CCAMLR

We present information to investigate the significance of Antarctic toothfish as a prey item for Weddell seals in the Ross Sea. • We summarise the life history of Weddell seals to provide an overview of their use of the Ross Sea. As consumption of prey by Weddell seals (both the amount and type of prey) will vary between different life history stages at different times of the year in different areas, this is relevant to the question of whether seals predate significantly on toothfish. • There is evidence that Antarctic toothfish have lower densities near to seal breeding colonies in McMurdo Sound than further away (Testa et al. 1985). • Direct information on diet of the Weddell seals, including diver observations, animal-mounted camera information, and observations from field scientists in the McMurdo Sound region suggest that toothfish are a significant prey item for Weddell seals. • In contrast, research using seal stomach contents, vomit and scats provides no evidence that Weddell seals consume toothfish at all. Diver observations suggest that seals may feed selectively on only parts of toothfish so that otoliths and vertebrae may be under-represented in remains. • Indirect information using stable isotopes of carbon and nitrogen, even including recent analyses that have not been previously reported, remains inconclusive. We recommend further research using stable isotope analysis of blood samples from seals not at the breeding colonies, and samples of muscle or other slower-turnover tissue of seals at the breeding colonies. • Information from fatty acids or other biomarkers could potentially be used to investigate the importance of toothfish as a prey item for seals, but no results are available. • We have compared mortality of Antarctic toothfish in McMurdo Sound to consumption by Weddell seals. The estimates, although preliminary and subject to uncertainty, indicate that it is possible that toothfish comprise a substantial proportion of the diet of seals in McMurdo Sound between October and January. We conclude that while there is strong evidence that toothfish are a prey item for Weddell seals in McMurdo Sound between October and January, it is plausible but unproven that they are an important prey item.

We report on the development of a mass balanced carbon-budget trophic model of the Ross Sea as a step towards investigating ecosystem effects of the fishery for Antarctic toothfish (Dissostichus mawsoni). The model has 30 trophic groups representing all the major biota of the Ross Sea. Many of the lower trophic level species in the model are grouped by functional role because information is not available at greater taxonomic resolution. The model separates the following apex predators by species: Emperor penguin, Adélie penguin, crabeater seal, Weddell seal, orca, sperm whale, Antarctic toothfish. A survey of the available literature and both published and unpublished data provided an initial set of parameters describing the abundance (seasonally and spatially resolved where possible, imports, exports), energetics (growth, reproduction, consumption), and trophic linkages (diets, key predators) for each model group. We also estimated the relative level of uncertainty on these parameters. We describe the method we used to adjust the parameters to give a balanced model taking into account estimates of parameter uncertainty and the large range of magnitude (>6 orders of magnitude) in trophic flows between different groups of organisms. Biomass, production, consumption, export and diet fractions are adjusted simultaneously. We set ecotrophic efficiency to unity for all non-primary producers. Changes to the initial set of parameters needed to obtain balance were significant, especially for bacteria. Excluding bacteria, the adjustments required for balance from the parameters estimated a priori were <46% (biomass), <15% (production, consumption), and <28% (diet fractions). The balanced model presented here has not yet been validated and should be considered a work in progress.

The proportional krill recruitment index is updated from 2002 to present using data from the US AMLR surveys around Elephant Island, Antarctica. Proportional recruitment indices were derived from the CMIX procedure, and were also derived as a proportion of the <30 mm length class for day and night samples. All indices showed that high recruitment (R1) occurred in 2003 and in 2008, with low recruitment occurring during the intervening years. Significant differences in the proportional recruitment indices occurred between legs within years indicative of the changing pattern of krill within the Elephant Island region.

This document provides information on krill fishery behaviour and fishing ground condition in 1999/2000 season to assist consideration of the regional krill density and distributional conditions observed in the CCAMLR 2000 synoptic survey. The vessels seemed to have been moving around more compared to other fishing seasons to look for preferred targets. The 1999/2000 fishing season was the most mobile season in the last 10 years. Through the analysis of relation between catch level and vessel travel distance, it was suggested that Japanese vessels were catching average of 13-15 tonnes per tow within their preferred fishing concentration, which seemed to be the lower end of their preference.

10 years worth of recent finescale haul-by haul krill data were used to characterize behaviour of krill fishery. Analysis of travel distance in relation to catch level revealed a pattern that mean travel distances are longer after the least catch levels, and the travel distances decreases as catch level increases to certain catch levels but distance increase again above that catch level. However, this pattern only holds for operations by Japan. Preferred level of catch by Japan derived through the analysis was 15-30 tonnes/haul, which is higher than the 1980s information (5-10 tonne/haul). Other nations do not have a preference for an upper limit of catch. Locations of operations were very close even after considerable number of hauls. The scales of distance after 50 tows from the original tows were 10-15 nm, which is the scale of a single concentration. However, there was considerable year to year variability in the probabilities of operating within a local range after a number of tows. In the 1999/2000 season the probability that hauls would be made within a 30nm range after 300 hauls was only 0.1, but in the 2004/05 season it was 0.7. Fishery behaviour differentiates between market type considerations/strategies which are often the argument for changing fishing patterns and catching efficiency/operational requirements in an area. These kinds of analysis show the importance of good year-round data from observers from all vessels participating krill fishery to assist in interpreting the annual fishing results.

