CCAMLR

The Australian Antarctic Division (AAD) has recently received funding to continue an ageing program for the purposes of routine processing of Patagonian toothfish (Dissostichus eleginoides) otoliths from the Heard Island and McDonald Islands fishery. With the reinitiation of this program a number of methodological refinements have been made to those outlined by Nowara et al. (2009), particularly in relation to the laboratory processing of otoliths and quality control in the assignment of fish age. These changes have contributed to increased efficiency within the program, with a greater capacity for ageing and at a lower cost per otolith. Greatest efficiency gains have been made in the laboratory, with otoliths now set in smaller resin blocks that take much less time to section, and in quality control and reporting procedures, which are now largely automated using R.

A key part of quality assurance in any ageing program is to minimise the effect that a reader has in assigning ages.  In the AAD program, two readers look at all otoliths, which has proved useful in helping to identify  otoliths that may be  interpreted differently by different readers, so they can be flagged, re-read, and consensus reached on the most likely age estimate.  Using the otolith weight/age relationship has also been useful for identifying otoliths that may have been aged with good precision between the two readers, but may represent systematic error in interpretation (e.g. both readers may have counted all sub-banding for a particular fish).

This year’s stock assessment includes new age data from the 2012, 2013 and 2014 RSTSs, as well as from the commercial fishery in 2013. The recent focus by AAD to age more large fish from commercial samples has substantially increased the information available on older age classes (i.e. fish greater than 20 years) available for use in the current assessment (Ziegler et al., 2014).
 

The annual Random Stratified Trawl Survey was undertaken in Division 58.5.2 in the vicinity of Heard Island during June 2014. This paper provides a preliminary assessment of mackerel icefish population structure, abundance and yield for the area of Division 58.5.2 to the west of 79° 20’ E using standard CCAMLR methods. A pattern of multiple year classes being present simultaneously in the population, which was first detected in 2011, has persisted. The large cohort observed in recent surveys was still numerically dominant, however there is evidence that recruitment to the 0+-3+ cohorts has taken place. Given the expectation that the current 4+ and 5+ cohorts are fully exploited, only the 1+-3+ cohorts were projected. These projections indicate that catches of 309t in the 2014/15 season and 275t in the 2015/16 season satisfies the CCAMLR decision rules.

Patagonian toothfish have been tagged during commercial fishing and research activities adjacent to Heard Island and the McDonald Islands (HIMI, CCAMLR Division 58.5.2) since 1998, with 27,679 toothfish tagged and released, and 4925 recaptures. The data derived from this program has been valuable in estimating key population parameters for toothfish in this region, and have been used in the 2014 stock assessment (Ziegler, et al, 2014) in various ways including:

•  local abundance estimators;
•  natural mortality;
•  movement rates;
•  growth;
•  stock structure; and
•  estimation of q of the trawl surveys;

However, due to the spatial pattern of releases, toothfish movement, and recapture effort, it is unlikely that these data can currently be used in an unbiased manner to estimate stock abundance. Developing spatially explicit models that account for fleet dynamics, and phenotypic variability in post-release behaviour, remains an issue for all assessments incorporating tagging data and, in particular, in Division 58.5.2. Plans to develop such spatial models, as well as increasing tagging rates and attempting to spread the release and recapture effort, are likely to rapidly improve the utility of this data for future assessments.
 

The Kerguelen Plateau supports the largest fishery for Patagonian toothfish (Dissostichus eleginoides) in the CCAMLR area, with landings of  >5000 t.yr^-1 from the French EEZ (Division 58.5.1) around îles Kerguelen and 2730 t.yr^-1 from the Australian EEZ around Heard and McDonald Islands (HIMI, Division 58.5.2). This paper provides a synthesis of the spatial distribution of the Patagonian toothfish drawn from biological data collected in the HIMI area (Division 58.5.2) on more than 500,000 fish caught since 1997 during fishery operations and research surveys. Statistical analyses were used to quantify the effect of bathymetry in structuring the spatial distribution of different length classes and sex composition, when controlling for gear selectivity, year and sex effects. Fish length increased with depths suggesting spatial segregation of life stages. Spatial predictions showed that small, immature, fish were mostly found over the Plateau (<400m) and banks tops (i.e. Shell Bank), whereas larger fish inhabit deeper waters (>1500m) especially on the eastern part of the Plateau, where the continental slope is steep. Being slightly biased towards females, sex ratio was also influenced by fishing depth. Proportion of females increased at shallower (<500m) and deeper (>1200m) depths, whereas a sex ratio of 0.6 was found in between. The recent discovery of extensive areas of spawning activity in the Australian EEZ revealed the importance of the western margin of the Plateau as spawning habitat. These results allow us to further refine hypotheses about the spatial segregation of life-stages and sex in the HIMI part of the Kerguelen Plateau. The distribution and ecology of the early life history stages, up to 2-3 years old, and the implications of sexual and phenotypic variability in growth and movement stand out as the priority for future research into the biology and management of Patagonian toothfish in this region.

