Quantitative stock survey and some biological and morphometric characteristics of the deep-sea red crab Geryon quinquedens off south west Africa

In order to assess the abundance of the red crab Geryon quinquedens, two otter-trawl cruises were undertaken in July and September 1978, on the continental slope off South West Africa. A bimodal frequency distribution of female crabs was evident with modal sizes at 7.7 cm and 8.7 cm carapace width, whereas the mode for males was at 11.2 cm. In general. larger animals tended to inhabit shallower water, i.e. size is inversely related to depth. Females preferred shallower water than males. Shell states indicated that males were predominantly in the inter-moult stage while most females were either approaching or had recently completed the moult. From morphometric relationships, it was calculated that, in processing the live material to a cooked frozen product, red crab is subject to a mass loss of about 54 per cent. Analysis of stomach contents by volume showed that only 12 per cent of male stomachs contained 5 per cent or more food and 2 per cent of female stomachs exceeded the 5-per-cent level. Highest crab densities occurred at depths of 472-849 m, whereas unusually high concentrations were encountered during two trawls at water depths of 549 and 590 m. The red crab survives at extremely low levels of dissolved oxygen and tolerates a temperature range of more than 7°C.