Much of what I’ve been working on lately has been Alison’s project, since it is time-sensitive. The crabs only spawn during a given period (usually late April through mid-July), and we can’t afford to miss crucial data. On the other hand, according to my advisor, this is supposed to be the biggest field season of my Ph.D. This is something that gives me pause, especially when I am spending time doing nothing that is directly applicable to this summer’s work. Fortunately, this week I had the opportunity to start my surveys of Barnstable Harbor and Stage Harbor.
As you may or may not recall, our boat was being fixed and thus our transportation was limited to driving around to access points and wading out to the pre-assigned locations. I had scouted out these points the week before, so it was merely a matter of going out there, counting crabs, and being done with it. But nothing is ever as simple as it sounds, particularly research efforts. For example, I realized that my transect marker, a rope strung between two thin PVC pipes, looked a lot shorter than 100 meters. My mental yardstick (to mix systems of units) for 100 meters is the width of the salt marsh where I did my undergraduate research, and it’s pretty wide. This was definitely not right. I found out through the use of the GPS that the rope was twenty-five meters, so I just ditched the rope. I might as well just use the GPS and not have to untangle the rope every time anyway.
I got lucky with some of my sites. They were very easy to access — walk down this path, 100 meters to the left once you reach the shore, and there you are. Start your transect here. Other sites were not so lucky but were improved by the kindness of strangers. One was directly behind a line of pleasure boats at the Chatham Yacht Basin, where nobody seemed to mind my being there and where we later assisted a yacht owner in casting off from the dock. It is unnerving to snorkel right behind a big engine though, however dormant. Images of manatees with multiple parallel slashes on their backs kept invading my thoughts. Another site was across a boat channel (more slashed manatees swimming sadly through my mind), and a man and his son offered to ferry me across. While I was being given a boat ride by the son and then swimming the transect, Alison stayed onshore and had to endure the man’s complaints about his ex-wife while a ferret slinked around his shoulders. Yet another was in knee-deep muck, and could either be accessed by walking 400 meters in salt marsh or 100 meters over the well-manicured lawn of what was definitely a million-dollar house. After initially peering suspiciously at the sketchy people marching up her driveway in bathing suits, with damp hair, rulers, and clipboards, the owner of said house was very kind to let me cut through. Hopefully she didn’t hear our discussion about how well-suited her lawn would be for a huge party. Once I was in the water, I had to crawl on the mud to prevent getting stuck, because the water at that point in time was only about a meter deep. Make a note. If we have to come back, it should be at high tide.
Another important thing to note is that these surveys serve two purposes. One is to measure as many crabs as possible, so a histogram of the size distribution can be constructed and life-history parameters such as growth and survival can be inferred. The other purpose is to calculate the number of crabs in the estuary by looking at a given area located at one of an evenly distributed set of points and compare that to the total size of the estuary. If I go to ten points, look at 100m2 of sediment and water at each of these, and find five crabs over all those ten points (a total of 1,000m2), that’s fifty crabs per hectare (100m x 100m). If the estuary is 500 hectares in area, that’s 25,000 crabs. The moral of this practice calculation is that over the seventy-five points or so that I will be surveying, I find a lot of zeros. No crabs. The upside of this is that as long as I find some crabs somewhere, that’s okay.