CCAMLR

A tagging survey in SSRUs B and C in Division 58.4.4 a & b was conducted in the 2011/12 fishing season with the aims of providing the data required for assessments of the population structure, size, movement and growth of Dissostichus spp. in the centred area of Division 58.4.4 a & b. An approximate stock biomass level of Dissostichus spp. in the survey area was tentatively estimated using Lincoln-Petersen and CPUE comparison methods. The medial estimate using Lincoln-Petersen (1 725 ton) was smaller than that 1 928 tonnes estimated in the WG-FSA meeting in 2011 (SC-CAMLR XXX, Annext 4, paragraphs 5.19-21).CVs of 20 % achievable from the biomass estimates may be achieved within three years with an annual research catch of approximately 50 tonnes. The estimate (976 tonnes) using CPUE comparison method was smaller than that using Lincoln- Petersen. We would continue the mark-recapture experiments in the 2012/13 season changing the targeted area from SSRUs B and C to SSRUs C and D due to avoid the huge loss of catch from killer whales in SSRU B. The catch biomass level in SSRUs B and C was calculated as 86 tonnes using Lincoln-Petersen and 54 tonnes using CPUE comparison at 5 % of exploitation rate. Because mean CPUE (67 kg /km) in SSRUs C and D was higher than that (62 kg /km) over the four year’s cruises (two year’s cruises for SSRU D), the proposed sample size as existing 70 tonnes for the next 2012/13 survey seems to be appropriate for the newly targeted area. To apply mark-and recapture studies, tagging rate of ≥ 5 fish / ton will be conducted. Only Trot line system will be used for all 71 hauls. However, if sufficient numbers of fish suitable for tagging are not captured using the normal trotline system, we would increase the comparison tests with trotline and Spanish line systems. We aimed the establishment of CASAL catch-at-age model for this Division by 2016/17.

A survey was conducted in order to collect information for the stock status and various biological information on toothfish in SSRU B and C of Division 58.4.4a & b (Ob Lena Banks) from April 15 to May 19, 2012. Total catch (excluding tagged and released fish) of Dissostichus eleginoides was 28.3 tonnes in the survey area in 70 longline sets. Mean CPUEs of D. eleginoides was 48.3 kg / km (CV = 79.1%) in terms of weight. The mean CPUE in terms of weight in SSRU B (32.1 kg / km) was rather lower than that (50.5 kg / km) in the same SSRU in 2010/11. A total of 172 individuals of toothfish with good physical condition and single-hooked were tagged and released during the survey, and 3 D. eleginoides, which were tagged and released in SSRUs B and C from the 2007/08 to 2010/11, were recaptured in the same SSRUs, respectively. Fish with good physical condition and single-hooked contributed 50 % to the total among fish caught by Spanish line system, while this kind of fish contributed 14 % to the total among fish caught by trotline system. A total of 133 killer whales（Orcinus orca）were observed at the 30 hauls. All of whales occurred in SSRU B. The vessel tried to avoid killer whales as in the previous surveys but could not escape from them effectively in SSRU B. Seventy-nine % of sets to the total were affected by killer whales in SSRU B in 2010/11 and 2011/12. On the other hand, no set was affected by killer whales in SSRU D in 2007/08 and 2009/10. Generalized additive model analysis indicated that the presence of killer whales leads to huge loss (ca. 40 %) of catch of D. eleginoides in SSRUs B and C.

Research-based New and Exploited fisheries have been conducted in order to collect information for the stock status and biology of toothfish in the Division 58.4.3b (Banzare Bank), using a Japanese commercial longline vessel Shinsei maru No. 3, during 2006/07 and 2011/12. Total number of hauls ranged from 22 to 148 during the six cruises. Total catch of Dissostichus spp. ranged from 9 to 108 ton. Predicted CPUE (catch/km) for D. eleginoides and D. mawsoni varied with years but showed no upward and downward tendencies with years. D. mawsoni mainly occurred in the shallower areas > 1 200 m but decreased in the CPUE as the depth decreased, while D. eleginoides mainly occurred in 600 – 1 000 m depths but rarely occurred in the deeper areas > 1 400 m. Progressed stages of GMI and high GSIs for D. mawsoni were observed in 2010/11 and 2011/12 when the researches were conducted in May and June, suggesting that Banzare Bank is one of important spawning grounds for D. mawsoni. On the other hand, such an apparent seasonal development of the maturity indices was not observed for D. eleginoides. Predicted trot line CPUE was significantly higher than Spanish line for D. eleginides, but no significant difference in the CPUE between gears was observed for D. mawsoni.

