The Gulf of Maine’s summer surface water is warming about four times as fast as the global ocean (Gulf of Maine Research Institute, n.d.), and blue crabs are moving north. Once rare north of Cape Cod, since about 2019 they have turned up in harbors, flats and lobster traps from Massachusetts to Down East Maine. This site tracks that spread, and what limits it, like cold winters. Press play to watch the sightings add up.
Coldest week of each winter, Maine to northern Massachusetts coast
Average of the coldest 7 days of sea surface water, December to mid-April. Dots below the 3°C line are winters cold enough to kill crabs.
Below 3°C: deadly if it lasts1982–2011 averageYears on the map
Source: NOAA OISST v2.1 daily sea surface temperature, 25 km grid (NOAA NCEI, 2026). Crabs winter on the bottom in harbors and rivers, where water can be colder or warmer than these offshore readings.
When they turn up
Share of each source's sightings by month. Bars point outward from the center; the shaded arc is July–October.
Survey reports have dropped
All Manomet survey reports per year. Fewer reports means fewer people reporting, not fewer crabs. iNaturalist sightings in the Gulf of Maine held steady over the same years.
Seen a blue crab this year? Report it.
Every report helps, even a single crab, a dead one on the beach, or just a claw. Note where and when you found it, and snap a photo if you can. Your sighting goes straight into Manomet's survey and helps show how far north blue crabs are spreading.
A swimming crab with paddle-shaped back legs and bright blue claws. Females have red tips on their claws. Adults are 5 to 9 inches across the shell. Common from Cape Cod south to the Gulf of Mexico, they were only an occasional visitor in the Gulf of Maine (Johnson, 2015).
The change
Why it matters
The Gulf of Maine is warming faster than most of the world's ocean (Gulf of Maine Research Institute, n.d.). Warmer winters may let more blue crabs survive here. They eat clams, mussels and other crabs, so researchers want to know where they show up, how many there are, and whether they're breeding.
You can help
How to help
If you catch or find a blue crab in Maine, New Hampshire or northern Massachusetts, report it, even if it's dead or just a claw. Note where and when, how many, and take a photo with something for scale. Each report helps track how far north they've spread.
References
Bauer, L.J. and Miller, T.J. (2010) ‘Temperature-, salinity-, and size-dependent winter mortality of juvenile blue crabs (Callinectes sapidus)’, Estuaries and Coasts, 33, pp. 668–677. Available at: https://doi.org/10.1007/s12237-010-9277-2.
Johnson, D.S. (2015) ‘The savory swimmer swims north: a northern range extension of the blue crab Callinectes sapidus?’, Journal of Crustacean Biology, 35, pp. 105–110. Available at: https://hdl.handle.net/1912/7194 (Accessed: 2 November 2026).
NOAA National Centers for Environmental Information (NCEI) (2026) Daily Optimum Interpolation Sea Surface Temperature (OISST), version 2.1 [dataset]. Distributed by NOAA CoastWatch ERDDAP. Available at: https://coastwatch.pfeg.noaa.gov/erddap/griddap/ncdcOisst21Agg.html (Accessed: 2 November 2026).
Rogers, T.L., Gouhier, T.C. and Kimbro, D.L. (2022) ‘Distinct temperature stressors acting on multiple ontogenetic stages influence the biogeography of Atlantic blue crabs’, Marine Ecology Progress Series, 690, pp. 97–111. Available at: https://int-res.com/abstracts/meps/v690/p97-111 (Accessed: 2 November 2026).
Rome, M.S., Young-Williams, A.C., Davis, G.R. and Hines, A.H. (2005) ‘Linking temperature and salinity tolerance to winter mortality of Chesapeake Bay blue crabs (Callinectes sapidus)’, Journal of Experimental Marine Biology and Ecology, 319, pp. 129–145. Available at: https://serc.si.edu/publication/31648 (Accessed: 2 November 2026).