DEI Completes Year One of Predator Exclusion Experiment

by Sarah Craighead Dedmon

DEI just completed year one of its three-year Predator Exclusion Experiment conducted cooperatively with Downeast clam committees.

DEI researcher Kyle Pepperman worked with six towns — Gouldsboro, Steuben, Milbridge, Pleasant Point, Pembroke, Machiasport and Addison — to seed their mudflats with juvenile softshell clams grown in DEI’s Beals Island hatchery. The teams covered half of the seeded flats with netting and left half uncovered.

In November, the towns went back with DEI to collect samples. In Machiasport’s unnetted areas, Pepperman found only .08 clams per square foot.

“Next year we won’t do unnetted,” said Pepperman, “because, why would we?”

DEI also deployed several “plant pot” experiments designed to test rates of growth and wild recruitment of clam spat. After filling ordinary plant pots with mud and 12 clams, the pots were covered with protective mesh and planted back in the flats.

Taken together, DEI believes these experiments can help towns make scientifically-informed decisions about managing their clams.

Machiasport Shellfish Committee Chair Rob Boynton said that he was encouraged by the amount of wild clams that settled in one of Machiasport’s plant pot locations.

“We are putting some serious thought into trying to catch some of our own seed,” said Boynton, something Pepperman encourages municipalities to consider. Though the cost of the predator exclusion experiment is heavily subsidized by a grant from the Maine Communities Foundation’s Broadreach Fund, shellfish committees do spend money to purchase the clam spat.

After seeding 100,000 clams in 2017, Machiasport has already ordered 300,000 clams for 2018, and plans to spread some nets without seed to protect settling clam spat. Boynton said that his committee is also building wire domes to simulate rocks, which they will cover with nets to catch wild seed.