CCAMLR

Tagging studies of skates and rays worldwide provide valuable information to help better understand a wide range of metrics including movements and migrations, stock units, growth rates, longevity, discard survival and abundance. Most Antarctic skate species are little known and, coupled with taxonomic and identification problems, this makes the tagging studies undertaken in the CCAMLR area a potentially valuable data source to better understand this group of fish. Despite tagging programmes being conducted in the CCAMLR area for several years now, only preliminary observations have been presented to CCAMLR Working Groups. This report provides an overview of global tagging studies on skates, a review of tag loss and tag shedding rates in fish (with emphasis on elasmobranchs), a summary of CEFAS tagging data for skates from European waters to inform on typical return rates and initial observations on some of the tagging work undertaken under the auspices of CCAMLR in the Southern Ocean with comments on data quality and suggestions for future work.

In 2009 CCAMLR agreed to incrementally and conditionally bring forward the start date of the Patagonian toothfish fishery in sub-Area 48.3. This allowed vessels that had been 100% compliant with CM 25-01 in the previous season to start 5-days early in 2010 (April 26th) and a further 5 days early in 2011 (April 20th). In 2011, following the success of the initial trial, CCAMLR agreed to further conditional extensions, such that the season could start on the 16th April in 2012 and April 11th in 2013. The season extensions have been successful and no birds were killed during the extension in either 2012 or 2013. Given the success of the trial, it is proposed that the start date of the season be brought forward to the 16th April and that a further two trial extensions (each of 5 days) be allowed.

To date, the stocks of toothfish in Subarea 48.4 have been divided, for assessment purposes, into northern and southern components. The northern component is assessed as a single species of D. eleginoides whilst the southern component is assessed as a combination of D.eleginoides and D. mawsoni. Both species are caught throughout Subarea 48.4 although D.eleginoides are predominantly caught in the north, whilst D. mawsoni are mainly caught in the south. CCAMLR WG-FSA 2012 concluded that species specific assessments, covering the whole of the subarea, would be a more appropriate method for assessing the stocks than the existing area based, species combined approach. This paper describes the revised assessment of D. eleginoides in Subarea 48.4. The main changes to the assessment are: the removal of D.mawsoni data and the inclusion of D. eleginoides for the southern region; revision of tagging data for the full time series; re-estimation of the maturity ogive; changes to the assumed selection pattern and revised growth assumptions. The revised assessment is compared with the previous assessment for this stock. Data deficiencies and areas for future work to further improve the assessment are identified.

A preliminary assessment of toothfish (Dissostichus eleginoides.) in Subarea 48.3 is presented.

1. The assessment results from this year’s analyses are very similar to those of 2011. SSB in the terminal assessment year continues to be estimated at around 54% of virgin biomass, consistent with the CCAMLR harvest control rule.
2. The 3-fleet assessment model provides slightly improved fits to CPUE data and to catch at age observations and achieves this by assuming a different selection pattern for the intermediate (1998-2003) period and a slightly changed selection pattern for the most recent period
3. Model outputs from the 2-fleet and 3-fleet assessments are very similar with the exception of the recruitment.YCS estimates which differ markedly in 1990 but follow similar trends in all other years.
4. Recruitment remains uncertain although there is some evidence of the progression of strong year-classes through the catch at age data.
5. MCMC diagnostics and trace plot indicate poorer results than for previous assessments and require further investigation.
6. Yield calculations have yet to be completed.

Mark-recapture data is a central element in the assessment of population size and growth and the stock assessment for Patagonian Toothfish (Dissostichus eleginoides) in CCAMLR subarea 48.3 relies on accurate tagging samples for its assessment. The bias in tagging survival and tag detection is assumed to be minimal in the model, but this assumption has not previously been tested; a pairwise comparison is used to examine the relative performance between vessels in subarea 48.3.

Tag retention in subarea 48.3 is generally good with less than 1% of double-tagged fish losing a tag. Individual vessel performance in tag detection was relatively good compared to all other vessels and tagging survival was also consistent.

This review summarises current knowledge of the elasmobranch fish occurring in the Antarctic and sub-Antarctic waters of the CCAMLR area. About 14–15 species of elasmobranch have been recorded, with skates (Rajiformes) the most speciose order. Two genera of skates are known (Amblyraja and Bathyraja), although the current taxonomic knowledge of some species or species-groups is incomplete.  Five genera of sharks are known from the area, the most frequently reported being Somniosus antarcticus and Lamna nasus. Although other squaliform sharks are thought to occur in the area, the taxonomic status of some of these species is also unclear. The current biological knowledge of the various species is summarised, focusing on those aspects of the life history that may inform on assessment and management.

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.