“Clam Recruitment” refers to the yield from the natural settlement of newly hatched clams (“clam spat”). Gouldsboro’s shellfish committee places recruitment boxes at selected locations along Gouldsboro’s shore to gather data about recruitment density. Identifying the bays and coves where recruitment is strongest is important when deciding where to focus restoration efforts. It is also great to collect recruits that we can grow in the Shellfish Lab for eventual use as clam seed. On December 17th we opened up the recruitment boxes that had been sitting out on mudflats during summer and fall. It was a sunny day, warm for December – a nice day to do wet work outside the Shellfish Lab. Opening up the boxes is kind of exciting. What will we find?
In late spring and early summer of 2021, the Gouldsboro shellfish committee placed recruitment boxes in John Small Cove, Prospect Harbor, and in the West Bay portion of Gouldsboro Bay just north of where it begins to become Grand Marsh Bay. The shellfish committee refers to this area as “Joy Seas” because that is the name of the road that leads to that part of the shore.
John Small Cove and Joy Seas have been productive clam harvest sites over the past few years; both have benefited from the shellfish committee’s investments in clam seeding and netting. The Prospect Harbor site is more of an unknown. It was productive decades ago but has been closed to clam harvesting for more than 30 years because of fecal coliform bacteria pollution. Early in 2021, Prospect Harbor was reopened to clam harvesting because water conditions had improved. (See the story about how inviting the community onto the flats in Prospect Harbor to celebrate the reopening and learn about restoring clam flats.) The shellfish committee focused on Prospect Harbor in order to get a better understanding of its potential as a harvest site. Prospect Harbor is important to harvesters because access is relatively easy, even in bad weather, and it has the potential to be an important winter harvesting site.
About Recruitment Boxes
Recruitments boxes are also known as “Beal Boxes” because their design and use were developed by Dr. Brian Beal, founder of the Downeast Institute and a close partner with the Gouldsboro Shore program. They can vary in size but typically measure 1 foot wide and 2 feet long and 3 inches deep. The top and bottom are covered with a kind of window screening known as “pet screen,” which is tough enough to resist attempts by seagulls and other clam predators to get inside the box to eat the clams.
The recruitment boxes are staked into the mud (so they won’t be washed away!). Newly hatched clams are so small that they can pass through the screening as they settle. The primary purpose of recruitment boxes is to gather data on clam settlement and recruitment for use in comparing different harvest sites. (For more on this, see the Downeast Institute’s report on recruitment monitoring.) A secondary purpose is that if recruitment is good, the box might contain hundreds, even thousands of juvenile clams that could be over-wintered in a place like the Shellfish Lab for use as seed clams in their second year.
What We Found
By chance, we opened the four boxes from John Small Cove first, and they looked really good. There were a few hundred good-sized clams in each box. That told us that there was good settlement and recruitment at the area in Jones Cove where we put the boxes.
This was an area that had performed well in a study that Heidi Leighton and DMR did back in 2017 with help from Sumner High School Students. This year, we placed the boxes in a part of the cove where fresh water runs into the ocean, which was where the recruitment looked best in the 2017 study. Only one box had a crab in it, which is one reason why the boxes still contained crabs at the end of the growing season.
After opening the John Small Cove boxes, we had about 1,000 more clams to add to the more than 30,000 in the Lab that we hope to keep alive through the winter. That felt good and we looked forward to opening the boxes from Prospect Harbor and Joy Seas.
And … we were disappointed. The recruitment boxes from these other sites all contained at least one crab, and sometimes 6 or 8 crabs. Most of these boxes contained no live clams; others contained 3 or fewer.
What we saw in the recruitment boxes matched up with our experience with the nursery trays: Newly hatched crabs are small enough to settle through screening just as the clams do, and they can grow very quickly over just a few months and do serious damage to clams. Heidi said that she saw the same kind of damage from crabs in other recruitment boxes at other sites in other towns this year.
Below is a linked, embedded copy of the Downeast Institute’s report on a 2020 clam recruitment study. The report shows that recruitment varies from place to place, but recruitment density tends to be greater Downeast. It also notes that recruitment densities in 2020 were lower than in previous years. Heidi’s informal observations about 2021, together with our results in Gouldsboro, suggest that the downward trend may have continued this year.
We do know that recruitment not only varies from place to place, but also from year to year. Gouldsboro will put out recruitment boxes again next year. It would be nice if we found out that we have just had a couple of bad years.
One strong take-away, given the similarity between our experiences with nursery trays and recruitment boxes: We need to focus on designs and methods to minimize green crab entry into our boxes and trays and, perhaps, to remove them when they do enter.
One other take-away: Once gain, the Lab facility was perfect for the work we needed to do. We had all the sea water and water pressure that we need through our hoses and could wash off the mud in a place where it dropped right back into the ocean from which it came.