Habitat Partioning by Blue Crabs

 

Population dynamics and habitat partitioning by size, sex, and molt stage of blue crabs ( Callinectes sapidus ) in a subestuary of central Chesapeake Bay

Marine Ecology Progress Series 36: 55-64
Volume 36, 1987, Pages 55-64

Hines, A.H. , R.N. Lipcius, and A.M. Haddon

Smithsonian Environmental Research Center, Edgewater, Maryland, USA


Abstract

Abundances, size-frequency distributions, sexual composition and molt-stage composition of blue crabs Callinectes sapidus were measured during 1983 to 1985 in the Rhode River, a subestuary of central Chesapeake Bay, USA. Crabs at the mouth and head of the river basin were sampled with monthly triplicate otter trawls. Crabs in the principal tidal creek of the river were sampled 3 d a week with a fish weir, which caught crabs moving upstream and downstream separately. Crabs exhibited consistent, marked seasonal cycles in abundance as well as considerable annual variation in July peak abundances. New recruits entered the subestuary in late fall and spring and grew rapidly to 70 to 100+ mm in their first summer; by the second year they reached mature sizes of 120 to 170 mm. 60% of crabs in the river basin were males; and after maturation and copulation in late summer to early fall, mature females left the subestuary. Crabs partitioned habitats within the Rhode River subestuary by size, sex, and molt stage. Polymodal size structures were similar throughout the river basin, but increased percentages of males were found at the head of the river. Predominantly (90%) medium-sized (80 to 120 mm) males utilized the tidal creek as a molting habitat. Most crabs moving upstream were in premolt, whereas most crabs moving downstream were significantly larger and in postmolt, so that 70% of crabs in the creek were near ecdysis. Males and females exhibited significantly lower, but still appreciable (about 25%) molting activity throughout the river basin. These data provide one of the best documented cases of habitat partitioning by size, sex and molt stage in crustaceans.