CCAMLR

In this paper, we address a number of aspects of the model inputs and parameters of the Antarctic toothfish stock assessment for the Ross Sea fishery. In particular we review catch history, length-weight relationships, catch-at-length and catch-at age. In addition, we report some preliminary model runs that investigate the sensitivity of the 2006 stock assessment to changes in these model inputs and parameters.
Tree-regression methods were used to investigate the areal structure of the length distribution of Antarctic toothfish. While tree-regressions suggested strong evidence of a high degree of small-scale areal complexity, we were unable to provide a stratification that resulted in improved or consistent patterns in length frequencies over the duration of the fishery. Including terms for nation, vessel, or vessel type did not provide any additional information as these tended to be highly correlated with the location variables.
The catch and CPUE indices for the Ross Sea Antarctic toothfish fishery were updated, as are some modelling parameters, and methods for calculating age- and length-frequencies. Most of these changes did not have a significant impact on the assessment results.
We also provide an update of the numbers of fish scanned at length by New Zealand vessels, and the numbers of tagged fish recaptured. Inclusion of observations of the 2006 fish recaptured in 2007 had the greatest impact on the assessment model results. Dunn et al. (2007) noted that the locations of the 2007 recaptures were highly aggregated and were mostly located on four key locations in the Ross Sea, and most had moved only short distances. This confirms the concern that the key uncertainty underlying the current model is the impact of movements and spatial structure in the Antarctic toothfish population. In particular, the level and nature of the bias from non-homogeneous mixing assumptions of tagged fish.

Descriptive analyses of the toothfish tagging programme carried out in Subareas 88.1 and 88.2 since 2001 are updated. The paper provides a preliminary update of the tag-release and tag-recapture data that were presented at the October 2006 meeting of WG-FSA by including data from New Zealand vessels and preliminary data for other vessels that fished in 2007.
Release and recapture data that previously were unavailable for about half of the non-New Zealand vessels for 2004 are now available and described in this paper for the first time. Overall, a reported total of 12 177 Antarctic toothfish have been released and 333 recaptured, and 859 Patagonian toothfish released and 29 recaptured since 2001.
The number of tags recaptured in the Ross Sea in 2007 by New Zealand vessels was the highest annual recapture to date and double the number caught in 2006, although the nature of these recaptures suggests that assumptions of homogeneous mixing may need to be investigated. For the first time, long distance movements of Antarctic toothfish were observed from fish tagged by fishing vessels. A total of four fish moved significant distances from the slope fisheries in SSRUs 88.1H, 88.1I, and 88.1K to Terra Nova Bay in SSRU 88.1J. There was also some evidence that more fish are recaptured after a longer time at liberty on the slope than in the North.
However, we note that data from the 2007 season for the non-New Zealand vessels were incomplete at the time of this analyses and will need to be updated in future analyses.

This report presents the data and preliminary results from developmental model for Antarctic skates in SSRUs 88.1H, 88.1I, 88.1J, & 88.1K of the Ross Sea. The developmental model attempted to create a catch history of all skates and rays in the Ross Sea, and integrate these data with the available observational data (including tag-recapture data) into a single integrated stock assessment model.
We conclude that aspects of the catch history were very uncertain, including the species composition, the weight and number of skates caught, the proportion discarded, and the survival of those tagged or discarded. The size composition of the commercial catch was also very uncertain because of the low numbers sampled each year. Most aspects of the tagging data were also uncertain including the actual numbers of skates released, the initial mortality of tagged skate, the tag loss rate, and the numbers of skates scanned for tags. While updated summaries of the numbers of skate tag releases and recaptures have been reported, these data are still preliminary, and further work is required. Lastly, there is great uncertainty over the biological parameters including age and growth, natural mortality, steepness, and size and age at maturity.
The applicability of a general model, such as presented here, to a multi-species catch has not been investigated. While is it plausible that a general model may be adequate if the productivity parameters of the different species of skates and rays are similar, we conclude that additional research is required to investigate the usefulness of such models. We also make a number of suggestions for areas where better data are required. These include recommending work that would improve species identification, increasing the detection rate of tagged skates, increasing the number of skates measured and sexed, validating estimates of age and growth, revising the skate tagging protocols, and undertaking more extensive skate survivorship experiments.

