Over the last few years, the designation of Marine Protected Areas (MPA) in Antarctica has been the subject of active discussion. This issue was widely discussed at the last meeting of the CCAMLR Working Group on Ecosystem Monitoring (WG-EMM-12); it has been the subject of voluminous documents prepared by CCAMLR Members, and also workshop reports of the Antarctic and Southern Ocean Coalition (ASOC). This is indicative of the broad public interest in the subject, and also the continuously increasing scope of proposed actions.

One aim of Marine Protected Areas (MPAs) is to protect a representative portion of specific ecosystem functions through spatial closures to extractive practices such as fisheries. Although they usually involve the displacement of fisheries, their design rarely takes into account the effect of that fishery’s displacement on the target fish population. We used a spatially explicit population model of Antarctic toothfish in the Ross Sea region to investigate the effects of a proposed MPA on the status of the toothfish population. This study indicates that the MPA design proposed in 2013 is likely to result in a small increase in the catch limit under existing harvest management rules, as well as a large increase in the area with little depletion of the population and no increase in the area with higher depletion. Such spatial modelling tools can be used to inform MPA planning and compare alternative MPA scenarios. In particular they can assist in quantifying potential effects on the fish population and likely effectiveness of the proposed MPAs to meet some of their conservation goals.

Between 2001 and 2013 the number of breeding pairs of Adélie penguins (Pygoscelis adeliae) at breeding colonies in the southern Ross Sea more than doubled from about 235 000 to more than half a million. It has been suggested that predation release of Antarctic silverfish (Pleuragramma antarctica) due to fishing of one of its predators, Antarctic toothfish (Dissostichus mawsoni), could have contributed to the increase in Adélie penguin numbers. This paper brings together information on the biomass, consumption rates and diets of toothfish and Adélie penguins over the Ross Sea shelf as a first test of the predation release hypothesis. In particular, new data from the examination of the contents of 615 Antarctic toothfish stomachs showed that toothfish consume only a small proportion of silverfish (1.9–5.6%W i.e. by weight of prey) over the southern Ross Sea shelf, including in McMurdo Sound (0.4–6.4%W) and Terra Nova Bay (1.4–6.0%W). These Antarctic toothfish were sampled over four years, between 2011/12 and 2014/15 as part of the sub-adult Ross Sea survey.

The mass of silverfish estimated as being released from predation by fishing (643 tWW/y) was equivalent to 2.4% of the amount of silverfish estimated to be consumed annually by Adélie penguins in this region. This result was inconsistent with predation release of silverfish due to the toothfish fishery being responsible for recent increases in the number of Adélie penguins breeding in the southern Ross Sea. Mixed trophic impact (MTI) analysis was used to look for alternative indirect pathways through the food-web by which changes to toothfish could affect Adélie penguins in the Ross Sea. The MTI analysis found only a weak link between changes in toothfish biomass and changes to the biomasses of silverfish and Adélie penguins. Essentially, Antarctic toothfish and Adélie penguins were not assessed as having overlapping diets over the Ross Sea shelf: Antarctic toothfish consume mainly small, bottom-dwelling fishes (especially icefish, and Trematomus spp.) while Adélie penguins consume crystal krill and silverfish in the water column. The large-scale trophic connection between toothfish and Adélie penguins over the Ross Sea shelf is hence weak.

As a sensitivity test, we also estimated the amount of predation release of silverfish if toothfish consumed 100%W of silverfish i.e. ate only silverfish. In this case, the predation release effect was larger but still not sufficient to explain the observed increase in the number of Adélie penguins in the southern Ross Sea.

We encourage the development of further specific hypotheses of mechanisms by which fishing could affect the wider Ross Sea ecosystem. However, we consider that understanding the ecosystem effects of the toothfish fishery on the demersal fish community of the Ross Sea slope and on Weddell seals and type-C killer whales are higher priorities. 

Data are collected for use in scientific research, the results of which are used to inform management decisions made to achieve specific goals. Any data collection plan should be drawn from the goals the management wishes to achieve. The long-term goals of the Ross Sea fishery based on Article II of CCAMLR can be summarised as: the target fished population is above a level which ensures stable recruitment; the ecological relationships between harvested, dependent, and related populations are maintained; and, prevention of changes or minimisation of the risk of changes in the marine ecosystem which are not potentially reversible over two or three decades, with the aim of making possible the sustained conservation of Antarctic marine living resources. Based on these goals, medium term research objectives for the Ross Sea fishery for the next 5–7 years were developed in 2014. These medium-term research objectives were used as the basis for the development of this Ross Sea region fisheries data collection plan. This paper provides context with the proposed medium term research objectives, specific data requirements to meet those objectives, the basis for the proposed sampling scheme, and the draft fishery-dependent medium term data collection plan. Feedback is sought from WG- FSA concerning any substantive gaps in the proposed data collection requirements, approaches to optimising sampling rates, and the proposed rotational approach to sampling the main species groups.

It is recommended that gonad weight be included as a requirement in the Type II biological measurements for observer sampling from the 2015/16 fishing year onwards. It is also recommended that observers avoid using generic species codes (such as GRV and SRX) when recording biological data for bycatch species. 

We provide extensive diagnostic plots for models R1 and R2 for Antarctic toothfish in the Ross Sea as recommended by SAM-2015 (2015). The stock assessment rationale and models as well as their main diagnostics are described in Mormede et al. (2015). The CASAL files for models R1 and R2 were provided to the CCAMLR Secretariat as a zip file.

In this paper we present the results for first model R1 and then model R2. The diagnostic plots cover input data, MPD and MCMC outputs. Key tables are given in Mormede et al (2015) including process error weightings and the MPD objective function components.

We provide an update of the Bayesian sex and age structured population stock assessment for Antarctic toothfish (Dissostichus mawsoni) in the Ross Sea region (Subareas 88.1 and SSRUs 88.2A–B), using catch, catch-at-age, and tag-recapture data from 1997–98 to 2014–15 and including the results from the Ross Sea shelf survey from 2012 to 2015. The model results were similar to the 2013 assessment suggesting that recent tag-recapture and proportion-at-age observations were consistent with previous observations. Sensitivity runs showed that the results were relatively insensitive to the use of logistic selectivity ogive, inclusion/exclusion of quarantined data, and restricting tag data to the most recent six years.

Model runs showed that the data from the Ross Sea shelf survey were required to reliably estimate relative year class strengths. Year class strengths were estimated from 2003 to 2009 and showed one strong year class and two weak year classes.

Overall, model fits to the data were adequate, and, as in previous assessments, the tag-release and recapture data provided the most information on stock size. Monte-Carlo Markov Chain (MCMC) diagnostics suggested no evidence of non-convergence in the key biomass parameters. The precautionary yield, using the CCAMLR decision rules and current relative catch distribution between the shelf, slope, and north areas of the Ross Sea region, was either 2855 t or 2870 t from the two reference case model runs R1 and R2.