CCAMLR

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.

1. The first Session of the Meeting of the Parties (MOP1) of the Agreement on the Conservation of Albatrosses and Petrels (ACAP) agreed to review the population status, trends and demography of albatrosses (21 species) and petrels (seven species) listed on Annex 1 of the Agreement (MOP1 Final Report, Paragraph 7.2).
2. To progress this review, ACAP’s Advisory Committee established a Working Group with the aim of collecting and collating information on breeding numbers and critical population and demographic parameters on each species. It was anticipated that this synthesis would then enable gaps in information to be identified and facilitate the prioritisation of actions to collect information to fill these gaps.
3. The data for this review was sought from Parties and Signatories to ACAP that are Breeding Range States for the ACAP-listed species. Rosemary Gales (Australia) was appointed to chair the Working Group. A summary of the findings of the Working Group are provided.

The upper-arm of the length-dependent fishing selectivity function for trawlers fishing for Patagonian toothfish around Heard Island (Division 58.5.2) was modelled as the exponential of a quadratic function in length. This function was calibrated using random length frequency (LF) data collected from commercial operations of each of trawlers and longliners fishing concurrently for 3 seasons assuming that, for the upper range of lengths, fish are fully selected by longliners but not by trawlers. To estimate the trawl gear selectivity while simultaneously adjusting for relative availability of length classes as a function of fishing depth, a log-linear hazard function for each gear type was fitted by a technique used to model grouped survival data. The hazard function relates to the event of a fish falling in a particular length bin, analagous to a death in a given time interval in survival analysis, and the ratio of the hazard function for trawlers to that of longliners for the length range where this ratio is less than 1 defines the upper-arm of the trawl gear selectivity function. This model of selectivity was estimated using the LF data and a fitted binomial generalized linear mixed model (GLMM). The GLMM was fitted to the number of fish in a bin using a complementary log-log link function and binomial sample size defined as the number of fish in that bin or a larger length bin. The resultant conditional binomial probability of the event is linked to an approximate integral of the hazard function to give the GLMM formulation. Random effects of haul identifier and ‘season by length bin’ were included in the GLMM which was fitted using an approximation to the marginal quasi-likelihood (MQL). The fitted trawl gear selectivity function showed a decline from 100% to 1% selection for a corresponding length range of 1030 to 1610 mm and relative availability of fish was also predicted to decrease across a similar length range for the median trawl depth of 580 m relative to the median depth of longline sets of 1200 m.