By Chris Petersen with edits by Madeline Motley
This is part of a series of Madeline and me trying to catch up on some of the things we have been doing in May and June both on our own and in a class, Ecological Research in Aquatic Systems, where I am the teacher and Madeline is one of the students.
The Saturday after the Frenchman Bay Partners meeting (see our last post), May 9, our class was out with some local clammers, some folks from the Bar Harbor Marine Resource Committee, and a few Bar Harbor residents to do a population survey of soft-shelled clams at Hadley Point. The committee closed this area because there were very few clams large enough to harvest (bigger than 2 inches), but has a lot of little clams. This was the first survey to see how they survived the epic winter we just went through. So, how did they do under all that snow?
Somehow, it seems like all that ice helped. There were more clams than anyone had ever seen (including guys that have been clamming for 20 or 30 years). It was just amazing. The average density was over 100 clams per square foot. The average size was just under an inch, but these guys are not quite a year old and we expect that in two years there will be a lot of clams to harvest.
So, why no large clams? Well, once they get above 2 inches they can be harvested – so that isn’t a mystery. But why aren’t there medium-sized guys growing to take their place? Over the last couple of years we have had harvestable clams around, but haven’t been seeing smaller clams coming into the mudflats. It’s like the clams of 2012 and 2013 were complete reproductive failures. It isn’t clear if this is because the young never were born, never made it to the mudflat, or if the little guys got to the flats and then died before we could count them. Clams have a complex life cycle. This species has a larval stage that spends 2-5 weeks in the water floating around, filter feeding and growing before it lands on a mudflat and transforms into something we would recognize as a baby clam. So it could just be that the currents never got them here.
However, the leading hypothesis is that a wave of invasive green crabs, Carcinus maenus, rolled into the mudflats like tourists into a Bar Harbor ice-cream shop in the summers of ‘12 and ’13 and ate their way through the small vulnerable clams. Green crabs are an introduced species in Maine, so why not blame a species from away? Seriously, there is some good evidence that green crabs might explain the size gap in our current clam population. Green crabs readily eat small clams. The winters of 2012 and 2013 were unusually warm, and there appears to be a correlation with warmer winters and green crab excess in the intertidal. Green crab abundance was so high that it inspired news stories, animations, and the Eastern Maine Skippers Program for high school students to focus on green crab eradication as their year-long project (see our earlier post on this program). Winter in 2014 (and this year as well) were colder and last summer green crabs were at much lower levels in mudflats in Frenchman Bay. Many clammers I talk with believe this is why there are so many small clams on so many clam flats throughout Maine and are hopeful for another year without a green crab explosion in the intertidal and high survival of clams.
This work intersects with us at COA in several ways. First, Chris was at the Grand in Ellsworth to judge the solutions of six high schools for the “Green Crab Problem.” Last summer, using money from a grant from the Maine Community Foundation to buy crab traps for clammers, we had students work with clammers to test how well different traps caught green crabs. In mid-May we also set up some plots at Hadley Point where we are trying to change pH by adding clamshells to the mudflats, a project we hope to talk about a couple of posts down the road.
Okay, that seems like enough for now. Still have a long way to go in May. We have fish scales and ladders, crushed clamshells, historic tide pools, slowfish, and how to net a clamflat to get through the month. Some last pictures of some more helpers below.