scallops (Pecten
maximus and Chlamys opercularis) from the MNR area. These measures do not specifically
protect crawfish, and although it is possible that a small bycatch of P. elephas in mobile fishing
gear may have been prevented, this is unlikely to be significant (P. Newman, pers. comm.).
Both pot and net fisheries are permitted within the site with pots targeting lobsters (Homarus
gammarus), brown crabs (Cancer pagurus), spider crabs (Maia squinado), and velvet crabs
(Necora puber). In the last decade potting has been carried out by up to ten vessels although this
activity has covered between 55 and 85% of the site. There has been a marked increase in
potting effort around Skomer since 2001, and although levels were reported to have reduced
somewhat in 2010 they remain around three times higher than they were in 1989 (Newman et al.,
2011).
There is currently a voluntary netting exclusion zone, which covers 50 m from the island coast,
but netting elsewhere in the MNR is permitted. There is currently little net fishing activity
within the MNR area and no activity at all was recorded in 2010 (Newman et al., 2011).
Crawfish were targeted through the use of nets in the 1970s and 1980s (B. Bullimore, pers.
comm.) within the MNR and were also targeted through nets elsewhere along the Pembrokeshire
coast during this same period.
There is a voluntary no take policy (which includes crawfish) in the MNR’s code of practice for
recreational divers and this is largely adhered to by visiting divers (P. Newman, pers. comm.).
Whilst recreational divers did take crawfish from both within the MNR and elsewhere around the
Pembrokeshire coast in the 1970s and early 1980s, the intensity of this activity has never been
documented. There was a short lived and intensive commercial dive fishery in the late 1970s,
but this was not within the MNR itself and mostly focussed on the offshore reefs around west
Pembrokeshire, such as at the Hats and Barrels reefs, approximately 10 - 15 miles west of the
MNR (B. Bullimore, pers. comm.).
Whilst MNR monitoring does not specifically gather data on crawfish, non-systematic
observations by MNR staff and volunteer divers have reported increasing sightings of juvenile
crawfish within the reserve since 2000, although adults are less common (P. Newman pers.
comm.). These informal observations of juveniles were not made by MNR staff prior to this
time, despite the same sites being surveyed each year. Although these observations are not
backed up by quantitative data they suggest an apparent increase in recruitment, either via larval
advection to the area or through migrations of juveniles into the MNR area. The source of the
juvenile crawfish within the site is not clear however, and this should be taken into consideration
when assessing the effectiveness of the MNR to aid in the recovery of crawfish.
In the case of an increase in recruitment to the MNR, the adherence by recreational divers to the
voluntary no take policy, including crawfish, within the MNR area will contribute to
survivorship of juveniles to adulthood and reproductive maturity, with possible spill over effects
outside the MNR area in the future (see also Section 3.2.7). Any spill over effects would be
dependent on the increased numbers of juveniles only being found within the site, and would
assume that the increase was a direct result of management measures within the MNR, as
opposed to a general increase in recruitment within the wider area. The reduction in netting
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occurring within the site is likely also to contribute to increased survivorship of juveniles to
adulthood.
3.1.4 Non-Commercial Catch Limit
Non-commercial catch limits apply to divers/snorkelers and recreational potting vessels. The
bylaws introduced by the sea fisheries committees state that in the both the NW&NWSFC area
and the SWSFC area there is a catch limit of one crawfish per person per day. All persons
wishing to fish using pots or traps are limited to five pots per person and the catch limits set out
above still apply. The introduction of voluntary codes of conduct in some diving organisations,
which promote a no take policy, may also have reduced the potential for divers to remove
crawfish when they are found. For all non-commercial fishing activity the existing MLS of 95
mm CL in the north and 110 mm CL in the south still apply.
Davis (1977) observed a recreational diver fishery within a protected area which allowed each
diver to take two Panulirus argus. The area observed within this study was a national park area
which attracted a large number of recreational divers and the sport fishery had a significant
impact both on the behaviour and numbers of P. argus within the area. In this specific instance
the author reported that such a level of removal would not have been sustainable within the area
and reported substantial decreases in experimental catch rates and lair occupancy after eight
months of fishing (see also Section 3.2.3.2). Given the current depleted status of the Welsh
crawfish fishery, and the fact that this study was carried out on different species, the catch limit
and scale of change reported may not be directly relevant to Welsh waters. This example does,
however provide a useful context within which to interpret the potential for such a measure to
aid in the recovery of Welsh crawfish populations.
The determination of a specific catch limit for a population within a specified area, such that it
contributed to population recovery, would need to be based on an assessment of the abundance
of crawfish within the area and on the potential for the population to recover. The potential
benefits of the non-commercial catch limit are difficult to assess. This is largely due to
difficulties in quantifying the level of recreational fishing and its potential to impact upon
populations. It has been shown that for a Panulirus argus non-commercial dive fishery,
restricted by catch limits, can cause significant disturbance to the distribution and social structure
of the population and that while distribution can recover in a period of months, the recovery in
terms of numbers of individuals may take several years (Davis, 1977). This may need to be
factored into assessments of recovery in areas where diver fisheries are prevalent.
