CCAMLR Science, Volume 8 (2001)
The design of the CCAMLR-2000 Krill Synoptic Survey (CCAMLR-2000 Survey) is described. The primary objective of the survey was to improve estimates of the pre-exploitation biomass of krill which are used in models to estimate sustainable yield in Area 48. The survey design includes two large-scale oceanic strata: one in the southwest Atlantic located in the Scotia Sea, and the other to the north of the Antarctic Peninsula (CCAMLR Statistical Subareas 48.1,48.2,48.3 and 48.4). Within these large-scale strata, four mesoscale strata were included in the survey design; these were located close to the South Sandwich Islands, north of South Georgia, north of the South Orkney Islands and north of the South Shetland Islands. The rationale underlying the selection of the strata and survey boundaries is described. The methods used for selecting the location of each survey transect are explained and the planned cruise tracks for each of the four vessels participating in the survey are shown. Details are also described for adaptively modifying the survey during its execution. This includes information how net haul stations should be selected and how transects should be modified if the planned survey tracks cannot be completed. The survey took place in January-February 2000 and involved ships from Japan, Russia, UK and the USA. Scientists from many more CCAMLR Member States and the International Whaling Commission (IWC) took part. The survey is by far the biggest single exercise ever carried out by Members in support of the Convention. Full analysis of the results of the CCAMLR-2000 Survey will take several years and will result in a significant increase in the knowledge of krill length frequencies, biomass and distribution in the area studied. |
Inter- and intra-annual variability of commercial krill trawling positions for the 1980/81 to 1999/2000 seasons in the area north of the South Shetland Islands were analysed in relation to biological and environmental factors. Commercial fishing operations concentrated on the outer shelf in the early 1980s, along the shelf slope in the mid to late 1980s, and from the shelf across to the outer shelf in the early to late 1990s. Intra-annually, trawling positions generally started from the outer shelf and proceeded towards the shelf later in the season. Trawling positions seemed to be primarily governed by the distribution of larger mature krill, especially at the beginning of fishing operations each season. In summer, biological factors that affect product quality, such as salp abundance and the proportion of green krill, also seemed to have an increasing effect on trawling positions. Ice conditions for recent fishing periods were also demonstrated to have an effect. |
Managing fisheries to achieve ecosystem objectives is in its infancy. A general approach is proposed for maintaining ecological relationships and providing for the recovery of depleted populations in food webs supporting fisheries. This paper addresses the following general questions for applying the ecosystem approach to managing fisheries: (i) how might fisheries impact incidentally on an ecosystem, (ii) what should be the conservation objectives for predators of fished species, and (iii) what approaches could be considered for achieving the conservation objectives? The approach proposed here takes account of uncertainties in knowledge of the structure of ecosystems. Estimates of predator production arising from the consumption of fished species (encapsulated in proposed indices P and W) may provide useful indicators for management purposes because they integrate across a range of 'ecosystem' effects and, as formulated here, can also be related directly to the effects of fishing. These features are currently unavailable in ecosystem approaches to managing fisheries, which do not weight input data for assessments, such as per-capita breeding success, according to the relative influence of fished species on those estimates. The paper describes the steps required to establish management procedures based on these indices. |
For the last three years, CCAMLR's Working Group on Fish Stock Assessment (WG-FSA) has accorded high priority to the development of methods of integrating different indicators of stock status into assessments using the Generalised Yield Model (GYM). In this paper, we propose a method, based on the use of importance sampling, for incorporating information on trends in standardised CPUEs into GYM assessments. The use of the method is illustrated using data for Patagonian toothfish (Dissostichus eleginoides) in Subarea 48.3. The method requires only very small adjustments to the computer program implementing the GYM assessments. |
Age composition is fundamental to understanding the population dynamics and productivity of a fish stock. The use of scales to estimate age can result in large errors in age data for long-lived species, usually due to compression of scale circuli with age. Patagonian toothfish (Dissostichus eleginoides) is considered to be a long-lived species whose age has been estimated using both scales and otoliths. We estimated the age of D. eleginoides caught off South Georgia using otoliths and scales. For scales, we made impressions on acetate slides; for otoliths, we used transverse sections prepared by baking and grinding the posterior and anterior sides. Using ANOVA, we compared data obtained from the two structures to test the hypothesis that otoliths and scales give the same age estimates, and compared the precision of age estimation for both structures and between readers. Ages estimated using scales were significantly less than those estimated using otoliths. For scales, bias occurred for both readers between readings; for otoliths, only one reader was biased. Residual variances indicated one reader was relatively more precise than the other in estimating age using otoliths, but less precise using scales. This reflected the comparative experience of the two readers in estimating the age of D. eleginoides using otoliths and scales. |
During the period March to May 2000, the UK undertook trials of a pot fishing method to catch Patagonian toothfish (Dissostichus eleginoides) around South Georgia (Subarea 48.3). This method has the potential to minimise, or eliminate, incidental bird mortality when compared to the standard longline method. This paper describes the trial and the results, and discusses the commercial viability of this fishing method for toothfish fisheries in the CCAMLR Convention Area. While the method successfully caught D. eleginoides, there was a large by-catch of crab species. The catch rate of toothfish was notably lower than that achieved in the longline fishery. Importantly, the use of pots eliminated bird by-catch. To capitalise on this feature, there is a need to improve the commercial viability of the method and minimise the quantity of by-catch. A number of potential changes are suggested to this end. |
