CCAMLR

Bathymetric data are used inter alia to define management boundaries, implement conservation measures, allocate catch among area, estimate spatial impacts due to fishing, and inform ecosystem-based management through bioregionalisation. Several data sources for bathymetric data exist, and these sources improve with time through additional data collection and analytical methods. In addition, the methods used to derive spatial statistics such as contour maps, seabed areas, or ecoregions are complex and also improve with research through time. We report on an effort to define the current “best available science” bathymetric data for the Ross Sea region along with a set of spatial tools in the form of computer scripts that provide a transparent and citable method to derive standard summary statistics for use by fishery managers. This is especially important because of the multinational use of such data. Currently, we have obtained publically available bathymetric data sources, created a spatial database, and have developed preliminary scripts for extracting an appropriate cell size, calculating seabed areas and generating rugostiy at user-defined scales. Future work will incorporate data from multibeam surveys, and potentially data from other nations and fishing vessels where available.

This study uses a histological assessment of age and length at spawning for female and male Antarctic toothfish Dissostichus mawsoni from fish sampled in the Ross Sea spanning the 2000-2009 fishing seasons. The female spawning ogive incorporates the proportion of sexually mature fish that do not spawn in a given year and is therefore appropriate to evaluate spawning stock biomass relative to stock management decision rules. A characterisation of the oocyte developmental cycle of Antarctic toothfish shows that primary endogenous growth can occur for an extended period with oocytes accumulating at the cortical alveoli stage at least a year prior to spawning. Individual oocytes are then recruited into the vitellogenic phase over at least a 6–12 month period, resulting in a developed batch of oocytes accumulating at the final maturation stage by May. Oogenesis is characterised to provide the biological basis for interpreting the histology. Both forecasting (using the most advanced oocyte stage) and hindcasting (using remnants of previous spawning) yielded similar results. The age at 50% spawning for females on the Ross Sea slope region is estimated to be 16.6 yr (range 16.0–17.3) or 133.2 cm (range 130.9–135.7) by length. Males are estimated to spawn at a younger age; 12.8 yr (range 11.9–14.0) or 120.4 cm (range 114.8–126.7) by length. Evidence of skip spawning by females results in a right-shifted ogive, increasing the functional difference between male and female ogives. Comparison of the spawning age distribution on the slope with the age distribution in the northern area and the lack of evidence for skip spawning in the north indicates that all fish in the north are spawning. The degree to which the overall population ogive is biased right (older) by excluding the mature fish in the north depends on the proportion of the total population occurring in the northern area, which is currently unknown.

The exploratory fishery for Dissostichus spp. has now been operating for 13 years in Subarea 88.1 and for 8 years in Subarea 88.2. During that time a large amount of distributional and biological data has been collected on toothfish and the associated bycatch. The purpose of this report is to characterise the general fishing patterns over time and, in particular, to identify possible changes to the fishery which may be indicative of localised stock depletion. We considered here the catch limit, changes in depth/location of fishing, and length and age structure of the population. The catch limit was under caught in both Subareas 88.1 and 88.2 during the 2008 and 2009 seasons. This was mainly due to difficulties in accurately predicting when catches would exceed the catch limit (using the Secretariat’s forecasting routines), but in 2008 was also partly due to the bad ice conditions. The median fishing depth steadily increased over the first seven years of the fishery but has since stabilised at about 1000–1200 m. However, the fishing effort in each of the SSRUs continues to vary due to several factors including the distribution of sea-ice, the SSRU catch and bycatch limits, and an increase in knowledge of the various grounds. Raw catch and effort data examined during this study suggest that the median toothfish catch per set has generally increased over the course of the fishery whilst the median number of hooks per set has remained relatively constant. Other indicators of CPUE including unstandardised catch per hook and catch per set have shown no consistent trend over time. The length frequency data from the Ross Sea fishery have been very consistent over the past 3–4 seasons. There is no evidence of any truncation of the overall length frequency distribution, and no evidence for a reduction in fish length in any SSRU over time. We conclude that from data examined from the fishery to date there is no strong evidence for localised stock depletion.

A dataset for the 2009 assessment of Antarctic toothfish (Dissostichus mawsoni) in the Ross Sea Region was selected on the basis of data quality metrics for individual trips. Initial informative datasets were selected comprising trips with high (above median) rates of recovery of previously released tags, and/or where tags released on the trip were subsequently recaptured at a high rate. These trips were used to define a range for various data quality metrics considered to be informative with respect to tagging data. Other trips with data quality metric values within these ranges were added to the dataset. Where the initial informative dataset was selected comprising trips with above median rate of tag recovery or where released tags were recaptured at a high rate, the majority of the catches, tag releases and tag recoveries are retained: the resulting dataset is only slightly smaller than the full dataset. However, where trips included in the informative dataset must have both an above median rate of tag recoveries and where tags released on the trip must be captured at an above median rate, the resulting dataset is smaller, but nevertheless substantially larger than that provided by New Zealand vessels alone. The methods used here provide a means of objectively selecting trips considered to have suitable tagging data quality for use in an assessment.

The random stratified trawl surveys (RSTS) for 2008 and 2009 were successfully completed on the RV Southern Champion, continuing the series that commenced in 1997. Catches in 2008 were generally reduced from the previous year’s survey, with the catch of toothfish being one third of that for the previous year and those of grey rock cod, unicorn icefish and skate species down by half. Catches of mackerel icefish and macrourids were similar to the previous RSTS. One of the most notable features of the survey was the very large catch of jellyfish. In contrast, overall catches for the 2009 survey were much higher than those from the 2008 survey. The total catch of fish was three times higher than that of 2008, with the catches of toothfish and icefish being four and five times higher respectively, and catches of skates being twice that of the 2008 level. The 2009 catches were closer to the average of the previous three years when there has been a stable survey design.

A survey of mackerel icefish, Champsocephalus gunnari, was undertaken in Division 58.5.2 in the vicinity of Heard Island in April 2009 to provide the information for an assessment of short-term annual yield in the 2009/2010 CCAMLR season. This paper provides a preliminary assessment of yield for the area of Division 58.5.2 to the west of 79o 20’ E using standard CCAMLR methods. The strong year class detected in the last two years’ surveys is now fully recruited as the 3+ cohort, and dominates the population.

Scales and whole otoliths were read for age determination of early stages of Notothenia rossii caught in Potter Cove, South Shetland Islands, in summer of years 2003-2006 and 2008. The sample was composed by blue phase fingerlings of 7-7.6 cm (TL) and age group 0 year and demersal young brown phase juveniles of 8.5-20.9 cm and predominant age groups 1-2 years. Counting of sclerites facilitated the interpretation of the rings, particularly in the central area of the scale. To clarify two issues of controversy in the literature: 1) we believe that the duration of the pelagic fingerling stage at sea is less than one year before migration to the demersal nearshore habitat; 2) the first well defined ring in scales corresponds to the first annulus, while a contiguous nearby ring is a secondary ring deposited after the first winter during the second year, attributable to a shift of habitat from pelagic to demersal. Our inferences, based on interpretation of the distinct sclerite structures that constitute the rings, are illustrated/supported by photographs. A von Bertalanffy growth curve was computed by combining age/length data of the juvenile phase of N. rossii from this and a previous study at Potter Cove, with literature data from the offshore adult population, resulting in the equation:

This paper summarized the chilean catch data for 1991. Especial emphasis is given to the analysis of haul-by-haul data and its use in understanding small scale spatial distribution of fishing grounds. The results show that the krill fishery in subarea 48.1 is particularly intense near CEMP sites. Other uses of haul-by-haul data are suggestted.