CCAMLR

Pilot studies were carried out in 48.3 in 2006 and in 88.1 and 88.2 in 2007 by the Argos Helena, testing 14/0 circle hooks and mackerel bait against hooks and bait routinely used by the vessel (14/0 EZ J-type hooks and squid bait respectively). Catch per unit effort (CPUE) of Macrourus spp. (kg 1000 hooks-1) was lowest with J-type hooks and mackerel bait for both regional trials. Variation in catch rates of Macrourus spp due to bait was significant, but not for hook-type. Bait type had similar effects on the catch rates of Dissostchus spp. and of all other by-catch species combined. However, variation in CPUE for target and non-target species due to geographical location, depth and soak time were also significant and when bycatch to catch ratios were analysed, the variation due to bait was not significant. In order for the benefits of mackerel bait in reducing macrourid (and other species) bycatch to be endorsed by the industry, further mitigation research is required to determine a gear configuration for automated longlines which maintains toothfish catch rates when this bait type is being used.

1. During the 2006/07 fishing season one UK and one New Zealand vessel fished in Subarea 48.4, catching 54 t of toothfish. A total of 291 D. eleginoides and 1 D. mawsoni were tagged and released during fishing operations. This represents a very high tagging rate of 5.4 fish per tonne of catch. Additionally, 100 rajids were tagged and released.
2. D. eleginoides and rajids appear to have different distributions of abundance around the fishing area. There were two tag recaptures in 2007, both of D. eleginoides. These were recaptured 84km and 14km from their points of release.
3. The UK proposes to continue the mark-recapture experiment in Subarea 48.4 in 2007/08. Initial estimates of population size will be made in 2008/09. However, given the currently low level of recaptures, and the difficulties experienced in catching and tagging the anticipated number of toothfish each year, the experiment and CM 41-03 may need to be extended for a few more years.

The UK undertook preliminary trials of the previously described “cone” or “bottle” longline configuration for mitigating cetacean interactions in 2006. This paper should be read in conjunction with the observer’s report of that cruise (Basson 2006). Initial results were promising, and the UK intends to proceed with further, more extensive trials, in the 2007/08 fishing season in Subarea 48.3. Although seabird interactions are expected to be minimal, the trials will stop if 3 seabirds are caught, and sink tests will be undertaken. Although we intend to change gear configurations as described all other conservation measures will apply.

IW longlines are effective in reducing the bycatch of birds in toothfish fisheries, but by putting the line closer to the seabed they increase the bycatch of macrourids and rajids. Experiments reported elsewhere demonstrate that some of this effect can be mitigated by the use of fish rather than squid bait, but even then autolines continue to catch more macrourid bycatch than Spanish systems. We intend to trial two alternative configurations against IW systems in 48.3 in the 2007/08 fishing season: non-IW autolines with spaced weights, and IW systems with alternately spaced weights and floats. All systems will have sink rates of at least 0.3 m.s-1. Comments on the experimental protocol are invited. Although we intend to change gear configurations as described all other conservation measures will apply.

1. The catch-at-length based CASAL model for toothfish at South Georgia is updated with data from the 2007 fishing season. The predicted spawning stock biomass and the yield is slightly higher than was estimated last year.
2. Improvements are made to the fit of tag data through (a) estimating a length-based ogive for tag-induced mortality, based on our 2005 survivorship experiment, in which smaller fish survive tagging better than large fish, and (b) by re-estimating from our tagging data that tag-induced growth retardation is also related to size, smaller fish suffering less growth retardation than larger fish, and that on average it is 1 year or more.
3. A new model is developed which uses estimates of catches at age from 1998 to 2006 (based on random sampling of the catch for age determination). Fits of all data (CPUE; catches at length for the early fishery; catches at age for the later fishery; tag recapture data) are all improved from earlier models, although some poor fits remain. The model estimates year class strength which corresponds, in some years, with estimates made from the South Georgia groundfish survey data.
4. Several of the requests of WG-FSA for developments of the South Georgia toothfish model have now been completed.
5. Note that the data used here are preliminary and lack some of the precaution previously included in assessments. We would recommend that only small changes to the current TAC be considered, and that the toothfish assessment is undertaken at periods of greater than one year.

