CCAMLR

Antarctic and Patagonian toothfish stocks in the Antarctic have been assessed within CCAMLR areas using integrated statistical catch-at-age stock assessment models. These models were initially run annually, but have been run biennially since 2007. This document investigates the impact on model outputs of withholding from a stock assessment between one and eight years of age frequency and/or tag recapture data. Examining the impact of considering a subset of the available data simulates both the effect of not updating an assessment every year, and also the evolution of stock assessments with time as more years’ data becomes available.
The 2009 stock assessment of Antarctic toothfish in the Ross Sea region was used as the working model. The 2009 stock assessment of Antarctic toothfish in Subarea 88.2E was used as a sensitivity to examine the impact of withholding data from an assessment based on a smaller and shorter data set. In both instances the ‘base case’ model was used, i.e., the models that were used to set the precautionary yields for each fishery in 2009. The change in the biomass estimated by the models arising from withholding data was found to be highest in the earlier years of stock assessments, when each extra year of withheld data represented a large contribution to the model. In later years, the change in estimated biomass arising from withholding data was much smaller, with values generally within the 95% percentile of the MCMC run from the 2009 assessment. For the 2009 assessment removing up to four years of the early tag data had little effect on the estimate of the initial biomass, or the range of the estimates.
Running updated assessments with catch data, or with catch data and age frequencies, provided no further information on the biomass trajectories in the model considered. Tag recapture data provided the most information to the model, although the model results were not very sensitive to changes in years of tag release and recapture data available to the model. For example even when the number of tag recaptures in the most recent year was doubled or halved, the corresponding estimate of current biomass changed by less than 10%; furthermore, these estimates remained within the 95% percentile envelope estimated by the MCMC posteriors.
 

The exploratory fishery for Dissostichus spp. has now been operating for 14 years in Subarea 88.1 and for nine years in Subarea 88.2. Associated research has led to an assessment of the fisheries potential yield, but a source of ongoing uncertainty in the stock assessment concerns recruitment dynamics. Although pre-recruit Antarctic toothfish fish are caught in various locations during fishing operations, different vessels catch different length classes in different locations and in different years, making it impossible to develop a consistent time series that would monitor trends in recruitment over time from the fishery. At its 2010 meeting, the Scientific Committee agreed that a time series of recruitments from a well designed survey could be a useful input into a stock assessment model and requested members develop a pre-recruit survey design. This paper develops a proposal for a CCAMLR sponsored research survey in response to the Scientific Committee request.
We consider here the objectives of the survey, the target fish age and length classes to be monitored, appropriate survey strata size and location, the number of sets in each stratum required to achieve target c.v.s, and associated sampling methodologies. Further, we propose that the first survey be a pilot, with two main objectives:  

(i)    To establish the feasibility of developing a time series of longline surveys to monitor 80–100 cm TL toothfish in parts of SSRUs 881.J and 881.L in the southern Ross Sea using standardised gear in a standardised manner; and
(ii)    To carry out experimental depth stratified fishing in 500–600 m depth adjacent to the survey boundaries to establish the most appropriate depth strata for future surveys.

We are submitting this proposal to WG-SAM for further evaluation as requested by the Scientific Committee (SC-CAMLR-XXIX, para 3.185). We are particularly interested in ways to improve the survey design, as well as additional work that could be undertaken to demonstrate the use of the results of such a survey in the provision of advice to the Scientific Committee.
 

The potential for data poor exploratory fisheries in the CAMLR Convention area to provide sufficient data to lead to formal stock assessments of Dissostichus spp. is evaluated and recommendations are made for optimizing this potential.  The types of data that have led to successful assessments in the past are reviewed. Exploratory fisheries and research questions for subareas without currently assessed stocks (48.6, 58.4, parts of 88.1 and 88.2) are summarized. The multi-nation, multi-year exploratory fishery in the Ross Sea leading to an assessment of D. mawsoni and the fishery for D. eleginoides in the northern South Sandwich Islands are used as examples of what can be achieved using exploratory fisheries to provide information for stock assessment. Three sources of data potentially collectable from exploratory fisheries have proved successful in the past: 1) tag mark and recapture; 2) collection and reading of otoliths; and 3) recording of length, sex and gonad stage. It is suggested that research standards for data collected by vessels in exploratory fisheries be focused on providing these three types of data and that detailed descriptions of CPUE data be de-emphasized. Focusing effort on subareas/divisions in which tagged fish have already been released is recommended to maximize recapture potential for existing tags while increasing the numbers of newly tagged fish.  The subareas/divisions should be prioritized according to the amount of information currently available, and the prospect of acquiring a sufficient amount of data with which to conduct a formal assessment.

This paper presents the updates to the CCAMLR tagging database in relation to tag recapture links, and the problems associated with linking tags.
 

