CHALLENGES TO THE LIMFJORDEN FLAT OYSTER STOCKMANAGEMENT AND PRODUCTION

Jens Kjerulf PetersenThe Danish Shellfish Centre

Danish Shellfish Centre

• Independent research facility (from 2013 part of Danish Technical University)

• Sustainable production in the coastal environment with focus on shellfish

• Research, consultancy, dissemination, production

• Laboratories, boats, hatchery for oyster, lobster and macro-algae, mussel culture units

• Currently a staff of 5 biologists and 7 technicians

History

History

History

Petersen 1907

Current population of oysters

Østerstætheder maj 2009g/m2

5.000000001 - 25

25.00000001 - 75

75.00000001 - 150

150.0000001 - 224.4031219

A fact

•Limfjorden is EU certified Bonamiaand Martelia free !!

The fishery

-

2.000.000

4.000.000

6.000.000

8.000.000

10.000.000

12.000.000

14.000.000Ostrea edulis harvested in Limfjorden

Utilization of stockFlat oyster abundance Fishery intensity

2007

2008

2009

Recent biomass development

Size distribution

Stock development

Mortality

Other challenges

Natura 2000 areas in Limfjorden

Summary of fishery management• Since the 1850’ies the stock – and thus the fishery – has been

very fluctuating• Some of the historic fluctuations can be ascribed to too high

fishery pressure, some to natural (climate dependent) fluctuations in recruitment (or predation pressure)

• The recent (after 2000) unprecedented high fishery yield has been triggered by high recruitment and good food conditions

• The recent fishery has not been unsustainable so far• The low current densities renders the fishery non-compliant

with Natura 2000 goals• New methods for production and/or stock stock restoration are

required or oyster production in Limfjorden will stop for ? yr

Alternative – in situ spat collection

In situ spat collection – 1. trial

1. trial results – spatial and temporal variation

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06 July 2010 20 July 2010 03 August 2010 17 August 2010

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Harre Vig 4 meters no. cement4 meters w. cement2 meters no. cement2 meters w. cement

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06 July 2010 20 July 2010 03 August 2010 17 August 2010

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Venoe 4 meters no.cement4 meters w. cement

2 meters no.cement

1. trial results – effect of settling medium

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10001500200025003000350040004500

4.m Chi w. cem.

4.m Chi w.o. cem.

4.m ord. Spon. W. cem.

4.m ord. Spon. w.o. cem.

4.m spec. Spon w. cem.

4.m spec. Spon w. o. cem.

2.m ord. Spon. W. cem.

2.m ord. Spon. w.o. cem.

2.m spec. Spon w. cem.

2.m spec. Spon w. o. cem.Nu

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Comparison of collectorsHarre Vig

20-07-2010

In situ spat collection – 2. trial

2. trial – effect of collector type

In situ spat collection - summary• Spat can be collected in situ – this has also been tested in e.g.

Holland and Ireland• Mussel shells in net bags and Chinese hats are the most

efficient in situ collection methods• The key to success is area, timing and getting off-bottom• Efficiency will depend on survival in the next step, i.e. when

transferring collected spat to the bottom or grow-out systems• DSC will (hopefully) test collection in large scale for stock

management purposes• There is huge difference in “science scale” and “real scale”

Alternative - hacthery produced spat

DSC hatchery work

Test of methods in all stages from broodstock to on-growing

Identification of reasons for larval mortality,comparison of intensive and extensivetechniques

Development of a new industry,focus on larval survival in hatcheries

Overall experiences• Extensive culture in ”poller” systems are very unreliable• Once spat has been produced, grow-out is the least

problem in aquaculture• Grow-out on bottom of flat oyster spat has (to my

knowledge) not been tested in large scale• Reliable spat production with acceptable yield (survival

>5%) is the key• Main problem has been larval survival

Larval survival

Technical improvements

Technical improvements

Summary – hatchery produced spat• Ostrea edulis spat can be

produced in hatcheries on land

• There is still a challenge i going from ”science scale”to production mode

• This challenge is (almost) solved but hatcheries in Europe still suffers from instability in spat production

• Reduced genetic variation can be one key

Lessons learned• The Limfjorden flat oyster stock has been fluctuating over

time – probably due to climatic reasons• The recent peak in stock size and fishery has been driven

by few years of good recruitment and eutrophication• The fishery has not been the direct cause of stock decline• There are methods in place for stock management• The efficiency of these methods on larger needs to be

investigated or improved further