CCAMLR

We satellite tracked four adult southern giant petrels (Macronectes giganteus), four adult northern giant petrels (Macronectes halli), and two fledgling chicks of each species during the summer of 2005-06. Adults of both species spent time in areas under CCAMLR jurisdiction. Adult southern giant petrels spent 37% of their overall time at sea in statistical sub-area 58.4.1, and 14% in sub-area 88.1, extensively utilising these regions during long foraging trips to the ice-edge zone during incubation. Northern giant petrels were tracked during chick rearing. While 3 of four tracked birds did not enter CCAMLR waters, one bird undertook a longer trip into division 58.4.1, where it spent 6% of its overall time at sea. We consider it possible that this trip may have been indicative of trips undertaken earlier in the season (prior to hatching). Both southern and northern giant petrel fledglings crossed the Pacific Ocean, travelling east towards the South American Continental Shelf. Southern giant petrel chicks took a more southerly route, traversing statistical subareas 88.1 and 88.2 along this course, while the more northerly route taken by northern giant petrel chicks did not take them into CCAMLR waters.

We provide an update of the Bayesian sex and age structured population stock assessment model for Antarctic toothfish (Dissostichus mawsoni) in the SSRU 88.2E, using revised catch, CPUE, catch-at-age and tag-recapture data from New Zealand and all vessels. The updated reference case resulted in a slightly higher estimate of initial biomass than in 2005, though this was mostly due to a different assumption of the level of natural mortality (M=0.13 y-1), and the revised length-weight and growth relationships. There was little difference between model runs using the New Zealand tag-release and recapture data and the all vessel tag-release and recapture data (B0= 10 300 t and 9 530 t respectively).
Model fits to the data were adequate, with the tag-release and recapture data providing the most information on stock size, but none of the data sets had much information about the maximum size of the stock. Monte-Carlo Markov Chain (MCMC) diagnostics suggested no evidence of non-convergence. Reference case MCMC estimates of initial (equilibrium) spawning stock abundance (B0) were very uncertain, with the median estimated as 10 300 t (95% credible intervals 5 340–25 210 t), and current (B2006) biomass estimated as 91.4% B0 (95% C.I.s 83.4–96.5%).
Estimated yields, using the CCAMLR decision rules, were estimated to be 352 t for the reference case and 366 t for the all vessels case, assuming a future fishing selectivity equal to the maturity ogive.

The Ross Sea toothfish fishery has operated during the Antarctic summer (December–May) since 1997 in CCAMLR Subareas 88.1 and 88.2. Previously, standardised analysis of toothfish CPUE (catch per hook) have been carried out for the Ross Sea (Subarea 88.1 and SSRUs 88.2A–B) for the 1998 to 2005 fishing years. This report revises and updates the previous analysis with the addition of data from the 2006 season for the Ross Sea using the revised location data for (a) all vessels and (b) core vessels that have been in the fishery for at least 4 years. We estimate indices using both lognormal generalised linear models and a Tweedie mixed model.
The variables included in the analysis appeared reasonable and were consistent between the models presented here and CPUE analyses for previous years. The yearly indices were relatively stable between 1998 and 2003, with a decline in 2004, and an increase in 2005 and 2006. Possible explanations for the decline in 2004 were gear conflict and competition between vessels to set lines, in addition to extreme ice conditions that limited where lines could be set. None of these factors were believed to be important in 2005 or 2006.
The CPUE indices for the Ross Sea have increased more than 50% since the beginning for the fishery in 1998. Favourable ice conditions, fisher learning and experience, including improved knowledge of optimum fishing practise, and improvements in gear are the most likely explanations for the increase in CPUE indices, rather than toothfish abundance. Hence the CPUE indices developed here are of limited use as indices of toothfish abundance at the current time.

Australia proposes that the possession and/or use of gillnets for commercial purposes be prohibited until such time as (1) the Scientific Committee has investigated and reported on the potential impacts of this gear in the Convention Area, and (2) the Commission has agreed on the basis of advice from the Scientific Committee that such a method may be used in the Convention Area.

A survey of Patagonian toothfish, Dissostichus eleginoides, was undertaken in Division 58.5.2 in the vicinity of Heard Island in May-June 2006 to provide the information for an assessment of short-term annual yield in the 2006/2007 CCAMLR season. This paper provides a preliminary assessment of yield for the area of Division 58.5.2 to the west of 79°20’ E using standard CCAMLR methods. It also investigates the impact on the recruitment series and predicted yields of:
i) excluding the unusually high length density data from the 1999 survey
ii) the exclusion of year classes 6+ which have been included in previous assessments (WG-FSA 2005) but are apparently not well selected.
iii) research removals only and reported fishing only.