As there is no information available on the levels of non-commercial removal of crawfish within
Welsh waters it is not clear what benefit this management measure has. The presence of a non-
commercial catch limit is certainly preferable to free access; however it is unlikely that it is
providing any current benefit to the recovery of depleted crawfish populations, as non-
commercial catches are likely to be low. In a recovering population however, where crawfish
were more abundant and therefore more available for capture, the existence of appropriate catch
limits could prove beneficial, supporting recovery by limiting any renewed interest in non-
commercial collection. This would be particularly relevant for recreational diver collection,
which is a more efficient and selective method of collection than potting and which may also
have wider effects on the population as described above.
3.2 Potential Management Measures
3.2.1 Maximum Landing Size
The introduction of a maximum landing size (M
ax
LS) is carried out in order to protect the largest
and most fecund individuals in the population from fishing mortality. The fecundity of female
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Palinurus elephas has been shown to increase linearly with size (Goñi et al., 2003a) and
therefore by protecting the larger females in the population it is possible to attain a greater
reproductive potential from the protected individuals. Larger females have also been shown to
produce larger eggs and it is suggested that these may produce larvae that are better able to
survive when the food supply was low (Goñi et al., 2003a). While absolute fecundity increases
with size, maximum relative fecundity (the greatest number of eggs per gram of body weight) is
seen in females with a carapace length of 100 to 110 mm in the Mediterranean (Goñi et al.,
2003a). Maximum relative fecundity for Welsh populations is likely to differ from this range
given the differing environmental conditions. Galhardo et al. (2006) showed that in a
Portuguese population 50% of females were mature at a carapace length of 110 mm, and that
although females above this size represented only 5% of the population they produced 59% of
the egg production. It can therefore be seen that the introduction of a M
ax
LS could protect and
increase the reproductive potential of a population with regards to egg production.
A M
ax
LS for male lobsters can be effective in protecting the reproductive potential of a fished
population where sperm limitation may be a factor affecting reproduction. Introducing a M
ax
LS
for females only can have implications on potential increases in the reproductive output of the
population through increased fishing pressure on males. Sperm limitation can become an issue if
large females are unable to find a suitable male to mate with, either through reduced numbers of
males due to fishing mortality, or through a lack of males of a suitable size with which to mate.
Reducing the numbers of males within the population can result in the remaining males being
unable to produce enough sperm to successfully fertilise all of the receptive females through
sperm depletion resulting in an inability to mate.
Egg production can also be reduced through insufficient numbers of sperm being transferred to
the female. A reduction in the numbers of sperm transferred to females has been shown for
several species of crab, for example Callinectes sapidus (Kendall et al., 2002) and Paralithoides
brevipes (Sato et al., 2006). In Panulirus argus the size of the spermatophore transferred has a
greater impact on the brood size than the size of the female (MacDiarmid and Butler, 1999b). In
both P. argus and Jasus edwardsii females that mated with smaller males produced smaller
broods than those females that mated with large males (MacDiarmid and Butler, 1999a, 1999b).
For J. edwardsii it was shown that female size, male size, and mate order all affected the number
of eggs produced by the female (MacDiarmid and Butler, 1999a). Female J. edwardsii are
reported to have only a short window of opportunity for mating and should there be a lack of
suitable mates, the female will resorb her eggs (MacDiarmid et al., 1999). This resorbtion of
ovarian tissue has repercussions in the following breeding season where females were seen to
have largely atrophied ovaries, and the small amount of normal egg development resulted in very
small brood sizes.
Davies (1999) states that successful mating in crawfish will only occur where the mating pair are
similar in size as the positioning of the spermatophore is important. It would therefore be
prudent to introduce a M
ax
LS for both sexes in order to achieve the maximum possible gains in
terms of egg production and reducing the potential for sperm limitation. This would be
especially important if there were other measures also protecting females (e.g. prohibitions on
landing berried females). It is however, difficult to determine the relationship between increased
egg production and recruitment levels. Factors such as predation on each of the different larval
and juvenile life stages, and density dependence, can affect recruitment. The relationships
between these different factors are often complex and hard to assess making it difficult to
determine the relationship between egg production and recruitment.
A possible concern with the introduction of a M
ax
LS is that it could result in larger individuals
utilising the resources which would otherwise be available to smaller, faster growing individuals,
which can be considered detrimental to the stock (Chapman, 2003). In such a case it is possible
that the benefits of increased egg production could be negated by a decrease in numbers. As
crawfish populations within Welsh waters are currently depleted it is unlikely that resources
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would be a limiting factor. The potential for limited shelters/habitat to limit numbers of crawfish
in an area is reduced as crawfish can sometimes be found sharing refuges in suitable habitats.
