After much planning, grant writing, waiting, then hiring, Wellfleet Bay’s two-year study of horseshoe crabs in Wellfleet Harbor is finally underway.
Study leader Mike Long and research assistant Colyer Woolston, working under the direction of UMass professor Ted Castro-Santos and science coordinator Mark Faherty, have already attached acoustic tags to 60 horseshoe crabs. They’ve also positioned 20 buoys with receivers in strategic locations throughout the harbor, as the map below shows:
As the map indicates, there is a virtual wall of receivers between Jeremy Point and the sanctuary’s beach. Mike says the idea is to try to ensure that no crab goes out into the bay without his knowing about it.
The key question is whether crabs come and go between the harbor and the bay or if they are an isolated population restricted to the harbor. “With the low numbers of crabs in (the harbor),” Mike notes, “it would be easier to get the stock to replenish itself if crabs are moving into Wellfleet Bay from Cape Cod Bay.
Having the acoustic tags on those crabs will help answer some other interesting questions, too:
- Do horseshoe crabs stay in the shallow waters in the bay, or move to the deeper bay waters?
- If the crabs leave the bay, do they leave immediately after spawning, or do they stick around for a while before they leave?
- Do males and females have different migration times/patterns?
- Do males and females prefer different habitat when they are not spawning?
The acoustic tags will send pings to the receivers which will record time, date and crab number. To offload the data, a magnetic key is inserted into the receivers which triggers a Bluetooth signal from the receiver to a tablet. The data goes into a database as a series of detections whenever a tagged crab is within range of a receiver. Ultimately, Mike says, there should be enough information to generate a map depicting the crabs’ movements through the next two years. And hopefully to get him his Masters at UMass!
Because years of data indicate a very low number of horseshoe crabs in the harbor, both the sanctuary and the Wellfleet Shellfish Advisory Board have been urging state officials to impose at least a temporary ban on horseshoe crab harvests to give the population a chance to recover.
“If the data indicate crabs are freely moving between the harbor and Cape Cod Bay,” says Faherty, “it may be necessary to shut down the harvest in the bay as well. The state has told us they are looking for this information. Crab numbers at beaches further west are just as dismal as they are here in Wellfleet.”
The two-year study has been underwritten by a 50,000 dollar grant from the Massachusetts Environmental Trust which is funded through the sale of specialty license plates. You can get yours here: