CCAMLR

A toothfish fishery has operated during the Antarctic summer (December - May) from 1997 to 2003, in Subareas 88.1 and 88.2 in the region of the Ross Sea. A preliminary standardised analysis of toothfish CPUE (catch (kg) per baited hook per set) carried out last year compared three alternative toothfish CPUE analyses for the 1998 to 2002 seasons. The analysis of a data subset including only the two main vessels and the 3 main fishing grounds was the best fit to the data.
This report updates the main grounds and vessels analysis to include the 2003 season. Seasonal indices were variable with no trend, and error bounds on the estimates were low, but the main grounds analysis model was a relatively poor fit to the data. The variables depth, soaktime, length of line, area, and season, entered the model, which explained 37% of data variability. Because of the poor diagnostics, the model was fitted to sets excluding zero catches of Antarctic toothfish as a sensitivity. The diagnostics for this model were substantially improved and the seasonal indices were slightly more optimistic. As fishing effort has extended to other grounds since 2001, a further sensitivity analysis was completed for the two main vessels. The seasonal indices were similar to the main grounds analysis. While the model explained 48% of data variability, it was influenced by the unbalanced nature of the data, and model diagnostics indicated a poor fit to the data.
Data are available from seven seasons, but the analysis was confined to the two vessels with a consistent fishing history, and as such only represents a small area of the entire Ross Sea toothfish fishery. The variables included in the analysis are plausible, but the models may be influenced by extreme values of soaktime, depth and length of line set, that reflect the exploratory nature of the fishery. The descriptive power of the main grounds model is reasonable, but it is still influenced by the unbalanced nature of the fishery and records of zero catches.
Seasonal indices show no trend between 1998 and 2003, but the relationship between these indices and relative abundance is unknown, and fishery independent data are unavailable to validate this relationship. Standardised CPUE indices have been validated for overseas longline fisheries, including Alaskan sablefish (Anoplopoma fimbria), Atlantic halibut (Hippoglossus hippoglossus), and Atlantic cod (Gadus morhua), using tagging, acoustic survey, and quantitative longline survey methods. These species have generally similar biology, distribution, and fisheries operation to Antarctic toothfish. Therefore, trends in standardised CPUE indices could be directly related to relative abundance for toothfish. The toothfish standardised CPUE data provide an index of fishery performance. Continued monitoring of CPUE for the main grounds, main vessels is recommended, and further research on other possible CPUE models, and inclusion of first order interactions in the analysis is suggested. Research into suitable methods for validating the relationship between CPUE seasonal indices and the relative abundance of toothfish is also recommended.

Scientific observers collected maturity data from skates caught by New Zealand longline vessels targeting toothfish in the Ross Sea during 2002–03. Sample sizes were small, making it difficult to obtain accurate estimates of the length at 50% maturity. Results were compared with data collected in the previous season.
The length at 50% maturity for male Amblyraja georgiana is about 92 cm TL. Females appear to mature at a slightly greater length of 95–100 cm TL, but further data are required to confirm this. The length at 50% maturity of male and female Bathyraja eatonii could not be accurately determined, but may be around 85–90 cm and 100–120 cm, respectively.

Information on mackerel icefish that has been presented at WG-FSA is summarised and the information augmented by reference to published papers. The New Zealand government has released a draft National Plan of Action – Seabirds. The plan will apply to commercial and non- commercial fishing in New Zealand fisheries waters. It will also apply to high seas fisheries in which New Zealand flag carrying vessels participate. The plan proposes that Codes of Practice be developed for each fishery, and that the Codes specify fishing practices that will be adhered to, maximum bycatch limits, and methods to monitor compliance, education and public awareness. Specific fishing practices and bycatch limits will be made mandatory if not adhered to voluntarily in Codes of Practice. Economic incentives or penalties may also be developed if required. The New Zealand government will make final decisions on the plan in November 2003, following feedback from stakeholders.

