WS-CRAB-93

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 Read More
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This paper presents a simultaneous system-of-equations approach to modeling age-structured populations using trawl survey age/size frequency data. The analysis builds upon a Ricker spawner-recruit structure and provides a cohort-based estimation method that retains the underlying dynamic properties of a delay-difference model. The framework shares a common spawner-recruit function across age- Read More
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Change-in-ratio and index-removal estimators are presented in a general form suitable for fisheries studies. We also show how to combine the two approaches in a single estimator. It is necessary to sample the population before and after the fishery, and to determine the total harvest and its composition, in order to use these methods. We use the methods to estimate the population of legal-size Read More
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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.

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 Read More
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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 Read More
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The reproductive performance of commercially important crustaceans may be considerably affected by symbiotic nemertean egg predators and parasitic castrators. Because these parasites commonly affect only females or feminize males, they may be protected by management practices that protect females. To manage a parasitized stock, we suggest that strategies should vary depending on the Read More
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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 Read More
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Catch rate and catch composition of male snow crabs were compared for four sampling methods. These methods were: (1) large-meshed commercial traps, (2) small-meshed traps, (3) bottom trawl deployed during the day. and (4) bottom trawl deployed at night. Catches were characterized in terms of crab body sizes, shell conditions, and claw allometry. We concluded that: 1) mean and modal size of Read More
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