Antarctic krill, Euphausia superba Dana, has a heterogeneous circumpolar distribution in the Southern Ocean. Krill have a close association with sea ice which provides access to a critical food source and shelter, particularly in the early life stages. Advective modelling of transport pathways of krill have until now been on regional scales and have not taken explicit account of sea ice. Here we present Lagrangian modelling studies at the circumpolar scale that include interaction with sea ice. The advection scheme uses ocean velocity output from the Ocean Circulation and Climate Advanced Modelling (OCCAM) project model together with satellite-derived sea ice motion vectors to examine the potential roles of the ocean and sea ice in maintaining the observed circumpolar krill distribution. We show that the Antarctic Coastal Current is likely to be important in generating the large-scale distribution and that sea ice motion can substantially modify the ocean transport pathways, enhancing retention or dispersal depending upon location. Within the major krill region of the Scotia Sea, the effect of temporal variability in both the ocean and sea ice velocity fields is examined. Variability in sea ice motion increases variability of influx to South Georgia, at times concentrating the influx into pulses of arrival. This variability has implications for the ecosystem around the island. The inclusion of sea ice motion leads to the identification of source regions for the South Georgia krill populations additional to those identified when only ocean motion is considered. This study indicates that the circumpolar oceanic circulation and interaction with sea ice is important in determining the large-scale distribution of krill and its associated variability.

Management of human impacts in the Antarctic requires an effective system of monitoring to provide information about the process being managed and the effectiveness of management actions. Human impacts arise as a result of processes that originate in the region (endogenous) and those that originate outside the region (exogenous). A number of monitoring programmes have been established in both terrestrial and marine systems to measure impacts that arise as a result of endogenous process such as fishing, tourism and research. However, most of this monitoring is surveillance monitoring, which is not linked to a specific management objective, and does not produce quantitative metrics that can be assessed and compared to agreed targets. However, defining such target levels for the Antarctic, where the aim is to minimise human impacts, is a complex process. Although potential analogues for target setting exist in other parts of the world these are generally insufficiently precautionary to be applied in the Antarctic. The challenge for scientists and policymakers working in the Antarctic is to provide quantitative measures, with agreed trigger levels, and to develop appropriate monitoring schemes to manage human impacts in the future.

The Scotia Sea ecosystem is a major component of the circumpolar Southern Ocean system, where productivity and predator demand for prey are high. The eastward-flowing Antarctic Circumpolar Current (ACC) and waters from the Weddell–Scotia Confluence dominate the physics of the Scotia Sea, leading to a strong advective flow, intense eddy activity and mixing. There is also strong seasonality, manifest by the changing irradiance and sea ice cover, which leads to shorter summers in the south. Summer phytoplankton blooms, which at times can cover an area of more than 0.5 million km2, probably result from the mixing of micronutrients into surface waters through the flow of the ACC over the Scotia Arc. This production is consumed by a range of species including Antarctic krill, which are the major prey item of large seabird and marine mammal populations. The flow of the ACC is steered north by the Scotia Arc, pushing polar water to lower latitudes, carrying with it krill during spring and summer, which subsidize food webs around South Georgia and the northern Scotia Arc. There is also marked interannual variability in winter sea ice distribution and sea surface temperatures that is linked to southern hemisphere-scale climate processes such as the El Niño– Southern Oscillation. This variation affects regional primary and secondary production and influences biogeochemical cycles. It also affects krill population dynamics and dispersal, which in turn impacts higher trophic level predator foraging, breeding performance and population dynamics. The ecosystem has also been highly perturbed as a result of harvesting over the last two centuries and significant ecological changes have also occurred in response to rapid regional warming during the second half of the twentieth century. This combination of historical perturbation and rapid regional change highlights that the Scotia Sea ecosystem is likely to show significant change over the next two to three decades, which may result in major ecological shifts.

This paper is a published book chapter examining how goals and reference points might be set for higher trophic levels – such as marine mammals, birds and fish. It briefly explores the general characteristics of objectives for higher trophic levels within the context of ecosystem-based management, noting that the emphasis for managing the effects of human activities on higher trophic levels is biased towards fisheries-based approaches rather than approaches that take into account the maintenance of ecosystem structure and function. Following this, the precautionary approach developed in the Commission for the Conservation of Antarctic Marine Living Resources (CCAMLR) for taking account of higher trophic levels in setting catch limits for target prey species is described. The last section considers indicators of the status of predators with respect to establishing target and limit/threshold reference points that can be used directly for making decisions. These indicators include univariate indices summarising many multivariate parameters from predators, known as composite standardized indices, as well as an index of predator productivity directly related to lower trophic species affected by human activities.