CCAMLR

This paper presents further progress towards a two-area stock assessment model for Antarctic toothfish (Dissostichus mawsoni) in the Amundsen Sea region, defined here as SSRUs 88.2C–H. The region is split into two main areas: the North (SSRU 88.2H) comprising large mature fish, and the South (SSRUs 88.2C–G) comprising a mix of large mature fish and small immature fish.

Two-area stock assessment models were first developed for the region in 2014 and refined in 2015. Results showed the need to collect mark-recapture data in the South to help inform the estimation of biomass in the South. We present an update on these two-area stock models, which include two years of new data collected under a research plan. The assessment models were fit to the proportions-at-age in the catch and the mark-recapture data from the two areas. The results suggest that the research plan is successful in starting to inform the model, and in particular the size of the fish population in the South. We recommend that the current research plan be extended for a further 2-year period so that additional mark-recapture data can be collected particularly from the South, and that the models be developed further in the interim period. We also recommend that all Members, where possible, contribute to the development of annual age-length keys, using agreed otolith reading protocols and aging validation.

A multi-year research plan as outlined in CM 41-04 (2012, 2013, 2014) was initiated in Statistical Subarea 48.6 by Japan and South Africa during the 2012/13 fishing season. Two vessels participated in the research project in each of the three fishing seasons and the progress achieved during the first 3.5 years is reported.

The emphasis of the progress report is on block 486_2, since more tag returns have been recovered from this block and a preliminary stock assessment has been attempted using data mainly from block 486_2.  

We present preliminary results on age and growth of Dissostichus mawsoni for the second season (2013/14) of the Spanish research fishing in the 58.4.1 Division obtained for growth rings on otolith readings. It is included the age-length key and growth parameters estimates by sex. Growth parameters obtained using length-age pair values are: L_∞: 175.7, k: 0.1078 and t₀: 1.528 for females; L_∞: 150.3, k: 0.1491 and t₀: 1.809 for males; and L_∞: 169.8, k: 0.1087 and t₀: 1.168 all combined. These results are very similar to those reported previously for the first season (2012/13) although they differ slightly with the values used in the Ross sea assessment for males.

The second year survey and observations of Dissostichus spp. in statistical subarea 48.2 on board the Ukrainian vessel SIMEIZ were conducted in accordance with the recommendations of the Scientific Committee and Commission. The second year survey design was amended in comparison with the one of the first year and approved by WGs SAM, FSA and SC CCAMLR.  Obtained data used for the preliminary biomass estimation of the target species and making decision for the future fishing on that fishing ground. During the survey the fragments of IUU nets were taken on board.

The third year research plan of Ukraine in subarea 48.2 by the fishing vessel SIMEIZ is provided. The survey design remains the same as in the second (2016) year. Ukraine proposes to divide the stock (the catch limit) in the researched area on two blocks – Northern and Southern, in order to reach maximum coverage of the subarea by the research stations.

The stock of Antarctic toothfish (D. mawsoni) in CCAMLR subarea 48.4 was conservatively estimated from tagging returns to be 1068.7 tonnes. In previous years the harvest rate used for Patagonian toothfish (D. Eleginoides) in Subarea 48.3 (γ = 0.038) has been used as a precautionary harvest rate which would imply a 2016/17 yield of 40.6 tonnes compared to the 2015/16 TAC of 39 tonnes.

Net monitor cable systems have been prohibited in CCAMLR trawl fisheries since 1994. This paper advocates a change in the CM 25-03 that opens for use of such cable. It is argued that this is beneficial for management as well as fishery.

The first winter longline survey of Antarctic toothfish in the northern Ross Sea region was successfully completed during June and July 2016. A total of 55 longlines sets were completed in the 4 strata, and 55.2 t of Antarctic toothfish and 3.4 t of Patagonian toothfish were caught. Spawning and spent Antarctic toothfish were captured late in the survey on undersea features to the northwest of stratum 1. Gonad staging and gonadosomatic indices suggest that males in spawning condition may aggregate earlier than females and that spawning begins in early July. There were a higher proportion of male fish caught during the survey than during the summer fishery (73% vs. 60–65%), and the sex ratio varied substantially among sets. Nineteen toothfish eggs were captured using a plankton net in the top 200 m of the water column, and eggs from two running ripe females were successfully fertilised and reared for several days in flow through incubators. Egg buoyancy measurements, conducted with fertilised eggs in density gradient cylinders, are being analysed and compared with CTD data to indicate the depth of neutral buoyancy. We recommend that a survey be carried out from mid-July through August to further document the temporal extent of spawning, although much of the likely spawning habitat is under sea ice at that time.