CCAMLR

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.