Setting locally appropriate and meaningful M
ax
LS within Welsh waters will be important. The
length composition of crustacean populations can vary, sometimes over relatively small spatial
scales (e.g. Tuck et al., 2000). In Jasus edwardsii it has been shown that SOM can vary by
depth (Linnane et al., 2009). If significant spatial variability was observed in Welsh crawfish
populations it may be that more than one M
ax
LS could be appropriate in order incorporate local
variability. Given the depleted status of the crawfish populations in Wales it may be the case
that fewer large individuals are currently present within the population, as has been observed in
other areas (Galhardo et al., 2006). This could compromise the initial potential for the
introduction of a M
ax
LS to increase the reproductive output of the population. It may be that a
M
ax
LS could be introduced, along with appropriate area closures (see also Section 3.2.7), within
which individuals would be allowed to reach these larger sizes through protection from fishing
effort. Data on the length frequency distribution of populations would be required in order to
determine the scale and level of such a measure and whether or not it should be implemented
alongside area closures.
The aim of this management measure is to increase the reproductive output of the population. If
this is successful, and results in increased recruitment, it would take a minimum of four to five
years for this to translate into increased catch rates in the fishery, based on the growth rates of
crawfish and the current MLS (see Table 1.1). The scale of any recovery may be limited by the
current depleted status of crawfish in Welsh waters. Benefits with regards to a return to an age
length frequency that is indicative of GES may be achieved more quickly (depending on the
current length frequency distribution) with the retention of older larger individuals within the
population.
As there is uncertainty about the source of recruitment into the Welsh crawfish population it is
not possible to determine the impacts on recruitment of the introduction of a M
ax
LS at a
European scale or other relevant sea area. However, should connectivity between populations be
identified then a M
ax
LS, at an appropriate scale, would be important to maximising recovery
potential. In the absence of firmly establishing connectivity between Welsh populations and
those in other areas, the main benefit the introduction of an EU or sea area M
ax
LS would be if it
was introduced to mirror a management measure implemented for Welsh waters. As Welsh
Statutory instruments would only apply to UK vessels this would mean that all vessels fishing
crawfish populations in Welsh waters would be subjected to the same M
ax
LS.
3.2.2 Landing Prohibition
As crawfish are captured as a bycatch in other fisheries, prohibitions in the context of this section
of the report are taken to mean the prohibition of landing crawfish rather than a direct prohibition
of all fishing activity. A landing prohibition as discussed here would apply to all crawfish
caught, irrespective of the fishing method used.
A prohibition on landing crawfish using a Welsh Statutory Instrument could be applied to the
Welsh Zone, i.e. out to the meridian line with Ireland, England and the Isle of Man (see Section
1.3); this would only apply to UK vessels fishing in this area. However, this would not prevent
UK vessels, including Welsh vessels, from landing their catch in another country. Depending on
the extent to which this would be an issue, consideration could be given to inter-country landing
prohibitions on crawfish. It is known that Belgian beam trawlers do catch crawfish in Welsh
waters (P. Coates, pers. comm.) and that French and Irish vessels also have historical fishing
rights within the six to 12 nm limit. The total UK landings of crawfish by non-UK registered
vessels in the period 2001 to 2011 was 0.0457 tonnes and of this less than 2% of this total was
landed in Wales (data from the Marine Management Organisation). The Marine Management
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Organisation does not hold information on fishing being carried out by foreign vessels within the
six to 12 nm zone that is landed outside the UK. It is possible therefore that a proportion of
fisheries removals from the Welsh crawfish population is not accounted for nationally and would
not be able to be controlled through the introduction of Statutory Instruments. If the catch by
foreign vessels was found to be significant or increasing, this could be addressed by seeking a
derogation to make the Welsh SI applicable to the relevant Member States in order to facilitate
and maintain recovery of crawfish in Welsh waters.
Prohibitions on landing are likely to be most effective in pot and dive fisheries as there are likely
to be high survival rates of live returns from these fisheries. Net fisheries can however result in
mortalities of captured crawfish depending on the length of time they have been caught in the net
and on levels of damage through contact with the net. Further information on the spatial
distribution of crawfish captured in net fisheries could permit area prohibitions in order to
mitigate any fishing mortality if it was considered to be a significant problem.
The effectiveness of a Welsh landing prohibition, in terms of recovery of stocks, will also be
affected by the source of recruitment into Welsh populations. If larvae are being produced by
populations in other areas and then brought to Welsh waters through the movement of tides and
currents, the level of recruitment will not be affected by a Welsh prohibition on landing crawfish.
However, in this situation a landing prohibition would increase population numbers and could
eventually benefit recruitment in an area outside Welsh waters. A regional sea or EU level
prohibition could aid recovery in Welsh waters if it was implemented to protect an area with
proven larval connectivity to Welsh crawfish populations. Should the source of recruiting
individuals be from within Welsh stocks, the potential rate of recovery could be increased
through both the reduction in removals from the population by fishing, and through increased
recruitment to the resident population.
