CCAMLR

Antarctic toothfish (Dissostichus mawsoni) from the Ross Sea (CCAMLR sub-area 88.1) have been aged assuming that one translucent zone is formed annually in the otoliths of this species. However, no evidence to validate this assumption has previously been presented. In the current work, sagittal otoliths were examined from D. mawsoni that had been injected with oxytetracycline some years before recapture. The number of zones between the fluorescent oxytetracycline line and the otolith margin indicates that one translucent zone is formed annually in otoliths of post-mature D. mawsoni. Otoliths from four distinct juvenile length-frequency modes were also examined, and the translucent zones counted. Zone counts were consistent within modes, and increased by one in each consecutive mode. This indicates that the modes represented year classes and that one translucent zone is formed annually in otoliths of juvenile D. mawsoni. Mean fish lengths at ages 0.5, 1.5, 2.5, and 3.5 years were estimated to be 14, 28, 37, and 46 cm TL, respectively. These estimates agree with growth curves calculated previously from a sample of data that was large but lacked any fish younger than 3.5 years. Counting translucent zones in the otoliths of D. mawsoni appears to be a valid method for determining the age of this species.

Samples of macrourid rattail bycatch from the toothfish fishery in sub-areas 88.1 & 88.2 in 2002 were identified by observers and returned to New Zealand for subsequent confirmation of their identity by NIWA researchers. Two species were found, Macrourus whitsoni and M. holotrachys. A previously aged sample from 1999 was confirmed as being M. whitsoni based on otolith comparisons and the geographic source of the aged sample. This confirms the preliminary age estimates from the ageing study. Regression equations relating total length to snout-vent length, total length to weight, and snout-vent length to weight were generated. For all regressions there were significant differences between the sexes and between the data origins (NIWA and observer). Observer data were derived from fresh specimens and NIWA data were derived from frozen-and-thawed specimens. The age and length at maturity for M. whitsoni males is 12 years and 46 cm TL, for females it was 14 years and 50 cm TL.

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.