CCAMLR

The development of the National Plan of Acton for Reducing the Incidental Catch of seabirds in Chile is presented.

We carried out a pilot research program in collaboration with industry to identify techniques for future testing that are likely to reduce seabird interactions with catcher processor trawl vessels operating the Bering Sea fishery for pollock (Theragra chalcogramma) and that are practical and safe. Emphasis was placed on reducing seabird interactions with trawl cables: nets warps, as well as the netsounde cable (3rd wire). Third wire mitigation techniques included pulling the third wire as close as possible to the water at the stern with a snatch block, paired streamer lines and various deterrents attached directly to the third wire (3rd wire scarers). Warp deterrents included a boom array or a buoy placed in the offal stream forward of the warps. Results showed that both the snatch block and paired streamer lines have great potential to reduce seabird interactions with the 3rd wire, but both require refinement for practical and safe application. Deterrents applied directly on the third wire were less effective and impractical. The boom array effectively excluded birds from the area around the trawl warps. Buoys were less effective and were difficult to position effectively. Formal testing of streamer lines, the snatch block, and the warp boom on two factory trawlers retrofitted to allow for the safe and practical deployment of the seabird interaction deterrents was proposed for 2005. Limited tests suggested fish oil has great potential as a seabird deterrent.

Given the lack of information on appropriate seabird avoidance measures for small Alaskan longline vessels, we determined the “2-m access window”, or the distance astern that longline hooks were accessible to surface foraging Alaska seabirds, for 8 fishing vessels > 7.9 m to 16.8 m (> 26 to 55 feet) using two gear types: snap-on gear and fixed gear. We also determined the capability of these vessels to deploy streamer lines and/or buoy lines according to performance standard guidelines. Vessel speed was found to be a primary determinant of both the distance astern that longline hooks were accessible to surface foraging seabirds, and the performance standards of streamer lines. Vessels deploying snap-on gear at 2 to 3.5 knots produced mean access windows of 28 to 38 m while the mean access window produced by vessels deploying fixed gear at faster speeds averaged 90 m. Gear sink rates among vessels and gear types were similar (0.09 to 0.13 for snap on gear vessels and 0.07 m/s for fixed gear). We determined that the current single streamer line requirement for snap-on gear vessels over 16.8 m and with infrastructure (a 45-m streamer line with a minimum aerial distance of 20 m) was achievable and practical regardless of vessel size, especially with a lighter streamer line design. However, the current requirement for small vessels using fixed gear of a single streamer line with no mandatory material or performance standards is unlikely to provide sufficient protection to seabirds. Specific recommendations for seabird avoidance requirements are proposed for these small vessels based on these results.

In our study skeletal elements from fish species of the Antarctic waters were extracted by bioenzyme and compared with the aim to provide a computer supported identification system, including a database of bone pictures and in the near future various identification keys as well, completed by a simple tool to compare the same skeletal elements of different species. In the database most of the skeletal elements of the cranial and axial skeleton (apart from a few bones of the neurocranium) are represented by pictures, otoliths and vertebrae included. Furthermore cooperation with other institutions is needed to extend the existing work.

An updated descriptive analysis of the toothfish tagging programme carried out in Subareas 88.1 and 88.2 since 2001 is presented. Tag-release and tag-recapture data are presented for both toothfish species for the Ross Sea (Subareas 88.1 and SSRUs 88.2A–B), and SSRU 88.2E for New Zealand vessels. A total of 4903 Antarctic toothfish have been released and 89 recaptured, and 443 Patagonian toothfish released and 9 recaptured. For the last two years, when tagging has been part of the Conservation Measure, New Zealand vessels have tagged between 1.0 and 2.77 toothfish per tonne of catch. Tagging rates by area over the past three years have been in the same proportion as the catch by area. However, recapture rates have tended to be higher in the northern and eastern SSRUs 88.1C and 88.2E.
The maximum movement of Antarctic toothfish from the New Zealand data set has been about 200 km. However, most (80%) Antarctic toothfish have moved less than 50 km. Consequently, nearly all fish have been recaptured from the same SSRU where they were released. The mean size of tagged Antarctic toothfish has increased since 2001, but is still smaller than the mean size of fish taken in the commercial catch. Larger toothfish (>35 kg) are difficult to tag without significant damage to fish, and there is be a trade-off between maximising size of released fish and minimising tagging mortality. Growth rates of Antarctic toothfish that have been at liberty for 2–3 years have averaged 5–7 cm per year, which is consistent with growth rates predicted from the von Bertalanffy growth curve.

This report outlines a Bayesian sex and age structured population stock assessment model for Antarctic toothfish (Dissostichus mawsoni) in the Ross Sea (Subareas 88.1 and SSRUs 88.2A–B). A range of model sensitivities were examined, with the base case assuming the Ross Sea fishery as a single homogeneous area (single-area) with catch removals from three spatially based fisheries (shelf, slope, and north).
Model fits to the data were adequate, with the tag-release and recapture data providing the most information on stock size. Monte-Carlo Markov Chain (MCMC) diagnostics suggested some evidence of non-convergence, particular in the declining right-hand limb of the fishing selectivity parameters. However, multi-chain comparisons and sensitivities with fixed selectivity ogives suggested that this would have little impact on the estimates of key model parameters and yield estimates.
MCMC estimates of initial (equilibrium) spawning stock abundance (B0) were 69 400 t (95% credible intervals 47 700–111 900 t), and current (B2005) biomass was estimated as 88% B0 (95% C.I.s 83–93%). Estimated yields, using the CCAMLR decision rules, were estimated to be 2964 t although continued catch at current levels (3207 t) would not be expected to breach the 50%B0 threshold until 2029.

