Application of Shell Hash Cover as a Deterrent of Cownose Ray Predation on Hard Clam Farms

View the project final report

Commodities

• Animals: shellfish

Practices

• Animal Production: aquaculture

Environmental change has presented new challenges for hard clam farmers, while a growing demand for limited shellfish leases creates a pressing need to utilize idle farm leases. The issue we will address is two-fold. First, cownose rays, a major predator of hard clams, have become a significant threat to hard clam farms as the species has increased in range and abundance.  Second, a significant amount of viable leased bottom is lying fallow because it is in relatively deep water, not suitable for established hard clam predator protection measures - screens. The objective of this project is to use farm-scale, collaborative experiments to assess the application of shell hash as a deterrent of cownose ray predation.  If successful, this strategy would provide the means to make hundreds of idle acres productive, while reducing labor costs.  We will evaluate predator losses and clam growth at three replicate plots of each of three treatments (9 plots total): unshelled bottom, shelled bottom, and predator screens. Further, we will monitor predator activity at each of these plots. Results will be conveyed to commercial shellfish aquaculturists, scientists, and extension specialists at state growers forums and national conferences.

This project seeks to test if shell cover protects farmed clam seed from cownose ray predation. The questions we will answer are:

Does clam survival increase when shell is applied to the sediment surface, relative to unprotected and screened clam seed?

Does clam growth and condition (shell thickness and body mass) increase when planted beneath shell on the surface?

Do cownose rays avoid feeding on plots covered with shell?

If this project is successful, it will provide information to help clam farmers prevent cownose ray predation losses, and a means to use deep water leases that are not suitable for netting. It will also provide important information about potential increases in natural clam recruitment at farm sites planted with shell.