A prohibition on the landing of crawfish in Welsh waters could contribute to the recovery of
crawfish. The rate of recovery facilitated by such a management measure in the context of the
depleted status of Welsh crawfish populations is not clear however. Preventing the removal of
individuals and potentially enhancing recruitment would both increase the abundance of crawfish
and result in changes in length frequency distribution towards one that was indicative of GES.
These potential benefits may make this a more effective management measure in terms of
recovery, than one which only protects part of the population (e.g. MLS) or has a spatial or
temporal component (e.g. area or seasonal closures) which still permitted fishing activity. It may
be appropriate to review a landing prohibition in a recovering population in order to determine if
other management measures, which allowed the removal of individuals, could be introduced.
3.2.3 Gear Restrictions
It has been shown that pot fishing is the least effective method for catching crawfish although it
is relatively environmentally benign (Eno et al., 2001). Dive fishing has the potential to cause
the least disturbance to the surrounding habitat; however it can result in quite high catch rates
and the potential for localized depletion of the stocks. The use of nets for capturing P. elephas is
the most effective, from a fisheries point of view, and there are concerns relating to damage to
other marine life and potential bycatch issues.
Prior to considering any prohibitions relative to fishing gear it is important to assess to what
extent the different methods are used and in what areas. Both net and pot fisheries have
continued to land crawfish in recent years, however, the dive fishery has declined and is now
almost non-existent (Marine Management Organisation; Figure 1.2). It is important to gather
further data about the geographical extent of each fishery and the effort deployed in order to
determine the potential for any prohibition to affect a recovery in the population. A further
consideration would be changes in fishing type due to the prohibition of a single fishing gear and
CCW Contract Science Report No 989
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what the implications of this change would be for population levels of crawfish. As with other
potential management measures the implications of the legislative framework will need to be
considered with regards to the effectiveness of each measure.
3.2.3.1 Prohibition of tangle netting
Prohibitions, as discussed in this section, refer to measures implemented in discrete areas rather
than a prohibition of the tangle net fishery as a whole. Tangle netting is one of the most
effective methods for catching crawfish and is therefore popular with fishermen. It can,
however, have an impact on the surrounding environment both through the bycatch of non-target
species and also by causing damage to fragile sessile reef species. This is particularly relevant to
marine SAC sites that have been designated for reef features. The total landings of crawfish
from all set net fisheries carried out by Welsh vessels were 2,373.6 kg in the period 2000 to 2011
(Marine Management Organisation). Data collected in south Wales showed that the catch rate of
nets, expressed as a percentage of catch rates for pots, was 37,850% (Davies, 1999). It is also
possible for fishermen to set nets on crawfish migration routes which can significantly increase
catch rates (see Section 1.2), whereas pot fisheries rely on individuals being attracted to the
fishing gear. It would therefore stand to reason that, for comparable levels of effort, the
prohibition of fishing for crawfish by tangle netting could provide much greater potential for
recovery than a prohibition of potting. Although general data is available on the distribution of
net fisheries (CCW, 2010) more detailed data on effort and spatial resolution for each gear type
in use within Welsh waters would be very useful in determining the potential recovery of
crawfish through the prohibition of netting.
There are also potential benefits of a prohibition on net fisheries in terms of reduced fishing
mortality on the non-commercial component of the catch. As nets are not very selective they can
result in catches of undersized individuals. If nets are not cleared regularly, this can result in
juvenile mortalities, which would normally be returned live to the sea (M. Robinson, pers.
comm.). Nets can also cause considerable damage should they trap recently moulted individuals
which are soft, although catch rates of such individuals tend to be low (Galhardo et al., 2006).
Prohibitions on net fisheries could contribute to the recovery of crawfish, through reduced
removals from the population. There would also be less chance of mortality of undersized
individuals being caught in gear. This would in turn provide the potential for greater
reproductive output of the population and possible increased recruitment. Reduced fishing effort
could also result in changes in the length frequency distribution to one that better represented
GES. Should prohibitions of netting be carried out in isolation however, the benefits of any
recovery could be reduced through pot or dive fishing. This could reduce the impact of any
increase in population numbers and would limit any potential changes in the length frequency
distribution of the population relative to GES.
3.2.3.2 Prohibition of diver collection
Commercial diver collection of crawfish can be an effective fishing method, particularly in areas
where potting or netting is not possible, for example on steep rock faces. Diver collection does
have the potential to severely deplete localised populations, although the extent of removals
would be limited by the depth at which divers can fish and there will therefore be a depth refuge
for this species where collection cannot take place, although other fisheries can.