The Ross Sea toothfish fishery has operated during the Antarctic summer (November–May) since 1997 in CCAMLR Subareas 88.1 and 88.2. Previously, standardised analysis of toothfish CPUE (catch per hook) have been carried out in 2004 calculated CPUE indices for the 1997–98 to 2003–04 fishing years in Subarea 88.1 and 88.2. This report revises and updates the previous analysis with the addition of data from the 2005 season for the Ross Sea (Subarea 88.1 and SSRUs 88.2 A–B) using data sets based on (a) all vessels and (b) the two main New Zealand vessels that have been in the fishery over most of the period. We estimate indices using both lognormal generalised linear models and a Tweedie mixed model, in which data were modelled using the methods described by Candy (2003)
The variables included in the analysis appeared reasonable and were consistent between the models presented here and CPUE analyses for previous years. The yearly indices were relatively stable between 1998 and 2003, with a decline in 2004, and a sharp increase in 2005. Possible explanations for the decline in 2004 were described by Phillips et al. (2004) as gear conflict and competition between vessels to set lines, in addition to extreme ice conditions that limited where lines could be set. None of these factors were believed to be important in 2005.
Investigation of additional explanatory terms included an index of ice cover and an index of vessel crowding. Neither of these terms was found to be significant or explain the decline in 2004 or the increase in 2005. Lack of a balanced experimental design and possibly the choice of parameterisation of the variables are likely to be the reasons why neither of these terms were found to be significant.

This report outlines a Bayesian sex and age structured population stock assessment model for Antarctic toothfish (Dissostichus mawsoni) in SSRU 88.2E. The model structure was assumed to be the same as used for the Antarctic toothfish in the Ross Sea (see Dunn et al. 2005b), except that catch removals were modelled as a single fishery.
Model fits to the data were adequate, with the tag-release and recapture data providing the most information on stock size, but with the catch-at-age data excluding preventing very low estimates of stock size. Monte-Carlo Markov Chain (MCMC) diagnostics suggested some evidence of non-convergence, particular in the declining right-hand limb of the fishing selectivity parameters.
MCMC estimates of initial (equilibrium) spawning stock abundance (B0) were very uncertain, with the median estimated as 7720 t (95% credible intervals 3760–22 240 t), and current (B2005) biomass estimated as 91.8% B0 (95% C.I.s 83.1–97.1%).
Estimated yields, using the CCAMLR decision rules, were estimated to be 670 t. However, as the fishing selectivity was estimated to be to the right of the maturity ogive, there was a significant biomass of mature, but ‘invulnerable’ fish in the projection period. Moreover, the mean catch that could actually be taken under this scenario was 450 t. Hence, two revised methods for assessing risk are also considered. The first assumed that the future fishing selectivity was equal to the maturity ogive, and hence the yield was calculated as 273 t. The second used the model estimate of the vulnerable biomass as the reference biomass in the risk evaluation, and hence the yield was calculated as 218 t.

A survey of Patagonian toothfish, Dissostichus eleginoides,was undertaken in Division 58.5.2 in the vicinity of Heard Island in June 2005 to provide the information for an assessment of short-term annual yield in the 2005/2006 CCAMLR season. This paper provides a preliminary assessment of yield for the area of Division 58.5.2 to the west of 79°20’ E using standard CCAMLR methods. It also considers the sensitivity of the assessment to (i) further consideration of the survey series and the sensitivity to exclusion of observations of older cohorts in recent surveys, (ii) implementation of revised growth parameters, including the use of a length-at-age vector, (iii) consideration of a vulnerability function for the future projections based on full selection of adult fish, and (iv) consequence of reducing the range of natural mortality from 0.13-0.2 to 0.13 – 0.165, consistent with slower growth rates of fish.

The exploratory fishery for Antarctic toothfish (D. mawsoni) has been operating for eight years in Subarea 88.1 and for four years in Subarea 88.2 with a large amount of data collected on toothfish and the associated bycatch.
The 2005 D. mawsoni catch was the highest on record with a total of 3477 t against a catch limit of 3625 t. The catch limit was almost reached in Subarea 88.1 and exceeded in Subarea 88.2. D. mawsoni was the dominant catch in all 11 SSRUs fished. The main bycatch species were rattails, which contributed 12% of the catch, and skates which contributed to about 2% of the total catch1.
Comparison of the location of fishing effort with ice distribution over the past six years has clearly demonstrated the strong influence of ice on this fishery. In 2001, 2003, and 2004, ice conditions were particularly bad and fishing was restricted to suboptimal areas. However, in 2005, ice conditions were very good, allowing vessels access to most of the main fishing grounds in both Subareas. This resulted in the closure of all SSRUs due to catch limits for toothfish, or bycatch limits for rattails, being reached by 18 March 2005.
The change in fishing patterns between seasons is reflected in the mean length and age composition of the catch. During the development of the fishery there has been a steady increase in depth fished, which peaked in 2003, but decreased slightly in 2004 and 2005. This is reflected in the mean length and age composition of the catch, which also declined slightly in 2004 and 2005.
1 Note that this does not include skate released at the surface.