CCAMLR Science, Volume 10 (2003)
Data on the Soviet krill fishery in the Atlantic Sector of the Antarctic from 1977 to 1992 are discussed. The total fishing effort from 1977 to 1991 was 50 086 vessel-days fished, in Subareas 48.3 (45% of the total for the period), 48.2 (36%) and 48.1 (19%). Three distinct patterns in the distribution of monthly fishing effort between subareas were recognised: Type I covered the period 1981–1982, Type II 1983–1986 and Type III 1987–1988. It is likely that environmental conditions and operational constraints influenced the distribution of fishing effort. The three types of distribution correspond to the spatial and temporal variability of the meridional atmospheric processes. Retrospective data analyses show that the fishing effort is most intense in the subarea where air transfer from the south is greatest. The phenomenon occurs in Subareas 48.1 and 48.2 under conditions of increased westward component of the zonal air exchange and in Subarea 48.3 of decreased westward component. |
This paper provides an assessment of the impact of the commercial fleet on the krill population in different months during the 1987 to 1990 fishing seasons within Subareas 48.2 and 48.3. During this period catches reported by the Soviet fleet amounted to more than 95% of the total catch. The calculations were based on haul-by-haul data from the Soviet fleet, using a probability statistical theory of fishery systems developed at AtlantNIRO. The impact of the commercial fleet on the krill population – on biomass and the density of krill aggregated in the fishing grounds – was assessed using data from 22 800 hauls. The results of this study indicate that during periods of maximum fishing intensity, the Soviet fishing fleet had no impact on the krill stock or, consequently, on krill-dependent predators. It is concluded that although there is a spatial overlap of the dependent species and the fishery, this is not sufficient to amount to a functional overlap. |
Samples of macrourid rattail by-catch from the toothfish fishery in the Ross Sea dependency in 2002 were identified by observers and returned to New Zealand for subsequent confirmation of their identity by researchers from the National Institute of Water and Atmospheric Research (NIWA). Two species were found, Macrourus whitsoni and M. holotrachys. A previously aged sample from 1999 was confirmed as being solely M. whitsoni, based on otolith comparisons and the geographic source of the aged sample. Counts of translucent zones were made from baked and cross-sectioned otoliths of the ridge-scaled macrourid (M. whitsoni) sampled from the commercial longline fishery in the Ross Sea (CCAMLR Subarea 88.1). The zones are assumed to form annually as this ageing methodology has yet to be validated for this species. Von Bertalanffy growth parameters were calculated from the readings, separately by sex. M. whitsoni appears to be a slowgrowing and long-lived species, living to at least 50 years. Females grow at a faster rate, and reach a larger size, than males, but both sexes exhibit comparable maximum ages. Regression relationships were calculated, by sex, between total and snout–vent lengths, snout–vent length and weight, and total length and weight. The species exhibited a degree of sexual dimorphism. The age at which 50% of fish are sexually mature was estimated to be from 12 to 14 years. |
Demographic parameters (age-specific survival rates, fecundity levels and population numbers) were analysed for the Béchervaise Island Adélie penguin colony in eastern Antarctica after 12 years of monitoring under the CCAMLR Ecosystem Monitoring Program (CEMP). A life table was constructed, and predicted rates of population growth and breeding success calculated. The population model predicted an annual population growth rate of 0.3% compared to the 1.2–1.8% increase per annum indicated from field counts. Underestimation of adult survival rates was considered the most likely explanation for the discrepancy. As is the case for most long-lived seabird species, growth/decline rates of the Adélie penguin population at Béchervaise Island were found to be more sensitive to changes in annual survival rates, especially of young breeding adults, than to changes in fecundity parameters. Results are discussed in comparison with data from a declining Adélie penguin population in the Ross Sea studied during the 1960s and 1970s (Ainley et al., 1983), and in relation to other CEMP parameters, environmental factors and fishery regulations. The data collection and analysis methods outlined in this paper provide a basis for the development of data reporting formats for CEMP Standard Method A4. |
Temporal variability in a series of CCAMLR Ecosystem Monitoring Program (CEMP) parameters and the interrelationships between these parameters were examined for Adélie penguins over a period of 12 years. Data were collected from 1990/91 to 2001/02 at Béchervaise Island, Eastern Antarctica. Parameters relating to chick survival (brooding nest counts, counts of chicks when two-thirds were crèched and fully crèched chick counts) display large temporal variability while other parameters, such as arrival counts and incubating nest counts, are more stable between years. The low degree of correlation between parameters collected before incubating nest counts with those collected after brooding nest counts reinforces the notion that events occurring during the hatching Within-season penguin weights, the simplest output from the Automated Penguin Monitoring System (APMS), were also examined in terms of their correlation with breeding success. Results indicate that low weights of females at the time they depart after egg laying appears to be the fi rst indication that a season may have low breeding success. The results obtained throughout these analyses indicate that knowledge of the sex of birds can be important for understanding breeding success and the interrelationships between CEMP parameters. |