The effects of diver collection have been shown to be two-fold in populations of Panulirus argus
(Davis, 1977), with both a behavioural aspect and reduction in numbers. Panulirus argus
populations have been shown to recover reasonably quickly from the behavioural effects of diver
capture, however, recovery in terms of numbers of individuals was much slower and may take
CCW Contract Science Report No 989
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several years. The introduction of a recreational dive fishery for P. argus in a previously closed
area showed a reduction in trap catch rate by 58% and a 42% decrease in lair occupancy rates,
over a period of just eight months, even with a catch limit of two P. argus per diver (Davis,
1977). The recovery of this area post fishing was observed and it was shown that the catch rate
increased to 78% of the pre harvest level after one year and lair occupancy levels recovered to
71% after 16 months, however, overall numbers of P. argus did not recover quickly.
There has been little commercial collection of crawfish carried out in Welsh waters in recent
years with a total of only 8.8 kg landed over two separate years (Marine Management
Organisation). It therefore stands to reason that a prohibition of commercial diver collection at
current levels would have little or no impact on the recovery of crawfish populations. Despite
current levels of commercial dive fishing being at a low level, this fishery could become viable
again in a recovering population of crawfish. In this situation a prohibition on dive fisheries
could be a necessary management measure to prevent efficient dive fisheries from reducing the
impact of any recovery. If commercial diving was considered to be a threat to recovery, it would
also be appropriate to introduce a zero catch limit for recreational divers alongside any
prohibition on commercial dive fisheries.
3.2.3.3 Prohibition of potting
Prohibitions of potting activity as discussed in this section refer to the implementation of
management measures in discrete areas rather than the prohibition of pot fisheries in general.
The total landings of crawfish by Welsh vessels fishing with pots between 2000 and 2011 were
2,554 kg (Marine Management Organisation), which was slightly higher than the landings from
net fisheries. The prohibition of potting in discrete areas could therefore provide as much
potential benefit in terms of absolute removals from the fishery as a prohibition of net fisheries.
It is worth bearing in mind however that pot fisheries also catch other species which are
important components of inshore fisheries. Due to the relative inefficiency of pot fisheries in
capturing crawfish, a prohibition could have a disproportionate knock on effect on several other
fisheries. Should the size of areas required to secure positive benefits for crawfish populations
mean that knock on effects on other fisheries are an issue, a prohibition on the landing of
crawfish may be a more appropriate management tool (see Section 3.2.2). As noted in Section
3.2.3.1, tangle netting is a much more efficient method for capture of crawfish and also has the
potential to cause greater environmental impact. Consideration would need to be taken to
fishermen changing to fish with nets should potting be prohibited. Again this may mean that a
prohibition on landing crawfish was a more effective management measure.
As for net fisheries, a prohibition on potting would have the potential to benefit the recovery of
crawfish in terms of reduced removals from the fishery and the potential for increased
recruitment. In terms of reduced landings, the benefits with respect to increased crawfish
abundance would be similar to those seen through a prohibition of netting, although the
characteristics (e.g. age and length distribution, sex of individuals) of the catch may vary
between fishing methods. As potting is a relatively inefficient method for capturing crawfish,
which is a bycatch species, it may be more appropriate to look at a prohibition on landing
crawfish from pot fisheries, as there is likely to be high survivability of live returns from this
fishery.
3.2.3.4 Design specifications for gear
Design features of gear could include features such as escape gaps within pots which would
allow smaller or undersized individuals to leave the pot before it is hauled; this reduces any
potential handling stress. Specifying the types of pots which could be fished could have an
impact on the catch of crawfish. Inkwell pots have larger entrances or eyes than parlour pots and
CCW Contract Science Report No 989
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therefore are easier for crawfish to enter and limiting the numbers of these pots could reduce
landings of crawfish from pot fisheries.
Nets with greater area appear to have a higher LPUE (Davies, 1999). It may therefore be
possible to modify net design to reduce the catch rate to a level which was considered
appropriate for a specific area/fishery. The Spanish Mediterranean fishery for Palinurus elephas
is managed using net regulations which include a specified mesh size and length of trammel net
(Goñi and Latrouite, 2005).
Given the depleted status of the fishery it is unlikely that design specifications for gear would
have a significant effect on the recovery of crawfish as a stand-alone measure. Design features,
such as escape gaps in pots, could be more useful in areas where recovery was observed through
increased numbers of juveniles, as these would be able to leave the pot while commercial sized
individuals would be retained. The effectiveness of such measures for crawfish pot fisheries is
unclear and reducing the catch of smaller individuals would not aid recovery of the population
with regards to a length frequency distribution that represented GES. Technical conservation
measures such as gear design specifications are more likely to be appropriate in managing a
fishery on a recovering population, or one that has made good progress towards recovery, rather
than for the purpose of effecting recovery itself.
3.2.4 Catch Limits
The implications of the existing non-commercial catch limits were discussed in Section 3.1.4;
however it is possible that a commercial catch limit could also be set to reduce the effects of
fishing on crawfish populations. The levels at which such a catch limit should be set would have
to be determined based on the current depleted population status and the levels of fishing being
carried out.