We would continue the survey focusing mark-recapture experiment in the 2012/13 season with a little modified spatial design. An approximate stock biomass level of Dissostichus spp. in the target stock area was estimated to be 8 444 tonnes, using CPUE comparison method. Applying a precautionary discount factor for biomass estimated of 0.3 and a precautionary exploitation rate of 0.01, catch biomass level was calculated as 84.4 ton. Thus the existing catch limit of 40 tonnes seems to be appropriate for the 2012/13 survey. We aimed the establishment of CASAL catch-at-age model for this Division by 2016/17.

Grenadiers Macrourus spp. are the main bycatch species in the exploratory longline fishery for toothfish Dissostichus spp. in the Ross Sea, Antarctica. Ongoing monitoring tools are needed to assess stock status of grenadiers in the Ross Sea and to ensure ecological relationships are maintained. There may be potential to use fisheries acoustic methods to obtain estimates of grenadier abundance. Acoustic data collected during New Zealand’s International Polar Year Census of Marine Life survey in February–March 2008 provide evidence that single targets close to the bottom over the Ross Sea slope are grenadiers. The acoustic target strength distribution of single targets was very similar to that predicted based on the measured size range of grenadiers. There are also positive correlations between acoustic backscatter and trawl and longline catches of grenadiers. Key uncertainties of the acoustic method are mark identification away from the bottom, and technical issues with low signal-to-noise ratio at depths greater than 1000 m and the acoustic dead-zone close to the bottom.

Updated software is presented for the automated production of standardised image plots of spatially referenced bottom fishing impact assessments. This software is submitted to WG-FSA as an R library to assist the Secretariat or CCAMLR Working Groups in the production of integrated bottom fishing impact assessments, including routine update of the circumpolar impact assessment originally described in SC-CAMLR-XXIX/4, Appendix E.

We present the first differentiated information on the biology and ecological niche of Macrourus whitsoni and M. caml in the Ross Sea region of the Southern Ocean. Fish were caught by New Zealand vessels in the fishery for Antarctic toothfish (Dissostichus mawsoni) between December 2011 and February 2012 from CCAMLR subareas 88.1B, 88.1C, 88.1G, 88.1H, 88.1K and 88.2H. In total, 227 M. whitsoni and 636 M. caml were examined.

Macrourus caml grows larger than M. whitsoni and is about 19% heavier for a given length. The largest M. caml examined was 84 cm total length (TL) and 5.4 kg, whereas the largest M. whitsoni examined was 65 cm TL and 1.3 kg. The two main morphological characters (number of rays in the left pelvic fin; number of rows of teeth in the lower jaw) were very effective at distinguishing between the two species. Scientific observers on New Zealand vessels had an success rate of identification of the two species of 94% overall. We found that total length (TL) was no less precise a measurement than pre-anal length (PAL), even after catching fish on longlines, freezing and rethawing. On the broad scale, Macrourus whitsoni and M. caml seem to be almost completely sympatric by depth and area, with both appearing to be abundant between depths of 900 and 1900 m. There was a small but significant increase in the proportion of M. whitsoni relative to M. caml caught on baited autolines with increasing depth. Catches of females of both species exceeded that of males (especially for M. caml) and this sex-selectivity was not explained by size or age of fish.

Otolith aging data show that the two species have very different growth rates; M. whitsoni approaches full size at about 10–15 years of age and can live to at least 27 years; in M. caml, full size is attained at about 15–20 years of age and they can live in excess of 60 years. However, sexual maturity in female M. whitsoni is reached at longer length and older age than in female M. caml (length at maturity 52/46 cm TL; age at maturity 16/13 y for M. whitsoni/M. caml respectively). Our data were insufficient to estimate onset of sexual maturity for males of either species. Gonad staging data imply that the spawning period of both species may be extended, starting within or before December–January, and with the main part of the spawning occuring later than February. Gonad stage data did not reveal any substantial differences in spawning characteristics between areas.

Most stomachs from both species everted on capture, so we augmented stomach contents data with examination of material from intestines. Our diet data are preliminary but are consistent with previous feeding studies of Macrourus spp., suggesting that M. whitsoni and M. caml are euryphagous predators and scavengers. Both species were found to be partially piscivorous, and amphipods were probably one of the main crustaceans consumed. Our data suggest that M. caml may feed more benthically than M. whitsoni (evidence of feeding on coral, ophiuroid, echinoderm, benthic polychaetes), though both species had been recently feeding on both benthic and pelagic prey, and the sample size was small. Isotopic analysis of muscle samples led to an estimated trophic level of 4.4 for M. caml and 4.1–4.2 for M. whitsoni.

Two size classes of A. georgiana have been described in by-catch fishing data reported in the catch data from the Ross Sea fisheries. We extracted DNA from A. georgiana samples from both size classes collected by Scientific Observers in the Ross Sea. We determined the DNA sequences of five mitochondrial DNA (mtDNA) gene sequences and tested whether the two size classes represented genetically differentiated groups, which might have formed through a recent speciation event. We found no genetic differences among the samples of A. georgiana that were collected in the Ross Sea region, and the data did not support the hypothesis that the two size classes were reproductively isolated.

