Beautiful Swimmers: The Life of Blue Crabs

By Susan Buckingham

If you wade into the Chester River from Queen’s Landing, you may well see blue crabs at any time of year where they provide food for birds, fish, and humans. During the season, steamed crabs with Old Bay seasoning are a part of life here on Kent Island and have become the emblem of Maryland. While many know the intricacies of preparing and eating crabs, some may be unaware of the extraordinary life cycle that brings them to our shores and tables.

 

Between May and October in the brackish water of the mid-bay area, a mature male blue crab (Jimmy) finds his soft-shelled female intended (sook) and cradles her in his arms, or claws, for several days while he searches for a protected area, generally in subaquatic grasses. They are sometimes referred to as doublers at this stage. Safely protected, she molts and they can mate. Afterwards, he once again holds the mother-to-be for several days which both prevents another Jimmy from mating with her and allows her new shell to harden. The pair then separates so the female can travel many miles to the mouth of the bay holding the sperm in special receptacles. As the male looks for another mate, the female seeks the saltier waters near the ocean to fertilize her eggs and eventually release her larvae – often referred to as a sponge. She can release her babies up to a year after mating depending on temperature and salinity conditions. The 2 million larvae from one female, once free, molt several times in the lower bay or Atlantic before crawling along the bottom all the way to the upper bay. Maturity is at 12 to 18 months, and the process begins again. Males remain in the mid to upper bay throughout their adult lives, continuing to grow, molt, and mate for up to three years, while females, after maturing, mating, and traveling do not make another trip back up the bay once they have spawned. With such a complex life cycle, scientists continue to study and monitor the Chesapeake Bay blue crab.

 

The Chesapeake Bay Program estimates the number of female spawning crabs, calculated in the winter dredge, over the last few years at:

 

2017: 455 million

2018: 371 million

2019: 594 million

 

These numbers are used by a variety of agencies to make blue crab population management decisions around the bay. Crabs are susceptible to overfishing, pollution, water temperatures, and the loss of subaquatic vegetation. Their population has varied a great deal over the last few decades.

 

Although blue crabs are considered a native species all along the east coast of North and South America, they are most numerous along the mid-Atlantic coasts. Recently, a population of blue crab has been found proliferating in the Mediterranean where they have no natural predators. Considered an invasive species there, fishermen in Spain consider them a “menace”. Here on the Chesapeake, blue crabs remain a traditional delicacy of the season.

 

Sources:

Chesapeake Bay Magazine

Chesapeake Bay Program

NOAA

Queen's Landing