CCAMLR

The United States Antarctic Marine Living Resources (U.S. AMLR) program conducted a bottom trawl survey in March, 2001 of the South Shetland Islands. Information on species composition, size composition, spatial distribution, and dietary patterns are presented. Estimates of total stock biomass were computed for eight species: Champsocephalus gunnari, Chaenocephalus aceratus, Chionodraco rastrospinosus, Gobionotothen gibberifrons, Lepidonotothen larseni, Lepidonotothen squamifrons, Notothenia coriiceps, and Notothenia rossii. Biomass estimates were compared to the results from the 1998 U.S. AMLR Survey. For most species, the standing stock has decreased slightly, although in most cases the 95% confidence levels from the 2001 surveys were considerably decreased. The results indicate that stocks of N. rossii have not recovered even after commercial fishing has ceased for 20 years. The overall abundance of finfish in the South Shetland Islands has yet to reach a level at which commercial exploitation would be advisable. The potential role of habitat structure in demersal finfish assemblages in the South Shetland Islands is discussed.

Between March 2000 and April 2001 two commercial fishing vessels undertook trials at South Georgia of a method of fishing for toothfish (Dissostichus eleginoides) using pots. A significant bycatch of lithodid crabs (three species of Paralomis spp.) was encountered. Paralomis spinosissima occurred in shallow water, generally shallower than 700m. P. anamerae, not previously reported from this area, had an intermediate depth distribution from 400 – 800m. P. formosa was present in shallow waters but reached much higher catch levels (and, presumably, densities) between 800 and 1400m. Differences were also noted in depth distribution of the sexes and the size of crabs. Depth, soak time and area were found to significantly influence crab catch rates. Very few crabs (3% of P. spinosissima and 7% of P. formosa) were males above the legal size limit and could therefore be retained. All other crabs were discarded. Most crabs (>99% of P. formosa, >97% of P. spinosissima and >90% of P. anamerae) were lively on arrival on deck and at subsequent discard. Mortality rates estimated from re-immersion experiments indicated that on the vessel which emptied pots directly onto the factory conveyor belt 85% – 90% of crabs would survive discarding, whereas on the vessel where crabs were emptied down a vertical chute prior to being sorted, survivorship was 39% - 58%. P. anamerae was the most vulnerable of the three species to handling onboard and subsequent discarding. P. spinosissima seemed to be more vulnerable than P. formosa.

We conducted a preliminary analysis on the numbers of birds caught as a bycatch in the trawl fishery for icefish (Champsocephalus gunnari) in Subarea 48.3. From December 2000 – February 2001 92 birds were caught, principally black-browed albatross and white-chinned petrel, with 93% of the birds being caught in February. GAM/GLM analysis suggested that month and vessel were significant factors affecting the probability of a haul catching birds, but no significant factors were found that could explain the number of birds caught. Differences in the numbers caught in the last three years also suggest that there may be a year effect. We were unable, with the limited data available, to separate these various hypotheses and identify conclusively the causes of seabird bycatch in the icefish fishery. More work by scientific observers is required to enable effective mitigation measures to be designed for this potential problem. CCAMLR protocols and data formats for such observer studies need to be developed.

The incidental mortality of seabirds in tuna longline fisheries is estimated for the continental South African Exclusive Economic Zone (EEZ). Fishery observers accompanied 13 fishing trips and observed 108 sets (143 260 hooks) during the period 1998–2000. Despite most lines being set at night, seabird bycatch rates were high, with a mean of 1.6 birds killed per 1 000 hooks. Japanese vessels (1% effort observed) had a higher bycatch rate (2.6 birds per 1 000 hooks, range per trip 0.1–5.4) than South African vessels (0.8, range 0.0–4.3; 17% effort observed), possibly as a result of gear differences. Bird bycatch differed regionally in relation to the numbers of birds attending vessels. In international waters off the Northern Cape and southern Namibia, where there are few birds, only one bird was caught on 93 600 hooks (0.01 birds per 1 000 hooks). Shy Thalassarche cauta, black-browed T. melanophris and yellow-nosed T. chlororhynchos albatrosses, and white-chinned petrels Procellaria aequinoctialis were killed most frequently. Based on 1998–1999 fishing effort, simple extrapolation suggests that 19 000–30 000 seabirds are killed annually in South Africa’s EEZ, of which 70% are albatrosses. Confidence in these estimates is low, given the small proportion of effort observed, but it is clear that urgent steps are needed to reduce seabird bycatch within South African waters.

The white-chinned petrel (Procellaria aequinoctialis) is an abundat, widespread petrel breeding in tussock grassland at sub-Antarctic islands. Over the last decade it has been killed in large numbers in temperate and sub-tropical longline fisheries. However, no data are available on the global population status. We assessed the status of white-chinned petrels at Bird Island, South Georgia by comparing the distributioin and density of occupied burrows in 1981 and 1998. In both surveys white-chinned petrel burrows occurred in one-quarter of the 460–47736-m2 quadrats surveyed. The total number of burrows in each quadrat was consistent between each survey but we estimate an overall decrease of 28% in those occupied (with considerable variation between sites). Concurrent data on breeding frequency and success showed that white-chinned petrels are essentially annual breeders at Bird Island; breeding success was consistent at around 44%. Significant factors determining densities of occupied burrows were crown height and percent tussock cover (accounting for 77% of variance). The former has decreased significantly, the latter increased significantly between 1981 and 1998 but there was no relationship between white-chinned petrel occupancy rate and habitat modification due to the presence of fur seals (Arctocephalus gazella). This suggests that any population decline is due to factors operating away from the breeding colony, such as those attributed to fishing.

The foraging range and principal feeding areas of White-chinned Petrels breeding at South Georgia were determined using satellite telemetry. Foraging trips during incubation lasted 12–15 days and covered 3000–8000 km and 2–11 days and 1100–5900 km during chick-rearing. Adults covered less distance per day during chick-rearing (71 km) than during incubation (91 km) but the proportion covered at night (47%) was the same. Mean (31–34 km/h) and maximum (80 km/h) flight velocities were similar during both periods of the breeding season and during day and night. Between incubation shifts. White-chinned Petrels travelled to the Patagonian shelf: during chick-rearing they foraged more extensively. Most locations were between 30° to 55°W and 52° to 60°W around South Georgia, Shag Rocks and south to the South Orkney Islands. Diet samples from known foraging locations suggested birds fed mainly on krill and squid. They caught the squid Brachioteuthis? picta and Galiteuthis glacialis around Shag Rocks. South Georgia and also at sites close to the South Orkney Islands: Illex argentinus on the Patagonian shelf. Dispersal of adults after breeding failure was south to the South Orkney Islands then west to the Falkland Islands. This study confirms that breeding White-chinned Petrels are amongst the widest-ranging of seabirds: they may minimise competition with other Procellariiformes in the South Atlantic by their more extensive foraging range. The nature and extent of their range also brings substantial risk of high mortality rate in South Atlantic long-line fisheries.