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    Examination of the characteristics of the fishery for Dissostichus eleginoides in the CCAMLR Statistical Subarea 48.3 and its implications on estimating trends
    in catch per unit effort

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    A.J. Constable, S.G. Candy and B. Raymond (Australia)

    We investigate the spatial and temporal (i.e. fishing season) variation both systematic and random in haul-by-haul catch and effort data from the longline fishery for Dissostichus eleginoides in Subarea 48.3. We concentrate on presenting the results of preliminary work on the potential effects of changing fishing patterns on the standardisation of the CPUE time series. We consider whether the spatial pattern of fishing might have changed over the years, whether the current measure of fishing effort (number of hooks on a line) has changed in its fishing properties over time, and if soak time is a useful additional measure of effort. We then consider how these results might impact on the assessments, particularly the standardisation of the CPUE series. The results indicate that fishing for Dissostichus eleginoides is not uniformly distributed in its range. In some years, though not all, the fishery becomes concentrated into distinct grounds. In the CPUE standardisation procedure we found that although soak time was a significant predictor of catch the fitted relationship was not consistent with using soak time as a co-measure of effort by expressing CPUE as kg per hook-hour. In contrast the fitted log-linear relationship between catch and number of hooks set was consistent with using this variable directly as the measure of effort. The analysis of the interaction between the fishing season and the fitted coefficient for log(Hooks Set) in the regression model for catch suggested a declining trend in the coefficient over time. This may indicate that catchability has been changing and has perhaps become greater over time as a result of effort concentrating in productive locations. We recommend further consideration of the spatial characteristics of the fishery and its implications for using CPUE as an indicator of abundance.