This paper reviews the allocation of historical survey data to the new strata and the implications of this review to estimating the abundance of juvenile fish using CMIX. In addition, the paper examines how the latest length-at-age model for Dissostichus eleginoides (Patagonian toothfish) in 58.5.2 could affect the estimates of juvenile abundance. Model estimates were best incorporating the reassignment of hauls and the latest estimates of length at age, but quality of model fit and estimates of abundance of specific cohorts were sensitive to the number of cohorts assumed to be represented in the length density data. Assuming survey design produces unbiased estimates of length density, we suggest that best estimates of cohort abundance will be achieved when mixture analysis is informed by accurate estimates of length at age, an independent estimate of relative abundance of cohorts present in any survey year such as could be derived through an age length key, and the selectivity of the gear used in the surveys.
The consequences to the 2005 assessment of yield of toothfish of changing the time series of abundance of juvenile fish and the length-at-age model were also examined. Yield estimates were found to be most sensitive to the estimated recruitment series interacting with the estimate of mortality and the cohort abundances from CMIX, and to a lesser extent estimated fishing selectivities. A scenario equivalent to that used to recommend yield in 58.5.2 for 2005/06, incorporating the latest estimates of length at age, selectivity and the mixtures estimated from the assignment of RSTS hauls, resulted in a significant increase in estimated yield.

A survey of mackerel icefish, Champsocephalus gunnari, was undertaken in Division 58.5.2 in the vicinity of Heard Island in May-June 2006 to provide the information for an assessment of short-term annual yield in the 2006/2007 CCAMLR season. This paper provides a preliminary assessment of yield for the area of Division 58.5.2 to the west of 79°20’ E using standard CCAMLR methods. A lack of evidence of strong year classes recruiting to the population has led to a significant decrease in the estimated biomass of mackerel icefish, and a recommended catch over the projection period nearly an order of magnitude less than that set in 2005. Taking into account the fact that the 4+ year class, which contributed an estimated 80% of the biomass present during the survey, are unlikely to be available to the fishery next year, yield estimates for 2006/07 are a further 70% lower.

Random stratified trawl surveys (RSTSs) of the distribution and abundance of demersal fish species on the Heard Island plateau have been conducted annually since 1997. The survey conducted in May-June 2006 had two main aims:
• to assess the abundance and size structure of juvenile and adult Dissostichus eleginoides on the shallow and deep parts of the Heard Island Plateau. ]
• to assess the abundance and size structure of Champsocephalus gunnari on the Heard Island Plateau
This paper describes the survey design and gear configuration used during the 2006 RSTS, conducted from aboard the FV Southern Champion. It also describes the results of the survey, detailing the breakdown of catches overall and by stratum.
Patagonian toothfish Dissostichus eleginoides were the most abundant fish species overall, with Channichthys rhinoceratus, Champsocephalus gunnari and Macruronus whitsoni also locally abundant. Common bycatch included rocks, sponges, echinoderms, jellyfish and anemones.

This study estimates the mortality of seabirds in the South African deep water hake trawl fishery. Observations of interactions between seabirds and trawl gear were made on 331 trawls during 20 trips on 14 vessels between mid-2004 and end 2005. Long-winged albatrosses were killed most frequently, with Shy Albatrosses comprising 43% and Black-browed Albatrosses 37% of birds killed. Small numbers of White-chinned Petrels (10%), Cape Gannets (7%) and Sooty Shearwaters (3%) also were killed. Mortalities were greater in winter, when more birds attended fishing vessels, and most occurred during dumping of fishery wastes. Using a bootstrapping approach to estimate 95% confidence intervals (CI), the average mortality rates were 0.56 (0.32-0.82) birds killed per hour during dumping in winter, 0.21 (0.07-0.38) during dumping in summer, 0.09 (0.02- 0.19) when not dumping in winter, and 0.00 (–) when not dumping in summer. Serious warp incidents were independent of age among albatrosses, but there was a tendency for immature gannets to have a higher interaction rate than adults. Deaths resulting from entanglement in fishing nets occurred at an average rate of 3.02 (0.91-5.44) birds per 100 trawls. Estimating the total impact of the fishery requires assumptions about total fishing effort, the proportion of trawls where dumping takes place and the average duration of dumping. A simple model was developed which allowed these parameters to be varied, but the most sensitive parameters were bycatch rates. Based on conservative estimates of effort and dumping time, the total extrapolated mortality is some 18 000 (95% CI 8 000-31 000) birds killed per year, of which 85% are killed on warps and 15% entangled in nets. Of the birds killed, some 39% are Shy Albatrosses, 29% Black-browed Albatrosses, 14% Cape Gannets and 9% White-chinned Petrels, all listed as globally threatened or near-threatened. Active mitigation measures are required to reduce trawl mortality in this fishery.