Two-area population models for Antarctic toothfish in the Amundsen Sea Region were developed further as current single area models did not fully explain the patterns in the observed data on tag recaptures and age composition. Although the hypothesised stock structure spans SSRUs 88.2C–H, these models were limited to data collected in SSRU 88.2H as there were few data available to inform estimation of biomass in SSRUs 88.2C–G. Additional data resulting from a two-year research plan implemented in 2014/15 are expected to better inform the assessment of the entire stock including SSRUs 88.2C–G in the future.

Results showed that a two-area model with sex- and age-specific migrations from SSRUs 88.2C-G to SSRU 88.2H and back provided the best fits to the age and tag data collected in SSRU 88.2H. Furthermore, a resident population in 88.2H was not required to explain the patterns observed in the data, nor was annually-varying or density-dependent migration. Finally, using subsets of the data, or excluding small tagged fish, did not improve the fits to the data.

We recommend this model be further developed once additional age and tag data have been collected in SSRUs 88.2C–H as part of the two-year research plan. 

Appendix: CASAL files

Management Strategy Evaluation (MSE) has been acknowledged as the best practice to take account of uncertainties in the assessment of stocks and as a method to ensure robust management approaches. The Scientific Committee of CCAMLR has recommended MSE be used to determine the extent to which the management objectives for toothfish fisheries are being met. While the choice of management targets used by CCAMLR has been based on MSE simulations, formal MSE studies have yet to be fully implemented.

To date there have been a number of analyses and simulation studies reported for the assessment of toothfish that have evaluated the sensitivity of models and the resulting estimates of sustainable yields with respect to management objectives.

In this paper we develop approaches using operating and estimation models and show how they can be used to assist in identifying aspects of model and parameter misspecification that could then be evaluated using more computationally complex MSE approaches. We apply this to the assessment of Antarctic toothfish in the Ross Sea region with some example parameters and parameter values.

Our results can assist in prioritising further MSE analyses that fully account for the feedback mechanisms that the CCAMLRs decision rules provide. However, we note that different assessment models may be sensitive to different parameters and parameter values, and may require different approaches to MSE. We also note the importance of developing and maintaining data collections that can contribute to more accurate parameter specifications for any parameters identified as priorities through the MSE process.

We propose to conduct a scientific survey during the austral winter in the northern Ross Sea region to investigate spawning dynamics of Antarctic toothfish, as requested by the Scientific Committee in 2013. The longline survey is designed to cover key gaps in the knowledge of the life cycle of Antarctic toothfish (Dissostichus mawsoni) in the Ross Sea by collecting biological samples from a range of locations in Subarea 88.1 SSRUs B–C and begin in June 2016. The survey has two primary objectives, which are to investigate the spawning timing and locations of Antarctic toothfish in the northern Ross Sea region; and to investigate the maturity status, gonadosomatic index, histological characteristics, and condition of Antarctic toothfish during winter to further refine the developmental cycle. Other secondary objectives are to investigate the potential dispersion of eggs and larvae by studying the characteristics of Antarctic toothfish eggs with regards to buoyancy and to investigate the timing of the movement of Antarctic toothfish to and from the spawning grounds through an analysis of length and age composition of the catch, sex ratio, fish condition, and stable isotopes.

New Zealand FV Janas conducted research in two research blocks (882A_5 and 882B_4) as part of a multi-year and multi-member research plan using standardised longline gear to sample toothfish populations in the northern areas (60°‑ 66° S) of Subarea 88.2 SSRUs A–B. Sampling strategy and data collection adhered to standards set in CM 41-10 (2014). A total of 49.85 t of Antarctic toothfish and no Patagonian toothfish were caught. Toothfish catch rates, size, sex ratio, and reproductive maturity status were similar to existing data from SSRU 88.1C. In contrast, the gonadosomatic index and the sex-specific Fulton’s condition factor observed in the northern region of SSRU 88.2B were lower than those observed in SSRUs 88.1C, northern 88.2A, and 88.2H. The percentage of fish with empty stomachs was high, but prey diversity and quantities of prey items were similar to those reported from the northern Ross Sea. Bathymetry data were collected during the survey and during transit across research blocks and have been provided to the CCAMLR Secretariat.

A research proposal to continue the southern Ross Sea sub-adult toothfish survey for the next two years, 2016–2017, is presented. The survey will continue to focus primarily on estimating the relative abundance of sub-adult (<110 cm TL) toothfish in the core strata (A, B, C) in SSRUs 88.1J and 88.1L. This is a continuation of the time series of CCAMLR-sponsored research surveys of these strata carried out from 2012–2015.