The annual random stratified trawl survey (RSTS) at HIMI was conducted during June of 2014, with the completion of 158 stations. An additional five stations were completed at Shell Bank, which had not been sampled since 2005. The catches of C. gunnari were less than half of those in 2013, but catches of both D. eleginoides and C. gunnari were higher than the long-term average (2006-2013). Catches of Channichthys rhinoceratus and Lepidonotothen squamifrons were higher than average. Skate catches in 2014 were slightly higher than the average RSTS take. Catches at Shell Bank consisted mostly of L. squamifrons and a small quantity of C. rhinoceratus. There were no C. gunnari  caught in this stratum.

The catch of invertebrates in the 2014 survey was 3.4 t, with the most abundant taxa being the poriferan sponges. Catches were half the long-term average.

Biological measurements were taken for 8,500 fish and lengths of a total of 18,000 fish were recorded. Otoliths were collected from 617 D. eleginoides, and 245 were tagged. Additionally, 124 sets of otoliths were collected from L. squamifrons.
 

This paper reports on the trial of daytime fishing during the 1-15 April pre-season extension, in the Patagonian toothfish longline fishery in statistical division 58.5.2.

During the 1-15 April pre-season extension two vessels fished, and all setting was carried out during nautical dusk or night. No seabirds were caught.

Any fishing that occurs in the 1-14 November 2014 post-season extension period, and the planned in the April 2015 extension will be reported to WG-FSA in 2015.
 

During the 2012 CCAMLR toothfish ageing workshop, otoliths from 31 Antarctic toothfish were exchanged between Russia and New Zealand ageing programmes to compare consistency in ages estimated by different readers and using different methods. Both “break and burn” and “bake and embed” techniques were used to prepare otoliths and each were read by an experienced reader from each program. The resulting four-way comparison enabled differences in preparation method to be distinguished from differences in interpretation of otolith banding patterns. Results suggest broad agreement in ages determined by each reader and with each method. However, there were enough inconsistencies in preparation technique and in interpretation of the break and burn preparation method to warrant further coordination and comparisons before merging data. Bake and embed preparations were consistently interpreted by both readers. This experiment highlights the importance of monitoring and comparing ageing protocols within and between fish ageing programmes. The criteria for determining similar age interpretation used here (mean paired age difference statistically equal to zero, overall CV less than 10%, and slope of regression across ages equal to 1) were useful diagnostics in interpreting age comparisons.

Sea ice is recognised as a core driver of both ecosystem dynamics and fishery performance in the Southern Ocean. Sea ice can limit access to fishing grounds, for both commercial fishing and scientific research. Although satellite data are available and have been used for ecosystem monitoring purposes and to inform research plans by CCAMLR, no quantitative summaries relative to fishing access are in use by CCAMLR. We develop a method to spatially and temporally summarise satellite-derived sea ice concentration data in the Southern Ocean, and relate it to data on commercial fishing vessel operations around the Antarctic continental margin. A spatial view is used to characterise the spatial dynamics of sea ice in a target location for a specified period, and a temporal view is used to characterise the inter-annual patterns within a target area. Both can be viewed relative to ice conditions during historical fishing events. The distribution of local ice concentration at the time of each fishing event relative to the weighted ice concentrations within the fishery footprint was used to develop the relationship between sea ice concentration and fishing. Although more than 85% of fishing events occurred in areas with less than 20% sea ice, a threshold of 40–60% sea ice indicated the transition from fished to non-fished conditions. We present a summary of conditions in SSRUs 88.2C-G as a case study to identify and characterise areas with reliable access for the collection of fishery data.

This report summarises the timing, depth, and location of fishing together with the biological aspects and catch of Antarctic toothfish up to an including the 2014 season. In 2014, the Ross Sea slope SSRUs were not constrained by sea ice and catches were evenly distributed across the three SSRUs. As in recent years, the remaining catches came mainly from SSRUs 88.1C, 88.1J, and 88.2H. Unstandardised Antarctic toothfish CPUE in the Ross Sea and Subarea 88.2 fisheries have fluctuated over the past 12 years with a slight decline in the past two years.

Length frequency distributions of Antarctic toothfish in the Ross Sea fishery have continued to be stable in the North and variable on the Shelf. The strong mode of smaller (90–120 cm TL) toothfish present in the Slope fishery from 2010–2013 was not present in the 2014 season, and the size composition in 2014 was more similar to that in the early period of the fishery – the reason for this is unclear. There has been a slight reduction in mean age in SSRU 88.2H, but the data are very uncertain due to the paucity of otolith readings and it is recommended that additional otolith readings for this area are given a high priority. There was a marked increase in the proportion of males in the Ross Sea North fishery from 2001 to 2009, but this has decreased slightly since then. There has been little change in sex ratio in the other areas.

The effect of sea ice is acknowledged as a major influence on fishing operations in high latitudes but not widely understood in detail other than by fishers and specialists in Antarctic fisheries research and management. Using the toothfish fishery in CCAMLR Subarea 88.1 as a case study we provide a method to quantify the effect of sea-ice on fishing.  We discuss the ways in which ice effects fishing operations and the result of these impacts on fishing such as the time required to reach the catch limit and compression of fishing effort due to a reduction in fishing ground extent in years when sea ice is more extensive. The method is a retrospective analysis of past seasons to quantify the level of impact that ice conditions have on fishing.  Graphical summaries of the last 15 austral fishing seasons are included for reference.