CCAMLR

The ICES Benchmark Protocol is a review process for evaluating the data and analyses that form the basis of ICES management advice for a stock. The review examines stock structure, fishery characteristics, biological and assessment data, stock assessment and projection methodology. The review is conducted outside of the ICES annual assessment and advice environment. It includes experts from outside of the ICES community and stakeholders to broaden the knowledge and enhance credibility. The goal of a benchmark is agreement on an assessment methodology that is to be applied in annual update assessments, for a fixed short term period. Introducing benchmarking of CCAMLR assessments would be expected to provide greater transparency, quality control and stability to the SC-CAMLR management advice and to improve communication between science, the industry, stakeholders and administrators.

Submitted format for reporting finfish research proposals of the Ukraine in Subarea 48.2 in 2015.

This paper presents an analysis of data gained from a nine-year tagging programme of Patagonian toothfish (Dissostichus eleginoides) in Subarea 48.3. It describes the tagging procedure, the information gained about biology, growth and movement of Patagonian toothfish, and explains the overlap of tagging length distributions with those of the landed catch and survey data. The characterisation of tag recapture data from Subarea 48.3 shows that the tagging programme is successful in providing substantial information for the stock assessment.

We propose a multi-year and multi-member research plan using standardised longline gear to sample the toothfish populations in the northern areas (61° - 66° S) of SSRUs 88.2A–B. The purpose of the research as requested by the Scientific Committee (SC-CAMLR XXXII, paragraph 3.76) is to characterise the local toothfish populations found there to better understand stock structure, movement patterns and improve estimation of population characteristics predicted by Ross Sea spatial population models. Additional outcomes of the research relate to mapping the bathymetry of the fishable area, documenting relative abundance of Patagonian and Antarctic toothfish, tagging toothfish for biomass estimation and for stock linkage studies, and collecting information on distribution, relative abundance, and life history of bycatch species.

Life history characteristics of Antarctic toothfish (Dissostichus mawsoni), were evaluated using otolith microchemistry techniques. Our aims were to (i) determine whether fish from in CCAMLR SSRUs 88.1C (Ross Sea) and 88.2H (Amundsen Sea), could be differentiated by the trace elemental concentrations in the otolith edge and then to (ii) assess the potential of natal signatures to distinguish  stocks among these regions. For the elements (Mg, Al and Sr) spatial variation in otolith chemistry was shown. This resulted in the correct classification of 63% of fish overall to their original capture sites. Discrimination of otolith natal signatures using Al:Ca and Zn:Ca showed greater classification success (79%), compared to the otolith edge which suggested the majority of fish from SSRU 88.1C and 88.2H show similar patterns of structuring consistent with their known capture location, indicating they may have used different spawning habitats between areas. PCA analyses of natal signatures apportioned in total 83% of fish from both SSRU 88.1C and 88.2H to 88.1C. The remaining group consisted entirely of individuals from SSRU 88.2H (17%), suggesting SSRU 88.2H fish may have used different spawning habitats. However, given these analyses only included adults, further investigations using a larger sample base of both adults and juveniles collected from shelf and slope regions within SSRU 88.1 and 88.2 would provide stronger evidence of structuring between these regions.

This paper presents the data and assessment approach for the revised stock assessment for Patagonian toothfish, Dissostichus eleginoides, at Heard Island and the McDonald Islands (HIMI) in CCAMLR Division 58.5.2. Since the last assessment in 2013, an extensive program for ageing otoliths has been launched, length-at-age has been re-estimated, and research into tag-recapture data has started. We have therefore made substantive progress in addressing the main points raised during WG-FSA 2013 for the next stock assessment.

We propose a process by which to select the version of software generally used for stock assessments in CCAMLR, with the specific example of the CASAL software used for stock assessment. The latest published version of any stock assessment software approved by CCAMLR should be used by default, unless the latest development version is necessary, in which case it is the responsibility of the author to demonstrate that the latest development version performs as expected. As an example, the latest published version of CASAL should be used by default for stock assessments unless particular features available only in a more recent development version are necessary. If a different version is used, then the scientist proposing the stock assessment is responsible for ensuring the version used is performing as expected.

