Penobscot: Recruitment and settlement experiments

Contacts

Bailey Bowden – Shellfish Conservation Committee Chair
clamchair@gmail.com

Short project summary (PDF)

Background

The Bagaduce River is one of the most productive estuaries in the state. The estuary is characterized by broad coves, shallow waters, a reversing falls, and provides protected habitat for shellfish, eelgrass, horseshoe crabs, and bald eagles, among other species. The Northern Bay holds around 800 acres of soft mud ideal for hand-picking clams.

In 2008, despite depuration harvesting, soft-shell clam landings in Penobscot totaled about 150,000 pounds annually. Concerned about the sustainability of the soft-shell clam population and keeping harvesters employed, the Shellfish Conservation Committee embarked on a series of recruitment and settlement experiments.

Recruitment & Settlement Efforts

In 2009, the Shellfish Conservation Committee purchased clam seed from the Downeast Institute and studied soft-shell clam growth rate through a plant pot experiment and sowing seed plots. The following year, Penobscot worked with the area biologist on a clam recruitment study with lobster trap doors wrapped in plastic netting—the most successful models used AstroTurf. The study ended in 100% mortality, mainly due to moon snails. On a positive note, 2010 also saw the reopening of most of the town’s flats from water quality issues.

In the Spring of 2011, moon snails arrived in the thousands. That year’s conservation project focused on picking snails and collars from four acres of flats. The snails disappeared in 2012, and then the green crabs arrived.

After surveying the damage from the green crabs for several years, the Shellfish Conservation Committee decided to research whether the decline in the soft-shell clam population in Northern Bay was due to a lack of a breeding population of adult clams. To start, they transplanted adult clams into Northern Bay. With the help of students from Penobscot Community School and Maine Maritime Academy, the Shellfish Conservation Committee started a plastic box recruitment study at eight stations around the Bay. The results found an average of about 300 clams per station, which indicated enough adult clams to repopulate Northern Bay. Speaking at the 2018 Shellfish Focus Day, Bailey Bowden stated that having not seen any clams for five or six years, it was impressive to see any. However, these recruitment numbers have been decreasing each year.

The ongoing work of Penobscot’s Shellfish Conservation Committee will be guided by questions such as: how do we sustainably grow clams in areas open for harvesting? How do we maintain clam recruitment? How do we stop predation?

Takeaways

The Shellfish Conservation Committee has been unable to make meaningful progress on restoring the soft-shell clam population since 2012. Through recruitment and settlement experiments Penobscot has built connections with local schools. Joining in on the work on the Northern Bay mudflats provides an opportunity for students in Maine Maritime Academy’s marine biology program to engage in field work on a project with local impact.

The Town plans on installing Beal Boxes with HOBO temperature sensors in the spring of 2022 to investigate the relationship between soft-shell clam spawning activity and seawater temperature.

Project timeline

2009

Purchased clam seed for recruitment studies
2010

Worked with area biologist on recruitment study

Most flats reopened from water quality closures
2016

Area biologist helps with plastic box recruitment study

Penobscot Community School and Maine Maritime Academy students participate

(Photo courtesy of Sarah O’Malley)
2017

Results of recruitment study indicate adequate adult soft-shell clam population to repopulate Northern Bay
2022

Start of HOBO temperature sensor study