Browsing by Subject "South Coast rock lobster"

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    The 2006 age-structured production model assessments and projections for the South Coast rock lobster resource-routine update
    (2006) Johnston, Susan J; Butterworth, Doug S
    The assessment conducted in 2006 has been routinely extended, taking account of a further year’s catch, CPUE and catch-at-age data. CPUE shows a continuation of the increase that commenced in 1998. The sustainable yield estimates are generally very similar to those for the 2005 assessment, although estimates of current biomass levels relative to K increase. The Reference Case (RC) scenario suggests that a TAC of about 360 MT or less would be appropriate to prevent biomass decline in the future. Other scenarios suggest either higher or lower values than this. If the catch-at-age data are down-weighted, then this 360 MT level for the TAC is increased to 390 MT. On the other hand, the scenario which assumes the 1996+ recruitment to be equal to the average of the previous 10 years is more pessimistic and suggests an appropriate TAC level of only some 300 MT or less to prevent biomass decline.
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    The Age-Structured Production Model for the South Coast rock lobster population extended to be sex- and area-specific and to fit to catch-at-length data
    (2007) Johnston, Susan J; Butterworth, Doug S
    The south coast rock lobster resource is modelled using an age-structured-productionmodel (ASPM) which fits to catch-at-length data directly. The model is sexdisaggregated (m/f) and area-disaggregated (A=1,2,3).
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    The Age-Structured Production Model for the South Coast rock lobster population extended to be sex- and area-specific, to fit to catch-at-length data, and to use Pope's approximation
    (2008) Johnston, Susan J; Butterworth, Doug S
    The south coast rock lobster resource is modelled using an age-structured-productionmodel (ASPM) which fits to catch-at-length data directly. The model is sexdisaggregated (m/f) and area-disaggregated (A=1,2,3). Population equations have been modified from Baranov equations to Pope’s approximation. This has reduced the number of estimable parameters, and speeded up runtime of the program. Note that the model now includes an option for annual variability in the proportion of recruitment (age 0 lobsters) to each area each year. Though formally there is not interArea movement after this recruitment, in effect this means that there is allowance for such movement, but only for ages less than those which the fishing exploits.
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    Alternative calculation of catches per Area in the South Coast rock lobster fishery
    (2008) Glazer, Jean Patricia; Butterworth, Doug S
    A method to separate the South Coast rock lobster annual catches by Area for the areadisaggregated assessments was described in WG/04/08/SCRL08. Concern was raised about an assumption made with respect to the calculation of those catches, namely that the spatial distribution for HBF was the same as for other companies over the period in which HBF under-reported catches (19971 -2000). The calculations presented in this paper offer an alternative method of separating the annual catches, taking the concern raised above into account.
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    A Generalized Linear Model applied to the South Cost rock lobster CPUE data to obtain area-specific indices of abundance
    (2008) Glazer, Jean Patricia; Butterworth, Doug S
    Area-disaggregated assessments for South Coast rock lobster are currently being developed. An important input to these assessments is the catch per unit effort (CPUE) data. A Generalized Linear Model (GLM) has been applied to the data to obtain areaspecific standardized indices of abundance for input to the assessment models.
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    Preliminary specifications for the sex- and area-specific Operating Models for testing OMPs for the South Coast rock lobster resource
    (2008) Johnston, Susan J; Butterworth, Doug S
    Johnston and Butterworth (2008b) presented some initial results for sex- and areaspecific age structured production models intended to serve as operating models for testing OMPs for the south coast rock lobster resource. Here the authors update those results as well as produce results for a model which takes effort saturation into account. Results are presented in detail for the following models: • Model 1: no time-varying selectivity or effort saturation effects, but does have the two selectivity functional forms for Area 3. • Model 2: time varying selectivity – MARAM method – Area 3 has 2 selectivity functional forms • Model 3: time varying selectivity – OLRAC method – Area 3 has 2 selectivity functional forms. Scenario Model 3e is presented here (see Johnston and Butterworth 2008b for details of Model 3e parameters). • Model 4: Model 1 but with effort saturation effects.