The exploratory fishery for Antarctic toothfish (D. mawsoni) has been operating for ten years in Subarea 88.1 and for five years in Subarea 88.2. This report summarises the large amount of data collected on toothfish and the associated bycatch by all vessels participating in the fishery. All SSRUs in the two subareas except for 881D and 882C have now been fished. The 2007 D. mawsoni catch was the second highest on record with a total of 3431 t against a combined catch limit of 3579 t. The management of the SSRUs within the two subareas was changed for the 2006 season as part of a 3-year experiment (SC-CAMLR-XXIV). One of the aims of the experiment was to simplify the administration of the fishery by having fewer catch limits. This appeared to be moderately successful, with only one catch limit being slightly exceeded in the 2006 season, and two catch limits exceeded in the 2007 season. Although there was a large overrun of the catch limit in the North region, the overall catch limit for Subarea 88.1 was only exceeded by 2%. The catch limit was under caught in Subarea 88.2. The concentration of effort within smaller spatial areas in Subarea 88.1 has undoubtedly contributed to the large increase in tag recoveries over the past two seasons (Dunn et al. 2007).
The length frequency data from the Ross Sea fishery have been very consistent over the past 3–4 seasons. There is no evidence of any truncation of the overall length frequency distribution, and no evidence for a reduction in fish length in any SSRU over time. Although moderate numbers of small fish are caught in some years (e.g., on the Shelf in 1999 and 2001), these year classes are not seen in large numbers in later years in the fishery. So at this stage there is no evidence for strong variation in year class strength in the fishery.

Two regions of mitochondrial (mt) DNA: cytochrome b and cytochrome c oxidase subunit 1(COI) were sequenced in 9 species of Bathyraja skates from the Southern Oceans and New Zealand. Based on significant sequence divergence, the species that has been referred to as Bathyraja eatonii from the Antarctic shelf and slope is a species distinct from B. eatonii from the Kerguelen Plateau (the type locality), and is a new and undescribed species, and should be provisionally referred to as Bathyraja n. sp. cf eatonii. There was no sequence divergence among samples of B. n. sp. “dwarf” from the Ross Sea and South Atlantic. However, for Bathyraja n. sp. cf. eatonii and Bathyraja maccaini in the Ross Sea and South Atlantic Ocean, the DNA sequence divergences are indicative of differentiation among ocean basins; and for Bathyraja n. sp. cf. eatonii are similar to divergences among recognised Bathyraja species in the North Pacific Ocean.
Despite investigating four colour characters, eight meristic characters and six morphometric characters, relatively few were diagnostic for the Antarctic Bathyraja. Ventral colouration appeared reliable for distinguishing Bathyraja meridionalis and B. n. sp. dwarf, but dorsal colouration was unreliable. Proportional disc width showed substantial changes in shape between the juvenile and adult stages of Bathyraja n. sp. cf eatonii; hence, the common name “allometric skate” is proposed. Eight meristic characters were evaluated. Pectoral radials and monospondylous vertebrae were useful in diagnosing B. n. sp. dwarf, and midline thorns for B. meridionalis. The presence/absence of thorns around the eyes and on the scapular appeared to be a reliable character to distinguish species in the Ross Sea. A field key for identification of Ross Sea skates is provided.