While the introduction of catch limits would restrict the landings of crawfish, it would not reduce
levels of fishing activity. Continued fishing activity can alter the size distribution of a
population by removing larger individual with resulting implications for reproductive output of
the population (see Sections 3.1.1 and 3.2.1). The removal of larger individuals could well be
accelerated where commercial catch limits were applied if fishermen were ‘high grading’,
preferentially keeping only the largest individuals for landing due to their higher market value.
This could reduce the potential benefits of management with regards to the reproductive output
of the population and also result in a length/age frequency distribution which was not
representative of GES. As crawfish are a bycatch species caught at relatively low levels care
would need to be taken that individuals were not simply stored at sea in keep creels and then
landed according to the catch limits in place. While commercial catch limits could provide
protection to crawfish populations through limiting landings, in view of the depleted state of
crawfish populations, it is likely that this measure would have limited effect on the initial
recovery of crawfish as a stand-alone measure. It may be more appropriate to implement a catch
limit to manage fishing activity within a more advanced recovering crawfish population where
removal of individuals was permitted.
3.2.5 V-notching
V-notching can be an effective methodology for temporarily removing individuals, usually
females, from the fished population thus allowing them to continue breeding without the
potential of removal. Legislation is already in place for Welsh waters out to 12 nautical miles,
which prohibits the landing of v-notched crawfish, through the Lobsters and Crawfish
(Prohibition of Fishing and Landing)(Wales) Order 2002. The effectiveness of this management
measure will depend on a number of factors: the length of time the v-notch will remain visible in
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the tail, the frequency of reproduction of the individual, and the ability of the individual to find a
suitable mate. In European lobsters (Homarus gammarus) it is generally thought that the v-notch
will remain visible for around four years, however, in larger individuals that may moult less
frequently this period may be longer. Moult frequency in crawfish does decrease with size,
particularly in females, with the largest individuals moulting once every two years (Hunter,
1999). It has been reported that v-notching can substantially increase the reproductive potential
of highly exploited small scale H. gammarus fisheries and increased catch rates of juvenile
lobsters were reported four to five years after the implementation of a v-notching scheme (Tully,
2001). However, reports from a v-notching experiment carried out on H. gammarus in Orkney
indicated that the egg production of v-notched females (totalling 5,728 individuals) represented
only a small portion of that produced by the total population (Chapman, 2003). V-notching of
crawfish has been carried out in Ireland, however relatively high mortality rates were observed
(M. Robinson pers. comm.). The telson of the crawfish is not as calcified as that of a lobster and
this could mean that the v-notching process causes greater tissue damage, and healing may not
be as straightforward as is seen in H. gammarus. This may make v-notching a less relevant
option as a management tool to facilitate recovery and it would certainly limit any potential
benefits. However, if v-notching was carried out, it might be considered appropriate to notch
both males and females in order to prevent any potential sperm limitation, as discussed in
Section 3.2.1.
The effectiveness of v-notching in recovery of a population of crawfish will be difficult to
determine and any changes in LPUE would be likely to take a minimum of four to five years at
the current MLS (see Table 1.1). V-notching ensures the potential for increased levels of egg
production within a population; however, this may not translate into recovery in terms of
numbers of individuals. The length of the planktonic larval phase and the potential for dispersal
of the larvae needs to be taken into consideration. If v-notching is taking place in an area where
there is a net removal of larvae from the area then it will not be effective in restoring the local
population, but may have benefits in areas remote from the management measure. Given the
potentially high levels of mortality associated with v-notching it is unlikely there would be a
straightforward gain in increased egg production at the population level. The potential gains
through v-notching could also be limited in a depleted population where there would be reduced
opportunities to notch individuals through low catch rates. As such this management measure is
unlikely to be effective in terms of the recovery of a depleted crawfish population.
3.2.6 Prohibiting the landing of berried females
For some crustacean fisheries the landing of ovigerous or “berried” females is not permitted and
these individuals are returned to the sea to complete their reproductive cycle. Such a prohibition
exists in the Portuguese fishery (Galhardo et al., 2006) although no assessment of its
effectiveness has been carried out. This method can be particularly appropriate where the
minimum landing size is close to the size at maturity as it ensures that berried females are
permitted to breed prior to entering the fishery. It has been indicated that for the lobster
(Homarus gammarus) fishery in south Wales, the potential for increased egg production through
protecting berried females was much greater than through the introduction of a minimum landing
size (Davies, 1999). This is likely to also be the case for crawfish, as larger reproductively
active females produce greater numbers of eggs.
In order to assess the potential benefits of a prohibition on the landing of berried females it is
important to determine when, and at what levels, they appear in the populations. Hunter et al.
