Transcript x10 3

Pros and cons of small-scale native oyster (Ostrea
edulis) restoration programmes: experiences
gained in Strangford Lough Northern Ireland
Dai Roberts, David Smyth
& Lynn Browne, Queen’s University, Belfast
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
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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)

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).

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).
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History of exploitation of oysters in Strangford Lough

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)
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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
5
Figure 1: Study site
Strangford Lough
N
Ireland
4 km
6
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)
350
Coastline (km)
240.0
Salinity range
32-34o/oo
Glacial origin
Substrata: bedrock to fine sediments laid out
according to tidal water movement
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Study site: Strangford Lough, Northern Ireland:

Multi use: over 16 stakeholder organisations represented
on Strangford Lough Management Committee [SLMC]

Approximately 60,000 people live around the lough
and a further 1 million are within a one hour’s drive

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.
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The Historic Fishery
Newtownards
• Kircubbin
Dredging area
19th century
Portaferry
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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
50
45
140
40
120
Kg (x103)
35
100
30
80
25
20
60
15
40
10
20
No. of licensed dredgers
160
5
0
0
1820s 1830s 1840s 1850s 1860s 1870s
DATE
Landings
No. Dredgers
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
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Restoration project
1997-1999
Newtownards
Licensed sites [hectares]
(not to scale)
Boretree Is
113
Calf rock
94
Chappel Is
65
Mahee Is
24.7
Connelly Is
22.7
Portaferry
Main oyster aquaculture
areas 1990s
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Restoration 1997-99
•
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
250,000 O. edulis
spat
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Surveys
•Intertidal
- 30 coastal sites
- 8 Island sites
•Subtidal -
15 dive sites
• Plankton sampling
- over tidal flux
• Spat Collection
- 13 collectors
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Newtownards
Sites surveyed
Castleaverry
2002-2004
Ballyreagh
Island Hill
Newtownards
Sailing Club
Mount Stewart
Chapel Island
Grey Abbey
N
Castle Espie
Herring Bay
Horse Island
Paddy’s Point
Nendrum
Whiterock
E
W
Kircubbin
Horse Island
Ringhaddy
Simmy Island
Marlfield
Island sites
Killyleagh
S
Ballyhenry
Nickey’s Point
Portaferry
Shore surveys
Castle Island
Castleward Bay
Spat collectors
Granagh Bay
Barr Hall
Bay
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Estimates of standing stocks
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.
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Estimates of standing stocks: Intertidal surveys
Substrate
Correction
factor
(Kennedy
& Roberts
1999)
Area
Standing stock
suitable
Oysters (x103)
for
settlement
2003
m-2 (x106) 1998 2002
North 19.64
0.056
1.1
102 1,017 1,242 964
South 4.701
0.019
0.236
0.027
0.089
1.064
0.146
3.628
0
0
8
110
Intertidal
areas
m-2
(x 106)
East
4.509
West 5.438
Total 34.29
NA
0
0.6
2.8
1021
0.3
0.2
1.2
1244
2004
0
0.1
0.5
965
• Proportionally weighted correction factors were applied to account for
the amount of suitable substratum present.
• Drop due to unregulated harvesting
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Estimates of standing stocks: Sub-tidal surveys
Substrate
Correction
factor
(Kennedy &
Roberts
1999)
Standing stock
Area
Oysters
suitable for
settlement
(x103)
m-2 (x106) 1998
2003
North 26.816
South 68.001
0.234
0.023
6.274
1.564
0
0
376
0
East
West
Total
0.236
0.019
7.627
0.185
15.650
0
0
0
152
595
1124
Subtidal
areas
m-2
(x 106)
32.318
9.789
136.092
• Proportionally weighted correction factors were applied to account for
the amount of suitable substratum present.
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Estimates of total standing stocks
Kennedy &
Roberts
1999 (x103)
2002
(x103)
2003
(x103)
Intertidal
wild stock
Subtidal
wild stock
110
1021
1244
0
No data
1124
Commercial
oyster mats
Subtidal
licensed sites
125
0
0
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
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Estimates of unregulated harvesting

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.
20
Impacts of unregulated harvesting on standing
stocks

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)
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Impacts of unregulated harvesting on coastal populations
Ballyreagh 2003
Ballyreagh 2002
Ballyreagh 2004
0.6
0.6
0.5
0.5
0.4
0.4
Nos
0.3
m2
0.2
0.3
0.3
0.2
0.2
0.1
0.1
0.1
0
0
0.6
0.5
0.4
0
10-20mm 40-50mm 70-80mm
100110mm
10-20mm
40-50mm
70-80mm 100-110mm
10-20mm
NSC 2003
NSC 2002
0.6
0.6
0.5
0.5
0.5
0.4
Nos
0.3
m2
0.2
0.4
0.4
0.3
0.3
0.2
0.2
0.1
0.1
0.1
40-50mm
70-80mm 100-110mm
0
10-20mm
70-80mm
NSC 2004
0.6
0
10-20mm
40-50mm
100-110mm
U
N
F
I
S
H
E
D
F
I
S
H
E
D
0
40-50mm
70-80mm
100-110mm
10-20mm
40-50mm
70-80mm
100-110mm
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Impacts of unregulated harvesting on island populations
0.6
0.6
0.6
0.5
0.5
0.5
0.4
0.4
0.3
Nos
0.3
m-2
0.2
0.2
0.1
0.1
0.1
0
0
0
ND
0.4
Nos
0.3
m-2
0.2
1020mm
3040mm
5060mm
7080mm
90100mm
1020mm
110120mm
3040mm
5060mm
7080mm
90100mm
110120mm
1020mm
0.6
0.6
0.6
0.5
0.5
0.5
0.4
0.4
0.3
0.3
0.2
0.2
0.1
0.1
0.1
0
0
0
ND
0.4
Nos
0.3
m-2
0.2
1020mm
3040mm
5060mm
7080mm
90100mm
110120mm
1020mm
3040mm
5060mm
7080mm
3040mm
5060mm
7080mm
90100mm
90110100mm 120mm
1020mm
3040mm
5060mm
7080mm
110120mm
F
I
S
H
E
D
Sheelahs Island 2004
Sheelahs Island 2003
Sheelahs Island 2002
F
I
S
H
E
D
Dougherty Rock 2004
Dougherty Rock 2003
Dougherty Rock 2002
90100mm
110120mm
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Further consequences of harvesting
•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)
• Decrease in suitable cultch for larval settlement
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Summary


>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

is unlikely to be due to recruitment from wild stock

Restoration of O. edulis will increase biodiversity
within Strangford Lough,
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Summary



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
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

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.
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Should restoration of Ostrea edulis be continued in
Strangford Lough?
Yes- because:
• the Lough has suitable regions where local
circulation will promote larval retention (Kennedy
& Roberts,1999)
• the restoration of O. edulis assemblages have the
potential to increase biodiversity within Strangford
Lough.
• Strangford Lough oysters largely disease free
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Acknowledgements




The Worshipful Company of Fishmongers
Strangford Lough Fishermen’s Cooperative
Department of Agriculture and Rural
Development for Northern Ireland
Richard Kennedy
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