In Duxbury, NSRWA and the MassBays National Estuary Partnership Program (MassBays), will be conducting its 18th year of horseshoe crab monitoring. Duxbury is one of sixteen sites across the state that are part of the Massachusetts Horseshoe Crab Spawning Surveys managed by the Massachusetts Division of Marine Fisheries (DMF).
We are excited to see if new regulations will eventually mark a rebound of Horseshoe crab populations. While these crabs are cool in their own right, they also serve many important functions in our local ecology. They mix up sediment and add oxygen back into the mudflats. Their eggs are a crucial food source for migrating shorebirds, like red knots and ruddy turnstones. And they are also very important to humans–a compound in their blood is used to test for bacterial contamination, they are used for bait in the eel, conch, and whelk fisheries, and for vision research. The citizen science programs throughout the state provide critical data that help DMF manage and protect the species.
For the Duxbury surveys, the North and South Rivers Watershed Association (NSRWA) and MassBays puts out a broad call for citizen science volunteers. Partner organizations such as Duxbury Beach Reservation helped broaden that call throughout the community. In 2025 almost 60 individual volunteers attended a series of training sessions and then conducted 24 different surveys from May 10th to June 28th. The surveys occur on the high tides around the new and full moons. Beaches are surveyed at both high tides during a given day. This means that about half the surveys are conducted in the middle of the night from 11pm to 3am. This makes for some incredibly unique experiences under moonlit or moonless nights out on the beach!
In 2025, the total density of crabs (crabs/m^2) and the spawning index (females/m^2) both peaked during the third daytime survey on May 14 (Fig. 4). There were a total of 63 females and 140 males observed during the May 14 survey! We anticipate that it would take several years before the new regulations result in any changes to our local horseshoe crab populations.
Volunteer for 2026!!
This May and June, for the 18th year, in partnership with the MassBays National Estuary Partnership Program, the NSRWA will be conducting horseshoe crab spawning surveys in Duxbury Bay. To do this, a team of 3-6 volunteers walks/wades along a ~800 meter stretch of the Duxbury Bay shoreline north of the Powder Point Bridge. The team uses poles and rope to define a 5m x 5m square; crabs inside the square are counted, sexed, and the different clusters in which they are arranged (single crabs, pairs, larger groups) are noted. This process is then repeated in approximately 40 squares along the shore.
Surveys occur around the full and new moons in May and June. During each moon phase we conduct three days of daytime surveys and three nights of nighttime surveys. Because of the timing of moon cycles this year, we get an extra set of surveys for a total of 30 individual surveys this year (instead of the typical 24).
The link below will take you to a self-service, volunteer sign-up page that includes the schedule, training dates, and other important information for participating in this project. Please click here to begin
Thank you as always for your interest, your time, and your efforts in support of the NSRWA!
