CCAMLR

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.

The stone crab Lithodes murrayi was exploited briefly off South West Africa between November 1979 and April 1980, the fishery being terminated when the catch per unit effort fell to an uneconomic level. The extent of the L. murrayi grounds is examined on the basis of catch-per-unit-effort data. The species is largely confined to a bathymetric corridor of 500–700 m off South West Africa. Prior to commercial fishing, there was a densely populated region between 24°00'S and 24°40'S, although the crabs were present in small numbers over a much larger area. Over 90 per cent of the fishing effort was applied in this area of high concentration, accounting for almost 95 per cent by mass of the total catch. Although the catch rate declined, the mean size of exploitable crabs and of undersize crabs stayed virtually constant. Some morphometric relationships and a factor for converting processed crab section mass to whole crab mass have been calculated.

A quantitative analysis was carried out to estimate the maximum sustainable yield of blue crab distributed around the waters of Korea and in the East China Sea without using fishing effort data, fitting monthly catch data to a modified surplus production model.
The maximum sustainable yield of this fish stock was estimated to be about 22,400 tonnes per year and Fmsy to be 0.95.

If we could determine the relationship between catch rates in a trap survey and absolute population size, then we could estimate the standing stock of snow crabs before the fishing season from a survey conducted with traps. One way to calibrate the catch rates is to examine available historical Leslie analyses of commercial catch data obtained over several years and quantify the relationship between catch rate at the beginning of the season and the corresponding population estimate obtained by the Leslie analysis. Data from several different regions can be made comparable by expressing catches and efforts on an areal basis. Results obtained from data from Newfoundland and Nova Scotia suggest that this approach may be feasible.