CCAMLR

In 2008-2009 New Zealand developed an impact assessment framework to estimate the likely impacts of bottom longline fishing on vulnerable benthic invertebrate taxa, termed Vulnerable Marine Ecosystems (VMEs), consistent with the requirements of Conservation Measure 22-06 (Bottom fishing in the Convention area). The impact assessment framework was subsequently endorsed within CCAMLR for routine application by Members submitting notifications of their intent to participate in new or exploratory fisheries using bottom fishing gear (SC-CAMLR XXVIII, paragraph 4.247 v–vii), and was applied to estimate the cumulative historical bottom fishing footprint of all fisheries in the CCAMLR area. The Scientific Committee called for additional work to address remaining uncertainties about the nature and extent of bottom fishing impacts on potential VMEs (SC-CAMLR-XXVIII paragraph 4.251). The purpose of this paper is: i) to estimate impacts on VMEs per unit effort using a simulation approach with explicit incorporation of uncertainties in the input assumptions; ii) to examine the application of the impact assessment framework at different spatial scales, and implications for the validity of the underlying structural assumptions of the assessment framework; and iii) to express impact estimates in a spatially explicit manner with reference to areas of distinct environmental characteristics arising from a benthic bioregionalisation of the Ross Sea region (Sharp et al. 2010). We conclude that bottom fishing impacts on VME taxa in the Ross Sea are low.

An important management objective for CCAMLR in the high seas region of the Antarctic is to develop appropriate methods of monitoring and managing impacts of bottom fisheries on vulnerable marine ecosystems (VMEs). We describe a spatially explicit production model that can be used to investigate a range of simple scenarios for simulating the effect and management of benthic impacts from longline fishing effort. Simulations were carried out under a range of productivity assumptions, impact, and spatial scale, with and without management by areal closures. Further, the management action simulated considered a range of areal closure radii and bycatch trigger thresholds. We conclude that spatially explicit production models can provide a useful tool for the investigation of impacts of fishing effort on benthic organisms. They have the advantage that they are relatively simple to construct, run, and interpret. In general, the results of the simulations suggested that management action of areal closures in the Ross Sea region are likely to result in an improved outcome over scenarios where there was no management action, but that the size of effects under the plausible models was often very small. We also note that further work on these simulations are required — including investigating how changes in the distribution of future fishing may result in alternative impacts or how different assumptions of the underlying distributions of benthic organisms may influence the results. However, as the size of these impacts in the scenarios tested were small, we recommend that research be focused, at least in the short term, to provide observational or experimental data necessary to constrain important model parameters, to reduce uncertainty and provide more plausible scenarios.

Bathymetric data are currently used inter alia to define management boundaries, implement conservation measures, allocate catch among areas, estimate spatial impacts due to fishing, and inform ecosystem-based management through bioregionalisation. Several data sources for bathymetric data exist, and these sources improve with time through additional data collection and improved analytical methods. We developed an algorithm to summarize bathymetric point data (x,y,z) for the Ross Sea region to provide a transparent and citable method to derive standard summary statistics for use by CCAMLR. This is especially important because of the multinational use of such data. The method is applicable to the entire Southern Ocean, but is currently applied only to the Ross Sea region. We have obtained publically available bathymetric data, created a spatial database, and have developed scripts for defining polygons of user-specified bathymetric areas, calculating the areas of those polygons, and displaying them as contour maps. As data sources improve, this process can update the summary statistics as needed in a comparable and transparent manner.

Sources of variability of krill mean length and fish bycatch number was investigated to explore proper allocation of scientific observers on Japanese krill fishing vessels using the data from 1995 to 2008. Based on the multistage sampling theory, we derived the equation of variance in four stage cluster sampling units (i.e., vessel, year, subarea, and haul), and examined changes in the coefficients of variation (CV) caused by the shifts in coverage at different sampling stages. Vessel coverage had the largest impacts, and year coverage had moderate impacts on CV for both mean krill length and fish bycatch. The impacts of subarea and haul coverage were different between krill length and fish bycatch. Fish bycatch required moderate coverage for haul but low improvement were made by increasing subarea coverage, whereas krill length allowed very low haul coverage but preferred higher subarea coverage. To determine the proper level of observer coverage, the purpose and cost of observer monitoring should be discussed.

Distribution, relationship between sizes and depths, sex ratio, size composition and maturity condition for Dissostichus eleginoides and D. mawsoni were investigated on Banzare Bank, using the biological data sampled by a Japanese commercial fishing vessel during austral summer from 2006/07 to 2008/09 fishing season. D. eleginoides was mainly caught in the shallower bank <1000 m, while D. mawsoni was mainly caught in the deeper slope >1500 m. The separation of the two species by depths may be related to the physical intolerance to the cooler temperature by the lack of antifreeze for the former species. The mean total length (TL) of females was significantly larger than that of males for both species. The proportion of males to the total adults decreased significantly with the depths with gradual slope for both species. Male D. mawsoni showed a significant correlation between depth and the TL with gradual slope. The size structure varied among the fishing seasons and showed the polymodal distribution in D. eleginoids, while the size structure was very similar among fishing seasons and showed the unimodal distribution in D. mawsoni. D. eleginoides showed resting stage in sexual maturity, while D. mawsoni was in running ripe condition. In both species, small fish contributed low proportion in abundance, which suggest that substantial recruitment does not take place on Banzare Bank and the population may consist primarily of adults migrating from other area

