CCAMLR

A bootstrap procedure was applied to estimate the demersal biomass of mackerel icefish (Champsocephalus gunnari) in CCAMLR subarea 48.3 using data from the UK trawl survey conducted in January 2013. The CCAMLR harvest control rule was then applied to determine catch limits for the 2013/14 and 2014/15 fishing season. Application of the CCAMLR rule, which ensures 75% biomass escapement after a two year projection period, yielded total allowable catch limit advice of 4635 tonnes for 2013/14 and 2659 tonnes for 2014/15.

Data on demersal fish species composition and abundance was collected from 1277 research hauls conducted in depths < 350m during 19 research random stratified trawl surveys carried out on the Shag Rocks and South Georgia Shelf region between 1986 and 2013. Consistent hotspots of fish biomass were seen across survey years. Species counts were highly variable across the shelf region and appeared to be linked to habitat type. Low diversity in species was seen consistently over the Shag Rocks shelf. There was no detectable change in species composition across the region over three decades. Eight species from two families, the Notoheniidae and the Channichthyidae dominated the survey biomass in all years accounting for 97% of total demersal fish biomass. The relative abundance of these species was observed to change over time and between area strata. Considerable inter-annual variability in total demersal fish catch rates was observed with the highest mean CPUE s seen in surveys since 2010 but this was not uniform between strata. Trends in SSB for the five most abundant species of the South Georgia shelf show no consistent trends between species. There is evidence of increasing biomass in the marbled rock cod (N. rossii) and Mackerel icefish (C. gunnari), an overall decrease in the abundance of the Scotia Sea Icefish (C. aceratus) fluctuating but consistent biomass of the South Georgia icefish (P. georgianus) and a crash followed by a steady recovery of the Humphead notothen (G. gibberifrons). The preliminary results are considered in the context of considerable regional ecological change and a massive reduction in fishing mortality over the survey time period.

Analytical data on determination of reproductive potential of Antarctic toothfish D. mawsoni in the Pacific (SSRUs 88.1, 88.2, 88.3), Indian Ocean (SSRUs 58.4.1 и 58.4.2) and Atlantic (SSRU 48.6) Antarctic areas are presented. Morphological indices of females and males, indices of gonads, fecundity, and condition by Fulton are described. Spawning time and regions for Antarctic toothfish are discussing.

Using a modeling framework for toothfish (Dissostichus spp.) population dynamics, fishing, and data collection, this study investigated how the bias and precision of biomass estimates from an integrated tag-based assessment are influenced by various aspects of a multiyear tagging program, particularly the effects of the size of tagged fish compared with the size of fish in the catch (tag size-overlap), numbers of tagged fish, duration of the tagging program, using catch-at-length or catch-at-age data as auxiliary data, and stock depletion levels. Biomass estimates generally improved with more and better-quality tagging data. The results showed that even when tag releases were distributed over a relatively large number of size classes, low recapture numbers collected in short tagging programs with a 100% tag size-overlap were sufficient for robust and unbiased assessments. Particularly in the early stages of the tagging program, a high tag size-overlap was imperative to maximize the likelihood of a robust assessment. Biomass estimates were largely unaffected by the stock depletion level; however, using catch-at-age compared with catch-at-length improved recruitment estimates and resulted in more conservative biomass estimates.

This paper presents an updated assessment for Patagonian toothfish (Dissostichus eleginoides) at the Heard and the McDonald Islands (Division 58.5.2) with data until the start of August 2013. Compared to the last assessment in 2011, this assessment updated the growth model and compared the effects of a range of alternative fishery structures and model assumptions for year class strength (YCS) on stock assessment estimates and projected catch limits that satisfy the CCAMLR decision rules. Re-defining the fishery structure was based on a method by Candy et al. (2013) that suggested a simplification of the longline hauls into two sub-fisheries that were depth-stratified but not regionally-explicit. Alternative trawl sub-fisheries were evaluated within the assessment model in different scenarios.

All evaluated scenarios produced similar spawning stock biomass (SSB) patterns and estimates of current status. Across scenarios with YCS estimation, estimates of virgin spawning biomass (B₀) ranged from 89 448 - 101 847 tonnes, and SSB status in 2013 ranged from 0.63 - 0.69 of B₀. A model scenario that ignored information on YCS variation resulted in an SSB status of 0.58 in 2013, but was considered to be less realistic. The impact of altering the sub-fishery structure for trawl on model estimates was relatively small, however the selectivity functions for the different trawl sub-fisheries varied substantially indicating that a separation of the trawl sub-fisheries is appropriate. The scenario with estimating a YCS from 1992-2009 compared to 1984-2009 was the preferred model, since the estimated YCS pattern was more consistent and did not show an early period with stronger inter-annual fluctuation.

Based on this assessment, we recommend that the catch limit for the 2013/14 and 2014/15 seasons be set at 3005 tonnes.

The annual Random Stratified Trawl Survey was undertaken in Division 58.5.2 in the vicinity of Heard Island during April 2013. 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 large cohort of fish, estimated to be 3+, dominates the population in both abundance and biomass. Two scenarios for harvest are presented – a typical two year projection of the population, and a projection accounting for the fact that the abundant 3+ year class is likely to be unavailable beyond 2013/14. Under the first scenario, a catch limit of 764 t is recommended for 2013/14 and 571t for 2014/15, while under the second scenario, a catch limit of 1267 t is recommended for 2013/14 and 0 t for 2014/15.

The fisheries targeting Patagonian toothfish (Dissostichus eleginoides) and mackerel icefish (Champsocephalus gunnari) in the Australian Fishing Zone surrounding Heard Island and McDonald take three species of skates, Bathyraja eatonii, B. irrasa and B. murrayi, as their most common bycatches. A tagging program has operated in these fisheries since 2001 to learn more about the movement and biology of these species. In the 13 years, over 12,000 skates have been tagged, with 112 recaptures, a recapture rate of less than one percent. The average distance between release and recapture for each of the three species was 4 nm, and the longest distance travelled was 23 nm. The skates appear to move equally in all directions. Most recaptures occurred within the first three years, with the maximum time at liberty of nearly eight years for one B. irrasa. Range of movement in depth was between -266 m and 280 m from release to recapture, with B. irrasa tending to move in depth more than the other two species. Growth increments for tagged and recaptured B. eatonii indicated growth of ~20mm/year for both sexes between 600 and 1000mm total length, indicating maximum ages of several decades. In combination with biological and catch and effort data, the ongoing program of skate tagging will continue to contribute data which will be used for better informed risk assessments in the future.

The annual random stratified trawl survey (RSTS) at Heard Island and McDonald Islands (HIMI) was completed during April of 2013. The catches of D. eleginoides for 2013 were half that of 2012 and lower than the long-term (2006-2012) average. Conversely, mackerel icefish catches were seven times the long term average. Catches of Channichthys rhinoceratus were higher and those of Lepidonotothen squamifrons lower than average. Skate catches in 2013 were slightly higher than the average RSTS take.

The catch of invertebrates in the 2013 survey was 6 t, which was lower than the long term average. This year there was a large abundance of jellyfish (Cnidaria) which formed about half of the catch of invertebrates. Catches of individual invertebrate taxa were generally much lower than in previous years.

Lengths and biological measurements were taken for 13,000 fish, 276 pairs of otoliths collected and 179 toothfish were tagged.