CCAMLR

A revised bathymetric map of the South Orkney Islands (Subarea 48.2) was generated using several integrated bathymetric databases and newly available acoustic seafloor data. The region extends from 60.2ºS-62.2ºS latitude and 42.5º-47.5º longitude. From the integrated data sets, areas of seabed within the 500 m isobath were computed for 50 m depth intervals. Areas were calculated based on interpolated surface area of seabed incorporating seafloor slope. These results were compared to the previously reported estimates of Everson (1997) for the 50-150, 150-250, and 250 to 500 m depth intervals. The updated estimates are about 1,424 (20%) nautical miles larger in area within the 50-500 m isobaths than Everson’s estimates, though changes in area are specific to the depth interval. There is a corresponding change in estimated biomass within strata when these areas are incorporated into swept area trawl survey models, though not for total estimated biomass. Of the nine species examined, the point estimate of total biomass increased from 5%-30% for eight species and decreased 20% for one.

Stocks of finfish around the South Orkney Islands (Subarea 48.2) suffered substantial declines during the period the fishery was open from split year 1977/78 through 1989/90. Scientific bottom trawl surveys of finfish biomass within the 500 m isobath of the South Orkney Islands have been conducted by the Federal Republic of Germany in 1985, Spain in 1991, and the United States in 1999. Estimates of total stock biomass were computed for eight species that comprised 98% of survey nominal catch. Biomass levels in March 1999 were compared to previous trawl surveys conducted in Feb. 1985, and Jan-Feb 1991. Species examined were Gobionotothen gibberifrons, Lepidonotothen squamifrons, Pseudochaenichthys georgianus, Champsocephalus gunnari, Chaenocephalus aceratus, Chionodraco rastrospinosus, Notothenia rossii and Lepidonotothen larseni. Although there is substantial variability in point estimates, biomass levels of most species appear to be unchanged or may have declined slightly since 1991. The stock of C. gunnari is currently extremely low, while there appears to be a strong signal of recovery for N. rossii. However, overall levels of biomass indicate very little potential for commercial exploitation at this time.

In 1998, an offshore scientific trawl survey of bottom fish sampling within the 50-500 m isobath of the lower South Shetlands Islands (King George Island to Low Island) was conducted. In addition, the abundance of two commercially important Antarctic fish, Notothenia rossii and Gobionotothen gibberifrons has been monitored relative to another potentially exploitable fish, Notothenia coriiceps, in the lower South Shetlands Islands from inshore sites mainly at Potter Cove from 1983 to 1999. These studies have been conducted using trammel nets sampling bottom depths from 5 to 50 m. Information from this trawl survey was compared to the 1998 Potter Cove data to examine potential inshore-offshore relationships for these three species. In general, these two data sets are complementary, and demonstrate well-defined changes in size that take place between inshore and offshore sampling. By combining samples collected from a single year, the sample size and regression range available for length-weight relationships can be increased. However, the value of these data as a combined singular data set for one year of sampling is limited. A future offshore survey coupled with inshore sampling would provide substantially more information, and allow a more direct comparison of the two data sets to be realised, particularly with respect to trends between the three species.

A monitoring program of demersal fish in inshore sites of the South Shetland Islands has continued in Potter Cove from 1991 to 1999, covering a continuous sampling period of sixteen years and in Harmony Cove, Nelson Island, in the austral summer 1995/96. The decline in trammel net catches of fjord fishes of the species Notothenia rossii and Gobionotothen gibberifrons in relation to the non commercially fished Notothenia coriiceps, which was already reported for the period 1983-1990 in a previous study, is still evident. An increasing trend of N. rossii catches was observed, but the actual levels of relative abundance of this species and G. gibberifrons are well below those found in the early 80´s. These results are supported by our knowledge on the diet of the piscivorous Antarctic shag Phalacrocorax bransfieldensis in the South Shetland/Antarctic Peninsula area in this decade. The most likely explanation for the decrease in recruitment to the inshore sub-populations of N. rossii and G. gibberifrons in the last sixteen years is the effect of the offshore commercial fishery in the area in the late 1970s. This interpretation is consistent with the information on the historical offshore commercial fishing and with the results of scientific surveys in the area.

