Oysters, that is. An assessment of oyster restoration of in Harris Creek, MD is in, and it has an interesting result. In addition to the fact that the restoration was going well, with lots of oysters surviving, the study found that oysters planted on rocky substrate survived much better than those on shell (the traditional substrate) and substrate free spat:
Of the 350-acre oyster sanctuary in Harris Creek, the assessment, completed last year, gives a snapshot of 90 of those acres completed in 2013. It is those reefs’ three-year assessment, and another will be performed in 2019. Other reefs in Harris Creek completed in 2014 and 2015 will get three-year and then six-year assessments, too.So, planting oysters on big rocks increases the survival of oysters kind of like the chain on pens in banks increases the survival of pens? Hmmm.
According to the assessment, 97 percent of those 90 acres met minimum threshold success criteria for both oyster density and oyster biomass, and 80 percent exceeded the higher target for density and biomass. One hundred percent of the reefs had multiple year classes.
The assessment also found the highest average oyster densities were found on stone-base reefs — four times higher than shell-base reefs, followed by shell-base reefs and then seed-only reefs, or those with only baby oysters planted in the water.
“It is unknown at this time why the stone-base reefs show higher average oyster densities than other treatments,” the assessment reads.
The assessment states there likely is more exposed surface area on the stone-based structures, which act as man-made reefs, for baby oyster to set on and grow. Another supposition is that traditional oyster harvest gear is ineffective on stone reefs, therefore the reefs are protected from poaching that shell-base and seed-only reefs lack, the assessment states.