The diet of Antarctic toothfish (Dissostichus mawsoni) in the Ross Sea region was examined based on stomach samples obtained from observers on New Zealand fishing vessels in 2003 and 2010. Overall, the diet of sub-adult toothfish was similar to that of adult toothfish, with a dominance of piscivory on benthic fishes and cephalopods, augmented by benthic invertebrates. Sub-adult toothfish ate a greater variety of smaller prey than adults, including smaller fishes (such as Trematomus sp., dragonfish, mainly Bathydraco spp.), and large decapod prawns (Nematocarcinus). By weight and index of relative importance (IRI), grenadiers (Macrourus spp.) were the most important fish and overall prey species. The study did not distinguish between M. whitsoni and M. caml, but this should occur in future. Over the Ross Sea continental shelf, icefish (probably mainly Chionobathyscus dewitti), and eel cods (probably mainly Muraenolepis evseenkoi) were important prey items. Glacial squid, P. glacialis, were the most important cephalopod prey species, especially over the northwest Iselin Bank. On oceanic seamounts, toothfish fed substantially on Macrourus spp. but also deep sea cod (Antimora rostrata), a variety of cephalopods and the occasional mesopelagic to epipelagic fish.

A key aim of this study was to see whether stomach contents of toothfish could be used to detect ecosystem change in the Ross Sea region, with a focus on the area of highest fishing intensity – the northern parts of the Mawson and Iselin Banks on the Ross Sea continental slope (70°–73°S, 175°E–175°W). Variation of stomach contents with toothfish length, weight, sex, month, depth and location was analysed to investigate whether a residual year effect was discernible in stomach contents in this region between 2003 and 2010. Although these factors explained some variation in stomach contents in the Mawson and Iselin Bank block, the proportion of variance explained was relatively small, and we found no statistically significant change in toothfish diet between 2003 and 2010. Holling type I and type II feeding relationships were determined for the Mawson and Iselin Bank on the continental slope using catch per unit effort (CPUE, fish per 1000 hooks) for grenadiers, ice fish and eel cods. Compared to CPUE, icefish and eel cods were over-represented in toothfish stomachs relative to grenadiers. The fitted feeding selectivity for toothfish relative to the selectivity of baited autoline fishing gear was found to be nearly 11 times higher for icefish than for grenadiers; the relative selectivity was more than 4 times higher for eel cods than that for grenadiers. It is not known whether this is due to lower catchability by longlines, greater availability to toothfish predation for a given abundance, or higher toothfish feeding preference for icefish and eel cods relative to grenadiers.

Reliable estimates of demersal fish community composition and population densities are essential for understanding the ecological effects of fisheries. Such estimates are conventionally derived from research trawl surveys but video techniques afford an alternative, or complementary, approach. Using data collected during a survey of demersal fish communities in the Ross Sea region of Antarctica, we compared measures of community composition, population density, and biomass derived from three sampling methods; a large demersal fish trawl, a beam trawl, and a towed camera system. Twenty-three sites spanning the continental shelf, northern continental slope, abyssal plain, and two seamounts were sampled using the towed camera and at least one of the trawl types, allowing direct comparisons between sampling methods. Patterns of species turnover between sites were similar across all methods. Estimates of fish population densities from the towed camera and beam trawl data were also comparable but those from the demersal trawl were consistently lower than for the other methods. Macrourus spp. grenadiers were ca. eight times less abundant in the demersal trawl than the video data but more large individuals were sampled by the trawl than the video and biomass estimates were similar. We hypothesise that this pattern could result from size-specific depth preferences in Macrourus spp. and conclude that video and trawl methods provide complementary information and if used together could be effective in routine assessments of demersal fish populations.

Muraenolepis species are caught in low numbers with bottom longline and trawl gears throughout the CCAMLR Convention Area. There are seven known species in the genus, but more work on the taxonomy of the group is needed and the number of species is uncertain. The few biological studies published suggest a relatively fast growing, semelparous, life history with a maximum age of 11 years. The estimate of K from the growth function for specimens assumed to be M. evseenkoi is much higher than for other Antarctic species. Individuals selected by longline gear are almost exclusively female, and a localised area of high catch rates occurs on Iselin Bank on Ross Sea slope. However, effects of fishing on this bycatch species depend on other factors, such as productivity, distribution pattern, and total biomass. Further directed sampling to determine species composition, life history attributes, reproductive strategy, and sex-specific distribution, and any trends in biomass is needed from the Ross Sea area and throughout the Convention Area.