Hydroacoustic and net sampling data were used to determine the distribution and abundance of krill. In an attempt to address the effect that variability in sampling gear type may have on specific population parameters (e.g. size frequency, abundance and distribution), a multi-year comparison of these types of samp1ing gear commonly used in the Antarctic has been initiated.
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Abstract:
Foremost in the elucidation of accurate population dynamics parameters in fish is a necessity for an errorless estimation of age. Age determination can provide basic life history information, including mortality, population age structure, and changes in individual growth. Most investigations have used annual rhythmic deposition in calcified tissues as time marks but, due ts the lack of distinct periodicity in Antarctic hydrographic conditions, age determination of Antarctic fish has proven to be difficult. It is now possible to determine the age of fish through the utilization of daily increments in otoliths, calcified tissues which may contain a large amount of biological and ecological information about a fish's past history. As part of an effort to study Antarctic fish growth and population dynamics, investigations were performed on otoliths from the Antarctic fish Champsocephalus gunnari and Notothenia rossii. External and internal examination of otoliths from by Scanning Electron Microscope (SEM) methodology revealed internal rhythmic patterns which make it possible to estimate the age of these species. Multivariate mathematical models relating age to otolith morphometrics and fish size demonstrated that age could be reliably determined from body measurements and otolith measurements. These techniques allowed us to determine that the Champsocephalus gunnari grew 55cm in 17 years and the Notothenia rossii grew 55 cm in 7 years. The lack of: the large size groups for Notothenia rossii may be indicative of over fishing and that only the younger age groups are available for harvest. It appears that length at age data determined a yearly basis for these species would provide valuable management data.
There is no abstract available for this document.
There is no abstract available for this document.
Abstract:
The swept area method was used to estimate biomass density changes in the stocks of five fish species Champsocephalus gunnari, Chaenocephalus aceratus, Pseudochaenichthys georgianus, Notothenia gibberifrons, and Notothenia rossii marmorata in the South Georgia area in the seasons of 1976/77-1986/87. In most of the seasons analysed, the estimates covered a near-bottom layer in about 1/6 of the area of the island shelf.
Assessment results point to considerable variations in fish biomass density, in the studied period. Estimates of fish stocks biomass ranged from 43 to 158 thous.tons. The changes in the biomass level are first of all a result of periodical fluctuations in the biomass density of C.gunnari stock. High biomass density appeared with 2-4 years intervals after recruiting an abundant year-class to the exploited stock. Biomass of other bottom species is more stable, especially in case of N.gibberifrons. Recently, an increase of the C.aceratus stock is observed and, at the same time, a gradual decline of the P.georgianus.
Abstract:
Simple relationships expressing dependence of sampling relative error in biomass estimate (by means of a survey) on statistical characteristics of fish concentration density field under examination and on parameters of survey itself, have been derived with the help of mathematical statistics and methods of calculus of probabilities; biomass estimate is determined as a product of average density for region under examination and area of this region. As to hydroacoustic survey, anisotropy parameter, correlation radius along transects and variation coefficient serve as field characteristics on which error depends, and direction of survey with respect to the axis of the correlation ellipse and frequency of transects (sections) serve as survey parameters. Dependences offered here, can be used in practice both for a posteriori estimation of error made when calculating biomass, and for survey planning on the basis of a priori estimates of statistical characteristics of concentration density field. They might make a basis for the procedure of survey operative control.
Abstract:
A model is set up for the operation (which includes both searching and fishing) of a Japanese krill trawler over a half-month period, and the output is compared to statistics from a sample of data from the commercial fishery. Twenty-four candidate "CPUE" biomass indices are considered, and their performance investigated in response to six different ways in which the overall krill biomass in a 600 n. mile square oceanic sector might decline by 50%. In most cases there is essentially no response of the index, or a response rather smaller in relative magnitude than the biomass decline. Catch statistics collected at present (centred primarily on catch per fishing time) are of low utility in detecting biomass declines. Indices incorporating search time information may give improved performances, but would probably be reliable only for detecting changes in within-concentration krill distribution parameters. Other approaches (e.g. research vessel surveys) need to be considered to monitor changes in the number, distribution and density of krill concentrations. Priority for further analyses should be given to examination of existing scientific krill survey data to improve the krill distribution model underlying this analysis (this might perhaps be appropriately effected by constituting and organising a meeting of a small joint CCAMLR-BIOMASS Working Group). This is because of a major discrepancy between the typical length of Japanese tows (generally through a single swarm) which is much larger than the typical size of krill swarms recorded in scientific surveys; this discrepancy needs to be resolved before greater confidence will warrant being placed in the results from a simulation model of the fishery.