Areal cover is calculated for the Statistical Sub-areas (48.1, 48.2 and 48.3) from which the bulk of the commercial krill catch has been taken. Correspondingly, the areas of the following four regions are also calculated - (a) the CCAMLR Convention Area, (b) south of 55°S, (c) containing krill concentrations and (d) south of the mean summer position of the 0°C isotherm using specialised computer software based on a Lambert Geographical Projection. As a secondary step, the mean krill density estimate for the West Atlantic during FIBEX (First International BIOMASS Experiment) is expanded to give a global biomass for krill within each of the above four regions. Similarly, the maximum estimated krill density for the West Atlantic during FIBEX is used to obtain an upper limit for the biomass of krill in the three Statistical Sub-areas being considered. The implications of the results is that the impact being made by the current krill fishery on the krill resource in Sub-areas 48.1, 48.2 and 48.3 merits discussion.
Abstract:
Finfish have been harvested in the Atlantic sector of the Southern Ocean since the end of the 1960s mainly by the Soviet Union. Notothenia rossii marmorata ,vas the target species in the first peak years 1969-71 which yielded about 500,000 tonnes in 2 seasons around South Georgia. Since 1975/76 fishing has been mostly directed to the icefish Champsocephalus gunnari. and to a lesser extent Patagonotothen brevicauda guntheri. Catches of C. gunnari were highest at about 240,000, 220,000 and 100,000 tonnes in 1976/77-1977/78, 1982/83-1983/84 and 1986/87-1987/88.
N. rossii marmorata is the species most adversely affected by the fishery. The present stock size around South Georgia is less than 5 % of the level before the fishery started. Recruitment has fallen since the second half of the 1970s. At the present level of recruitment, simulation studies indicate that the stock size will recover slowly, only doubling over a period of 10 years.
Stock size of C. gunnari around South Georgia is largely dependent on the strength of the recruiting yearclass which also forms the bulk of catches in the fishery. Stocks of C. gunnari around the South Orkney Islands and in the Antarctic Peninsula region seem to be heavily depleted by fishing and are in need of conservation measures.
P. br. guntheri is the only species in the fishery which was unregulated until 1988/89. Stock assessment is largely influenced by uncertainties in the determination of the natural mortality. At high levels of M (0.8-0.9) stock size as well as recruitment indicate a downward trend.
Abstract:
An operational management procedure for krill in sub-Areas 48.1 + 48.2 + 4 48.3 requires a basis for the assessment of resource status, and an algorithm for specifying the levels of regulatory mechanisms (e.g. a catch control law) that depends on the results of the assessment. Developing and selecting a procedure requires a basis for the simulation testing of procedures, and an operational definition of CCAMLR Article II to provide criteria against which to assess procedure performance. Suggestions are made under each of these headings. Assessment of resource status is provided by the CPUE "Composite Index" proposed by the Workshop on the krill CPUE simulation study. Annual TAC'S are restricted to an initial ceiling (Cc) for a 5 year period, with a reference CPUE level (CPUEref) calculated as the average CPUE over that time. Thereafter TAC'S may increase by Cr% per annum. However, this increase may be suspended or reversed in any year depending on how many of the previous three year's CPUE values fall below a target level of 0.75 CPUEref. An operating model of kril1 dynamics in the region is developed for simulation testing purposes. A provisional operational interpretation of Article II is proposed: the primary objective is to prevent the expected lowest biomass of krill over a 20 year harvesting period failing below 60% its average unexploited level; subject to this constraint, accumulate catches should be as large as possible without substantial associated probability that TAC reductions may prove necessary during the 20 year period considered. Simulation tests, including one particular test of robustness to the assumptions of the operating model, are carried out to ILLUSTRATE the overall process proposed; for this illustrative exercise, the choice of catch control law parameters would probably lie between (Cc = 1 million tonnes; cr = 15%) and (Cc = 2 mi11ion tonnes: cr = 10%). Suggestions for proceeding with further investigations of possible operationa1 management procedures are made. It is proposed that possible alternative suggestions for such procedures should be made in a similar fashion to that set out in the paper. Suggestions by others for alternative forms and parameter values (or likely ranges) for the krill dynamics operating model used for testing procedures are encouraged.
Abstract:
Available information on key reproductive parameters of Champsocephalus gunnari has been reviewed and discussed in the light of existing conservation measures. Length at first spawning is c. 25 cm around South Georgia and Kerguelen Islands, but c. 35 cm around the South Orkney Islands and in the South Shetland Islands/Antarctic Peninsula region. Around South Georgia spawning takes place from March to May. Spawning around the South Orkney Islands and the South Shetland Islands probably occurs in June/July. Around South Georgia males start their spawning migration earlier than females. Fjords have been reported to be important spawning grounds. Fecundity is highest around South Georgia and Kerguelen but is decreasing towards higher latitudes.
Mesh size regulations presently in force offer very little protection to first spawners around South Georgia and juveniles and first spawners on the other South Atlantic fishing grounds. Spawning activities of Champsocephalus gunnari and those of other exploited species could be best protected by the establishment of permanent closed fishing season from 1 March to the end of each year's meeting of CCAMLR.
There is no abstract available for this document.
There is no abstract available for this document.
Abstract:
This research examines the energy budget of breeding female Antarctic fur seals, both when food was plentiful and when it was scarce. The energy expenditure and change in body mass of lactating female Antarctic fur seals, Arctocephalus gazella, foraging at sea was measured in two years using doubly labeled water at South Georgia Island. There was no difference between years in mass gain, water influx, mass-specific field metabolic rate (FMR), or absolute FMR. Mean at-sea FMR over both years was 9.52 ± 0.55 W/kg (n = 22), a value that is 6.7 times the predicted basal rate but only 1.9 times the FMR measured onshore. Comparable results have been reported for similar-sized northern fur seals.
Krill, the nearly exclusive prey of breeding females, were very scarce in 1984 at South Georgia. Fur seal foraging trips were twice as long in 1984 as in 1985 and total mass-specific energy expended by females during these trips was significantly greater. In addition, females were significantly lighter at parturition in 1984, and both pup mortality and the proportion of pups that died from starvation were double the 1985 values. Female condition at parturition and average foraging-trip duration (i.e., offspring-provisioning rate) appear to reflect prey availability. The similarity between years in mass increase suggests that females do not return to feed their pups until they replenish their own reserves. Antarctic fur seal females may have a limited ability to increase the relative time spent foraging because even in normal years only 5% of their time at sea is spent resting. This contrasts with northern fur seals, Callorhinus ursinus, which typically spend 17% of their time at sea inactive. Apparently these northern seals can increase their foraging effort by increasing the proportion of time spent foraging. This would account for the observed between-year difference in at-sea FMR of C. ursinus while foraging-trip duration remained fairly constant.