Download Invasive American razor clam Ensis directus in Belgian waters

Invasive American razor clam
Ensis directus in Belgian waters:
a true opportunity for shell-fisheries?
Kris Hostens1, Wouter Courtens2, Johan Craeymeersch3, Kees Goudswaard3, Jean-Sé Houziaux5†,
Bea Merckx4, Gert Van Hoey1, Francis Kerckhof5, Jack Perdon3, Eric Stienen2, Vera Van Lancker5,
Laurence Vigin5, Magda Vincx4 & Steven Degraer5
NIS symposium, Oostende, 22 November 2013
EnSIS: Ecosystem sensitivity to invasive species (Houziaux et al. 2011)
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Introduction
Ensis directus
Labrador
Ballast water
North Carolina
North Atlantic
Ocean
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Transportation
Ensis arcuatus early development (Da Costa et al. 2008)
Trochophora larvae
Labrador
Ballast water
Veliger larvae
North Carolina
North Atlantic
Ocean
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Invasion pattern in Europe
Ensis directus
1979: first sightings in German Bight
1987: first sightings in Belgian waters
VLIZ & Severijns 2002
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Motivation
Massive strandings on (Belgian) beaches
Current exploitation in the Netherlands
3000
Dutch coast
Voordelta
2500
tonnes
2000
1500
1000
500
0
2006
2007
2008
2009
2010
2011
Hervás et al. 2012
What is exploitation potential of razor clams in Belgian waters ?
 Population structure (size classes)
 Abundance / Spatial distribution of Ensis directus
 Potential threats to the ecosystem
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Datasets
 ILVO and Ghent University Macrobenthos databases 1977–ongoing
–
Van Veen grab samples
Dave Cowles www.wallawalla.edu
Van Veen = Not efficient for adults
 mostly only broken tips of Ensis
 not measurable nor identifiable
 OK for juveniles
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Long-term data : Van Veen grab samples
Sampling locations
 Ensis sp. limited to 12 nM zone
Presence of Ensis directus
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Datasets
 Schelp survey – ILVO July 2008
–
Trawled dredge (IMARES, NL)
Random stratified sampling
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Datasets
 EnSIS survey – ODNature, Ugent February 2010
–
–
Box-Core sampler
Target: higher density areas
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Datasets
 ILVO epibenthos database 1989-2013
–
8m shrimp beam trawl samples
 Less efficient
 mainly ‘moving’ animals ?
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E. directus: an introduced invasive species
Houziaux et al, 2008
 Gilson data 1899-1914:
E. arcuatus most abundant
E. directus not present yet
 ILVO VV data 1993-2012:
E. directus most abundant
 Probably displaced other Ensis species
nearshore
 E. arcuatus (E. magnus) disappeared,
but present again (offshore) in low
numbers since 2000
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Relative densities of E. directus on BPNS - 2008 and 2010
Ensis directus population structure
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Contribution to total - % (2008)
Contribution to total - % (2010)
Contribution to total - % (2010) - >= 6cm
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% abundance
Winter 2010
40
Summer 2008
30
20
10
0
-18
17
-17
16
-16
15
-15
14
-14
13
-13
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-12
11
-11
10
cm
cm
cm
cm
cm
cm
cm
cm
m
cm
cm
cm
cm
cm
cm
cm
cm
0c
9-1
8-9
7-8
6-7
5-6
4-5
3-4
2-3
1-2
Shell length (cm)
Ensis Spat density
(VV)
 Strong recruitment
in spring 2009
Also observed in Dutch
waters
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Relative densities of E. directus on BPNS - 2008 and 2010
Ensis directus population structure
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Contribution to total - % (2008)
Contribution to total - % (2010)
Contribution to total - % (2010) - >= 6cm
50
% abundance
40
30
20
 Proportional biomass
 same pattern in 2008 & 2010
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Relative contributions to total weight - %
0
-18
17
-17
16
-16
15
-15
14
cm
cm
cm
cm
% Biomass
Contribution to total - % (2008)
Contribution to total - % (2010)
Contribution to total - % (2010) - >= 6cm
cm
cm
cm
cm
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-14
13
-13
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-12
11
-11
10
m
cm
cm
cm
cm
cm
cm
cm
cm
0c
9-1
8-9
7-8
6-7
5-6
4-5
3-4
2-3
1-2
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 Max. 17 cm length
NL min
EU min
 11-12 cm most common
length class
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 minimum landing size
EU = 10 cm ; NL = 12 cm
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 6-9 cm class (~ 2 years)
under-represented
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 Predation effect?
0
cm
-18
17
cm
-17
16
cm
-16
15
cm
-15
14
cm
-14
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cm
-13
12
cm
-12
11
cm
-11
10
cm
cm
cm
cm
cm
cm
cm
cm
cm
0
9-1
8-9
7-8
6-7
5-6
4-5
3-4
2-3
1-2
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Ensis directus abundance
Summer 2008
Juveniles (#/m²)
Adults (#/m²)
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Ensis directus adult biomass
 ‘Gap’ off Wenduinebank
 coarser sands?
Summer 2008
 Small yearly shifts
Adult biomass max 5kg/m²
 Stable subtidal populations around:
Nieuwpoortbank
Oostendebank
Vlakte van de Raan (Northern slope)
Winter 2010
 Extending to shallow subtidal
in front of coasts
Nieuwpoort and Oostende
(western part of BPNS)
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E. directus response curves
Depth 5-25m
Low current velocities
Low mud%
Low mud% in water
Fine/medium sands
Soft slope
High Chla%
Medium POC
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Habitat Suitability models Be-Nl
Based on environmental parameters
Hydrodynamics (currents)
Water quality (Chla, POC, %mud)
Geomorphology (depth, %sand, %mud)
 Broad tolerance to env. parameters
 High reproductive and dispersal
capabilities
 Difficult to predict abundances
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An opportunity for commercial exploitation
in Belgian waters ?
