Belchier, M., T. Peatman and J. Brown (2012), The biology, ecology and development of fishery management advice for the anomuran crabs at South Georgia (CCAMLR Subarea 48.3)

This review summarises the available information on the biology and ecology of the lithodids at South Georgia and provides an overview of the development of a management regime for them. Finally it aims to highlight areas in which further research should be directed in order to provide information on which to base the most appropriate assessment and management methods in light of continuing interest in the regional crab fishery. Considerable gaps in our knowledge of the biology, ecology and demography of the lithodid species at South Georgia remain. Uncertainty surrounds estimates of biomass, growth rates and long-term survivorship of discards of the targeted species. In addition, there is doubt surrounding the identification of the less frequently caught species. The ecosystem interactions and function of all lithodids in the region remain poorly understood with great uncertainty surrounding their trophic ecology and life histories. Recent analyses suggest that the current precautionary catch limit may not be sustainable in the long term if it were reached consistently. Further research to address many of the areas outlined above should be undertaken if there is continued interest in the fishery. However, low market value and interest coupled with the very high level of discarding are likely to render the fishery commercially unviable.

Webber, D.N. and S.J. Parker (2012), Estimating unaccounted fishing mortality in the Ross Sea region and Amundsen Sea (CCAMLR Subareas 88.1 and 88.2) bottom longline fisheries targeting Antarctic toothfish

Stock assessments rely on estimates of total mortality resulting from fishing activities. However, fish that are captured by fishing gear that is not subsequently retrieved are generally not counted in estimates of total fishing removals or otherwise accounted for in stock assessment models. The mortality resulting from the loss of sections of bottom longline gear in the Ross Sea region and Subarea 88.2 Antarctic toothfish (Dissostichus mawsoni) fisheries is not currently known. A method to estimate unaccounted fishing mortality from lost lines in these fisheries is provided. These estimates suggest that on average 208 tonnes of Antarctic toothfish mortality may be unaccounted for annually. While the current estimates may be improved through the adoption of better data reporting practices, these estimates were incorporated as sensitivity analyses in the 2011 stock assessments for the Ross Sea region and Subarea 88.2 toothfish fisheries.

Okuda, T. and M. Kiyota (2012), Analysis of variability of krill size and fish by-catch in the Japanese krill fishery based on scientific observer data

To estimate the optimal relative sample size of scientific observer data collected on Antarctic krill commercial fishing vessels, the relationship between statistical precision and sample size was estimated by using variance component analysis. Observer datasets from the Japanese krill fishery from 1995 to 2008 were analysed using a hierarchical Bayesian model. The models were composed of multistage cluster units (i.e. year, subarea, vessel, cruise and haul) based on a state–space model, separating biological process error in the population dynamics from fishery process as observation error. In both krill length and by-catch fish number, the parameters estimated by the Markov chain Monte Carlo (MCMC) method hardly show difference among years, subareas and vessels. The potent interaction effect between year and subarea suggests large spatio–temporal variability in the size structure of the krill population, which is presumably derived from large variability of recruitment causing difficulty in predicting krill population dynamics. Variances of observer datasets were calculated by the multistage sampling formula with the variance terms derived from the Bayesian model. For both krill length and by-catch fish number, vessel sample size shows marked effects on the coefficient of variation (CV), although haul sample size affects CV for only krill length data up to 10% haul coverage. These results suggest that data collection by scientific observers on board commercial vessels provides important information for the management of krill resources and the Antarctic ecosystem, while further discussion is needed about the optimal relative sample size to ensure the statistical precision required for the specific objective of a study that includes consideration of the cost of observer deployment.

Southwell, C., J. Bengtson, M. Bester, A.S. Blix, H. Bornemann, P. Boveng and M. Cameron, J. Forcada, J. Laake, E. Nordøy, J. Plötz, T. Rogers, D. Southwell, D. Steinhage, B.S. Stewart and P. Trathan (2012), A review of data on abundance, trends in abundance, habitat use and diet of ice-breeding seals in the Southern Ocean (submitted to the 2008 Joint CCAMLR-IWC Workshop)

The development of models of marine ecosystems in the Southern Ocean is becoming increasingly important as a means of understanding and managing impacts such as exploitation and climate change. Collating data from disparate sources, and understanding biases or uncertainties inherent in those data, are important first steps for improving ecosystem models. This review focuses on seals that breed in ice habitats of the Southern Ocean (i.e. crabeater seal, Lobodon carcinophaga; Ross seal, Ommatophoca rossii; leopard seal, Hydrurga leptonyx; and Weddell seal, Leptonychotes weddellii). Data on populations (abundance and trends in abundance), distribution and habitat use (movement, key habitat and environmental features) and foraging (diet) are summarised, and potential biases and uncertainties inherent in those data are identified and discussed. Spatial and temporal gaps in knowledge of the populations, habitats and diet of each species are also identified.

