Aspects of the biology of the jonah crab,Cancer borealis Stimpson, 1859 in the mid-Atlantic Bight

Summary

Jonah crabs, Cancer borealis, were collected in October 1971, June 1973, and March and April 1974 during trawl surveys of the continental shelf of the mid-Atlantic Bight and the shelf and slope east of Beaufort, North Carolina. In 171 trawls made from the M/V Blesk, R/V Columbus Iselin, R/V Albatross IV and R/V Eastward, 1626 jonah crabs were captured. Crabs were contagiously distributed within a depth range of 20–400 m. Maximum abundance occurred within 150–400 m and 8–13·9°C.

Male crabs ranged from 12 to 175 mm in carapace width; females from 13 to 152 mm. Three modal size groups for males and females were recognized: 13–40 mm, 41–80 mm and 81–110 mm. There was a fourth group of male crabs over 110 mm width. Crabs 40 mm were most abundant at depths of 75–150 m; crabs 41–80 mm were not captured in depths < 150 m, but were the dominant group in strata > 150 m. Larger crabs (81–110 mm) occurred from 40 to 400 m and reached maximum numbers at 150–400 m. Male crabs ≥ 111 mm were found only in 150–400 m.

Male crabs predominated in June. Sex ratios (M:F) ranged from 1·1:1 to 17:1. In October the ratios ranged from 1:16 to 2·4:1. In March and April the ratios were 2·9:1 and 1·9:1, respectively. In most cases the ratios were significantly different from 1:1.

The species was actively moulting in June, but recent or incipient ecdysis was not observed in October. Only one recently moulted crab was noted in March.

Gonad development in June was related to size. Most crabs ? 80 mm width were undeveloped or only slightly developed. Mature gonads were seen only in crabs ≥ 100 mm width. Testes and vasa deferentia of most males ≥ 150 mm were well to very well developed. No ripe ovaries were seen and no ovigerous individuals were taken in June. One berried female was observed in March.

The incidence of fouling organisms on crabs reflected the moulting history of the crabs. Sixty per cent of crabs in anecdysis and 14% of those in postecdysis were fouled. The predominant organism was the lepadid barnacle, Poecilasma inaequilaterale Pilsbry, which was attached to the gills in the branchial chamber.