Icefish (Channichthyidae) specimens were randomly collected by observers during the 2005–06 fishing season. These observers were placed aboard three longline vessels targeting Antarctic toothfish in the Ross Sea (Areas 88.1 and 88.2). Biological data from 303 returned specimens was collected. These data included species identification, fish length, weight, sex, meristics, reproductive biology, diet, and age estimation. All of the icefish sampled were identified as Chionobathyscus dewitti, and showed no significant difference in sex ratio. Meristic, diet and age data were consistent with previous research. Regression equations for converting standard length to total length and for defining length-weight relationships were calculated and presented for both male and female fish. Gonad maturity stage data showed that most fish were either immature or resting (mature). Gonado-Somatic Indices (GSI) were calculated and plotted against sample month. There was a weak positive trend in GSI between December and February, but this was limited, probably due to the short temporal distribution of the data. Length-at-maturity and age-at-maturity ogives indicated that 50% of the fish sampled were mature at about 340–360 mm (TL) and about 3–4 years of age and that 95% were mature at about 370–400 mm (TL) and 6–8 years of age. Counts of growth zones in sectioned otoliths were used to determine ages and von Bertalanffy growth parameters. Fish growth was rapid for both sexes, and females approached a significantly larger mean asymptotic maximum size than males. Maximum ages of 8 and 11 years were obtained for male and female fish, respectively. Diet analysis showed most icefish stomachs were empty and the few prey items recovered were generally in advanced stages of digestion. This may be due to regurgitation of prey during capture.

The mean mercury level for the D. eleginoides 1998 sample was 0.43 mg/kg-1, which is slightly lower than the permissible level of 0.5 mg/kg-1 set by the New Zealand Food Safety Authority (NZFSA). In contrast, mean levels of mercury for D. mawsoni were 0.10 mg/kg-1 in the 1998 samples and 0.16 mg/kg-1 in the 2006 samples, both of which are well below the permissible level.
Mercury levels were highly variable both within and between the five species studied. Once the factors length and year had been accounted for, the mercury levels in D. eleginoides were over four times greater than in D. mawsoni. The three prey species had intermediate mercury levels, with Whitson’s grenadier (Macrourus whitsoni) being only slightly lower than D. eleginoides, whilst the levels of ice fish (Chionobathyscus dewitti) and blue antimora (Antimora rostrata) were at low levels, similar to that of D. mawsoni. Mercury levels were positively correlated with fish length in four of the species. Mercury levels also showed positive trends with depth for D. eleginoides and C. dewitti, and with area for A. rostrata. Mercury levels showed no trends with any factors for M. whitsoni.
The low levels of mercury in D. mawsoni relative to its prey species and the four-fold difference in mercury concentrations between it and D. eleginoides were unexpected. Reasons for these different levels of bioaccumulation were explored including differences in diet, growth and longevity, and location. We conclude that these results can only be explained by a lower rate of mercury assimilation and/or a higher rate of mercury elimination by D. mawsoni.

This paper describes the interaction between sperm whales (Physeter macrocephalus) and the toothfish fishery (Dissostichus eleginoides) carried out by longline fishing vessels operating in two different fishing zones at 40º and 50º latitudes in the Southwestern Atlantic from March to May 2007. 62 hauls were performed in the northern zone (latitude 40º 00’ S), while 41 hauls were performed in the southern zone (latitude 50º 00’ S) at an average depth of -1282 m. 57.2% of the total number of hauls were observed. Onboard observers recorded: a) quantity and quality of fish parts remaining in the recovered longline; b) presence and number of sperm whales and c) comparative fishing yields with and without sperm whales effective predation. The observations were performed using both, the traditional Spanish longline and the Mammals and Birds Excluding Device (MBED). The longline with MBED sinking rate was determined in 1.14 m/seconds. In both fishing zones, the sperm whales presence was observed in 77.4 % of total observed sets and the effective predation was determined in 22.6 % with MBED. Effective predation was determined in 44 % of observed sets during the day period from 12:00 to 18:00 hours GMT. Lips and buccal parts were observed in 71 % of sets with traditional longline and in 27 % with MBED. The estimated fishing yields of northern and southern zones were 11.05 kg/hour and 15.53 kg/hour respectively, using the MBED and with sperm whales effective predation. In the southern zone the fishing yield increased to 23.03 kg/hour, using MBED but without sperm whale evidence of effective predation. No incidental mortality of birds was registered using both tory-line and MBED simultaneously, in spite of remarkable abundance of the southern black-browed albatross (Thalassarche melanophrys) and cape petrel (Daption capense) in 40.76 % and 23.13 % of total observed sets respectively.