CCAMLR

According to the Conservation Measure 10-09 (2009) paragraph 6, Japan reports on transhipment activities by its krill fishing vessel in the CCAMLR Convention Area in 2010, as a background paper for CCAMLR annual meeting to be held in October 2011.

The study of animal movement and distribution has been a central focus in ecology since the inception of the science. However, continuous-time, discrete state models have received relatively little application in data analyses or prediction in studies movement. Here we develop a continuous time, discrete state stochastic model, a continuous time Markov chain (CTMC), for analyzing movement data, including an inferential framework which can accommodate heterogeneous sampling effort. We explore the accuracy of estimates arising from this model using simulated data with known movement rates. Finally, we apply the model to estimate the equilibrium distribution of Patagonian toothfish in the region around Heard and MacDonald Islands in the Australian Antarctic zone using to mark-recapture data from the Australian Patagonian toothfish fishery.

This paper reviews the data used to estimate the abundance of juvenile Dissostichus eleginoides in Division 58.5.2 and examines the sensitivity of the assessment of yield to these results. Primarily, it is proposed to revise the use of historical survey data by reassigning them to the strata established in 2003. In addition, the sensitivity of the estimates of abundance to the latest length-at-age model is examined. The best fits using CMIX to estimate cohort densities were obtained using the updated assignment of survey data to the 2003 stratification along with the latest estimates of length at age. The quality of model fit and estimates of abundance of specific cohorts were sensitive to the number of cohorts assumed to be represented in the length density data. Assuming survey design produces unbiased estimates of length density, we suggest that best estimates of cohort abundance will be achieved when mixture analysis is informed by accurate estimates of length at age, an independent estimate of relative abundance of cohorts present in any survey year such as could be derived through an age length key, and vulnerability of the stock to the surveys. The consequences to the 2005 assessment of yield of toothfish of changing the time series of abundance of juvenile fish and the length-at-age model were examined. Yield estimates were found to be most sensitive to the estimated recruitment series interacting with the estimate of mortality and the cohort abundances form CMIX, and to a lesser extent the estimated fishing vulnerabilities. A scenario equivalent to that used to recommend yield in 58.5.2 for 2005/06, incorporating the latest estimates of length at age, selectivity and the mixtures estimated from the assignment of RSTS hauls, resulted in an increase in estimated yield.

This paper follows preliminary work in 2005 in developing an integrated assessment for Patagonian toothfish in Division 58.5.2. It focuses on developing a “base-case” assessment, which is primarily based on the 2005 assessment implemented in the Generalised Yield Model (GYM) using survey data of the abundances of juvenile fish but adding fishery catch-at-length data, including a standardised catch-per-unit-effort (CPUE) series. The base-case scenario was then extended to include estimates of IUU catch and mark-recapture data. Key sensitivity trials were also used to explore the tension between estimating natural mortality and selectivity for the different fisheries. The results of this work show that an integrated assessment for Dissostichus eleginoides in Division 58.5.2 seems tractable. The recruitment series derived from surveys has similarities with the recruitment series estimated by Welsford et al. (2006), but with a recognition that some age classes are only partially selected in these surveys. Although computer processing time is substantially increased, the inclusion of the catch-at-length and the mark-recapture data generally improves the confidence in the estimates of B0 and the recruitment series. Despite these results, there is considerable tension in the estimation model between natural mortality and fishing selectivities. The uncertainty arising from this tension will need to be explored further in order to appropriately accommodate this uncertainty in the estimate of long-term annual yield. Further discussion is needed on the choices being made in how the datasets are used in this assessment and the approaches being used to estimate the key parameters. An important stage in the development of this assessment will be to evaluate the robustness of these assessments to the uncertainties identified here as well as uncertainties in the spatial dynamics of the stock and the fisheries.

During the year 2005 meeting of the WG-FSA two different methods for assessing Patagonian toothfish stock in CCAMLR Subarea 48.3 were available to the Working Group: CASAL and ASPM (WG-FSA-05/16; WG-FSA-05/73). Although the underlying basic age-structure population dynamics models in both cases were similar, there were considerable differences in assumptions and implementations of the two methods. In this paper, we discuss the related effects considering constant h parameter and deterministic recruitment over time vs. considering a fitted h parameter and variable recruitment. The first alternative produces a more stable population structure and would introduce bias in the biomass and spawning stock biomass estimated. In the second case (variable recruitment and fitted h), the model have more flexibility to fit the changes in population structure and abundance. The parameter r from the stock recruitment relationship is also analyzed, in relation with the current underlying assumption of fish stock resilience.

Two Operating Models (OMs) reflecting an “Optimistic” and a “Pessimistic” current status for the toothfish resource in the Prince Edward Islands region that were developed last year are updated given further data. These models are for use for initial trials of candidate Management Procedures (MPs) which could provide future TAC recommendations for this resource. Deterministic projections under a constant future catch suggest that the two scenarios will only be qualitatively distinguished in the short-term by an increase in the mean length of longline-caught toothfish over the next five years for the “Pessimistic”, but not the “Optimistic” case. Accordingly the performance of a simple MP control rule based upon recent trends in both CPUE and this mean length is investigated. This MP is able to secure a faster increase in the TAC for the “Optimistic” case, and some recovery in abundance for the “Pessimistic” scenario, but neither is as appreciable as one might wish. Suggestions for future work are made.