We used data collected by CCAMLR International Scientific Observers in 1997 and 1998 to examine potential relationships between seabird incidental mortality rates on longline vessels fishing for Dissostichus eleginoides and various factors, including the nature and use of mitigating measures as well as environmental variables such as time of day, time of year.
Out of 3283 longline sets analysed only 311 caught birds (9.4%). Data conformed most closely to a Delta distribution (many zero values and log-normal distribution of non-zero values) and were analysed using two Generalised Linear Models, a binomial model for presence/absence of seabird catches and a Gamma model for the magnitude of non-zero catches.
Sparsity of data precluded analysis of seabirds at a taxon level more detailed than albatrosses and petrels combined. Other analytical difficulties, particularly in using generalised linear models, related to the large number of potentially important factors, the lack of overlap between factors and the fact that fishing has purposely avoided making catches of seabirds. There are, for instance, only three records in the entire dataset where none of the mitigation measures have been used.
The only factors consistently significant were time of year (very few birds caught after April) and use of streamer lines but the effects of most other factors cannot be fully analysed with the present data. Even vessels using streamer lines and setting at night were found to catch albatrosses occasionally. The “residual” mortality associated with using all prescribed mitigation measures provides a more useful indication of the success of mitigation measures than general bird bycatch rates.
Given the difficulties of analysing this dataset, especially the problem of very low numbers of hauls not using mitigation measures and hauls catching birds, experimental approaches to identifying effective mitigation measures may be preferable to post-hoc analysis of observer data.

The factors affecting the number and the mortality of seabirds attending long-liners and trawlers fishing in the Kerguelen area were studied during four successive seasons (1994-1997), based on observations carried out onboard by dedicated observers. Twenty-four species of seabirds were observed attending fishing vessels representing 591 birds / census. The total numbers attending varied mainly according to the year, the cloud cover and the presence of offal for long-liners. The dumping of offal increased the numbers of birds attending the vessel, especially when offals can be handled easily by birds. The activity of the vessels also affected the numbers attending, birds being more abundant during line setting and during trawl hauling. The white-chinned petrel was the most abundant ship-following seabird followed by Black-browed albatrosses, giant petrels and cape pigeon. The number of white-chinned petrels, black-browed and grey headed albatrosses attending fishing vessels increased through the season whereas it was the reverse situation for giant petrels and cape petrels. Four species of birds were caught by fishing gears mainly by long-lines, in order of importance white-chinned petrels, black-browed, grey-headed and wandering albatrosses. Taking into account the number of birds from each species attending long-liners and known to be potential by-catch, it appears that some species appear to be more susceptible of being caught than others. White-chinned and grey-headed albatrosses appear to be caught in much larger proportion than the number of potential by-catch present, whereas black-browed are caught in lower numbers. Giant petrels are abundant around long-liners but were never caught. In long-liners, most birds were killed when the lines were set during the day or when the deployment of the scaring device was not successful with an overall figure of 0.47 birds / 1.000 hooks. No albatross except one was caught when the lines were set during the night. The white-chinned petrel represented 92.2 % of all birds killed by long-liners. The number of birds caught varied significantly between months and between years. The type of bait used also affected the catch rate. The catch rate was related to the number of birds attending the long-liner only for black-browed albatrosses. Most birds killed by trawlers were caught by the netsonde cable. The efficiency of mitigation measures in order to reduce seabird mortality is discussed and it is stressed that night setting is the most efficient method way to reduce mortality and should be enforced everywhere when possible. However further methods should be developed to reduce the mortality of species active at night, especially the white-chinned petrel whose populations in the Indian ocean may by threatened by long-line fisheries.

Grey-headed mollymawks Thalassarche chrysostoma are killed by longline fishing operations in the southern Indian Ocean. We studied the foraging ecology of breeding grey-headed mollymawks at Marion Island, by tracking their foraging trips and sampling their diets. During the incubation period, birds made longer foraging trips, mostly towards the subtropical convergence and Subantarctic zone. This brought them into contact with areas of intense Southern Blue-fin Tuna Thunnus maccoyii longline fishing. During the early post-guard phase, foraging trips were shorter and to the southwest of the island, in the Polar frontal and Antarctic zones. Short foraging trips (

The effect of an intensive sampling programme on an inshore population of Notothenia coriiceps was studied at Potter Cove, South Shetland Islands, by comparing catch data taken in successive summers of 1992/93 to 1994/95 at one specific zone (site 1) with those taken in the same last summer at two close but not previously sampled zones (sites 2 and 3). The fish were caught with trammel nets under similar sampling conditions (depth, net measurements, bottom type). In site 1, a marked decrease in length (TL) of the fish was observed throughout the whole period. The fish from sites 2 (x=32.4 cm) and 3 (x=31.8 cm) exhibited no significant differences in mean length. They were significantly larger than those from site 1 caught in the summers of 1994/95 (x=28.8 cm) and 1993/94 (x=30.2 cm), but were similar in size to those sampled in the summer of 1992/93 (x=31.7 cm), just when the sampling programme started in site 1. Present results show that the size variations of N. coriiceps observed at Potter Cove were not due to a natural decrease of the proportion of larger fish in the population, but related to an intensive sampling effort carried out at one specific site.