CCAMLR

Cooperation between the Scientific Committee of CCAMLR (SC-CAMLR) and the Committee for Environmental Protection (CEP) has been steadily increasing over the last few years to the mutual benefit of both. In order to avoid duplicate reporting between the two committees, and following discussions between the Chairs of the CEP and SC-CAMLR, the report of the CEP meeting is presented to SC-CAMLR by the CEP Observer to SC-CAMLR and the report of the meeting of  SC-CAMLR is presented to the CEP by the SC-CAMLR observer to the CEP. An agreed standard reporting template, to be routinely followed by both committees, has also clarified and simplified the reciprocal reporting.  Accordingly this report provides the CEP’s annual report to SC-CAMLR XXXIII. A highlight of the 2014 CEP meeting was a proposal for a second joint CEP-SC-CAMLR workshop.

We revised the method of Candy et al. (2012) to estimate the ageing error matrix (misclassification matrix) to address some issues regarding true ages not being the mode at the extremes of the matrix and a lack of smoothness in the probabilities for ages above 25 years. Positive errors now aggregate into the plus group, negative errors are truncated below the minimum age, and fish with true ages greater than the plus group are incorporated into the final row of the misclassification matrix. We expanded the reference collection to include an additional 50 otoliths with a mean age above 25 years. The revised method was applied to the expanded reference collection to re-estimate the misclassification matrix.We assessed misclassification matrices obtained using the revised Candy method along with two other methods of accounting for ageing error, approximation by a Gamma distribution and a constant coefficient of variation (c.v.) of 0.1. We compared the misclassification matrices with the observed age determinations from the expanded reference collection. We then used estimates of spawning stock biomass (SSB) and year class strength (YCS) from the CASAL assessment of the HIMI fishery to evaluate the effects of these three methods along with assuming no ageing error. The Gamma and revised Candy methods both provided satisfactory representations of the observed age determinations. The constant c.v. method provided a poor representation of the observed ages, underestimating the variability at the younger age classes and over estimating the variability at the older age classes. Estimates of SSB were similar for the revised Candy and Gamma methods. The constant c.v. method and assuming no ageing error produced similar estimates of SSB that were consistently lower than those from the revised Candy and Gamma methods. Not accounting for ageing error gave the most precise and least variable estimates of YCS while the Gamma method gave the least precise and most variable estimates. Estimates of YCS from the constant c.v. method and the revised Candy method were between the other two methods in terms of year to year variability and precision. The poor agreement of the constant c.v. method with observed ages and the similarity of SSB estimates to those obtained assuming no ageing error would suggest it is not appropriate for use in the HIMI assessment and we would caution others to assess its impact before applying it to their assessments. Estimates of SSB from the Gamma method were consistent with the revised Candy method, suggesting this method may be of use where there is insufficient data to estimate ageing error directly.

The Australian Antarctic Division (AAD) has recently received funding to continue an ageing program for the purposes of routine processing of Patagonian toothfish (Dissostichus eleginoides) otoliths from the Heard Island and McDonald Islands fishery. With the reinitiation of this program a number of methodological refinements have been made to those outlined by Nowara et al. (2009), particularly in relation to the laboratory processing of otoliths and quality control in the assignment of fish age. These changes have contributed to increased efficiency within the program, with a greater capacity for ageing and at a lower cost per otolith. Greatest efficiency gains have been made in the laboratory, with otoliths now set in smaller resin blocks that take much less time to section, and in quality control and reporting procedures, which are now largely automated using R.

A key part of quality assurance in any ageing program is to minimise the effect that a reader has in assigning ages.  In the AAD program, two readers look at all otoliths, which has proved useful in helping to identify  otoliths that may be  interpreted differently by different readers, so they can be flagged, re-read, and consensus reached on the most likely age estimate.  Using the otolith weight/age relationship has also been useful for identifying otoliths that may have been aged with good precision between the two readers, but may represent systematic error in interpretation (e.g. both readers may have counted all sub-banding for a particular fish).

This year’s stock assessment includes new age data from the 2012, 2013 and 2014 RSTSs, as well as from the commercial fishery in 2013. The recent focus by AAD to age more large fish from commercial samples has substantially increased the information available on older age classes (i.e. fish greater than 20 years) available for use in the current assessment (Ziegler et al., 2014).
 

The annual Random Stratified Trawl Survey was undertaken in Division 58.5.2 in the vicinity of Heard Island during June 2014. This paper provides a preliminary assessment of mackerel icefish population structure, abundance and yield for the area of Division 58.5.2 to the west of 79° 20’ E using standard CCAMLR methods. A pattern of multiple year classes being present simultaneously in the population, which was first detected in 2011, has persisted. The large cohort observed in recent surveys was still numerically dominant, however there is evidence that recruitment to the 0+-3+ cohorts has taken place. Given the expectation that the current 4+ and 5+ cohorts are fully exploited, only the 1+-3+ cohorts were projected. These projections indicate that catches of 309t in the 2014/15 season and 275t in the 2015/16 season satisfies the CCAMLR decision rules.