Pros and cons of small-scale native oyster Pros and cons of small-scale native oyster ((Ostrea edulis)Ostrea edulis) restoration programmes: restoration programmes: experiences gained in Strangford Lough experiences gained in Strangford Lough
Northern IrelandNorthern Ireland
Dai Roberts, David SmythDai Roberts, David Smyth& Lynn Browne, Queen’s University, Belfast& Lynn Browne, Queen’s University, Belfast
22
Oysters: component of human diets since prehistoric times
Cultured - in Europe during Roman times
- in Japan during 17th century Complex legislation failed - stocks collapsed in many
parts of the world by the early 1900s due to pollution, disease, over-fishing and habitat loss
Early restoration attempts - introduction of non-native species and the co-transfer of pests and diseases which further exacerbated impacts on native species
1960s, hatchery-based aquaculture (mainly Crassostrea gigas) developed worldwide to meet global demand - now accounts for about 75% of total world production
33
Ostrea edulis:
Natural Range - Norway to Morocco and into the Mediterranean Sea (Alcaraz and Dominguez 1985).
self-sustaining populations due to introductions in Australia (Morton et al. 2003)
Natural beds are now rare in Europe (Gardner & Elliott, 2001).
Listed in UK Biodiversity Action Plan as a species which should be maintained and expanded (Gardner & Elliott, 2001).
is cultivated in many other parts of the world such as Australia, Japan, New Zealand and North America (Hidu and Lavoie, 1991; Gardiner and Elliott 2001).
44
History of exploitation of oysters in Strangford History of exploitation of oysters in Strangford LoughLough
Mesolithic shell middens with large numbers of O. edulis at several locations (McErlean et al. 2002)
Oysters dredged in great numbers from deep water as well as being gathered along the shore (Montgomery, 1683)
Oyster beds commercially exploited with a peak in the 19th century (Brown, 1818).
Oyster fishery collapses about 1903 (government report – Browne, 1903)
Culture of Crassostrea gigas starts in 1970s (Parsons, 1974; Briggs, 1978)
1998 – Ostrea edulis restoration project starts (Kennedy & Roberts, 1999)
55
The present paper reviews :
the historical decline of Ostrea edulis in Strangford Lough
the outcome of restoration attempts
the need to reconcile ecological restoration and sustainable species exploitation
66
Ireland
Figure 1: Study site
4 km
N
Strangford Lough
77
Physical characteristics of Strangford Lough
Catchment Area (km2)
771.5
Length (km) 30.0
Maximum Width (km) 8.0
Surface Area LW (km2)
106.2
Surface Area HW (km2)
182.8
Tidal range (m) 3.5
Max. Depth (m) 60
Volume (106 m3) 1 250
Tidal exchange (106
m3)350350
Coastline (km) 240.0
Salinity range 32-34o/oo
Glacial origin
Substrata: bedrock to fine sediments laid out according to tidal water movement
88
Study site: Strangford Lough, Northern Ireland:
Multi use: over 16 stakeholder organisations represented on Strangford Lough Management Committee [SLMC]
Strangford Lough is currently on the UK designation list as a Special Area of Conservation (SAC) under the European Commission (EC) Habitats Directive (92/43/EEC) the aim of which is to conserve certain habitats and species within the EC.
Approximately 60,000 people live around the lough and a further 1 million are within a one hour’s drive
99
Dredging area 19th century
• Kircubbin
Portaferry
NewtownardsThe Historic Fishery
Oyster landings in Strangford Lough over a 60 year period during the 19th century in comparison with licensed dredgers.
