Back in June of 2021, we placed 100,000 juvenile clams — all just a few weeks old and quite small (about 2 mm) into nursery trays. Here is the July 12 post about how we did that — with lots of pictures. On November 18 we hauled the trays back from the old lobster pound behind the shellfish lab and opened up the trays. This is a report on what we found.
The clams grew a lot over the summer. Starting out, their shells measured about a tenth of an inch (2.5 mm) or less. Now, the average shell length was about a half-inch (12.5 mm), and some measured three-quarters of an inch or more. Though we still had lots of clams (between 31,000 and 35,500), the mortality rate was much higher than we expected. Green crabs that settled into the trays and grew quickly were the primary cause of clam mortality. We were not the only place where green crabs were a surprisingly large problem this summer. The Downeast Institute, which has been successfully growing clams in nursery trays for years, also had a bad summer due to green crabs.
This summer’s findings set our course for 2022: we will focus on growing clams in upwellwers inside the lab while also revising our approach to using nursery trays in the harbor. We will collect data on survival, cost, and effort so that we can compare the approaches.
When first set out on this project and on designing the shellfish lab, we expected that growth in the summer would be relatively straightforward since it had been done many times before. We thought the challenge would be finding an economical way to support overwintering. Now we see that keeping clams alive in the summer may be the bigger challenge. Fortunately, our newly completed shellfish lab is capable of supporting the new investigations and data collection that we now know we need to do.
Below is a more complete report, including more information about the data we collected and how collected it.