Conservation Measure 22-06 was adopted to ensure that significant adverse impacts of bottom fishing gear on Vulnerable Marine Ecosystems (VMEs) are avoided. In order to satisfy the requirements of CM 22-06 a method is proposed to notify CCAMLR of the presence of VMEs and their location using a simple pro-forma. Two VMEs identified during the Australian CEAMARC-CASO cruise are notified using this form from Statistical Area 58.4.1, SSRU H. The use of 5 nm buffer zones around the location of the observations is proposed to mitigate the risk of spatial uncertainty in the notified position and the deployment of bottom-fishing gear.

CCAMLR adopted a new conservation measure in 2007 (CM 22-06) to ensure that significant adverse impacts of bottom fishing gear on Vulnerable Marine Ecosystems (VMEs) are avoided. Due to the high levels of uncertainty surrounding both the evidence of VME presence and the consequences of interaction with different types of gear, a risk management framework is proposed, similar to that which has been used successfully by IMAF to minimise the effects of longline fishing mortality on seabirds. The aim of this risk management is to avoid significant adverse impacts on VMEs from bottom fishing activities. This paper provides definitions of VMEs and summaries of their characteristics including natural agents of disturbance, frequency of disturbance and longevity and growth rates of dominant habitat-forming organisms. The likelihood and consequences of bottom fishing activities, with associated uncertainties, is then analysed and evaluated using standard techniques. Different types of evidence of VMEs in the CCAMLR Area are used in the risk analysis. Risk mitigation can then be used to reduce risk to acceptable levels.

During the 9th research cruise of the R/V Kaiyo-maru, copepod samples were collected from three layers between the surface and 200 m with RMT 8m2 along the three longitudinal lines in the Ross Sea and its neighboring waters. Twenty three copepod species belonging to 13 families were identified and 8 unidentified taxa appeared in the study area. Samples were categorized into four major groups by cluster analysis based on species abundance and composition. Group 1 located in the north of the Southern Boundary of the Antarctic Circumpolar Current was characterized by high abundance (157.5-2279.5; mean 610.5 inds. 1000 m-3) and dominance of Rhincalanus gigas (mean 88.4%). Group 2 located off the Ross Sea (175°E; north of 72°S, 170°W; north of 75°S) was characterized by high abundance (22.6-1542.1; mean 301.9 inds. 1000 m-3) and high composition of Calanus plopinquus (mean 19.0%), Rhincalanus gigas (mean 23.2%) and Calanoides acutus (mean 38.7%). Group 3 and 4 located in the Ross Sea (175°E; south of 72°S, 170°W; south of 75°S) were characterized with low abundances (2.6-5.2; mean 3.6 inds. 1000 m-3, 6.5-50.6; mean 18.5 inds. 1000 m-3).

Distribution patterns and biomasses of Antarctic and ice krill in the Ross Sea in austral summer in 2005 were studied using a multi-disciplinary survey data set combining cetacean, krill and oceanography data. Two research vessels, KM and KS2, conducted the hydroacoustic surveys independently in the same area. Distribution patterns and length frequency information for two species were obtained from samples of RMT hauls and stomach contents of Antarctic minke whales. Ice krill was distributed on the continental shelf region (shallower than 1000m water depth). In contrast, Antarctic krill was distributed mainly in the oceanic waters where water depth is deeper than 1000m though it distributed on the continental shelf where the mean water temperature between 0-200m was higher than -1°C. The Ross Sea was stratified into two strata based on the distribution patterns of two krill species to estimate their biomasses. Biomass densities of Antarctic krill using KM and KS2 data were estimated as 5.13±7.14 and 2.53±2.25 g/m2, respectively. Biomass densities of ice krill using KM and KS2 data were estimated as 2.58±1.47 and 1.13±0.65 g/m2, respectively. Because there was no significant difference between the biomass density estimates from both vessels, two data sets were combined to estimate the biomass. The biomasses of Antarctic and ice krill in this study were estimated as 1.40 (CV=0.32) and 0.60 (CV=0.18) million t, respectively. School sizes of Antarctic minke whales were large where the densities of Antarctic krill were high. Distribution pattern of Antarctic minke whales in the Ross Sea could be regulated by distribution patterns of Antarctic krill.

A work plan to establish an observer scheme for krill fishery was agreed at the previous Scientific Committee and the Commission. The first step was to consider ‘systematic coverage’ of the observers. In this document, Japan proposes a framework for scientific observer system for krill fishery in order to obtain ‘systematic coverage’.