CCAMLR

An assessment of the environmental processes influencing variability in the recruitment and density of Antarctic krill (Euphausia superba DANA) is important as variability in krill stocks affects the Antarctic marine ecosystem as a whole. Naganobu et al. (1999) had assessed variability in krill recruitment and density in the Antarctic Peninsula area with an environmental factor; strength of westerly winds (westerlies) determined from sea-level pressure differences across the Drake Passage, between Rio Gallegos (51°32’S, 69°17’W), Argentina, and Base Esperanza (63°24’S, 56°59’W), at the tip of the Antarctic Peninsula during 1982-1998. Fluctuations in the westerlies across the Drake Passage were referred to as the Drake Passage Oscillation Index (DPOI). They found significant correlations between krill recruitment and DPOI. Additionally, we calculated a new time series of DPOI from January 1952 to May 2003.

This paper responds to a request (WG-EMM-02 paragraphs 3.46 to 3.47) for standard methods for determining demographic parameters. It is noted the methods (CEMP A4) as published in CEMP Standard Methods 2003 appear adequate. Revision may be required in the future following consideration of how aspects of predator demographics may be used for management in the CCAMLR context. The considerable tagging and search effort required to obtain demographic data and the period over which such effort needs to be sustained is described.

Parameters measured under the CCAMLR Ecosystem Monitoring Program (CEMP) for Adélie penguins at the Béchervaise Island CEMP site were compared between seasons of contrasting krill availability. Krill biomass estimates were derived from shipboard surveys carried out within the penguins’ normal foraging range during the 2001 and 2003 breeding seasons. More than three times as much krill was present during the two-week survey period in 2001 than in 2003. Penguin parameters that showed significant differences between the two seasons included A5: foraging trip duration, A6: breeding success and A8: meal mass and dietary composition. Penguins travelled further to forage in 2003 than 2001, stayed away longer and brought back smaller meals. Fish (mostly Pleuragramma antarcticum) contributed significantly to the diet in 2003 but was only a minor component in 2001. Differences between years were particularly apparent during the late guard to early crèche stages of chick rearing, coinciding with the timing of the krill survey. Chick mortality peaked during this period also. The findings illustrate the sensitivity of parameters A5 and A8 to prey availability during the short time scale of the chick rearing period. Data on meal mass and foraging trip duration were combined to provide an index of provisioning rate, analogous to the functional response referred to in predator-prey theory. This showed the expected concave monotonic relationship to krill biomass over the period of investigation. These results are discussed in relation to aspects of foraging behaviour, monitoring programs and management issues.

The ability to use upper-trophic level species as ecosystem indicators is determined by the ability to relate changes in indices of their performance to changes at lower trophic levels. Using indices of predator performance from four species of krill-eating predator together with independent ship-based acoustic estimates of krill abundance from South Georgia the relationship between a range of indices of predator performance and krill abundance was examined. There was a distinct relationships between the variability of indices and the biological processes that they measured; body mass parameters had the lowest variability (CV 50 %. Predator parameters that reflected processes occurring during the summer showed the closest relationship with krill abundance, especially those for species with foraging ranges similar to spatial scales at which krill surveys were undertaken. Population size parameters showed no functional response relationship with annual krill abundance estimates. Combining the summer parameters into a single combined index provided a better fit with the krill data than any of the individual parameters.

Mackerel icefish have been harvested in the CCAMLR Region for over thirty years. In the Atlantic sector of the Southern Ocean they feed preferentially on krill and are themselves preyed upon by fur seals and several avian species. These attributes make them suitable for consideration within the CEMP. With that in mind the following indices are outlined that might be incorporated in the programme: Standing Stock, Cohort Strength and Recruitment, Natural Mortality, Length at Age 1+ and 2+ years, Condition, Gonad Maturity and Diet

Exchange of 61 wandering albatrosses Diomedea exulans has been recorded between the French Crozet Islands and the South African Prince Edward Islands, 1 068 km apart in the Southern Ocean. Most movements of banded birds (57) have been westwards, from the Crozets to the Prince Edwards. In all, 18 fledglings banded at Possession Island, Crozets, have bred at Marion Island, Prince Edwards, but only one fledgling from Marion Island has been recorded breeding on Possession. The wandering albatrosses of the two island groups form a metapopulation that ideally should be conserved as a single unit. Its is suggested that France and South Africa collaborate through the Agreement on the Conservation of Albatrosses and Petrels to effect an improved conservation status for the wandering albatrosses of the two island groups.