A generic spatially-explicit age-structured model framework is in development that will enable to evaluate data collection protocols, assessment methods and management strategies. The model framework is programmed in R to promote transparency and interactions between researchers. It is based on the FLR framework and will incorporate links to external assessments programs such as CASAL. The model framework will have a number of modules representing the fish population dynamics, harvest by fishing fleets with different gear types or metiers, sampling of data, stock assessment, and implementation of fishery management decisions.
 

At its 2010 meeting, the Scientific Committee agreed that a time series of recruitments from a well- designed survey in the Ross Sea could be a useful input into the stock assessment model and requested members develop a pre-recruit survey design. A preliminary proposal for a pre-recruit survey was presented to the 2011 meeting of WG-SAM. In this paper we provide an update of the preliminary proposal by taking into account the comments of WG-SAM. It provides the scientific rationale and background for the research proposal for a longline survey of pre-recruit toothfish in the southern Ross Sea, which has been submitted as a paper to the Scientific Committee.

We consider here the objectives of the survey, the target fish age and length classes to be monitored, appropriate survey strata size and location, the number of sets in each stratum required to achieve target c.v.s, and associated sampling methodologies. As a result of this review, we propose that the first survey be a pilot, with two main objectives:
 
(i)    To establish the feasibility of developing a time series of longline surveys to monitor pre-recruit (<100 cm TL) toothfish in the south of SSRUs 881.J and 881.L in the southern Ross Sea using standardised gear in a standardised manner; and
(ii)    To carry out experimental depth-stratified fishing in 400–600 m depth adjacent to the survey boundaries to establish the most appropriate depth strata for future annual surveys.
 

Le présent document propose un système représentatif d'aires marines protégées (RSMPA) dans le domaine de planification de l'Antarctique de l'Est identifié par l'atelier de la CCAMLR sur les aires marines protégées (AMP) en 2011 (WS-MPA-11).  Il propose, de plus, de faire approuver le RSMPA de l'Antarctique de l'Est par le SC-CAMLR qui le recommanderait à la Commission dans le cadre de son engagement à créer des AMP d'ici à 2012.  Cette proposition est une nouvelle version de celle de 2010.  Elle comporte les résultats de l'atelier qui s'est déroulé en France sur les AMP en mai 2011 et tient compte des discussions menées par le WS-MPA-11.  Ce rapport est divisé en trois sections : 1) la description du RSMPA, 2) l'analyse des valeurs à conserver et des compromis pour les AMP dans le domaine de planification de l'Antarctique de l'Est et 3) la documentation fournissant le complément d'informations à la base des analyses et de l'approche générale.  Si cette proposition est acceptée, les zones qu'il est prévu d'inclure dans le RSMPA seront désignées par des mesures de conservation individuelles dans le cadre de la mesure générale sur les AMP proposée dans CCAMLR-XXX/30.

The model of tag shedding implicit in CASAL is that of Kirkwood and Walker (KW) (1984) which models the annual tag shedding (i.e. loss) rate as a constant for individual tags. The CASAL software applies this model correctly for fish released with a single tag but does not have the facility at present to correctly apply the KW model for fish released with two tags. The solution of Dunn et al. (2005) and Hillary et al. (2006) to apply the square of the individual tag loss annual rate in CASAL over-estimates the correct proportion of fish that have retained at least one tag, and are therefore detectable, as a function of time at liberty. This over-estimation is shown to be significant and the implications for stock assessments of this are discussed.
Models of tag shedding were calibrated using data for a large sample of recaptures of fish released in the Heard and MacDonald Island (HIMI) (Division 58.5.2) Patagonian toothfish fishery that were double (Tbar) tagged fish. These models included the single-parameter KW model and 2 and 3 parameter extensions of this model. A Generalized Additive Model (GAM) was also fitted and is the most flexible in shape. The estimation method accounts for the fact that fish that have shed both tags cannot be detected and therefore do not contribute to the data but in the theory need to be considered. The KW model gave a considerably poorer fit than the other models. It is recommended that CASAL be modified to correctly handle double-tagged releases and at the same
time allow more flexible models of probability of shedding of individual tags. In lieu of this an  improved approximation compared to squaring the rate parameter is given. This approximation could be combined with a sensitivity analysis that varies the KW constant rate parameter in CASAL assessments.

According to the application that has been applied by Russian Federation in 2010 for season 2010/2011 research fishing in subarea 88.3 has been done. The work has been done by longliner “Sparta”, with two scientific observers aboard. They deployed 20 sets (trotline) at different depths. Total amount of set hooks is 87096. Research catching was carried out in SSRU B, C, and D. In SSRU A sets had not took place because of complicated ice conditions. The catch was totally analyzed for its biological characteristics. Additional catch’s biological characteristics have been analyzed too (excluding fish food analysis). According to the catch’s length variation, 30 fishes of different length have been tagged. Total catch is 256 toothfishes – 5230 kilograms weight. Data about spatial and bathymetrical distribution and nutrition of toothfish in subarea 88.3.B-D were collected 240 otolithes for age identification, 53 genetic specimens and 42 histological specimens have been collected.