Ratcliffe, N. and P. Trathan (2012), A review of the diet and at-sea distribution of penguins breeding within the CAMLR Convention Area (submitted to the 2008 Joint CCAMLR-IWC Workshop)

Managing fisheries in an ecologically sensitive manner demands that catches do not depress stocks within the foraging areas used by predators to levels that reduce their reproductive success or survival. Spatially–explicit bioenergetics models that estimate the amount of prey consumed by predators are required to inform such policy. These models require information on the number of predators in a population, their nutritional demands, their diet composition and their seasonal distribution in the marine environment. This paper reviews all published information on the diet and at-sea distribution of the six penguin species that breed in the CAMLR Convention Area, the methods used to collect these data and the uncertainties inherent in them. The review will be of utility to modellers as a source of parameters, and to penguin biologists by providing comparative information for their own findings and by highlighting significant gaps in existing knowledge and methods that could be used to fill these.

Kock, K.-H., E. Barrera-Oro, M. Belchier, M.A. Collins, G. Duhamel, S. Hanchet, L. Pshenichnov, D. Welsford and R. Williams (2012), The role of fish as predators of krill (Euphausia superba) and other pelagic resources in the Southern Ocean (submitted to the 2008 Joint CCAMLR-IWC Workshop)

Krill forms an important part of the diet of many Antarctic fish species. An understanding of the role of fish as krill predators in the Southern Ocean is critical to understanding how changes in fish abundance, such as through fishing or environmental change, are likely to impact on the food webs in the region. First attempts to estimate the krill and pelagic food consumption by Antarctic demersal fish in the low Antarctic were made in the late 1970s/early 1980s. Those estimates were constrained by a paucity of biomass estimates and the mostly qualitative nature of food studies. Food consumption estimates were extended to the mesopelagic realm and the high-Antarctic Zone in the late 1980s and early 1990s when these areas were exploited commercially for Electrona carlsbergi. Currently, the
best estimates of annual krill consumption by fish are 23 000 000–29 000 000 tonnes of krill and other pelagic prey taken annually by demersal fish in the 1980s in the whole Southern Ocean, and 5 000 000–32 000 000 tonnes taken by mesopelagic fish in the Atlantic sector of the Southern Ocean.

It is clear from this review that fish are important predators of krill, in particular the larger myctophids and some channichthyids and nototheniids, and that the importance of krill in fish diets varies substantially both with time and location on various scales, as well as with the availability of alternate prey in the different regions in the Southern
Ocean. Ecosystem models therefore need to account for their role. However, several key areas of uncertainty exist, which need to be considered in ecosystem and food-web models for the Southern Ocean. For instance, no robust estimates of food consumption by mesopelagic fish can be provided for the vast areas of the Indian and Pacific Ocean sectors, or for several of the most abundant myctophid species in the Atlantic sector, due
to the paucity of relevant studies in these regions. Where biomass estimates do exist, such as in the Atlantic sector, there can be a lack of precision in trawl and hydroacoustic surveys. Studies that adequately capture the seasonal variation in consumption rates and changing importance of krill in the diet of fish are also rare. Furthermore, the effects of large changes in abundance and community structure of fishes brought about by industrial
fishing need to be considered when evaluating patterns that have emerged in Southern Ocean ecosystems in the course of the 20th century.

As a first step towards a modelling approach to include fish in krill-based food-web models, it is suggested to incorporate data on Champsocephalus gunnari from the western Atlantic sector and Dissostichus mawsoni from the Ross Sea into modelling approaches within the CCAMLR Ecosystem Monitoring Program. Both species are important predators of krill (C. gunnari) and fish (D. mawsoni) in turn form key prey for top predators in each region.