Historical information on the distribution of spawning and larval mackerel icefish (Champsocephalus gunnari) within CCAMLR Subarea 48.3 (South Georgia and Shag Rocks) is assessed. This is considered alongside new data from commercial fisheries and research surveys. It is concluded that there is strong evidence of inshore spawning at South Georgia during April within and close to the bays on the north side of the island. Some spawning almost certainly occurs over much of the island shelf, although is this appears to be at a very much lower intensity than inshore. There is some evidence of spawning at Shag Rocks. There are also indications of a possible second spawning season in January, although the evidence is weak. Concentrations of larval icefish within Cumberland Bay are an order of magnitude higher than in adjacent coastal waters and their density declines exponentially offshore. All this evidence indicates that the most important spawning locations are within the bays. |
Mackerel icefish (Champsocephalus gunnari) are widespread on the South Georgia shelf, Antarctica, and have been fished commercially since the early 1970s. They are known to feed predominantly on krill. An index of condition which uses the ratio of the measured total mass to the estimated mass is shown to provide a good indicator of local krill density. The index is likely to be little affected by the reproductive cycle unless there is high krill availability during the months around the spawning time, and even then the effect is much less than the highest observed values. The condition index responds rapidly to changes in krill density and therefore can provide indications of short-term variations in krill availability. Condition index provides a useful proxy for krill density and is likely to be of considerable value in interpreting the results from ecosystem assessments such as that in progress under the auspices of CCAMLR. |
Biostatistical data obtained by Soviet research and commercial vessels from 1970 to 1991 have been used to determine the age-length composition of mackerel icefish (Champsocephalus gunnari) from different parts of the South Georgia area. An analysis of the spatial distribution of C. gunnari size and age groups over the eastern, northern, western and southern parts of the shelf, and near Shag Rocks, revealed a similar age-length composition for young fish inhabiting areas to the west of the island and near Shag Rocks. Differences were observed between those those two groups and the eastern group. The larger number of mature fish in the west is related to the migration of maturing individuals from the eastern and western parts of the area. It is implied that part of tlne western group migrates towards Shag Rocks at the age of 2-3 years. It has been found that, by number, recruits represent the largest part of the population, whether a fishery is operating or not. As a result of this, as well as the species' ability to live not only in off-bottom, but also in pelagic waters, an earlier age of sexual maturity compared to other nototheniids, and favourable oceanographic conditions, the C. gunnari stock could potentially recover quickly from declines in stock size and may become abundant in the area, as has been demonstrated on several occasions in the 1970s and 1980s. |
The first instance of anti-Brucella antibodies in the Southern Hemisphere was recorded in two pinniped species from Antarctica: Antarctic fur seal (Arctocephalus gazella) and Weddell seal (Leptonychotes weddellii). Taking into account these first records, this paper describes additional data on Brucella antibodies in A. gazella obtained at Cape Shirreff, Livingston Island, Antarctica. Eighty-six A. gazella body fluid samples were collected from 77 live animals and nine from dead animals. Body fluid samples (blood, pleural fluid or pericardic fluid) were tested using the Rose Bengal (RB) test, the Competitive Enzymoimmunoassay (c-ELISA) test and the Competitive Enzymoimmunoassay 'COMPELISAO®' test. Antibodies against Brucella spp. were detected in one sample with the RB test, and in five of the 86 samples (5.8%) using the c-ELISA test. These results present serological evidence of Brucella infection in A. gazella. We suggest the utility of extra-vascular fluid for this serological research. We recognise the c-ELISA test as the best option in this regard, and suggest that Brucella spp. has an extended distribution and is probably found worldwide in marine mammals. We highlight the importance of evaluating in the CCAMLR Working Group on Ecosystem Monitoring and Management (WG-EMM) the incidence of infectious diseases, since diseases like brucellosis may produce reproductwe failure in predatory species. However, it is not possible to relate evidence of Brucella infection to any anthropogenic event in Antarctica since the bacteria have not yet been isolated and no studies on this subject have been conducted there previously. |
The relationship between krill abundance and predator performance is fundamental to an ecosystem-based approach to resource management. We propose a method using krill sampled from the diet of predators to provide a length-frequency distribution of krill at times when it is possible to run automated shipboard acoustic systems but not to conduct scientific netting, i.e during logistic/resupply operations. This will allow a robust estimate of krill abundance to be calculated from acoustic data. Changes in the length-frequency distribution of krill over a period of a few weeks produced a 10% difference in TS, whereas simultaneous samples from predators and nets produced only a 1% difference, illustrating the need for simultaneous length-frequency data. By integrating data from land-based predators directly with automated on-board data collection systems it will be possible to gain important estimates of krill biomass at times of the season hitherto unavailable from shipboard scientific surveys. |
Shust, K.V (2001), Book review: Fish and Fish Resources of the Antarctic This work by K.V. Shust (Doctor of Biological Sciences), published in 1998, remains fairly unknown beyond a Russian-speaking readership. The book represents the first complete summary, prepared by a Russian author, of original material and published data describing comlnercial and potentially commercial Antarctic fish species. Moreover its value is enhanced by the author having participated in many fisheries research expeditions in Antarctica. The introduction notes that until the 1960s Antarctic waters were still among the most poorly studied regions from the point of view of their fisheries potential. The USSR began regular, largescale multidisciplinary studies here in the early 1960s. Starting from the first South Atlantic expedition carried out by the research vessel Alademilc Knipovich in 1964/65 and up until 1992, scientists from VNIRO and all of its regional branches carried out systematic research into Antarctic bioresources, especially fish. The mid-1970s saw other countries beginning to carry out research and commercial fishing in Antarctic waters. This led to international cooperation in the study of Antarctic bioresources, firstly by individual groups under the auspices of SCAR (Scientific Committee for Antarctic Research), and later, after the coming into force of the Convention on the Conservation of Antarctic Marine Living Resources, under the guidance of the intergovernmental Commission also known as CCAMLR. |