CCAMLR

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.

Over 6000 male snow crabs were tagged during a 6-year period in Conception Bay, Newfoundland, in order to estimate the increase in size at the time of molting. Ninety-two animals were recaptured which had usable information on growth increments. Based on the amount of growth, we hypothesized that 20 of these had molted once while the remainder molted twice. Two lines of evidence support this interpretation. First, animals in the group presumed to have molted twice were at liberty on average twice as long as those presumed to have molted once. Second, a regression line fitted to data on single-molters predicted the size after two molts in close agreement with a regression line fitted to data on double-molters. A nonlinear regression model was developed to estimate the parameters of the relationship between post- and pre-molt sizes using the combined data set for single and double molters. The method was also generalized to account for a quadratic relationship between post- and pre-molt size. For crabs in the size range 80-110 mm carapace width, the predicted size after molting in mm is equal to 7.398 + 1.038 x pre-molt size. A similar study conducted in Bonavista Bay, Newfoundland, yielded growth information for 18 animals. The molt increments appear similar to those observed from Conception Bay.