Barnegat Bay is home to several species of crabs, but the Blue crab is the most common and sought after.
Crabs Crustaceans
Rock Crab / Jonah Crab – similarities and differences
Two species:
Cancer irroratus – Atlantic Rock Crab
Cancer borealis – Jonah Crab
Often misidentified
They are similar in appearance and habitat but there are some differences:
Jonah crabs (Cancer borealis)<right image> and Atlantic rock crabs (Cancer irroratus)<left image> have essentially been bycatch in the American lobster fishery for more than 80 years
Jonah crabs are larger than Atlantic rock crabs and they are more commonly found at depths of 165 feet to 1000 feet and up to 2,600 feet.
Rock crabs are smaller and prefer shallower, inshore waters ranging from 20 to 1500 feet and are most often found at depths less than 65 feet.
Size:
Jonah crab size: males up to 8 inches and females up to 6 inches.
Rock crab size: males up to 6.5 inches and females up to 4 inches.
Size is not always a good method of identification as mature rock rock crab may be the same size as younger jonah crab.
Size: chelea (claws)
Jonah crab claws: large, typically with black tips
Rock crab claws: not really large – slender
Movement:
Jonah crab: slow moving, easy to catch.
Rock crab: quick, agile. very quick to “bite”
Seasonal Habitat:
Jonah crab: It is widely accepted that this species moves offshore in the fall and winter, and females have been documented moving inshore in late spring and summer.
Rock crab: Each season this species moves between varying depths.
In the autumn, which is their season of reproduction, most rock crabs remain at shallow depths.
They tend to bury themselves in rocky areas, in tide pools and wander into lagoons.
Physical difference:
The antennae on jonah crabs are long and short on the rock crab.
Both the Jonah crab and the Rock crab have oval carapaces (shells) but…
The Jonah cr
ab’s carapace has a more rounded, dome-like surface with jagged marginal spines *.
The Rock crab’s carapace is flatter and flares out at the sides, and its spines come to a single point
* marginal spine run from either eye along the side of the carapace
If you are in the vicinity of Barnegat Bay and you think you saw a….
- Dungeon crab Cancer magister
- Stone crab Menippe mercenaria
Odds are pretty good that you didn’t.
