CCAMLR

This paper further develops an integrated assessment for Patagonian toothfish in Division 58.5.2. It updates the model used at WG-FSA in 2006 using data from the 2007 season as well as 2006 data not available for WG-FSA in 2006. It also includes the following refinements: (i) estimation of the coefficient of variation (CV) for length given age, (ii) use of non-informative priors for year class strength parameters, (iii) separate selectivity parameters used for the pre-2006 compared to the 2006-2007 fishing seasons for the main trawl ground, (iv) separate selectivity parameters for the late (within-year) season compared to the combined early (within-year) seasons for the main trawl ground, and (v) the use of an improved method of determining effective sample size for commercial catch-at-length data. The estimated long-term yield was 2500 tonnes with depletion probability of 0.081 and escapement probability of 0.505. As expected, the assessment was sensitive to the inclusion of different datasets and to the choices of parameters used in both the stock assessment and projections. It is concluded that until the difficulties with the use of mark-recapture data are resolved, recruitment surveys provide the best means of establishing current stock status as an absolute index of abundance.

Fish samples collected through an overall period of 24 years at Potter Cove after the impact of the fishery in the area in 1978-80, allowed the comparison of the variations in mean annual lengths and density distributions of the commercially exploited species N. rossi and G. gibberrifrons with the ecologically similar but unexploited N. coriiceps. The sharp decline in the abundance of N. rossii reported for the period 1983 - 1991/2 is consistent with the increase in mean size observed between 1983 and 1986/7 and the duration of the inshore phase of the species, which is known to last for 6-7 years. In the following years, until 1991/92, the decreasing abundance is consistent with the entrance of low strength cohorts with the consequent reduction in mean size. The above interpretation is supported by the length distributions observed between 1982/83 and 1985/86, where the modal age changes from 2/3 to 6/7 years. After 1991/92 the densities, mean sizes and abundances do not depend on a single forcing event but on several interacting factors. The length data of G. gibberifrons, available from 1986, show a decrease until 1991/92, exhibiting a similar pattern to that of N. rossii. After a period of relative stability in mean sizes (1992-1994) a sharp increase is associated with a continuous decline in relative abundance suggesting that it is due to increasingly low recruitments. The length frequency distributions of N. coriiceps through the whole studied period do not show any definite change in modal size, nor a pattern in mean lengths as is the case with N. rossii and G. gibberifrons.

We analyzed data collected during 2005 seabird mitigation experiments on integrated weight longlines (IW) in a demersal longline fishery for effects on skate bycatch. Trials took place on two vessels targeting Pacific cod (Gadus macrocephalus) over a five-month period in the Bering Sea, Alaska, USA. The skate catch rate was 11% lower on the IW gear compared to unweighted gear. Location, month and depth were also significant predictors of skate catch rates. While results indicate IW shows potential to reduce skate catch rates, further evaluation and analysis by individual species should be performed in specific regions where skate bycatch is a problem.

Feeding of Antarctic toothfish Dissostichus mawsoni was studied in new fishing ground for this species in the Pacific sector of Antarctic: Amundsen Sea (Subarea 88.2). In terms of occurrence, the most important fish items in toothfish diet were: Whitson’s grenadier (Macrourus whitsoni), crocodile icefish (Chionobathyscus dewitti), antimora (Antimora rostrata), Antarctic jonasfish (Notolepis coatsi) and other species.
Cephalopod beaks were quite abundant in the stomachs of toothfish. These beaks were identified as belonging to large Antarctic squids: M.hamiltoni, P.glacialis ? K.longimana. Analysis of distribution and ecology of species prayed by Antarctic toothfish shows that D. mawsoni apparently represents a fast-swimming predator with wide feeding spectrum. Its diet includes bottom, bathy- and mesopelagic fishes as well as large squids.

The results of the histological analysis of the Antarctic toothfish (Dissostichus mawsoni) reproductive system, caught in December-March, 2004-2005 by the longliner VOLNA in subareas 88.1 and 88.2 in the Ross Sea are presented. The morphological parameters, indices of gonads have been described. The histological criteria of the assessment of the ovary maturity stages and cytological parameters of oocytes and type of the toothfish oogenesis have been determined. Under the maturing of toothfish ovaries from the stages II to IV show a slow increase in oocyte diameter. It was shown that for Antarctic toothfish during the fishing period the individuals with gonads of the III late stage of maturity were dominated. Their ovaries contained three size groups of oocytes: cytoplasmic group and two groups of vitellogenous oocytes. The type of the toothfish oogenesis has been defined as intermitted. The large oocytes of the nearest spawning season with average diameter 1000 - 1200?10-6 m have composed 5.4% of total cell number. The oocytes in the ovaries of analyzed fish did not reach the maximum size; consequently Antarctic toothfish was not matured for spawning in the Ross Sea during the investigation period.

Australia has conducted a scientific tagging program in the Dissostichus eleginoides fishery in 58.5.2 since the 1997/98 season. This program has yielded data which has assisted with understanding growth rates of toothfish, small and large scale movements, stock structure and local abundance. This paper serves as an overview of the tagging dataset, and an update to previous summary papers. Tagging effort and recaptures are very concentrated in a relatively small area of this species’ habitat in this Division. Furthermore, as toothfish appear to have complex patterns of movement in space and time; being generally sedentary, but occasionally moving large distances, using tagging data to assess the status of stock in 58.5.2 remains difficult, and is likely to remain so until sufficient data to provide unbiased estimates of movement rates between areas and fisheries can be included in an integrated assessment framework.