This paper presents Maximum Entropy (MaxEnt) reconstructions of krill distribution and estimates of mean krill density within two survey boxes (dimensions 80 km × 100 km) north of South Georgia. The reconstructions were generated from line-transect acoustic survey data gathered in the boxes during austral summers from 1996 to 2000. Krill densities had previously been determined at approximately 0.5 km intervals along each of the ten 80 km transects in each box, providing about 1 600 density estimates per box. The MaxEnt technique uses an iterative Bayesian approach to infer the most probable krill density for each of the 32 000 0.5 × 0.5 km cells in each box, taking explicit account of the spatial relationship between densities in the observed data. Despite some very large interannual and regional differences in mean krill density, the MaxEnt approach works well, providing plausible maps of krill distribution. The maps reveal some consistent ‘hot spots’ of krill distribution, knowledge of which could aid the understanding of mechanisms influencing krill distribution, and hence krill/predator interactions. The MaxEnt technique also yields mean krill densities for each survey, for which the confidence limits are often narrower than those determined from conventional statistical analyses. |
In 2000 the UK started a Patagonian toothfish (Dissostichus eleginoides) tagging program to investigate the spatial and temporal movement of fish and to validate otolith-based growth estimates. Approximately 2 260 toothfish have been tagged and released during groundfish surveys and CCAMLR observer trips. This includes about 900 that have been injected with either strontium chloride or oxytetracycline that places a permanent chemical marker on the otolith indicating the date of injection and release. To date, 51 fish have been recaptured, mostly around Shag Rocks where there is greatest fishing activity. Most of the fish recaptured to date were tagged and released during experimental pot fishing in 2000 and 2001, and have been at liberty from one to two years. Four fish were tagged and recaptured from the same longline vessel in 2002 after up to two months at liberty. The fish tagged during the groundfish surveys may not yet be large enough to be available to the longline fishery and there have been no reported recaptures of these fish tagged at South Georgia or elsewhere in the South Atlantic. Similarly, D. eleginoides tagged and released on the Patagonian Shelf have not been recaptured at South Georgia. Fourteen tags have been recovered from a high seas area on the Patagonian Shelf at 42°S after about one year at liberty from some opportunistic tagging carried out on a toothfish pot vessel in international waters at that latitude in 2001. |
The diet of Antarctic toothfish (Dissostichus mawsoni) captured by bottom longline in the Ross Sea during the 2001 and 2002 fishing seasons was analysed (3 937 and 5 426 stomachs examined respectively). Fish sampled in 2001 were caught at depths of 317 to 2 154 m and ranged from 58 to 190 cm in total length (TL). Fish sampled in 2002 were caught at depths of 815 to 1 623 m and ranged from 62 to 197 cm TL. A high proportion of stomachs were empty (34% in 2001 and 49% in 2002) and the remaining stomachs often contained prey in advanced stages of digestion, making prey identification difficult. Fish were the most important prey category (%F = 86 in 2001 and %F = 77 in 2002), in particular icefish (family Channichthyidae) and Whitson’s rattail (Macrourus whitsoni). Squid, bait and prawns followed in importance in the diet. |
Antarctic toothfish (Dissostichus mawsoni) from the Ross Sea (CCAMLR Subarea 88.1) have been aged assuming that one translucent zone is formed annually in the otoliths of this species. However, no evidence to validate this assumption has previously been presented. In the current work, otoliths from four distinct juvenile length-frequency modes were examined, and the translucent zones counted. Zone counts were consistent within modes, and increased by one in each consecutive mode. This indicates that the modes represented year classes and that one translucent zone is formed annually in otoliths of juvenile D. mawsoni. Mean fish lengths at ages 0.5, 1.5, 2.5 and 3.5 years were estimated to be 14, 28, 37 and 46 cm total length (TL) respectively. These estimates agree with growth curves calculated previously from a sample of data that was large but lacked any fish younger than 3.5 years. Counting translucent zones in the otoliths of D. mawsoni appears to be a valid method for determining the age of this species. In addition, sagittal otoliths were examined from D. mawsoni that had been injected with oxytetracycline some years before recapture. The six recaptured fish were all large (129–145 cm TL at tagging) and had been at liberty from 1 to 7 years. The number of zones between the fluorescent oxytetracycline line and the otolith margin indicates that one translucent zone is formed annually in otoliths of post-mature D. mawsoni. |
Estimates of age and growth were obtained from 156 Macrourus carinatus otolith samples collected during two research voyages to Heard and McDonald Islands (Division 58.5.2) in 1992 and 1993. The range of estimated ages was 4 to 25 years. There were no significant differences in growth parameters calculated for males and females. Von Bertalanffy growth parameters for both sexes combined were: L∞ = 690 mm, K = 0.069 and t0 = -2.4. The size at sexual maturity of M. carinatus was determined from 162 specimens collected during commercial trawl fishing operations in the Heard Island region in 2000. The length at first maturity (L50) was 418 mm (total length) and the length at first spawning (Lm50) was 511 mm (total length), for both sexes combined. The length–weight relationship for M. carinatus from Heard and McDonald Islands was statistically different to that from Macquarie Island. Otolith and body size relationships are presented for M. carinatus from Heard and McDonald Islands. |