We present an updated spatially explicit age-structured population dynamics operating model for Antarctic toothfish in the Ross Sea region, for a medium scale spatial resolution (189 spatial cells) covering the Ross Sea region. We build on the previous working medium-scale model in which the population was restricted to those cells in which at least 5% of cell area was of a depth deemed suitable as habitat for toothfish (120 cells – semi-restricted model).

Model fits to the reproductive data were unsatisfactory in previous models, with a much flatter maturity ogive than that derived through histology. In the previous model reproductive parameters (proportion maturing and proportion spawning) were derived from two gonadosomatic index thresholds. In this model we keep only proportion spawning data, and retain the assumption that a proportion of the mature fish spawn each year. The model estimation of the maturity ogive is now similar to that estimated by histological analysis. This model represents our current best model of the spatial distribution and movement of Antarctic toothfish in the Ross Sea region given the movement hypothesis proposed.

Further data collection would be useful to improve the parameterisation of the model, in particular obtaining gonad weight measurements from all fished areas, biological characterisation of fish on the spawning grounds during winter, and characterising the fish population in areas not fished to date.

We propose that the modelling platform presented here can be used to test the likelihood and examine the consequences of alternative fish movement hypotheses given the data available. For a given movement scenario the model can also be used to examine the likely effects on the toothfish stock assessment of alternate spatial management options or alternate tagging programme designs affecting the distribution of fishing effort, data collection, and/or tagged fish releases.

Vessel-specific indices of tag detection rates and tagging mortality rates have been developed using a methodology which controls for the spatial and temporal variability of fishing operations by pairing each individual tag release or recapture event with all other fishing events which occurred in the same time and place (i.e. within a specific distance and in the same fishing season). The method showed that when the confounding effects of variable fishing location and time were controlled, there were nonetheless significant differences between vessels with respect to the tag detection index in the Ross Sea region. This index was subsequently used in 2013 to select the tagging data to be included in the stock assessment for the Ross Sea region and Amundsen Sea region, with the understanding that additional work should be undertaken to further develop this method.

Previous applications of the pairwise method utilised an index of tag detection with an arbitrary threshold to determine which tag data to include in the stock assessment, with respect to both tag release and tag recapture data. Here we present new results of simulations which indicate that the index of tagging mortality rate previously generated using this method is as useful as the index of tag detection rate. We further develop a method to estimate effective tag releases and effective numbers of fish inspected for tags based on those indices. This method allows the use in the stock assessment of tag data from all vessels, via direct application of the continuous indices, i.e. without reliance on arbitrary vessel selection thresholds. This method accounts for differences in tagging mortality and tag detection rates among vessels, and therefore is less likely to over-estimate the stock biomass than if tag data were used indiscriminately.

We recommend that the method proposed be used in the Ross Sea region stock assessment and in the Amundsen Sea region stock assessment.

This paper presents further investigations of the Bayesian sex and age structured population stock assessment of Antarctic toothfish (Dissostichus mawsoni) in Subarea 88.2 covering SSRUs 88.2C, D, E, F, G, and H (SSRUs 88.2C–H). Annual age-length keys were applied, and the time trends in the tag-derived biomass index were investigated. The impact of hypothesised stock structure, fish movement, tag mixing and the potential for localised depletion on the stock assessment were also investigated.

We recommend the following:

• That the Amundsen Sea region be considered as a single stock, with the stock assessment including all data from SSRUs 88.2C-H and the catch limit applied to the same region.
• That R3 be chosen as the base case model for providing management advice for the 2014/15 fishing year once it has been updated with the 2014 fishery data.
• That ways to obtain a better estimate of the biomass in SSRUs 88.2C-G are considered, in particular by improving the spatial overlap between tags released and subsequent fishing effort.
• That the recent high exploitation rates and localised depletion in SSRU 88.2H is recognised by allocating a greater proportion of the catch limit to SSRUs 88.2C–G and less to SSRU 88.2H.
• That all Members, where possible, contribute to the development of annual age-length keys, using approved otolith reading protocols and aging validation.