(1996) reported that the first berried females were observed in August and represented 10% of
females caught in the south Wales fishery. By September 23% of females from the Welsh
fishery and 17% of caught Cornish females were berried. In the Cornish fishery this increased to
89% in December and 90% in January. No data on the percentage of berried females during the
CCW Contract Science Report No 989
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winter for the south Wales fishery were available, although it can be assumed that the values
would be similar. Hunter et al. (1996) also reported that in May 57% of females caught in south
Wales were still carrying eggs. These data indicates that the majority of females are spawning
annually and would therefore be protected by a prohibition on the landing of berried females.
They would however, still be available to the fishery when not carrying eggs.
It is has been reported that pot fisheries preferentially catch females (Goñi et al., 2003b), which
would increase the impact of this management measure on those fishermen using pots to fish for
crawfish. Although this is a relatively straightforward management measure to apply, it has
resulted in the rather unscrupulous practice of scrubbing the eggs off in fisheries for the
European lobster (Homarus gammarus). Given the high value of crawfish it is possible that this
method could be used to illegally land berried females as it is difficult to detect. Where females
are returned to the sea survival rates are likely to be high, however, egg loss through capture is
possible and this may particularly be the case for tangle net fisheries where the action of the net
could remove eggs. Should these factors be a concern a seasonal prohibition of fishing in areas
where berried females were found may be a more appropriate measure should the protection of
berried females be considered a management priority.
The scale of recovery produced through the introduction of a prohibition on the landing of
berried females is difficult to assess. As the data suggest that the majority of females moult on
an annual basis this measure could result in increased egg production. Although a prohibition on
the landing of berried females would protect egg production during the winter months when
females were berried, it would not prevent them from being caught during the summer months
when they were not carrying eggs. Data from the period 1980 to 1997 (see also Section 1.2.2)
showed that between 77 and 90% of the catch was landed between May and September (Davies,
1999) when the majority of females would not be in berry. This could compromise the
effectiveness of a prohibition on the landing of berried females, should the pattern of fishing
activity remain in this seasonal pattern.
Up to date information on the catch rates of berried females, fecundity, and length distribution of
females caught in the Welsh fishery would allow calculations of the potential increases in egg
production which could be expected through this prohibition. Should larvae produced through
this increased potential recruit to the population it would take around four to five years for them
to reach the fishery with the current MLS in place (see Table 1.1). If larvae are not retained in
the same area as the prohibition there may not be any substantial benefits in terms of population
recovery as females would still be available to the fishery for several months of the year.
3.2.7 Area Restrictions
There is a large volume of literature on the effects of area closures on spiny lobster populations,
largely through studies on marine protected areas (MPAs). The information provided here is not
intended to be a review of the effectiveness of MPAs in protecting fished species in general, but
rather a collation of the most relevant information with regards to the recovery of crawfish
within Welsh waters.
There are several factors which should be considered in the use of area restrictions for the
protection of crawfish. These include the scale and location of the area and its relevance to the
behavioural and ecological requirements of crawfish relative to its life history (Childress, 1997).
Permanent area restrictions will be most effective where there is a resident population. If the
population which is protected within the area is only present for a particular part of the life cycle
the closure will not afford protection to the population at other times. MacDairmid and Breen
(1993) indicated that extensive migrations of juvenile Jasus verreauxi resulted in ineffective
protection for this species through a marine reserve. In the same reserve an increase in density
of Jasus edwardsii was much more stable in females than males and this was linked to the
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migratory behaviour of adult males taking them outside the reserve where they were subject to
fishing activity (MacDiarmid and Breen, 1993). Tagging studies of a Mediterranean population
of Palinurus elephas have shown that there was little movement of individuals and that larger
animals in particular were more likely to remain resident (Follesa et al., 2009), however, it has
been shown that some Atlantic populations do undertake seasonal reproductive migrations
onshore in spring and offshore in the autumn (e.g. Ansell and Robb, 1977).
There may be habitats which are important to different stages of the life cycle, for example areas
with suitable habitat for the settlement of juveniles may be different to those required by adult
individuals. In Ireland, high densities of juvenile crawfish were discovered on exposed vertical
habitats which had a high proportion of fissures and holes for shelter (Robinson et al., 2008). In
the Spanish Mediterranean concentrations of juveniles were found in deeper water after
migrating from shallower settlement areas (Goñi et al., 2001). Where specific areas can be
identified that are important to the life cycle for part of the year, e.g. spawning grounds, these
could also be identified for a seasonal restriction in fishing (see Section 3.2.8).
It has been shown that closing an area to fisheries can have considerable benefits in terms of
numbers of crawfish. Goñi et al. (2001) calculated an abundance index for P. elephas from
fished areas and from within a reserve which had been closed to fishing for eight years. They
showed that the abundance of crawfish within the fished areas was around 0.6 to 20% of that in
the reserve. Catch rates from experimental fishing within the protected area showed CPUE
values of four to 154 crawfish per 600 m of net per day while outside the protected area CPUE
was in the range zero to ten crawfish per 600 m of net per day (Goñi et al., 2006). Following the
establishment of a marine reserve in 1976 the density of J. edwardsii was seen to increase 4.5
fold between 1978 and 1983, whereupon density levelled off (MacDiarmid and Breen, 1993).
