WG-FSA-91

The method of refining the natural mortality coefficient is based on the notion that the free component of the regression equation between the mean-weighted coefficient of natural mortality as defined by the VPA and fishing effort must be equal to zero if the natural mortality coefficient has been correctly identified and something other than zero if it has not been correctly chosen.
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Otoliths from Champsocephalus gunnari were collected during a fish stock assessment survey in sub-area 48.3 during January and February 1991. An age length key based on age readings taken from these otoliths is presented.

Discrepancy was noted between the age length key and modes in the length distribution of Ch. gunnari from the Hill Cove survey around South Georgia in January 1990. A revised age length key for this survey is proposed, based on data from a previous survey in the area. The revised age length key corresponds well to modes in the length distribution from the survey and to another key derived from Read More
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Shnyute’s generalised cohort analysis of size composition in catches was used to estimate the Dissostichus eleginoides stock in Area 48.3. This made it possible to ignore the hypothesis of equilibrium in the stock and to examine the dynamics of its abundance and biomass.
At the start of the 1990/91 season the D. eleginoides stock is estimated to be 91.5 thousand tonnes.
It has been Read More
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An adaptive approach was used to assess the Champsocephalus. gunnari stock in Area 48.3. Values of catch/effort by age group and by year of fishing were used in conjunction with abundance indices from trawl surveys in tuning the VPA.
The C. gunnari stock at the start of the 1990/91 season is estimated at 184 thousand tonnes.
Calculation of TAC was carded out keeping in mind the Read More
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The seventh cruise of the RV Atlantida was a continuation of regular AtlantNIRO research into the status of Chaenichthyidae and Nototheniidae fish in Statistical Subarea 48.3 (South Georgia, Shag Rocks and Black Rocks). The minimum biomass of commercial fish species was calculated from the results of a census trawl survey carded out in April-May 1991. This paper contains data on distribution, Read More
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Dissostichus eleginoides is becoming an increasingly important species in the fisheries of the Southern Ocean. In Division 58.5.1, a directed trawl fishery has been in operation since 1984/85 and has expanded in the deep western sector of the Kerguelen shelf. This fishery harvests the sub-adult/adult part of the stock. Fishing effort and corresponding catches are very variable from one year to Read More
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Feeding patterns of four Nototheniid, three Channichthyiid and two Bathydraconiid species were investigated and their daily diets were assessed from data obtained at a day-long station carded out in the Cosmonauts Sea (67°50 S - 41°25 E) in March 1988.
The type of food consumed by Chaenodraco wilsoni and Trematomus eulepidotus indicates that they are plankton-eaters as their diet Read More
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The diet composition and feeding intensity of mackerel ice fish (Champsocephalus gunnari) around South Georgia in January/February 1991 was analyzed in 3877 stomachs collected on 44 stations. Both, the proportion of krill (Euphausia superba) in the stomachs and the feeding intensity were uncommonly low in a period when energy-rich food is needed for the final maturation of the gonads.

Genetic population structure of the mackerel icefish, Champsocephalus gunnari, in waters from around South Georgia, South Orkneys, and Heard Island (Australian Antarctic) was examined using allozyme electrophoresis.
Icefish were collected from Heard Island (N = 47; November 1990), South Georgia (N = 267; January/February 1991) and the South Orkneys (N = 44; January/February 1991) and Read More
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Existing antecedents are presented from technical publications concerning chilean fisheries of the patagonian toothfish Dissostichus eleginoides related with the selectivity of the type and size of hooks used in the longlines. Original data obtained during 1991 on the coast of Valdivia, South East Pacific, are added. The data show that the circle hooks are far more efficient that the right Read More
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The species composition and bathymetric distribution of the fish fauna of Terra Nova bay (Ross Sea) was investigated during the 6th Antarctic Italian Expedition (austral summer 1990/91).
Samples were collected using fixed gears (nets, hooks and traps) and working along four transects from the coast to off-shore, down to 680 m.
The bulk of catches were Nototheniidae (10 species, 83 Read More
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An adaptive approach was used to assess the Notothenia gibberifrons stock in Area 48.3. It is demonstrated that when tuning the VPA using abundance indices from trawl surveys it is imperative to estimate the catchability coefficient. This parameter was equal to 0.326 to 0.635.
An adaptive approach in this case involved using a target function in the form of the sum of square deviations Read More
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The results are presented of studying icefish vertical migration based on the data of R/V cruises during the seasons of 1982-83, 1983-84 and 1986-87, when this species was highly abundant on the South Georgia shelf. It is revealed that at day time the fish distributes near the bottom and the maximum catches were available at the middle of the light hours of the day. At twilight the fish Read More
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Capture statistic analyses from the different regions of Chile where fishery of patagonian toothfish (Bacalao de profundidad), Dissostichus eleginoides, has been developed are based in statistics published by the SERNAP (National Fishery Service). It shows that activity has lasted few years in each geographic region considered. As captures have decreased in the northern zone, the artisanal Read More
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Two similar methods for preparing aggregate length frequency distributions from survey data are discussed. The Mackerel Icefish, Champsocephalus gunnari at South Georgia is used as an example.

Sexual maturation in the Mackerel Icefish, Champsocephalus gunnari, was studied by macroscopic examination of gonads. Evidence in support of the hypothesis that a proportion of mature fish fail to spawn was obtained. Histological examination of ovaries indicates that some ova were undergoing regression and resorption at least two months prior to the normal spawning date. It is concluded that Read More
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Samp1es of fjord fish of the species N. rossii and N. neglecta collected at Potter Cove, King George/25 de Mayo Island, South Shetland Islands, from 1983 to 1991, allowed to study the previously reported abundance changes as a size-related process. The data were analyzed using a Nested ANOVA design to obtain variance components and expected values. An increase and then a decrease in the Read More
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An assessment of the Champsocephalus gunnari fishery in sub-area 48.3 using VPA from 1976/77 to 1990/91 is presented. The analysis was tuned to abundance indices derived from fishery independent stock assessment surveys between 1986/87 and 1990/91. The results indicate a very different situation to assessments in 1989/90 with a decrease in overall biomass and recruitment over recent years. Read More
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Recently a longline fishery has developed for the Patagonian Toothfish, Dissostichus eleginoides, in the vicinity of Shag Rocks, South Georgia. Assessment of this stock is not possible by conventional methods because the bulk of the adult population may be dispersed over a wide area in deep water whereas the Shag Rocks’ shelf may be a nursery ground for juveniles. An assessment of the stock Read More
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Criteria for the choice of a trawl for demersal fish surveys are discussed. Details of the construction and performance of the 120 Bolt Rope Bottom Trawl used during the recent fish stock assessment survey around South Georgia on the Falklands Protector are presented. It is proposed to use this trawl during future surveys in the area in order to improve continuity in the survey series. The Read More
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