CCAMLR

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 four surveys were completed in February 2012, 2013, 2014, and 2015. In this paper we provide results of the fifth survey in the time series. The objectives of this survey were: (1) to continue a time series of longline surveys to monitor sub-adult (≤ 110 cm TL) toothfish in the south of SSRUs 881.J and 881.L in the southern Ross Sea (Strata A–C) using standardised gear in a standardised manner; and (2) to monitor trends in larger (large sub-adult and adult) toothfish abundance in two areas (both situated in SSRU 881.M) of importance to predators: McMurdo Sound in 2016 and Terra Nova Bay in 2017.

The 2016 survey was successful in completing all of the planned stations and objectives. Standardised catch rates of sub-adult (<110 cm) toothfish for the core strata showed an increase to the highest point observed in the time series. Age frequency data from the surveys have shown the progression of a cohort from age seven in 2012 to age nine in 2014 and to age ten for females in 2015. In 2016, the survey length frequency distributions indicate than another stronger year class has entered the population with a mode at 75 cm, and that the older year class has 100 cm. The decline in the catch rates from 2012–2015 was correlated with the decline in the abundance of the older cohort over time through mortality and the movement of older fish out of the core survey area, as well as the relatively weaker subsequent year classes. The increase in 2016 is also reflective of the introduction of a new, stronger year class into the population. These results suggest that the surveys are indexing local abundance and are providing a method for monitoring recruitment and estimating recruitment variability. We notify here that the survey will be conducted in 2016-17 as endorsed by the Commission.

Understanding the spatial distribution of the release of tagged fish and the subsequent spatial coverage of fishing effort to recapture tagged fish is an important consideration when interpreting the biomass estimated from mark recapture data. In 2015, the Scientific Committee identified that measures of spatial overlap and potential bias in the development of tag-based biomass estimates are an important focus topic for WG-SAM (SC-CAMLR-XXXIV, 2015, para 3.83). This paper outlines developments towards new biomass-weighted spatial overlap summary statistics for tagging data. The method calculates two statistics: (i) a single measure of the degree of spatial overlap between the release of tagged fish and subsequent fishing effort for tag recovery, labelled the tag spatial overlap (TSO) statistic and (ii) a measure of the potential bias in the biomass estimate calculated from non-homogenous spatial mark-recapture data, labelled the tag spatial bias (TSB) statistic.

We apply the method to a single case study area, SSRUs 88.2H to illustrate its use. We found that the median tag spatial overlap statistic in 2012 was 70% (95% CIs 53–80%), and the median tag overlap bias was 88% (95% CIs 64–114%). In 2014 the median tag spatial overlap statistic 60% (95% CIs 50-69%), and the median tag overlap bias was 192% (95% CIs 141-268%).

The TSO statistic and TSB statistic provide a simple; and intuitive approach to indexing the degree of spatial overlap and potential bias from mark recapture data, with few assumptions required on the distribution of fish, movement, or catch history. Potential uses of these statistics could include a measure of the total spatial distribution of effort through time in research or developing fisheries, and a measure of the change in bias of mark-recapture estimates through time.

This paper evaluates present regulation of cabled net monitoring instrumentation and suggests an adjustment in the CCAMLR requirements that enable the industry and researches onboard the krill vessel to collect more and better monitoring and research data.

This paper evaluates present reporting procedures for the continuous fishing method and proposes a change in the CCAMLR requirements that produces more robust and correct catch statistics.

Exploratory fishing for toothfish (Dissostichus spp.) in East Antarctica (Divisions 58.4.1 and 58.4.2) began in 2003. Robust stock assessment and catch limits according to CCAMLR decision rules remain to be determined for these Divisions. The 2015/16 season was the first of a three-year research plan which was developed by Australia (WG-FSA-15/47 Rev. 1) under Conservation Measure 41–01. Australia will present to WG-SAM-2016 a full report on the fishing operation, catch composition, tagging and biological sampling undertaken by Australia during 2015/16 in SSRUs 58.4.1E and 58.4.1G. Here, we evaluate the original research plan set out in WG-FSA-15/47 Rev. 1, and propose continuation of this research in the 2016/17 season. Ongoing standardised longline fishing, in conjunction with fish biological measurements, tagging and aging, will be used to develop a stock assessment/s for Divisions 58.4.1 and 58.4.2, and inform the necessary considerations of spatial structure, biomass and connectivity of toothfish populations. In addition, environmental data from CTD (conductivity, temperature and depth) and video loggers will contribute to models of toothfish habitat use. These models will inform spatial management approaches for toothfish, and the conservation of representative areas of benthic biodiversity. Additional outcomes include mapping of the bathymetry of fishable areas, and improved understanding of the distribution, relative abundance, and life histories of bycatch species.