Decadal average annual landings per boat of Ostrea edulis from Strangford Lough 1820-1880
0
20
40
60
80
100
120
140
160
1820s 1830s 1840s 1850s 1860s 1870s
DATE
Kg
(x1
03 )
0
5
10
15
20
25
30
35
40
45
50
No
. o
f li
cen
sed
dre
dg
ers
Landings
No. Dredgers
1111
Cuan Oysters, Strangford Lough, Northern Ireland(http://www.cuanoysters.com/seafood/index/html):
the major producer of oysters in the lough - established 1974
played an important role in the development of oyster aquaculture in the United Kingdom by pioneering culture methods for very small hatchery-reared seed
now one of the main producers in the UK, handling over 400 tonnes of oyster (C. gigas; O. edulis)per annum
1212
Portaferry
Newtownards
Restoration project 1997-1999
Licensed sites [hectares](not to scale)
Boretree IsBoretree Is 113113
Calf rockCalf rock 9494
Chappel IsChappel Is 6565
Mahee IsMahee Is 24.724.7
Connelly IsConnelly Is 22.722.7
Main oyster aquaculture areas 1990s
1313
Restoration 1997-Restoration 1997-9999
• Spreading 70-75 tonnes cultch (mainly C.gigas and scallop shells) to form the basis for new beds
• Concentrating broodstock on new beds
•Seeding with with 250,000 250,000 O. edulisO. edulis
spatspat
1414
SurveysSurveys
• Spat CollectionSpat Collection- 13 collectors - 13 collectors
•IntertidalIntertidal
- - 30 coastal 30 coastal sitessites
-- 8 Island sites 8 Island sites
•Subtidal -Subtidal - 15 dive 15 dive sitessites
• Plankton Plankton samplingsampling -- over tidal fluxover tidal flux
1515
Ballyreagh NewtownardsSailing Club
Mount Stewart
Herring Bay
Kircubbin
Ballyhenry
Marlfield
Grey Abbey
Island Hill
Sites surveyed 2002-2004
Chapel Island
Horse Island
Granagh Bay
Barr Hall Bay
Castleaverry
Castle Espie
Paddy’s Point
Horse Island
NendrumWhiterock
Ringhaddy
Simmy Island
Killyleagh
Nickey’s Point
Castle Island
Castleward BayShore surveys
Spat collectors
Island sites
Newtownards
Portaferry
N
EW
S
1616
The total number of inter-tidal and sub-tidal O.edulis in the North, West, East and South were estimated using the following formula adapted from Gunderson (1993).
h _ P= ∑ ﴾ Ri .F ﴿ C i I=1 a
Where; P= Total population resident in full survey area. Ri= Area of region I in m2 . a= Area sampled within a single sampling unit. F= Correction factor estimating substrate types. _ Ci= Mean number of oysters observed per sampling unit in the region based i on n samples. h= Number of regions composing the survey.
Estimates of standing stocks
1717
Intertidalareas m-2
(x 106)
Substrate Correction factor(Kennedy & Roberts 1999)
Area suitable for settlement m-2 (x106)
Standing stockOysters (x103)
1998 2002 2003 2004
North 19.64 0.056 1.1 102 1,017 1,242 964South 4.701 0.019 0.089 0 0 0.3 0East 4.509 0.236 1.064 0 0.6 0.2 0.1West 5.438 0.027 0.146 8 2.8 1.2 0.5Total 34.29 NANA 3.628 110 1021 1244 965• Proportionally weighted correction factors were applied to
account for the amount of suitable substratum present.• Drop due to unregulated harvesting
Estimates of standing stocks: Intertidal surveys
1818
Subtidal areas m-2
(x 106)
Substrate Correction factor (Kennedy & Roberts 1999)
Area suitable for settlement m-2 (x106)
Standing stockOysters(x103)
1998 2003
North 26.816 0.234 6.274 0 376
South 68.001 0.023 1.564 0 0
East 32.318 0.236 7.627 0 152
West 9.789 0.019 0.185 0 595
Total 136.092 15.650 0 1124 • Proportionally weighted correction factors were applied to Proportionally weighted correction factors were applied to
account for the amount of suitable substratum present.account for the amount of suitable substratum present.
Estimates of standing stocks: Sub-tidal surveys
1919
Kennedy & Roberts 1999 (x103)
2002(x103)
2003(x103)
Intertidalwild stock
110 1021 1244
Subtidal wild stock
0 No data 1124
Commercial oyster mats
125 0 0
Subtidal licensed sites
Not present
No data * 639
TOTALS 235 1021 3007
*Based on known areas of licensed sites and assuming 100% suitable subsratum and sub-tidal density estimates elsewhere
Estimates of total standing stocks
2020
no formal records of the levels of regulated or unregulated shellfish harvesting by hand for Strangford Lough
used the following approximation:
Total removal per month
= nos of collectors X removal rate X nos suitable low tides per month
Estimates based on the approximation above were compared to changes in estimates of standing stocks over Christmas (November - January), the most intense harvesting time when shellfish are at a premium in Europe.
