Clam decline in Harpswell puzzles experts, who suspect disease
HARPSWELL — Over the past several years, shellfisherman have noticed a decline in clams. Last month, the Marine Resources Committee set out to find out why.
“We've noticed the decline in our clams for probably the past three to four years,” committee member David Wilson said. “They're just not where they usually were. What we've seen on the beds is that clams set into a spot and only get to around one and a half inches long and die.”
He said that this year the clam population is not up to what it has been in the past, an unfortunate problem as diggers just regained access to nearly all of the flats, some of which have been closed for eight to 10 years due to contamination and conservation.
Wilson said clammers and the committee wondered if their beds were infected with neoplasia, a blood disease that ultimately destroys the physiological function of soft-shelled clams and kills 90 percent of infected mollusks.
Denis Nault, a biologist with the state's Shellfish Management Division, and his team conducted tests on clams and the mud they inhabit and have confirmed that some of the clams tested are infected with the disease. Full results on the mud samples are not expected back until next month.
“We got test results back on the clam end, which we know they do have a higher prevalence of neoplasia, a known blood disease of clams,” Nault said. “I don't expect anything unusual for the mud, it's the clam itself. We've seen (neoplasia) in different locations and different areas and we're trying to work out how to deal with that aspect.”
He said that there are other factors that could be contributing to lower-than-usual clam numbers, including environmental changes and the early emergence of predators.
“Last year, because of the weather and environmental factors, there was too much rain when clam larvae were setting and they didn't settle down on the flats,” Nault said. “Also, green crabs came out and ate those larvae, which is a whole other issue.”
Neoplasia, Nault said, is a disease that has been around for a long time and is one that doesn't usually give biologists a second thought. But its high prevalence in Casco Bay and areas just outside the bay are cause for question.
“We're trying to figure out if we're seeing it higher in juvenile clams and if it's a localized issue, in a specific cove,” Nault said. “One of the complexities of Harpswell is that they have been moving clams around for quite a while, so we have to eliminate where they were moving them, where they got the seeds from and where they moved them to.”
He said the “$64 million question” is how to control the problem so that it doesn't effect future generations of clams.
“We don't know (what's going on),” he said. “It's hard to pinpoint in each area. They do have, in certain areas, neoplasia killing both adult and seed clams. When we do plantings or transplanting, we have to think about how we work around those areas.”
Nault said that he and a team of two other biologists will continue to study the problem in Harpswell and the nearby environs to, hopefully, come up with a solution that will bolster clam populations. He said the quick reaction of the Harpswell Marine Resources Committee allows them to get a jump on the problem, even though, at the moment, it has the team perplexed.
“They certainly have clams in Harpswell and they're growing, but in other areas they're not,” Nault said. “You can stare at West Bath from Harpswell and those areas are doing perfectly fine, not having that kind of an issue, so why is that? We're kind of scratching our heads trying to figure it out.”