Enhancement of the native flat oyster (Enhancement of the native flat oyster (Ostrea Ostrea chilensischilensis) in Tasman Bay, New Zealand: ) in Tasman Bay, New Zealand:

Summary of research outcomesSummary of research outcomes

Stephen Brown, Sean Handley, Stephen Brown, Sean Handley, Keith Michael, David Schiel, Keith Michael, David Schiel, Sophie Mormede, Mitch CampbellSophie Mormede, Mitch Campbell

NIWANIWA

University of CanterburyUniversity of Canterbury

Challenger Oyster Management Co LtdChallenger Oyster Management Co Ltd

BackgroundBackgroundCommercial flat oyster fishery in Commercial flat oyster fishery in Tasman Bay since 1845Tasman Bay since 1845

Catches and biomass have Catches and biomass have declined in the last three decades declined in the last three decades (Harvest peaked at 750 tonnes in (Harvest peaked at 750 tonnes in 1983 down to 20 tonnes in 2008) 1983 down to 20 tonnes in 2008) and fishery is economically and fishery is economically marginal.marginal.

Anthropogenic impacts from land Anthropogenic impacts from land based activities and dredge and based activities and dredge and trawl fishing may have modified trawl fishing may have modified the seabed, increasing sediment the seabed, increasing sediment deposition and resuspension and deposition and resuspension and homogenising benthic habitathomogenising benthic habitat

Goal is a sustainable oyster fisheryGoal is a sustainable oyster fishery

Key points about the reproductive Key points about the reproductive biology of biology of Ostrea chilensisOstrea chilensis

Female incubates or ‘broods’ fertilised Female incubates or ‘broods’ fertilised larvae to the pediveliger stage, longer than larvae to the pediveliger stage, longer than any other oyster (approximately 1 month)any other oyster (approximately 1 month)

Some larvae may be released throughout Some larvae may be released throughout brooding period – most released at fully brooding period – most released at fully developed stagedeveloped stage

Larvae released earlier may be more or Larvae released earlier may be more or less planktonic while late-stage larvae can less planktonic while late-stage larvae can settle within minutessettle within minutes

Require a hard substrate (such as shell) Require a hard substrate (such as shell) for settlement and metamorphosisfor settlement and metamorphosis

Late stage larvae

HypothesesHypotheses Lack of available substratum for Lack of available substratum for

oyster settlement and growth limits oyster settlement and growth limits productivity of the fishery. productivity of the fishery.

Placement of waste scallop and or Placement of waste scallop and or mussel shell on the seabed (Habitat mussel shell on the seabed (Habitat enhancement) will increase numbers enhancement) will increase numbers of oysters recruiting to the fishery.of oysters recruiting to the fishery.

Shell enhancement may improve Shell enhancement may improve ecosystem function by restoring ecosystem function by restoring seabed habitat heterogeneity seabed habitat heterogeneity

Plentiful supply of waste shell from Plentiful supply of waste shell from local scallop fishing and mussel local scallop fishing and mussel aquaculture industries.aquaculture industries.

Photoquadrat (0.25 m2) showing seabed in Tasman Bay

When to enhanceWhen to enhance Determine seasonal patterns of Determine seasonal patterns of

reproductive activityreproductive activity

Brooding - Monthly sampling of Brooding - Monthly sampling of oyster population to determine % oyster population to determine % brooding larvaebrooding larvae

Spatfall - Monthly monitoring for 2 Spatfall - Monthly monitoring for 2 years at locations throughout Tasman years at locations throughout Tasman BayBay

Reproductive Reproductive seasonalityseasonality

Commencement of brooding Commencement of brooding and spatfall detected in and spatfall detected in September/OctoberSeptember/October

Peak spatfall between Peak spatfall between November and JanuaryNovember and January

Best time to deploy shell is Best time to deploy shell is late October/early Novemberlate October/early November

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Where to enhanceWhere to enhance

Utilised oyster biomass survey Utilised oyster biomass survey and spatfall monitoring to and spatfall monitoring to investigate potential predictors of investigate potential predictors of spatfall distribution:spatfall distribution:

Want to predict spatfall Want to predict spatfall distribution to guide shell distribution to guide shell placementplacement

background oyster densitybackground oyster density water depth water depth east/west position within east/west position within

the baythe bay

Predicting spatfall intensityPredicting spatfall intensity

Parameter Background oyster density

Water depth Longitude

Correlation coefficient 0.58 0.23 -0.05

Pearson probability <0.001 0.114 0.711

Spat density correlated most strongly with background oyster densitySpat density correlated most strongly with background oyster density

So….So….

