Centre for

Shellfish Research

SHELLFISH CULTURE AND

NATURE CONSERVATION

Aad Smaal

Institute for Marine Resources and Ecosystem Studies

Yerseke, NL

Centre for

Shellfish Research

Delta

North Sea

IMARES: NEW INSTITUTE

Former Fishery Institute merged

with 2 other groups

ENVIRONMENT

FISHERY

AQUACULTURE

Shellfish Research, Yerseke

- population dynamics

- carrying capacity

- culture innovation

Centre for

Shellfish Research

PROBLEMS IN CULTURE AND CONSERVATION

• Shellfish culture / fisheries always has an impact on the

ecosystem

• Shellfish culture occurs often in areas that are now

protected for nature conservation

• What are the impacts, positive / negative, acceptable ?

• Source of conflicts between stakeholders

• Role of science / politics / governments

Centre for

Shellfish Research

OUTLINE

• ROLE OF SHELLFISH IN THE SYSTEM

• IMPACTS OF CULTURE

• REGULATION

• STAKEHOLDERS

• CONSERVATION and EXPLOITATION

Centre for

Shellfish Research

Food

Habitat Feedbacks

ROLE OF SHELLFISH

Oosterschelde case: storm surge barrier

Analysis of the role of mussels in the ecosystem:

benthic tunnels, mesocosms, models

• Residence time >• Water transparency >• Nutrient loads <

• Internal nutrient cycles more important• Adaptation of phytoplankton• Maintenance of primary production

Prins & Smaal, 1994; Prins et al, 1998; Smaal et al, 2001

Nutrient (N) regeneration through direct excretion + biodeposit mineralization up to 40 % of total N regeneration

Through grazing increase in phyto plankton turnover ; optimal mussel growth at intermediate biomass

Bottom-up control at low mussel density and top-down control at high mussel density

Centre for

Shellfish Research

FUNCTIONAL ROLE:

• Grazing of phytoplankton

• Production of biodeposits

• Regeneration of nutrients

• Promotion of algal growth

• Stabilization of the ecosystem

feedbacks through filter feeding

Centre for

Shellfish Research

FOOD FOR BIRDS:

• shellfish beds are essential as food source for waders and diving ducks

• shellfish stocks may show large variability in time

• birds may switch prey

• collapse of both mussel and cockle stocks caused problems in Wadden Sea and Wash in ’90

0

50

100

150

200

250

mln kg fresh

1971 1974 1977 1980 1983 1986 1989 1992 1995 1998

0

1

2

3

4

1950 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000

bestand droog

Mussel stock(index)

Eider duck mortality

1991

Cockle

stock

Call for shellfishery policy

0

100

200

300

400

500

mln kg fresh

1990 1992 1994 1996 1998 2000 2002

BSF dynamics

mussel

macoma

cockle

0

50000

100000

150000

200000

250000

300000

350000

75767778798081828384858687888990919293949596979899000102

Oystercatcher decrease after

low shellfish stocks 1996 due

to severe winter

Centre for

Shellfish Research

CONCLUSION FOOD

FOR BIRDS

• Shellfish is major resource

• Minimum stock required for longterm maintenance of

bird populations

• high shellfish dynamics sometimes don’t match bird needs

• call for protective measures

0

20

40

60

80

100

120

140

160

180

51 55 59 63 67 71 75 79 83 87 91 95 99

mln kg fresh

Import

Wad

Delta

0

20000

40000

60000

80000

100000

77 80 83 86 89 92 95 98

MILJOEN KG VERS

vd

ws

os

wad

HARVEST IN NL FROM

CULTURE AND FISHERY

MUSSEL: 100 MLN KG

COCKLE: 20 MLN KG

OYSTER: 3 MLN KG

00.5

11.5

22.5

3

mln kg

52 57 62 67 72 77 82 87 92 97

oyster production

Crassostrea

Ostrea

ROLE AS HABITAT

Biocoenose (Mobius, 1880)

Epibenthic shellfish beds form structures

nr of species > 150 (Sayer, 2002)

Biodiversity higher in sublitoral (Buchsbaum & Sayer, 2003)

Impact of culture ?

