Preliminary assessment of mackerel icefish, Champsocephalus gunnari, on the Heard Island Plateau (Division 58.5.2) based
on a survey in April–May 2003

A preliminary assessment of yield of Champsocephalus gunnari for Heard Island Plateau (Division 58.5.2) was undertaken using the standard CCAMLR methods, based on the result of a randomly stratified trawl survey completed between 16 April and 10 May 2003. The 2003 estimate of abundance was approximately 20% of the 2002 estimate. This decline in abundance is consistent with the passage of the strong 1997 cohort through the population and relatively weak recruitment in 1999 and 2000. The 1+ fish evident in the survey were not fully sampled and as such are not included in the assessment. Estimates of the strength of this cohort will not be possible until the May 2004 survey is complete. The estimates of short-term yield for 2004 and 2005 using the Mathcad implementation were 259 tonnes and 196 tonnes, respectively. Consideration is given to the potential use of alternative technical measures to control harvest of un-assessed cohorts and provide for more stable catches between fishing years, while meeting the objectives of Article II. Comparison of yield estimates between Mathcad and Generalised Yield Model (GYM) implementations indicated that the GYM version provided slightly higher estimates of short-term yield. These differences will need to be considered by the working group. The implications of the interannual variability in recruitment, natural mortality and growth of these fish, combined with the need to maintain a steady yield if possible need to be explored further in the development of a management procedure that fulfills the objectives of Article II and is robust against the uncertainties inherent in the stock dynamics of this species.