Background oyster density derived from industry biomass surveys is a useful guide for Background oyster density derived from industry biomass surveys is a useful guide for shell placementshell placement

At low adult densities (< 0.01 mAt low adult densities (< 0.01 m-2-2), any ), any increase in adult densities is reflected by a increase in adult densities is reflected by a large increase in spat settlement densitylarge increase in spat settlement density

Adult oysters per m2

0.00 0.02 0.04 0.06

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y = 6.1742*x / (0.0046+x)

r2 = 0.88; p < 0.0001

Optimal gains achieved by placing Optimal gains achieved by placing shell where background oyster shell where background oyster densities are between 0.005 to 0.01 densities are between 0.005 to 0.01 oysters per moysters per m22, ie less than, but , ie less than, but close to, commercial density close to, commercial density threshold (0.02 oys per mthreshold (0.02 oys per m22).).

Shell Enhancement ExperimentsShell Enhancement Experiments 2 sites in Tasman Bay2 sites in Tasman Bay

2 shell treatments Piled, 2 shell treatments Piled, Scattered + Control plots (3 reps Scattered + Control plots (3 reps of each)of each)

Deployed in Deployed in October 2005October 2005

Monitored: Monitored: • spat spat

settlementsettlement• growth growth • survivalsurvival

Oyster background density 0.01 m-2

Loading bulk bags of shell onto the barge

Lowering shell 23m to the seabed (October 2005)

Surface markers

Plots ~4m in diameter

Scuba sampling after spat settlement season (March 2006)

Samples analysed in lab

Shell boosts spat densityShell boosts spat density

Site A

Pile Scattered Control Pile Scattered Control

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at m

-2 (

± 95

%C

I)

0

500

1000

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Site B

1438

1125

3

422

0

644

Oyster Growth on Enhanced HabitatOyster Growth on Enhanced Habitat

Percentage of oysters at legal size (58mm length) and marketable shell depth in each yr class

Age 0.25 1.25 2.25 3.25 4.25 5.25 6.25

% ≥ 58 mm length 0 0 71 96 98 98 98

% ≥ 20 mm shell depth 0 0 0 0 92 100 100

SurvivalSurvival Variable and Low survivalVariable and Low survival But enhancement resulted in elevated oyster density after 3 yrs (from 0.01 oys mBut enhancement resulted in elevated oyster density after 3 yrs (from 0.01 oys m-2-2 to between to between

0.1-0.4 oys m0.1-0.4 oys m-2-2 ) )

A Piled

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Bimodal length distribution for dead Bimodal length distribution for dead oystersoysters

Length (mm)

0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90

Cou

nt

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Disease? (3 yrs old)

Pre recruit Mortality (1 yr old)

Community level effects of habitat enhancementCommunity level effects of habitat enhancement

Species Species assemblage on assemblage on enhanced habitat enhanced habitat distinct from that distinct from that on control plots.on control plots.

Greater species richness and abundance on enhanced plotsGreater species richness and abundance on enhanced plots Enhanced plots contained more suspension feeding species, Enhanced plots contained more suspension feeding species,

mobile scavenger/predators, and different polychaete assemblage mobile scavenger/predators, and different polychaete assemblage Control plots had more deposit feedersControl plots had more deposit feeders

ConclusionsConclusions

Habitat enhancement benefits the oyster Habitat enhancement benefits the oyster fishery by increasing oyster productionfishery by increasing oyster production

Habitat enhancement is likely to confer Habitat enhancement is likely to confer benefits to ecosystem function by increasing benefits to ecosystem function by increasing benthic habitat heterogeneity and benthic habitat heterogeneity and biodiversity (ecological restoration)biodiversity (ecological restoration)

Further workFurther work

3 X 30 Ha sites in Tasman 3 X 30 Ha sites in Tasman Bay enhanced with scallop Bay enhanced with scallop shell at rate of 10 shells per shell at rate of 10 shells per mm2 2 plus 3 X control sitesplus 3 X control sites

Determined relative oyster Determined relative oyster density prior to shell density prior to shell placementplacement

Resample After 4 years Resample After 4 years (BACI) (BACI)

More community level More community level experiments in conjunction experiments in conjunction with fishery trialswith fishery trials

Fishery Scale Fishery Scale Enhancement TrialsEnhancement Trials

AcknowledgementsAcknowledgements

Board and Staff at Challenger Oyster Board and Staff at Challenger Oyster Management Co. Ltd. Management Co. Ltd.

All staff at NIWA Nelson office particularly, All staff at NIWA Nelson office particularly, Dan Cairney, Anna Bradley, Russell Cole, Dan Cairney, Anna Bradley, Russell Cole, Don Morrisey, Ken Grange, (All from NIWA) Don Morrisey, Ken Grange, (All from NIWA) Mike Hickford (University of Canterbury)Mike Hickford (University of Canterbury)

This work was funded by the Challenger Oyster Management Company Ltd and This work was funded by the Challenger Oyster Management Company Ltd and the New Zealand Foundation for Research Science and Technology (Technology the New Zealand Foundation for Research Science and Technology (Technology for Business Growth Grant CDOC0401, and Enterprise scholarship ENT 1928)for Business Growth Grant CDOC0401, and Enterprise scholarship ENT 1928)