CCAMLR

This document outlines the preliminary results of an Australian survey of CCAMLR Division 58.4.2 (the South West Indian Ocean Sector of the Southern Ocean 30-80°E) in January-March 2006, which was designed around an acoustic biomass survey for krill and a large-scale oceanographic survey. The survey is intended to produce a new estimate of krill biomass (B0) for this Division so that a revised precautionary catch limit can be established by CCAMLR. The survey utilised a standardised design as adopted in previous B0 surveys in the CCAMLR Area and was designed so that the results would be compatible with the 1996 BROKE (Baseline Research on Oceanography, Krill and the Environment) survey of the adjacent CCAMLR Division 58.4.1 which collected information on a wide range of ecological parameters. The survey was conducted from a single ship, the RSV Aurora Australis, and consisted of 11 meridional transects, between 30° and 80°E. On each transect a range of underway data were obtained and on six transects detailed sampling was conducted at predetermined stations. This background paper provides an overview of what was achieved by this survey; the detailed results are currently being analysed and are being prepared for a special Issue of Deep-Sea Research for publication in 2008.

We report on the further development of a carbon-budget trophic-model of the Ross Sea with which to investigate effects of the fishery for Antarctic toothfish (Dissostichus mawsoni). The Ross Sea is a low primary production system, with production being localised in space and time. In the relative absence of krill, Antarctic silverfish (Pleuragramma antarctica) are probably the major middle-trophic level link between primary production and the larger predators. Mesozooplankton (mainly copepods), and demersal fish (especially, Macrourus whitsoni, Bathyraja eatonii, Chionodraco hamatus, C. antarcticus) are other key linking species. The trophic model presented here is not complete and should be considered a work in progress. Overall, the model is close to balance, with total exports of organic carbon (mainly respiration) exceeding primary production by 7%. However, individual groups are generally not balanced, due in part to limited information on diet fractions of Ross Sea organisms. Methods to adjust diet fractions to take into account the relative abundances of prey items are suggested but not applied. The current version of the trophic model suggests that Antarctic toothfish have the potential to exert considerable predation pressure on some species of demersal fish. The significance of toothfish in the diets of predators (especially Weddell seal, type-C killer whale, sperm whale) cannot be tested reliably by the current version of the model, which is not spatially or seasonally resolved, and does not consider sub-populations of predators. More complete information on the abundances and diets of top predators in the Ross Sea are needed, especially with regard to the spatial, seasonal and interannual variability of these properties, and the population structures. Other recommendations for fieldwork, and work currently underway or planned by New Zealand scientists in the Ross Sea, are given.

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, Argentina, and Base Esperanza, 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 March 2006. We also tried to making comparison between DPOI and oceanic condition of the surface layer around the South Shetland Islands, and suggested response from DPOI to the oceanic condition.

A Spatial Multi-species Operating Model (SMOM) of the underlying krill-predator-fishery dynamics is developed in response to requests for scientific advice regarding the subdivision of the precautionary catch limit for krill among 15 small-scale management units (SSMUs) in the Scotia Sea to reduce the potential impact of fishing on land-based predators. The model is intended to complement the outputs from the KPFM. The model includes all 15 SSMUs and uses an annual timestep to update the numbers of krill in each of the SSMUs, as well as the numbers of predator species in each of these areas. The model currently includes only two predator groups (penguins and seals) but is configured so that there is essentially no upper limit on the number of predator species which can be included. Given the numerous uncertainties regarding the choice of parameter values, a Reference Set is used in preference to a single Reference Case operating model. The initial Reference Set used comprises 12 alternative combinations that essentially try to bound the uncertainty in the choice of survival estimates as well as the breeding success relationship. The model is coded in AD Model Builder and quickly generates large numbers of stochastic replicates to explore different hypotheses such as that related to the transport of krill. The SMOM developed here is intended for use as an operating model in a formal MP framework described in an accompanying paper. Different MPs are simulation tested with their performances being compared on the basis of an agreed set of performance statistics which essentially compare the risks of reducing the abundance of predators below certain levels, as well as comparing the variability in future average krill catches per SSMU associated with each MP.