Centre for

Shellfish Research

IMPACTS OF SHELLFISH CULTURE

Feedbacks

impact on Stocks

Food

Habitat direct:

bottom culture – infauna (clams, cockles)

- epifauna (mussels, oysters)

indirect: suspended culture

WILD LITORAL STOCK

WILD SUBLITORAL STOCK

CULTURE PLOTS

SHELLFISH FLOW

natural spatfal natural spatfal

Seed fishery

harvest

RESULT: NET INCREASE OF BIOMASS

IMPACTS on STOCKS

IMPACTS on STOCKS

Case study : Wadden Sea bottom culture

Model calculation wild beds vs culture plots:

Musselseed plots/wild - Growth 1.7 x higher

- Density 0.6 - Mortality 0.8

Net result: stock – harvest 1.15: 15 % more biomass

Note: Carrying capacity problems due to overstocking

IMPACTS on HABITAT

Bottom culture:

• Culture of mussels and oysters

on bottom plots,

frequent fishery activities

effects on biodiversity depend on

local conditions

• Culture / fishery of infauna :

sediment change ?

mortality of bycatch ?

less spatfal ?

many studies

controversial issue

ban on cockle fishery Waddensea 2003

Wild

bed

Cultureplots

muddy sub

(Von Westphalen, 2005)

sand

(van Gils et al, 2004)

Impact of cockle fishery

Seed fishery on wild beds

Mussels : focus on unstable beds

Littoral : experimental seed fishery

to test impact on stability:

no net effect of fishery on seed mussel density

Sublittoral : research topic

Major issue in actual discussion in NL

IMPACTS on HABITAT

Suspended culture:

• Sediment deposition

depomod application

mostly for fish farming

useful for shellfish

(no external input, only concentrating material)

• Benthic community

various studies: (Grant et al, 2005; DEPOMOD)

- local scale effects

- depend on hydrodynamics, site etc

- can both enhance or reduce species nr

Centre for

Shellfish Research

SUMMARY OF IMPACTS

Stocks: AVERAGE INCREASE

Habitats: bottom culture / seed fishery

epifauna BIODIVERSITY

HABITAT COMPLEXITY

infauna SEDIMENT/BENTHOS

suspended culture SEDIMENT/BENTHOS

POLICY & REGULATION

NATIONAL: policy document 2004

“Space for harvest”

- sustainable use

- innovation by industry, less impacts

- closed areas

EU: Bird and Habitat Directive (implementation NL 2004)

- For nature conservation areas

- in many cases shellfish culture areas

- permit required for each seed fishery period (2x p yr)

- industry has to perform an appropriate assessment

of possible impacts on management objectives

- permits can be stopped by court after objections

STAKEHOLDERS

INDUSTRY RESPONSE

• triple P approach : Profit, Planet, People

= continuous improvement

= planning + evaluation + research

= draws up fishing plans,

= uses black boxes onboard fishing vessels

= register activities in an electronic logbook

• Develop an innovation agenda

• Stakeholder involvement

• Setting up research: innovation

continuous improvement

ProfitProfit

PlanetPlanetPeoplePeople

INNOVATION: life cycle control

PRODUCT

HATCHERY

SEED

COLLECTORS WILD SEED

FISHERY

IMOZA - Doove Balg

IMOZA - Verversgat

IMOZA - Vlieter

IMOZA - Stompe

IMOZA - Malzwin

IMOZA - Bollen

Wietex - Texelstroom

Wietex - Oergat

Wietex - MalzwinPD - Malzwin

West 6 - Malzwin

Zaadinvang locaties

Kustlijn

Laagwaterlijn

Naam: Produs 1c

Auteur: J.M.D.D. Baars

Archief: q:/projects/kleine_opdr/pk05 Datum:juli 2005

Centrum voor Schelpdier Onderzoek

NederlandsInstituut voor

Visserijonderzoek

MUSSEL SEED HATCHERY/

COLLECTORS NURSERY

STAKEHOLDERS

NGO RESPONSE

• objected against seed fishery permits

• case in court in spring and autumn

• court decision: fishery could go on

BACKGROUND

Nature conservation areas should not be exploited

Editorial in PloS Biology of Nov 14, 2006 based on

culture

conservation restoration

X

?

NATURE CONSERVATION STRATEGIES

• Protection against adverse impacts

• Conservation of non-impacted areas

• Prevention of new impacts

• Habitat restoration

• Habitat creation

• Multi-functional use

• Sustainable use

exclusion

mitigation

integration

Dynamic / control

Static / spontaneous

NATURE CONSERVATION = CULTURAL ISSUE

PARADOX OF EXTENSIVE EXPLOITATION

• extensive exploitation is part of nature and contributes to

ecosystem processes (food, feedback, habitat)

• exploitation depends on natural dynamics and farmers

want to become less dependent

• nature conservationists want to restrict exploitation

• 2 forces in the direction of intensification

• more intensive culture in existing areas calls for more

criticism

• loss of extensive culture

• future need for shellfish restoration

Centre for

Shellfish Research

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