NativeNative OysterOyster RegenerationRegeneration inin DenmarkDenmark

ByBy ArneArne BaekgaardBaekgaard andand JørgenJørgen KampKamp NativeNative oystersoysters (Ostrea Edulis) inin ,Denmark, thethe LimfjordLimfjord.. HistoryHistory ofof oysteroyster fisheryfishery inin DenmarkDenmark

► Crown property from February the 4th 1587. ► Areas: ► Waddensea: 1587 until 1864 (lost to Germany in 1864) ► Ringkøbing 1587 until about 1800 (Declining salinity) ► 1770 until about 1860 (fishery ceased) ► Limfjord 1851 until 1984 ► The crown property was never extended to Norway. ► End of crown property in 1984 HistoryHistory catchcatch inin TheThe LimfjordLimfjord

Total fished

20000000

s 15000000 r e

b 10000000

num 5000000 0

n 0 0 0 0 70 80 90 00 10 20 30 so 86 8 8 8 9 9 9 9 94 95 96 a 1 1 1 1 1 1 1 1 1 1 1 se Year LimfjordLimfjord fishery.fishery.

► 1825 break through of , salinity jumped from 10 to 30 ppt in western part ► 1851 Oysters found at several places in western Limfjord. Investigated by Krøyer. ► 1852 The oyster fishery declared crown property and leased out ► 1852 – 1865 small scale fishery 30.000 up to 150.000 yearly ► 1865 – 1870 rise in catch from 1.1 mill to 5.3 mill per year. ► 1870 – 1875 peak in fishery 7.5 to 5.9 mill per year. ► 1875 – 1885 decline in fishery 5.5 to 0.9 mill ► 1885 – 1890 close period no fishery ► 1890 – 1910 fisheryfishery resumedresumed 0.6 to 1.2 mill (mainly fished with diver) ► 1910 – 1920 second peak and fishery reformed with: ► Oyster beds for relaying of undersized oysters ► Use of motor vessels equipped with dredges ► Improved storage facilities ► 1920 – 1945 cold period, fishery based on imported spat planted on the beds ► 1945 – 1955 varm period with abundant natural spatfall ► 1955 – 1984 decline period with no or limited natural spatfall ► 1984 lease abandoned end of crown property CausesCauses forfor fluctuationsfluctuations inin stock.stock.

► Northern limit of natural occurrence due to temperature ► 18° C for a period in the summer some years in succession. ( Sperck) ► Diseases introduced with imports. ► 1954 assumed disease imported from Holland causing major loss of stock. ► 1969 gill disease observed in oysters from the Limfjord. Confirmed by French laboratory. ► 1980 Bonamia found in flat oysters imported from Brittany France, and confirmed histologically. ► 1981 Found again in native oysters. Effect of temperature on growth and survival of O. edulis larvae

Survivors / temp. C days to 250 micron/day days to 300 brood

40% 50% 50%

16 19,4 3,9 32,3 0,000000 0,1 0,000000 0,0

17 14,5 5,2 24,2 0,000004 4,3 0,000000 0,1

18 11,6 6,5 19,4 0,000051 50,5 0,000001 1,5

19 9,7 7,7 16,1 0,000263 262,8 0,000014 13,9

20 8,3 9,0 13,8 0,000853 853,3 0,000069 68,5

21 7,3 10,3 12,1 0,002064 2064,0 0,000227 227,1

Walne 1965: Observed growth from 175 to 250 micron: days= 58.1 /(temp.- 13°) 1 brood equals 1mill. Larvae released at a size of 175 micron settling is supposed to occur at 300 micron TemperatureTemperature Factor.Factor.

Survival

8000 7000 6000 r temp. C 5000 be 4000 40% 3000 num 50% 2000 1000 0

C 6 7 8 9 0 1 2 . 1 1 1 1 2 2 2 p m te ConclusionConclusion 19841984

►►HavingHaving foundfound BonamiaBonamia inin thethe LimfjordLimfjord 19801980 –– 1981,1981, itit waswas generallygenerally believedbelieved thatthat thethe NativeNative OysterOyster populationpopulation inin DenmarkDenmark waswas history.history.