Krill length frequency distribution through subarea 48.3 in 1988 January-February is considered in the frame of hypothesis of krill resources forming from two sources: Antarctic Circumpolar Current and Weddell Scotia Sea water flow. It is shown, that small krill with the mode of about 33 mm is distributed in the coastal zone of about 7-40 miles wide, further is situated the boundary zone at the distance of about 30-60 miles, beyond boundary zone occurs larger krill with the mode of about 49 mm. Krill length frequency distribution is unimodal in the coastal and off-shore zones and bimodal in boundary zone. Krill distribution well corresponds to the water flows mentioned. Further analyses revealed heterogeneity in Weddell Sea krill distribution, there are spots of krill of increased length, where krill is retained for certain time and have a possibility to grow longer. Difference in krill length in such spots and main water flow may reach 6 mm. Such spots may be considered as initial stage of krill aggregations forming inside quasi-stationary vortices, further development of this scenario leads to the creation of commercially important krill aggregations.

Heart rate (fH), abdominal temperature (Tab) and diving depth were measured in thirteen free-ranging breeding female macaroni penguins. Measurement of these variables allowed estimation of the mass-specific rate of oxygen consumption (VO2) while diving and investigation of the physiological adjustments that might facilitate the diving behaviour observed in this species. In common with other diving birds, macaroni penguins showed significant changes in fH associated with diving, and these variables accounted for 36% of the variation in dive duration. When VO2 was calculated for dives of different durations, 95.3% of dives measured were within the calculated aerobic dive limit (cADL) for this species. Mean fH for all complete dive cycles was 147±6 beats min–1. When this fH is used to estimate VO2 of 26.2±1.4 ml min–1 kg–1 then only 92.8% of dives measured were within the cADL. Significant changes in abdominal temperature were not detected within individual dives, though the time constant of the measuring device used may not have been low enough to record these changes if they were present. Abdominal temperature did decline consistently during bouts of repeated diving of all durations and the mean decrease in Tab during a diving bout was 2.32±0.2°C. There was a linear relationship between bout duration and the magnitude of this temperature drop. There was no commensurate increase in dive duration during dive bouts as Tab declined, suggesting that macaroni penguins are diving within their physiological limits and that factors other than Tab are important in determining the duration of dives and dive bouts. Lowered Tab will in turn facilitate lower metabolic rates during diving bouts, but it was not possible in the present study to determine the importance of this energy saving and whether it is occurs actively or passively.

The study examined the distribution of critical habitat for foraging by female Antarctic fur seals breeding at the island of South Georgia. Bathymetric features of the continental shelf around the island of South Georgia were an important indicator for the localisation of foraging. This pattern was consistent among years of different prey availability. Lactating females were constrained to forage mainly within 100 km of the location at which the offspring was being raised. When this constraint was removed at the end of lactation, females foraged to much greater ranges and dispersed to specific regions of the continental shelf east of Patagonia (>1000 km) and to the northern edge of the Antarctic pack ice (500 km). The empirical distribution of foraging during the breeding season was used to develop a function that described the foraging distribution for the whole breeding population of females. The result was consistent with past observations from ship-based surveys and it allowed estimation of the spatial impact of breeding female fur seals on krill at South Georgia. This suggested that, in extreme cases and assuming that krill influx is limited, female fur seals could eat most of the krill present in some regions where they forage intensively. However, mean consumption was about one-tenth of the mean density of krill.

Chinstrap penguins Pygoscelis antarctica are one of the major consumers of Antarctic krill Euphausia superba in the Southern Ocean. To examine their foraging strategy, we studied foraging trip patterns and diving behaviour of chinstrap penguins breeding at Signy Island, Antarctica, using time-depth recorders. Foraging trips of penguins could be divided into 2 groups, short diurnal (7.8 h) and longer overnight (19.9 h) trips, with diurnal trips (74%) being dominant in number (263 out of 355 trips). The diving depths of our study birds were much deeper (to 179 m) than previous studies on this species, with modal maximum dive depth at around 90 to 100 m. Diving patterns and profiles included typical pelagic dives, but also included series of consecutive square-wave shaped dives reaching similar maximum depth, the typical characteristics of benthic dives. These benthic-type dives were more abundant in diurnal foraging trips than overnight trips. Analysis of stomach contents showed that penguins on both types of trip fed almost exclusively on Antarctic krill. There was a positive relationship between indices of the proportion of benthic feeding and of foraging efficiency (stomach content mass divided by foraging trip duration). These results highlight the potential importance of benthic feeding on Antarctic krill, the first such recorded instance for chinstrap penguins. This previously undescribed foraging strategy by one of the major avian consumers of Antarctic krill provides a new insight into the predator-prey interactions of the Antarctic coastal marine ecosystem.