CCAMLR

Data on maturity, gonadosomatic index (GSI) and length/weight of Antarctic toothfish Dissostichus mawsoni were collected from Sub-area 88.1 in the 2001-2002 season by the New Zealand bottom longline vessels Janas and San Aotea II operating in the Exploratory Fishery. The onset of the spawning season was identified as late autumn (May). A significant difference in the condition of fish between summer and autumn was noted, and this may be a result of migration f or spawning. The maximum GSI recorded for females was 26% with a 7.5 kg ovary. The maximum GSI was 43% for a stage 3 male weighing 20 kg, with the testes weighing 8.6 kg.

Digital pictures and morphological measures are presented to aid CCAMLR observers with the identification of three macrourid species caught as bycatch in the fishery for Patagonian toothfish, Dissostichus eleginoides, in Sub-Area 48.3. Scaling under the snout was used to separate Macrourus holotrachys (no scales) from both Macrourus whitsoni and Macrourus carinatus (which are both scaled). The relative positioning of the second dorsal fin and the anal fin can also be used to distinguish M.holotrachys from M.whitsoni and M.carinatus. To distinguish M.whitsoni from M.carinatus two scale counts were used. M.whitsoni has a head ratio (head length/inter orbital distance) of less than 5.2 whilst M.carinatus has a head ratio of greater than 5.2. There was some overlap in the ranges of most of these measures and so a single character will not always successfully I.D. a species. However, combinations of 2 or more characters should be successful. Genetic analysis of liver samples will confirm species identification

In 2000 the UK started a toothfish (Dissostichus eleginoides) tagging programme. The aims were to investigate the spatial and temporal movement of fish and to validate growth estimates. Since then approximately 2,260 toothfish have been tagged and released during groundfish surveys and CCAMLR observer trips. Of these, about 900 have also been injected with either Strontium Chloride or Oxytetracycline which places a marker on the otolith indicating the date of injection and release. To date, 50 fish have been recaptured, mostly from around Shag Rocks where there is greatest fishing activity. Most of the fish recaptured to date were tagged and released during the experimental pot fishing in 2000 and 2001, and have been at liberty from one to two years. Four fish were tagged and recaptured from the same longline vessel in 2002 after up to two months at liberty. The fish tagged during the groundfish surveys may not yet be large enough to be available to the longline fishery and there have been no recaptures of these fish tagged at South Georgia or elsewhere in the South Atlantic. Similarly, tags originating from elsewhere (e.g. the Patagonian shelf) have not been recaptured at South Georgia. 13 tags have been recovered at 42°S after about one year at liberty from some opportunistic tagging carried out on a toothfish pot vessel in international waters at that latitude in 2001.

The fecundity and egg size of three species of lithodid crab caught in CCAMLR Subarea 48.3 was examined. Relative fecundity (eggs-g body weight) and egg size was found to differ significantly between species. The highest relative fecundity and smallest egg size was found in Paralomis spinosissima which is found in shallower waters, whereas the lowest relative fecundity values and largest eggs were recorded in the deeper living species, Neolithodes diomedeae. In all species fecundity was observed to increase with increasing body size. Evidence is presented that closely related sympatric species and species found at different depths may employ quite different reproductive strategies.

Fecundity and size at sexual maturity were investigated in 486 bigeye grenadier, Macrourus holotrachys caught as bycatch in the Patagonian toothfish longline fishery conducted around South Georgia. Macroscopic and histological investigations revealed that absolute fecundity ranged from 22,000 to 260,000 eggs, a relatively high number for a macrourid. Mature ovaries were found to contain eggs at different stages of development suggesting that M. holtrachys may have an extended spawning season. Analyses of size at sexual maturity indicate that Lmat 50 occurs at 29cm (pre-anal length) whilst Lint 50 occurs at 20.57cm. The large difference between these values strongly suggests that yolk deposition and final ovarian development is a prolonged process in M. holotrachys which probably lasts for a period of greater than a year. Sex ratios of specimens caught in the longline fishery are highly skewed with females outnumbering males by a ratio of 32:1 which may represent the true ratio of females to males within the population or could suggest that females are more susceptible to capture by longlines than males.

Longlines that sink fast reduce the time available to seabirds to attack baited hooks and are important in efforts to minimise seabird by-catch in longline fisheries. We measured sink rates in still water of longlines made by Fiskevegn, the world’s leading manufacturer of demersal longlines. Lines with integrated weight (lead cores) sank two-three times faster (45- 52 cm/second) than conventional (unweighted) lines. Conventional lines made from 9 mm polyester sank at 23 cm/second compared to 18 cm/second for Silver lines of the same diameter. Samples of lines set by hand in still water sank significantly faster than longlines set from a fishing vessel.

Germany conducted a bottom trawl survey aboard R/V ‘Polarstern’ around Elephant Island and the South Shetland Islands in January – February 2002 in close collaboration with the U.S. Antarctic Marine Living Resources Program (AMLR). Information on species composition, biomass, and size distribution of the abundant fish species was provided. Estimates of total biomass for Elephant Island and the South Shetland Islands separately were computed for Notothenia rossii, N. coriiceps, Lepidonotothen larseni, L. squamifrons, Gobionotothen gibberifrons, Champsocephalus gunnari, Chaenocephalus aceratus and Chionodraco rastrospinosus. For these species, biomass estimates were found to be 3 comparable to survey results obtained in 1998 and 2001 for most species. Length compositions in the most abundant species resembled closely those in previous years. The proportion of juvenile G. gibberifrons, the most abundant species in the region, decreased significantly since 1998. No indication was found for the presence of a significant adult stock of N. rossii at Elephant Island where the species was known to occur in some quantities prior to commercial exploitation in 1979/80. It should be noted that more than 95 % of the population of N. rossii prior to exploitation was confined to a comparatively small area north of the island and may have been missed by a survey not specifically directed at N. rossii. It is suggested to conduct a specific survey targeting N. rossii in the near future to properly assess the status of this stock.

Conservation Measure # 216 requires vessels fishing in sub area 88.1 + sink longlines at 0.3 m/s to 15 m depth. Sink rates can be achieved by adding external weights to lines or by using lines with weigh integrated into the rope fibres. The sink rates to 15 m depth of 9 mm demersal longlines with integrated weight (IW) were tested against unweighted longlines and lines with externally attached weights (6 kg/49 m) in the New Zealand ling fishery. Longlines with 0 g/m (unweighted), 25 g/m, 50 g/m 75 g/m and 100 g/m integrated weight averaged 0.11 m/s, 0.227 m/s, 0.272 m/s, 0.317 m/s and 0.353 m/s, respectively. The longline with externally attached weights sank at 0.32 m/s. IW longlines sank instantly, reaching 1 m depth in 6-9 s whereas unweighted lines took >20 s to reach this depth. Catch rates of ling varied with line weight but results are indeterminant due to the small sample sizes. No operational effects of using IW lines were evident during the trial. IW longlines containing 50 g/m added weight are recommended for testing in a subsequent trial to examine the effectiveness of IW longlines in reducing seabird mortality in autoline longline fisheries.