Atkinson, A., P. Ward, B.P.V. Hunt, E.A. Pakhomov and G.W. Hosie (2012), An overview of Southern Ocean zooplankton data: abundance, biomass, feeding and functional relationships (submitted to the 2008 Joint CCAMLR-IWC Workshop)

There is an enormous amount of data on Southern Ocean (SO) zooplankton, mostly on their distribution with a minority addressing rate processes. This review aims to summarise these data and show where it resides, to assist SO food-web modellers or those with limited specialist knowledge of SO zooplankton. First, a brief overview is provided of the diversity and basic biology of SO zooplankton, with an emphasis on abundance, distribution and feeding. Second, advice is provided on the uses, strengths and limitations of zooplankton data as inputs to SO data compilations or food-web models. Copepods overall comprise >75% of the SO zooplankton biomass (excluding Euphausia superba). Total mesozooplankton biomass density differs little between the Antarctic sectors, but latitudinally it is maximal in the Polar Frontal Zone and declines to the north and south. Those compiling data on numerical density (no. m^–2 or no. m^–3) need to allow for differences in the extent of identification of early larval stages. Likewise, the time of year, depth of sampling and mesh size of sampler greatly influence the recorded abundance, since the populations can make seasonal vertical migrations and their pulsed reproduction causes great seasonal changes in size structure and abundance. Other issues are specific to polar environments, for example, lipid storage which leads to significantly different length-mass and mass-rate relationships than are reported in global literature compilations. Likewise, stenothermy (narrow temperature tolerance) means that fixed (Q10-type) temperature relationships based on global literature compilations must be applied with great caution in SO-specific studies. Protozoa/micrometazoa (<200 μm) are the main grazers in the SO, since mesozooplankton typically remove <30% of primary production. This emphasises the dominant role of microbial food chains involving small metazoans, relative to the classic short diatom-krill-whale type food chains. Even within regions of abundant krill, copepod production in summer roughly triples that of postlarval E. superba. This fact reflects a large flow of energy through multiple trophic levels, via copepods and their major invertebrate predators such as other predatory copepods, chaetognaths, small omnivorous euphausiids, amphipods up to myctophid fish and birds.

Atkinson, A., S. Nicol, S. Kawaguchi, E. Pakhomov, L. Quetin, R. Ross, S. Hill, C. Reiss, V. Siegel, G. Tarling (submitted to the 2008 Joint CCAMLR-IWC Workshop) (2012), Fitting Euphausia superba into Southern Ocean food-web models: a review of data sources and their limitations

This paper aims to provide the overview needed to include krill in food-web models and to guide modellers to key sources of data. It describes the strengths of each method of sampling krill, i.e. with nets (for historical time series, demographic information and live krill), acoustics (distribution, time series, biomass and swarm-scale information), the fishery (sustained sampling in one place and wide area and time coverage) and via predators (long time series, demographic indices). Each data source has caveats and more efforts to combine them are recommended. Observations that krill occupy the under ice layer, the 0–10 m layer, the deeper water column and the benthos have fundamental implications, both for assessing biomass and for modelling the food web. Temporally, the intense (order of magnitude) interannual variability in krill population size within the southwest (SW) Atlantic sector is a major scale of variability, driven by sea-ice and climate effects on recruitment. This variability masks top–down predation controls that may operate over multi-decadal scales. Growth in spring, summer and autumn is now fairly well quantified, but mortality remains an enigma. We are still not yet confident which are the major predators of krill but studies increasingly suggest that they are not currently birds or mammals. Krill feed across three trophic levels and can control food populations through locally high grazing impact and nutrient regeneration. They also have fundamental regional differences in overwintering strategies, on-shelf/off-shelf distributions, relationships with sea-ice and diet. Whether this reflects ‘subpopulations’ with regionally specific life cycles is still unclear. However, caution is urged when scaling up food-web models and their parameterisations, either from individual to schooling krill, or from one region to another.

Strutton, P.G., N.S. Lovenduski, M. Mongin and R. Matear (2012), Quantification of Southern Ocean phytoplankton biomass and primary productivity via satellite observations and biogeochemical models (submitted to the 2008 Joint CCAMLR-IWC Workshop)

This paper reviews Southern Ocean primary productivity within the framework of satellite remote sensing and the development of food-web models. The satellite ocean colour (chlorophyll) data record is described, from the Coastal Zone Colour Scanner (CZCS) in the late 1970s through to the Ocean Colour and Temperature Scanner (OCTS), the Seaviewing, Wide Field of view Sensor (SeaWiFS), the Moderate Resolution Imaging Spectroradiometer (MODIS) and the Medium Resolution Imaging Spectrometer (MERIS). The characteristics of these data and limitations, such as cloud cover and high solar zenith angle, are discussed with regard to their use in the Southern Ocean. A brief history of algorithms linking ocean colour to primary productivity is presented, focusing on the vertically generalised production model (VGPM) and more recent regional approaches. Using monthly climatologies of SeaWiFS chlorophyll, a phenology of phytoplankton blooms is presented for the major provinces surrounding Antarctica. Some of the published information regarding phytoplankton species composition and succession is summarised. A review of ecosystem and biogeochemical models for the Southern Ocean is presented, with a focus on those models that have been validated using satellite ocean colour data.