►►ButBut …….……. RecoveryRecovery

►►19881988 OystersOysters presentpresent locallylocally inin density,density, butbut nono fisheryfishery ►►1990ties1990ties renewedrenewed fisheryfishery onon aa limitedlimited scalescale ►► SearchSearch forfor BonamiaBonamia inin oystersoysters fromfrom thethe LimfjordLimfjord,, nothingnothing found.found. ►►AfterAfter 20002000 3rd3rd majormajor peakpeak inin fisheryfishery culminatingculminating nownow withwith 10001000 tonnestonnes thethe bestbest everever catchcatch inin thethe LimfjordLimfjord.. Why!!!!Why!!!!

► IncredibelIncredibel goodgood luck.luck. ► BonamiaBonamia disappereddisappered,, assumedassumed causescauses forfor thethe disappearance:disappearance: ► VeryVery lowlow naturalnatural populationpopulation ofof oystersoysters inin 1980.1980. ► BedBed withwith infectedinfected oystersoysters heavilyheavily fishedfished afterafter discovery.discovery. ► SeveralSeveral iceice winterswinters inin thethe 80ties.80ties. ► VeryVery hothot summerssummers moremore thanthan 20°20° CC temperaturetemperature inin successionsuccession inin thethe 90ties.90ties. European flat oyster Landings 1992 -2005 in the Limfjord.

Landinger (kg)

1.000.000

900.000

800.000

700.000

600.000

500.000

400.000

300.000

200.000

100.000

- 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005

Source : DFU Legend

Danmark VGT_G 0,000 - 0,932 0,933 - 3,205 3,206 - 6,488 6,489 - 10,971 10,972 - 17,553 17,554 - 23,120 23,121 - 35,838 35,839 - 56,202

56,203 - 84,688

84,689 - 164,807 Jegindø

Venø

Struer

052,5 101520 Kilometer PresentPresent statusstatus

► Large stock of market size oysters, but 2003 and 2004 without significant spatfall ?? ► Good health status. ► Fast growth, market size after 3 summers. ► Few problems with toxic algae. ► Growing importance for the local fishermen. ► Old know-how forgotten. ► Conservation measures enforced, but to some extend ignored. ► Licensed fishery with quota per vessel ► Size limits ( 60 gram) ► Only light dredges allowed ► Dredging only on depths over 3 m ► Closed periods in Summer ( May- Sept) ► Stock monitored by DFU ► Risk for reintroduction of Bonamia. ► Risk for invasion of Crassostrea gigas (already present on the Westcoast) Frekvens (%) Længdefordeling af østers i Nissum Bredning i 2002, juni 2004 og 2005

40 Ej konsum < 60 gram Konsum ≥ 60 gram 35

30

25

20 2002 15 2004

10 2005

5

0 0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 Skallængde (mm) FutureFuture

►►NeedNeed forfor somesome formform ofof cultivationcultivation ofof oystersoysters toto securesecure constantconstant supply,supply, cultivatedcultivated bedsbeds insteadinstead ofof naturalnatural wildwild catch.catch. ►►NeedNeed forfor cultivationcultivation ofof seedseed basedbased onon locallocal stock,stock, toto securesecure spatspat inin coldcold summerssummers ►►BetterBetter utilizationutilization ofof thethe catch,catch, oystersoysters atat presentpresent soldsold inin bulk.bulk. ►►BetterBetter utilizationutilization ofof thethe possibilitypossibility forfor thethe productionproduction ofof highhigh qualityquality oysters.oysters. OysterOyster farmingfarming

► Trials in trays. ► 2 mill + spat produceed this year. ► Ice ► Bottum culture ? ThankThank you.you.