Last week, Mike Pinkham and I spent a few days constructing five nursery trays that our small seed clams would soon be placed in. A nursery tray is a rectangular wooden tray about 3-4 feet in length and width, and about 3 inches high. The bottom and top of each tray is made of a 1.8mm aperture mesh (pet screen). Styrofoam is added to two sides of the tray to allow it to float in water. Our goal was to place some of our clams into these five nursery trays and float them out in the old lobster pound. The clams would have a secured space to feed and grow on the surface of the warm water. Mike had built nursery trays last year for our clams and learned what worked well and what didn’t. This year, we made a few changes to our tray designs in hopes that we will have less clam mortality.
The biggest difference between last year’s trays and this year’s trays is the addition of separating each tray into quadrants rather than halves. By splitting our trays into more sections, we hope to see a reduction in the amount of clam mortality we experience from green crab predation. If a green crab does happen to make its way through the mesh and into the tray, it will only have access to a quarter of the clams in that tray rather than half of the clams.
All of our seed clams have finally grown larger than the 1.8mm aperture mesh; therefore, they are safe to transfer into our nursery trays. Knowing that these clams will grow throughout the rest of the summer and fall, we wanted to give them plenty of space in each nursery tray. We decided to put around 10,000 clams in each tray (2,500 per quadrant).
I had counted and weighed a sample of small seed clams. Using this sample count and weight, I was able to get a conversion rate from grams to clams. There were about 500 clams in a 4.51 gram sample. I was able to use this conversion rate to figure out the weight of 2,500 clams. On Tuesday, Chantal Jennings and I worked together to weigh out 20 batches of around 2,500 clams. We then transferred each batch into a separate quadrant in the nursery trays. When all four quadrants had around 2,500 clams in them, Mike Pinkham and Michael Jennings worked together to seal up the trays by nailing in laths from the top and covering the trays with a black plastic sheet that helps increase the surface temperature of the water. Once all of the trays were sealed, we brought them down to the dock and tied them together using rope. We dropped them in the water and, using a skiff, Dana Rice brought them over to the old lobster pound and attached them to the mooring. It was a very productive day and everyone involved played a vital role in getting our nursery trays out on the water.
These nursery trays will be left untouched until the end of the clam growing season in November. When that time comes, we will open up the trays and collect data on how much the clams grew and what percent survived. We also plan on counting the number of green crabs, if any, in our trays, as well as their carapace length. The end goal of this project is to compare the data we collected from the clams in nursery trays with the data we collected from the clams in upwellers. We want to determine if there is a significant difference in growth rate or mortality between clams growing in the nursery trays and clams growing in the upwellers. Unlike nursery trays, we can check in on our clams daily when they are growing in upwellers. For this reason, we are expecting to see better results growing clams in upwellers rather than nursery trays, but the data will give us a better idea of which growing method is more efficient.