Although the IATTC does not have an established observer program in its longline fisheries, one does exist for a US-based pelagic longline fishery for tuna and swordfish. These vessels are subject to pertinent US regulations as well as under the purview of IATTC. In response to a CCAMLR query in 2002, IATTC informed CCAMLR of this US observer program. Information about seabird bycatch observed in the US West Coast pelagic longline fishery was reported by the US in WG-FSA-02/39. Per a standing request from CCAMLR for information on incidental seabird mortality in fisheries adjacent to the Convention Area, information is provided about the US West Coast pelagic longline fishery.
Pelagic longline vessels operating in the North Central-Eastern Pacific targeting broadbill swordfish (Xiphias gladius) and tuna (Thunnus spp.) inadvertently hook and kill black-footed (Phoebastria nigripes) and Laysan albatrosses (P. immutabilis) that nest in the Northwestern Hawaiian Islands. The US-based pelagic longline fishery does not interact with albatross or petrel species that breed in the CCAMLR Convention Area. Although procellarids demonstrate broad and far-ranging foraging distributions, it is doubtful that Southern Hemisphere albatrosses and petrels forage this far north.

The United States Antarctic Marine Living Resources (U.S. AMLR) program has conducted bottom trawl surveys of the South Shetland Islands (Subarea 48.1) during the 1998, 2001, and 2003 austral summers. Information on species and size composition, abundance, spatial distribution, and dietary patterns from the 2003 survey is presented. The spatial distributions and standardized densities for demersal finfish species have remained relatively consistent across all surveys. Shelf regions of importance for krill, fish, and benthic feeding guilds based on stomach content analysis demonstrate the most important feeding areas lie to the west and north of Elephant Island and to the north of King George Island greater than 200 meters. Estimates of total stock biomass from these surveys were computed for eight species: Champsocephalus gunnari, Chaenocephalus aceratus, Chionodraco rastrospinosus, Gobionotothen gibberifrons, Lepidonotothen larseni, Lepidonotothen squamifrons, Notothenia coriiceps, and Notothenia rossii. The standing stock for most species has fluctuated, with no signal of substantial year classes or significant recruitment for any species. Although standing stocks of G. gibberifrons remain the largest relative to all other species, there appears to be a decline in biomass. The overall abundance of finfish in the South Shetland Islands has yet to reach a level at which commercial exploitation would be advisable.

The Atlantic Yellow-nosed Albatross (Thalassarche chlororhynchos) breeds only at the Tristan da Cunha archipelago and Gough Island in the central South Atlantic Ocean, and is threatened by mortality from longline fisheries operating in the South Atlantic. Demographic data have been collected from two study colonies on Gough Island and Tristan da Cunha for 20 years. Annual variation in the number of breeding birds was strongly correlated between the two islands, and over the whole study period both study populations have trended downward at around 1.2% per year. The number of established breeders on Gough Island has declined more rapidly, and significantly, at an annual rate of 2.3%. Monitoring established breeders maybe a sensitive means of detecting population trends. Average breeding success (67–69%) and breeding frequency (66–65%) were very similar on the two islands. On Gough Island immature and adult annual apparent survival averaged 88 ± 3% and 92 ± 1%, respectively, and apparent survival from fledging to age 5 has averaged 31 ± 8%. Apparent adult survival on Tristan da Cunha averaged only 84 ± 2%. Annual survival of Tristan birds was negatively correlated with longline fishing effort in the South Atlantic Ocean. Population modeling predicts annual rates of decrease of 1.5–2.8% on Gough Island and 5.5% on Tristan da Cunha. Comparison with congeners suggests that the observed and predicted decreases are most likely to be caused by low adult and immature survival. The conservation status of Atlantic Yellow-nosed Albatrosses should be changed from Near Threatened to Endangered.