Estimates of unregulated harvesting
2121
no formal records of the levels of either regulated or unregulated shellfish harvesting by hand for Strangford Lough
used the following approximation:
Total removal per month = 12 X (nos) 92k X 8
= 8,832 kg
= 17,664 kg (November – January)
Estimated change in standing stocks
November – January = 278x103 (24,464 kg)
September – April = 1112x103 (97,856 kg)
Impacts of unregulated harvesting on standing stocks
2222
Ballyreagh 2002
0
0.1
0.2
0.3
0.4
0.5
0.6
10-20mm 40-50mm 70-80mm 100-110mm
Nos
m2
Ballyreagh 2003
0
0.1
0.2
0.3
0.4
0.5
0.6
10-20mm 40-50mm 70-80mm 100-110mm
Ballyreagh 2004
0
0.1
0.2
0.3
0.4
0.5
0.6
10-20mm 40-50mm 70-80mm 100-110mm
NSC 2002
0
0.1
0.2
0.3
0.4
0.5
0.6
10-20mm 40-50mm 70-80mm 100-110mm
Nos
m2
NSC 2003
0
0.1
0.2
0.3
0.4
0.5
0.6
10-20mm 40-50mm 70-80mm 100-110mm
NSC 2004
0
0.1
0.2
0.3
0.4
0.5
0.6
10-20mm 40-50mm 70-80mm 100-110mm
Impacts of unregulated harvesting on coastal populations
UNFISHED
FISHED
2323
Impacts of unregulated harvesting on island populations
Dougherty Rock 2002
0
0.1
0.2
0.3
0.4
0.5
0.6
10-20mm
30-40mm
50-60mm
70-80mm
90-100mm
110-120mm
Nos m-2
Dougherty Rock 2003
0
0.1
0.2
0.3
0.4
0.5
0.6
10-20mm
30-40mm
50-60mm
70-80mm
90-100mm
110-120mm
Dougherty Rock 2004
0
0.1
0.2
0.3
0.4
0.5
0.6
10-20mm
30-40mm
50-60mm
70-80mm
90-100mm
110-120mm
Nos m-2
Sheelahs Island 2003
0
0.1
0.2
0.3
0.4
0.5
0.6
10-20mm
30-40mm
50-60mm
70-80mm
90-100mm
110-120mm
Sheelahs Island 2004
0
0.1
0.2
0.3
0.4
0.5
0.6
10-20mm
30-40mm
50-60mm
70-80mm
90-100mm
110-120mm
Sheelahs Island 2002
0
0.1
0.2
0.3
0.4
0.5
0.6
10-20mm
30-40mm
50-60mm
70-80mm
90-100mm
110-120mm
Nos m-2
ND
ND
FISHED
FISHED
2424
Further consequences of harvestingFurther consequences of harvesting
• Decrease in suitable cultch for larval settlement
•Decrease in broodstock assemblage and therefore larval swarms
•Anthropogenic disturbance of intertidal habitats within a SAC•Decrease in the oyster shell as a habitat (Korringa 1945 listed 68 sp. on O. edulis) (Mistakidis 1951 listed 121 sp. on Essex oyster grounds)
2525
>95% Increases in the densities of native oysters in Strangford Lough between 1998 and 2003 in Northern basin
due to over-summering of commercial oysters initially, hydrographical conditions and restoration efforts
Restoration of O. edulis will increase biodiversity within Strangford Lough,
is unlikely to be due to recruitment from wild stock
SummarySummary
2626
Increase in standing stocks since 1998 has resulted in the first significant harvests from Strangford Lough for over 100 years.
However, harvests have resulted in the removal of an estimated 25% of the total intertidal oyster population and are unregulated
Dredging is currently banned
Until these issues are resolved, the very promising recovery of oysters in Strangford Lough with the tangible potential to reconcile ecological and harvest goals of restoration will not be realised.
Annual removal estimated at 97 tonnes which is nearly twice the levels at which the fishery collapsed (52 tonnes) in the 19th century and is unlikely to be sustainable
SummarySummary
2727
Should restoration of Ostrea edulis be continued in Strangford Lough?
• the restoration of O. edulis assemblages have the potential to increase biodiversity within Strangford Lough.
Yes- because:
• the Lough has suitable regions where local circulation will promote larval retention (Kennedy & Roberts,1999)
• Strangford Lough oysters largely disease free
2828
Acknowledgements
The Worshipful Company of Fishmongers Strangford Lough Fishermen’s Co-
operative Department of Agriculture and Rural
Development for Northern Ireland Richard Kennedy