It is also proposed that the survey be extended to include adult toothfish in McMurdo Sound following the recommendations of WG-FSA (SC-CAMLR-XXXIII, Annex7, para 5.108) and Terra Nova Bay where substantial numbers of larger sub-adult and adult toothfish were captured in the 2015 survey. As it is less critical to survey these larger sub-adult and adult toothfish on an annual basis, it is proposed that these two areas be surveyed in alternate years. Therefore, it is proposed to survey McMurdo Sound in 2016 and to survey Terra Nova Bay in 2017.

Survey timing and methods will remain the same as in previous years, and the number of sets will be retained at 45 sets for the core strata but reduced to 10 sets for the McMurdo/Terra Nova Bay strata making 55 sets in total. A nominal catch limit of 40 tonnes is requested for each survey. It is envisaged that the results of the 2016 survey, and trends in the time series, be presented to WG-FSA for review in 2016 and that a full review be completed and presented to WG-SAM and WG-FSA in 2017.  

At its 2011 meeting, the Scientific Committee agreed that a time series of relative abundance from a well-designed survey could be a useful input into the Ross Sea stock assessment model. The first three surveys were completed in February 2012, 2013, and 2014. In this paper we provide results of the fourth survey in the time series. The objectives of this survey were: (1) To carry out a longline survey to monitor sub-adult toothfish in the southern Ross Sea (strata A–C) using standardised gear in a standardised manner; and (2) To sample additional experimental stations in an adjacent area to identify areas of high sub-adult abundance that could be included as strata in future annual surveys.

The 2015 survey was successful in completing all of the planned stations. Standardised catch rates of sub-adult (<110 cm) toothfish for the core strata showed a significant decline in this fourth year of the survey series. Age frequency data from the surveys have shown the progression of a cohort from age 7 in 2012 to age 9 in 2014 and to age 10 for females in 2015. The decline in the catch rates during the survey is consistent with the decline in the abundance of this cohort through time through mortality and the movement of older fish out of the core survey area, as well as the relatively weaker subsequent year classes. These results suggest that the surveys are indexing local abundance and will provide a reliable means of monitoring recruitment and estimating recruitment variability. Stations in the experimental stratum in Terra Nova Bay also had high catch rates of slightly larger sub-adult and adult fish, and warrant future monitoring. We recommend the survey be continued to provide information on year class strength and recruitment variability, and an index of local abundance to be incorporated in the stock assessment. 

In 2014, FSA-14-36r1 presented a new assessment of Patagonian toothfish in the French EEZ. A singularity in the tagging fits was observed by the working group. A lower number of recaptures in the first year compare to the second year was noted (figure1). This paper is an overview of tagging data in Kerguelen area and the impacts on the Casal assessment.

A multi-year, multi-member research program was established to map and sample the fishable areas of SSRUs 88.2 A–B north of 66° S latitude. During the 5^th - 7^th February 2015, the Norwegian fishing vessel FV Seljevær surveyed SSMRU 88.2 A, research block 3, defined in the multi-Member 88.2 offshore research survey. Bathymetric data were collected and longline fishing conducted to release tagged fish and collect information on the characteristics of the toothfish inhabiting the region. The vessel had a technical failure with the echosounder and bathymetry data are of low quality. The vessel set 5 longline sets with all vessel operations conforming to the required research criteria. A catch of 11 t of D mawsoni and 33 tagged fish released at 3.1 fish tagged per ton.

Toothfish in SSRUs 882.A–B are currently managed as part of the Ross Sea region stock, but the stock structure and fish movement patterns are uncertain and more information is required for the management across all of the region. Recognising this requirement, the Scientific Committee endorsed two years of spatially stratified longline surveys in the northern region of SSRUs 88.2A–B (SC-CAMLR XXXII, paragraph 3.76 (iv-c)). A multi-year, multi-Member research program was therefore established to map and sample the fishable areas of SSRUs 88.2 A–B north of 66° S latitude. Following its successful completion of the first part of the two year survey, this paper presents the details of the vessel that will conduct the second year of research and summarises the research plan, previously agreed at CCAMLR XXXIII.

During March-April 2015 Ukraine began the research within statistical subarea 48.2 in accordance with the recommendations of CCAMLR-XXXIII. The certain number of the following bottom long line surveys are proposed to be conducted during March-April 2016. The research surveys will be conducted by the Ukrainian flagged FV SIMEIZ. The data collected in first year of the research showed the possibility of demarcation of investigated area on two blocks - Northern and Southern by the Dissostichus spp. habitat. Proposed to change the design of the research survey to reach the purpose of 3-years investigation.