Mortality in longline fisheries is a critical global threat to some seabird species. Identifying
andmainstreaming seabird avoidance methods that not only have the capacity to minimize bird interactions, but
are also practical and convenient, providing crew with incentives to employ them consistently and effectively,
will help resolve this global problem. Cooperative research and a commercial demonstration were conducted to
assess three methods’ effectiveness at avoiding incidental seabird capture, commercial viability, and practicality
in the Hawaii pelagic longline fisheries. A seabird avoidance method called side setting, which entails setting
gear from the side of the vessel, with other gear design the same as conventional approaches when setting from
the stern, had the lowest mean seabird contact and capture rates of treatments tested. Because side setting
promises to provide a large operational benefit for longline vessels, the incentive for broad industry uptake and
voluntary compliance is realistic. After making the initial conversion to side setting, there is no additional
effort required to employ the method. A seabird avoidance method called an underwater setting chute also
holds high promise, but requires additional research and evaluation to correct design problems, after which it
can be considered being made commercially available. Two chutes, one 9m long and one 6.5m long, which
deployed baited hooks 5.4m and 2.9m underwater, respectively, were used in this trial. The 9m chute had the
second lowest mean seabird interaction rates when used with swordfish gear, and the 6.5m chute had the second
lowest mean seabird interaction rates when used with tuna gear. A third seabird avoidance method, which
entails thawing and dying bait dark blue to attempt to reduce seabirds’ ability to see the baits by reducing the
bait’s contrast with the sea surface, was found to be less effective than the other two methods and was found to
be relatively impractical and inconvenient. If pre-dyed bait were commercially available, use of blue-dyed bait
in combination with other methods, such as side setting and adequate line weighting, has high promise.

A set of procedures for modelling catch and effort data using generalized linear mixed models (GLMMs) including data analytic methods for examining the appropriateness of model structure and parameter values was presented in WG-FSA-SAM 03-12 using Dissostichus eleginoides in Subarea 48.3 of the CAMLR area as an example dataset. The application of these procedures to trawl catches of Champsocephalus gunnari in Subarea 58.5.2 is described. For the trawl catch and effort data it was found the precision of the standardised CPUE estimates was considerably poorer than that of the longline data for Subarea 48.3. It is concluded that CPUE was relatively stable from the start of the fishery until 2000, after which time there was a sharp increase in 2001 with a steady decline thereafter. The sharp increase in 2001 is most likely the result of the large abundance of 3 and 4 year-old fish in that year, which has since diminished through a combination of

A set of procedures for modelling catch and effort data using generalized linear mixed models (GLMMs) including data analytic methods for examining the appropriateness of model structure and parameter values was presented in WG-FSA-SAM 03-12 using Dissostichus eleginoides in Subarea 48.3 of the CAMLR area as an example dataset. Further development of these procedures is presented in this report using trawl catches for Dissostichus eleginoides in Subarea 58.5.2. The extension described here deals with calculating an overall standardised CPUE series when the Subarea has been divided into sampling strata by incorporating ‘Stratum’ as a fixed effect term and the Stratum-by-Year interaction (S x Y) as a random effect term in the GLMM.
Statistical methods are presented for examining the validity of considering the S x Y term as random. A random S x Y term avoids the difficulty in calculating an overall standardised time series of CPUE estimates of weighting by the areal extent of each stratum which is necessary when the S x Y term is included in the GLMM as a fixed effect. Defining an areal extent of each stratum that is valid for use in calculating a weighted mean over all strata using the formula based on stratified random sampling is problematic given that hauls are not a spatially random sample within each stratum. Including the stratum term as fixed simply results in uniform scaling of the CPUE series as is the case with other additive fixed terms in the GLMM.
It was concluded that there was an increase in CPUE in the second year of the fishery with a sharp decline in the following year followed by a relatively stable series of CPUEs. It was also shown that the influence on the series of the random effects estimates for Stratum-by-Year is small.
For the trawl catch and effort data it was found that considering the S x Y term as random was valid. The precision of the standardised CPUE estimates was considerably poorer than that of the longline data for Subarea 48.3. A weak trend of decreasing CPUE values with entry into the winter months was detected using a cubic smoothing spline.