In order to clarify the stock status and biological characteristics of Dissostichus spp. In Division 58.4.4 a & b, we submit this research plan for toothfish in the Division by Shinsei Maru No. 3 to be conducted in April-June 2011. This is the second year of the survey of the 3-5 years consecutive research focusing on tagging program, recommended by WG-SAM-09 in this Division, following the first survey conducted in 2009/10 season, when total sample size for Dissostichus spp. Was allowed as 60,000 kg. The research hauls are allocated on 10-minute latitude x 20-minute longitude grid points, taking into account the need to deploy research hauls and tagging releases evenly throughout the survey area in the same manner as 2009/10 survey. A Trot line system will be employed for all hauls. To apply the mark-and-recapture studies, sufficient tagging rate of 5 fish / ton will be conducted in the same manner as the 2009/10 survey. We calculated the two values (78 and 114 tonnes) of total allowable sample size for the 2010/11 survey, taking into account the need for completion of the survey and impact on the fish stock, and will take advices for the method of estimations in the WG-SAM-10 meeting.

A survey was conducted in order to collect information for the stock status and various biological information on toothfish in Division 58.4.4a & b (Ob Lena Bank) by using a commercial bottom longline vessel, Shinsei Maru No. 3, from April 30 to June 20. The survey was undertaken according to the decision in the 28th CCAMLR Meeting of the Commission (28th CCAMLR report paragraph 4.43). This report described the results preliminarily during the survey in four SSRUs of Ob Lena Bank. The catch amounted the total allowable catch of 60 tonnes in 94 longline sets, which corresponded to 83 % to the total allocated fishable 113 sets. D. eleginoides contributed 80.1 % in numerical number and 96.1 % in weight to the total samples in SSRUs. Mean CPUEs of D. eleginoides for 71 hauls where only Trot line system was adopted were 13.1 indiv. / 1,000 hooks in number and 138.9 kg / 1,000 hooks in weight. These values were larger than mean CPUEs of 11.0 indiv. / 1,000 hooks and 108.0 kg / 1,000 hooks in the same Division in the 2007/08 season. D. eleginoides caught showed a broad polymodal composition for each SSRU, but the proportion of smaller fish caught in eastern SSRUs tended to be lower than that caught in the western SSRUs, as observed in the previous 2007/08 survey.

In accordance with the Conservation Measure 41-07 (2009), a survey was conducted in order to collect information for the stock status and biological information on toothfish in the southeast sector (24 allocated points) of Division 58.4.3b (Banzare Bank), using a commercial bottom longline vessel Shinsei Maru No. 3, from December 1 to 13, 2009. Shinsei Maru Trot line system was used as fishing gear. Total catch (excluding released weight) of Dissostichus spp. And the other by-catch species was 15.9 tonnes in the SE sector, where the catch limit of 18 tonnes was set. Dissostichus spp. Made up 16 % in number and 87.5 % in weight of the whole fish caught, while Macrourus spp. Made up 81% in number but only 11 % in weight to the total. Among two species of toothfish, Dissostichus mawsoni was dominant (82 % in number and 88 % in weight to the total). Mean CPUE of D. mawsoni was 3.4 indiv. / 1,000 hooks in number and 111 kg / 1,000 hooks in weight. D. mawsoni showed a broad modal composition at approximately 130-150 cm. Total of 60 individuals of toothfish were tagged and released during the survey. One male D. eleginoides was recaptured.

An age-based operating model was constructed and used to derive an initial numbers at age vector for the population. An age-based harvest control rule was then applied using the operating model dynamics and assuming perfect knowledge of the resource (initial numbers at age, maturity and weight at age). The initial numbers at age was also converted to numbers at length, which was used to initialise the length based harvest control rule, again assuming perfect knowledge of the resource. Total allowable catches (TACs) and harvest rates (H) from the length and age based methods could then be compared to test the performance of the length based method, with results suggesting that the two approaches determine similar harvest strategies.

Attempts to estimate natural mortality, as a single constant M, simultaneously with other model parameters in integrated assessments via CASAL for the Heard and McDonald Islands (HIMI, CCAMLR Division 58.5.2) Patagonian toothfish (Dissostichus eleginoides) fishery have been unsuccessful. An alternative estimation strategy was tested using simulation whereby catch-at-age and aged mark-recapture data were generated for 12 years of fishing. Two alternative estimation models were programmed in R. Both use the same Poisson likelihood for annual number of recaptures by age class, and both model the age-structured population for each fishing year by annual recursive use of difference equations for population numbers at age obtained by integrating a first order ordinary differential equation (ODE) for within-year population dynamics. The difference in the models derives from differences in their ODE. The BODE model is based on the well-known Baranov ODE and corresponding mortality equation. The model based on a new mortality equation (CCODE model) uses an ODE with constant within-year catch per unit time for each age class, and as a result allows catch to be removed directly from the population. Compared to the BODE model the CCODE model involves less parameters and does not have competing likelihood components avoiding the difficultly in appropriately weighting separate components. Also, for a fishery that is not substantially depleted within any single fishing season, given fishers tend to increase their effort if required to achieve their target catch for the year, the CCODE model is the more realistic. In simulation studies of multiple years of releases, both the BODE and CCODE models gave accurate estimates of M when all other parameters were fixed at their simulation values. When all parameters were jointly estimated and selectivity is low for older age classes there was a problem of substantial positive bias in estimation of M for both the BODE and CCODE models. This problem was reduced so that bias in CCODE model estimates of M became progressively smaller as less “severe” selectivity was imposed in the simulation model. If selectivity for older age classes is close to 1 then the CCODE model estimates M with small bias and reasonable precision assuming 500,000 fish caught and 1,000 released per year.