A survey of mackerel icefish, Champsocephalus gunnari, was undertaken in Division 58.5.2 in the vicinity of Heard Island in July 2007 to provide the information for an assessment of short-term annual yield in the 2007/2008 CCAMLR season. This paper provides a preliminary assessment of yield for the area of Division 58.5.2 to the west of 79o 20’ E using standard CCAMLR methods. Evidence of strong 1+ year class recruiting to the population has led to an increase in the estimated biomass of mackerel icefish, and an increase on the recommended catch over the projection. Based on a similar cohort structure seen in the population in 2003, this estimate is likely to increase further as this cohort is more fully selected.

Since the commencement of commercial fishing in Australian waters on the Heard Island plateau in 1997 an annual random stratified trawl survey (RSTS) has been conducted to assess the stocks of Patagonian toothfish (Dissostichus eleginoides) and mackerel icefish (Champsocephalus gunnari). The 2007 survey had two main aims:
• to assess the abundance of juvenile and adult Dissostichus eleginoides on the shallow and deep parts of the Heard Island Plateau;
• to assess the abundance of Champsocephalus gunnari on the Heard Island Plateau.
The survey had the same design as the 2006 RSTS survey in the number of stations chosen for sampling in each stratum. This paper describes the conduct of the survey on the FV Southern Champion during June to July 2007 and the resulting catches and biological sampling. The most abundant species in the catch was D. eleginoides, followed by Lepidonotothen squamifrons, Channichthys rhinoceratus, C. gunnari and Macrourus sp. Catches of these 5 main fish species were very similar to those in 2006, with the exception of Lepidonotothen squamifrons which was much more abundant in 2007. Holothurians, poriferans, medusae and anemones were the most common invertebrate biota caught in the net.

Scientific observers aboard vessels in the Australian fisheries in 58.5.2 have collected Dissostichus eleginoides otoliths since the fishery commenced in the 1996/97 season. This program has yielded data which has assisted with understanding age structure and growth rates of toothfish in this Division. This paper summarises the otolith collection housed at the Australian Antarctic Division, including individuals collected during research and commercial fishing, tag recaptures, and those individuals which have been processed by the Central Ageing Facility to provide size-at-age estimates. Over 21000 otoliths have been collected from toothfish in 58.5.2, and more than 2500 otolith pairs have been collected from recaptured tagged fish. More than 3200 otoliths have been processed to provide size-at-age estimates from fish captured between 1997 and 2003. A growth model based on these size-at age data is currently used in the assessment to predict growth and assign length-at-age to catch-at age, however an alternative method to assign catch at age is age-length keys. Relatively few otoliths have been collected or aged from the annual trawl survey or the longline fishery, making constructing historical season by season age-length keys for these fisheries impossible. It is likely that sufficient otoliths have been collected from the main trawl ground to construct age-length keys, however the feasibility and benefit of proceeding to age-length keys in terms of precision of stock assessment requires simulation analysis.

In 2006 the CCAMLR scientific committee noted several features of exploratory Dissostichus fisheries in the southern Indian Ocean (58.4) which gave cause for concern as to the status of the resource in this area, and the lack of a scientific basis for setting catch limits in these areas (SC-CAMLR XXV, paragraphs 4.184-4.192).
In its management advice for this and other exploratory fisheries, the Scientific Committee requested urgent consideration by Members of methods for collecting data and of assessing these stocks.
At its meeting in July 2007, WG-SAM agreed that fine-scale analysis of catch and effort would be a useful way of progressing an assessment of BANZARE fishery (WG-SAM 2007, paragraphs 3.1-3.7), including:
• Identification of grounds through analysis of spatial pattern in catch and effort;
• Exploration of standardising CPUE series for each ground; and
• Analysis of CPUE of Dissostichus spp. to provide initial estimates of biomass and rates of depletion in each ground.
This paper develops further the initial exploration of the C2 fine scale catch and effort data held by CCAMLR for the fishery in this Division presented to WG-SAM in 2007, as well as descriptive analyses of the B2 biological data submitted by scientific observers aboard vessels in the BANZARE fishery.
Data were too few, or with insufficient overlap between seasons, to permit meaningful standardisation for depletion analysis. However, these preliminary analyses indicate there is strong evidence for depletion of toothfish at the scale of individual fishing grounds in 2004/05 and 2005/06 seasons. There are also several inconsistencies noted between historical catch rates and catch compositions and those reported in the 2006/07 season, with Patagonian toothfish dominating in catches in one ground for the first time, and some observers reporting no biological information on important bycatch groups reported in the vessels catch records.
We recommend that WG-FSA evaluate management options in 58.4.3b, including the lowering of catch limits commensurate with the rapid and unsustainable depletion seen in the fishery, the development of SSRUs to better represent the concentrated nature of the fishery in 58.4.3b, commensurate management of areas that are obviously depleted, and the design of a longline survey to attempt to verify some of the trends in catch rates and catch composition seen in the main fishing areas.