Sampling catch rates in areas closed to dive fishing for P. argus showed an increase of 5% after
29 months, compared to a 22% reduction in an area which had been open to dive fisheries
(Davis, 1977).
The selection of the location and scale of a closed area will affect the potential benefits to a
fished species. Where closed areas are located in areas with unsuitable conditions (e.g. limited
habitat, food, or unsuitable temperature or salinity) there can be significantly reduced benefits to
exploited species. If suitable habitats are limited for example, there may be no benefit, in terms
of increased density, to closing an area (MacDiarmid and Breen, 1993). The size of a closed
area is also important. Positive outcomes in the management of spiny lobsters have been
observed in the Columbretes Islands Marine Reserve in the Spanish Mediterranean which covers
an area of 14 km
2
and has shown benefits to Palinurus elephas populations within, and to
fisheries outside this area (Goñi et al., 2001, 2006, 2010). Dry Tortugas protected area in Florida
closed a total of 19 km
2
to all harvesting of Panulirus argus and allowed a temporary
recreational dive fishery in a further 95 km
2
(Davis, 1977) which resulted in increased densities
of lobsters. In Looe Key National Marine Sanctuary in the Florida Keys, P. argus abundance
and length frequency were similar, both within and outside the area closed to commercial
fisheries, over a period of two years and the authors attributed this to the small size of the
protected area 0.5 km
2
(Hunt et al., 1991). Although small areas (~4 km
2
) have been shown to be
effective in the protection and recovery of crawfish stocks with regards to body size (Bevacqua
et al., 2010), it has been shown that individuals will be able to move into adjacent areas where
fishing is permitted (Childress, 1997, Rowe, 2001, Follesa et al., 2009) and therefore the benefits
of the closure will be reduced.
The movement of individuals outside a protected area can have beneficial effects for fisheries
(Goñi et al., 2008) which may mitigate to some extent the removal of fishing grounds at
closure/designation (Kelly et al., 2002, Goñi et al., 2010). Catch per unit effort was examined
for crawfish trammel net fisheries outside a reserve in the Spanish Mediterranean (Columbretes
Islands Marine Reserve). It was seen that catch rates were elevated at the reserve edge and there
was a gradient of density decrease with increasing distance from the protected area up to 4.5 km
CCW Contract Science Report No 989
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(Goñi et al., 2006). The authors also report that the level of spill over from the closed area had
the potential to maintain stable catch rates up to 1,500 m from the edge of the reserve. This
potential for increased abundance adjacent to reserves can attract additional fishing effort (Goñi
et al., 2006, Goñi et al., 2008). Impacts of this increased effort could reduce the effect of
increased numbers of crawfish in the surrounding area (Goñi et al., 2010). There could also be
cumulative increases in effort due to displacement of fishing activity from the closed area.
It is important to note that the scale of increase in abundance within an area will be related to the
level of fishing within the area. Where the removals through fishing activity are high the
provision of a closed area would provide a significant refuge, with resulting proportional
increases in abundance within the closed area. In areas where fishing effort is low, the impact of
an area closed to fishing crawfish would be likely to be much less significant. This is an
important consideration within the current depleted status of Welsh crawfish populations, where
crawfish abundance is low and removals through the fishery are low. This may reduce the speed
and scale of any recovery that could be brought about through area closures.
When looking at the impacts of protected areas on the recovery of a population it is also
important to note that data on the population prior to protection is important in assessing its
success. This data is often not collected and it is therefore not possible to quantify effectively
the level of protection that such a closed area would affect (Goñi et al., 2001).
The potential rates of recovery from various studies are summarised in Table 3.3. It is possible
that in appropriately identified areas, recovery of crawfish populations with respect to abundance
(and therefore CPUE) could be observed within a matter of months and that the potential scale of
recovery (both abundance and reproductive output) could be high. However, changes relative to
the size structure of the population may take longer to achieve and therefore GES may be a
longer term objective achieved through the amalgamation of various short term interim gains as
indicated in Section 2.2. Care should be taken in interpretation of data with regards to the timing
and scale of recovery possible through area closures in Welsh waters, as the environmental
conditions are different to those in the examples set out above (see Section 1.1.4).
3.2.8 Seasonal Restrictions
Seasonal restrictions are useful in protecting the population during specific periods of their
reproductive cycle, for example mating periods or closures for the avoidance of capture of
berried females. Female crawfish have been shown to carry their eggs for a period of eight to
nine months (Hunter et al., 1996) with egg bearing females seen in the population from August
to May. Should a total closure of the fishery be deemed necessary for the protection of berried
females (as opposed to a prohibition on landing berried females see Section 3.2.6) a seasonal
closure covering all or part of this time period would protect berried females from the fishery. A
six month closed season (September to February) for the protection of berried females is
implemented in the Spanish Mediterranean, and studies