This report presents results from a pilot study to investigate the use of acoustics to estimate middle trophic level prey organisms (e.g., krill and mesopelagic fish) in the Ross Sea. Single frequency (38 kHz) acoustic data were available from New Zealand longline vessels participating in the exploratory fishery for toothfish in 2002–03 and 2005–06, and multifrequency (12, 38, and 120 kHz) acoustic data were collected from the research vessel Tangaroa during a voyage to the western Ross Sea in February–March 2006. Analyses were carried out to assess data quality, describe different mark types, and quantify spatial and vertical distribution of acoustic backscatter in the upper 1000 m of the water column.
There were clear spatial patterns in the amount and type of mesopelagic backscatter observed. There was much more backscatter in the upper 1000 m and a wider variety of mark types north of 67° S. Common mark types in the northern region included a surface layer at less than 50 m depth, schools and layers centred on about 200 m and 400 m depth, and a diffuse deep scattering layer centred at 750 m depth. Average acoustic density was lower south of 70º S, and most of the backscatter was from schools and layers shallower than 100 m. Near bottom marks were associated with areas shallower than 1000 m on the Ross Sea shelf edge. In general, the amount of backscatter observed in the Ross Sea was much lower than that observed in shelf areas off New Zealand (Chatham Rise and Campbell Plateau).
Little direct information is available on the species composition of different mark types in the Ross Sea. However, different acoustic responses across the three frequencies available on Tangaroa provided some clues about the likely identity of the key scatterers. Marks shallower than 100 m depth were typically much stronger on 120 kHz than on 38 kHz, and weak on 12 kHz. This type of acoustic response is typical of krill or other large zooplankton. Schools and layers at 200–400 m depth showed a more consistent response across all three frequencies and may have been associated with small fish. This study identified key areas and mark types for further research, including directed sampling, and showed how fishing vessels could be used to opportunistically collect acoustic data.

A standardized krill net sampling survey was conducted in the Lazarev Sea (Subarea 48.6) in December 2005. Krill densities were low in the Lazarev Sea. No substantial day/night differences were observed in the catches. Spatial distribution of krill density and size/age classes is discussed for the Lazarev Sea. Recruitment indices were calculated for one-year-old (R1) and two-year-old krill (R2), showing high values for both recruitment indices. New information is given on the development of maturity stages in the early phase of the spawning season.

Cape fur seals (Arctocephalus pusillus) were estimated to kill some 6 000 Cape gannet (Morus capensis) fledglings around Malgas Island in the 2000/01 breeding season, 11 000 in 2003/04 and 10 000 in 2005/06. This amounted to about 29%, 83% and 57% of the overall production of fledglings at the island in these breeding seasons, respectively. Preliminary modelling suggests this predation is not sustainable. There was a 25% reduction in the size of the colony, the second largest of only six extant Cape gannet colonies, between 2001/02 and 2005/06. There has been a large increase in predation by Cape fur seals on seabirds around southern African islands since the mid 1980s, coincidental with both an increase in the seal population and altered management of the islands. At Malgas Island, most gannet fledglings were killed between 10h00 and 18h00, the period when most are in the water around the island, from mid January to mid March, the main fledging period. The Cape gannet is classified as Vulnerable.

We used radio telemetry and observations to study the activity patterns and behaviour of gentoo penguin chicks during their “fledging period”; defined as the time between a chick’s first trip to sea and its final dispersal from the breeding colony. Our study was conducted at a colony of approximately 2500 breeding pairs of gentoo penguins in Admiralty Bay, King George Island, South Shetland Islands during the 2004-05 austral summer. Gentoo penguins exhibited delayed dispersal of young coupled with extended parental provisioning, behaviours not observed in other Pygoscelis species. Chicks took their first trip to sea at a mean age of 70 days of age, before finally departing the colony at an average age of 82 days. During this fledging period, individual chicks made an average of five trips to sea. Trip duration increased significantly with chick age as trips to sea becoming more similar to adult foraging trips in both timing and duration. Behavioural observations confirmed that many chicks were still being fed during this fledging period, with parental feeding behaviours most often observed in the late afternoon to evening hours. We hypothesize that these behaviours not only provide the opportunity for chicks to gain experience at sea prior to dispersal, but also allow them to develop foraging behaviours and skills at this time. These results have implications to differences in life history traits and population trends among gentoo penguins and their congeners, the Adélie and chinstrap penguins.

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This paper summarises the notifications received from Members intending to particpate in the krill fishery in Area 48 in the 2006/07season.