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Impact of Hydraulic dredging technique ?
Addison et al. 2006
Pumping water in top sediment layers
 Fluidizes sediment over a depth of 30 cm
Dredge width upto 2.5 m (Tuck et al. 2000)
 Resuspension of PM (particulate matter)
(higher mud% in BPNS)
Mixing the sediment deeply  changed structure
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Impact on macrobenthic fauna ?
 Ensis HSM 70% match with Abra alba community HSM
Richest macrobenthos community
Community ‘used’ to disturbance (natural and humaninduced)
Low mortality rates in thick shelled bivalves and worms
Most species fast turnover rates
HSM – A. alba
community
Degraer et al (2008)
 Fast recovery (~ weeks) after dredging (e.g. Hall et
al, 1990 - Scotland)
 Fragile species selectively impacted
e.g. Echinocardium cordatum (green urchin) : 30 %
mortality; Lutraria lutraria (deep-burying bivalve) : 10 %
 Trawling/Dredging = slow
Low direct impact
HSM Ensis
macrodat
Indirect impact through seafloor structure disturbance?
 Overall ecosystem impact ≈ exploitation intensity !
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Impact on seabirds & fish ?
 Few seabirds prey upon benthos
 Mainly seaducks
(common scoter, velvet scoter & eider
duck)
2000 - 2011
Ensis in stomachs
 Literature research:
 Seabirds mainly prey upon Ensis length class
~ 6-9 cm
 Juvenile flatfish (dab, plaice, sole) mainly prey upon
siphons
 Impact of Ensis fishery on seabirds limited ?
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Impact on / interaction with other fisheries ?
 Ensis area largely overlap with coastal (shrimp) fishery
‘low impact’ on ecosystem  yet unknown impact of
Ensis fishery on shrimp and coastal fish stocks
 Duality in Belgian fishing industry:
Belgian
Shrimp trawls
2008-2011
•
Damage to beamtrawler nets (= main métier) 
fishermen don’t appreciate Ensis beds
•
Opportunity, but conservative sector
 will Belgian fishermen adapt to new resource or will
Dutch experienced Ensis fishermen be attracted?
 Demand-driven fishery
 Shellfish fisheries (still) forbidden by Belgian law
 Exploitation potential but proper management !
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Sustainable exploitation !
Dutch Ensis fishery started in 1990s
Since 2006: 8 fishing licenses (5 active)
2012: MSC label for Ensis fishery (Hervas et
al. 2012)
Harvest strategy complies with conservation
requirements of Voordelta & Dutch coastal
zone
Precautionary approach to maintain the
productivity of the stock at sustainable levels
 maximum allowed catch 8000 tons
 Maximum 2400 hours / year / vessel
~ 200 fishing days of 12 h
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Exploitation vs. standing stock in NL
 Stock estimates 2011 (IMARES):
100 000 million specimens
~ 500 000 to 0.8 million tons !!!
 Proportion >12 cm ~ 12.5% total biomass
= 62 500 – 100 000 tons
3000
Dutch coast
Voordelta
 2011: 3700 tons landed (Hervas et al.
2012)
2500
tonnes
2000
 On average 5 kg/m²
 in total 70 ha (0.7 km²) dredged
= 50% of allowed ‘surface’
1500
1000
500
0
2006
2007
2008
2009
2010
2011
 Ensis fishery
~ 4 to 6 % of adult stock biomass in NL
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Yield vs. Sustainable exploitation
2008
Belgian Coast
(1356 km²)
Amount
Avg ind. /ha
(millions)
Voordelta
(1276 km²)
Amount
Avg. ind/ ha
(millions)
Dutch Coast
(6438 km²)
Amount
Avg ind. /ha
(millions)
Small (<12cm)
3 890
28 630
10 120
79 310
26 430
41 050
Big (>12cm)
2 100
15 490
1 470
11 540
4 490
6 970
Siphons
6 470
47 710
14 780
115 770
34 840
54 110
12 460
91 820
26 370
206 620
65 760
102 130
Total 2008
2013
Total 2013
Big (>12cm)
Amount
(millions)
WetWeight
(tons)
!
Amount
(millions)
WetWeight
(tons)
Amount
(millions)
WetWeight
(tons)
21 280
95 300
71 000
51 160
323 700
182 200
ILVO - IMARES
IMARES
J. Craeymeersch
ILVO – 8m Beam trawl
1989-2013
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What about the consumer ?
I tasted
them:
they are
delicious !
Dutch Ensis mainly exported to Spanish & Italian markets
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Are you an Ensis eater ?
no; 1
Did you already
eat Ensis?
yes;
15
uk; 1
In which country
did you eat it?
Did you like it ?
ok; 6
no;
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yes; 8
fr; 2
es; 3
be; 10
mayb
e; 5
Would you
eat it again ?
yes;
10
no; 0
nl; 1
raw; 1
How was it
served/prepared?
soup;
1
boiled
;8
grilled
;8
fried;
3
Would you buy
it if it were
available at the
supermarket ?
yy; 7
ny; 14
yn; 7
nn; 12
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Conclusion
Implementation of an Ensis targeted fishery in Belgian coastal waters could be profitable
& probably with limited ecosystem impacts…
…if properly managed !
 Continuous monitoring and further research needed
 Change in Belgian legislation required
 Change in fishermen mentality might be necessary
Recipe: cooking, cleaning, baking with peas & ham
serving with tomato/basilicum/whipped cream
Chef-kok Eric van Veluwen, recept met scheermessen
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