Evaluating Success of Oyster Restoration

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Evaluating Success of Oyster Restoration

• Deriving Benchmarks
• From Natural Populations

Hadley, N. H., L.D. Coen, V. Shervette, and M.
Hodges
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• Success depends on your goals
• Harvestable product
• Ecosystem services
• Public awareness
• Sustainability may be an over-riding goal which
  applies to all

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Evaluating Success Based on Goals

• When can/should success be determined?
• What constitutes success?
• Multiple year classes
• Size/density comparable to natural populations
• How do you establish the targets?
• Habitat functioning

• Harvestable oysters
• Large percentage of market size oysters
• This does not reflect natural populations
  patterns and may never be achievable
• Ecosystem services
• Many are difficult to measure
• Develop at different rates
• Habitat functioning may be inferred from presence
  of other species but does not necessarily depend
  on having oysters present

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Evaluating Success Based on Goals

• When can/should success be determined?
• Multiple year classes
• Recruitment
• Survival/growth
• Size/density comparable to natural populations
  (convergence)
• Retention of hard substrate for continued
  recruitment

Sustainability
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Size Frequencies on 1 and 3 Year Old Reefs Fall
2004
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Size Frequencies on 2 and 3 Year Old Reefs Fall
2004
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Size Frequency of Oysters on 2 and 3 Year Old
Reefs Fall 2005
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Size Frequency of Oysters on 2 and 3 Year Old
Reefs Fall 2005
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Size/density comparable to natural
populations Whats your benchmark?

• Reference reefs
• Do they exist?
• Are they good?
• Long-term datasets
• Mean values
• Percentiles
• What proportion of natural reefs are in good
  condition?
• Classifying natural reefs along a continuum of
  goodness

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Reference reefs
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Targets based on population means
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Targets based on population means
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66 of reefs were fair or better Overall Rating
Fair
27 Reefs were less than 3 years old at time of
assessment.
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Reefs sampled at 3 4 years
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Alternative approach Classify Natural Reefs
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Strata E Excellent?
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Very Good
Good
Fair
Poor
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Characteristics of Natural Intertidal Oyster
Populations in South Carolina

• Few large oysters usually less than 20
• High recruitment usually 50 of populations
• Mean size for all strata ranges from 25 35 mm
• High variability within and among sites
• High variability among years
• A good reef one year may seem like a poor
  reef in another year

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Relative frequency of occurrence of different
strata in SC
gt50
Total beds classified 2519
Ben Dyar 12 June 2006
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Establishing Success Benchmarks

• What proportion of natural reefs are in good
  condition?
• Very Good 5 - Stratas A and E
• Good 37 - Stratas F and G
• Fair 38 - Stratas F1 and C
• Poor -19 - Stratas D and W

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Pinckney 3 Years
Population mean Fair Strata Mean Fair
Not yet converging
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Edisto 3 Years
Population means Poor Strata Means Fair
Different from all defined strata
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Trask 3 Years
Population means Good Percentiles Good
Strata convergence Similar to G, may reach A
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Palmetto 3 Years
Population means Good Percentiles Good
Strata Convergence Similar to A or E
Strata E Excellent? Or overcrowded
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Dataw - 3 Years
Population means Fair Percentiles Good
Strata Convergence Better than C, may reach G
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• 72 of planted area remained at the end of the
  study
• 77 of sites were fair or better
• Overall Rating Good

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47 of sites were above average 76 of sites
were average or better Overall Rating Good
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Shortcomings of Using Population Means or
Percentiles

• Targetting mediocrity?
• Site rankings all similar
• Even one year old sites rank fair
• No definition for Excellent

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CONCLUSIONS

• Size frequency of restored populations is useful
  for evaluating rate of development and
  sustainability.
• Using natural population means or percentiles as
  targets may be striving for mediocrity.
• Stratifying natural populations may provide more
  meaningful targets and allows us to examine
  development trajectories.
• Success ratings for large and small-scale
  restored sites ranging in age from 3 to 6 years
  are similar regardless of which of these targets
  are used
• Approximately 25 of restoration sites examined,
  both large and small scale, appear to be failures
  with little potential for development of
  sustainable populations of oysters.

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Future Directions

• vertical coverage
• Confidence limits
• Validation at natural sites
• Test targets in other geographic areas
• Habitat functioning
• Diversity indices
• Transient fauna
• Weighting of metrics
• Relate success to site characteristics

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Evaluation of Reef Success

• Footprint how much of the shell area remained?
  
• Resemblance to natural populations
• Quantity of oysters
• Size of oysters
• Percentage of recruits
• Percentage of large oysters
• Average of footprint and population scores
  composite score

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Conclusions

• A total of 76 reefs were constructed at 32 sites,
  totally 9 acres
• Overall 72 of reef area remains (Good)
• 77 of sites had average or better shell
  retention (Good)
• 64 of reefs fair or good compared to natural
  populations after 1-4 years (Fair)
• Composite success rating Good

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Acknowledgements

• Shellfish Research Section personnel who have
  measured thousands of oysters each year to
  generate this dataset.
• All the volunteers who helped build and sample
  the reefs!
• Funded by