Browsing by Subject "west coast rock lobster"

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    Implications of adding an extra annual 170 MT interim relief catch for the output of the west coast rock lobster OMP 2007 re-cast
    (2009) Johnston, Susan J; Butterworth, Doug S
    Introduction The current OMP used to set TACs for the West Coast Rock Lobster resource is called “OMP 2007 re-cast”. Results from stochastic simulations predict that this OMP is expected to produce (in median terms) a total exploitable biomass increase of 20% by 2016 compared with that at the start of 2006. This amounts to no more than restoring the biomass to its level in 1996 when OMP-based management commenced. The 10-year average annual commercial TAC is predicted to be 2312 MT. “OMP 2007 re-cast” does not take any interim relief catches into account. The full set of stochastic results for “OMP 2007 re-cast” was reported in Johnston and Butterworth (2008) and is reproduced here in Table 1.
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    Results for the updated trends in policing effort and the number of confiscations for West Coast rock lobster using the “old” database for the period 2008 to 2017
    (2018-08) Brandão, Anabela; Butterworth, Doug S
    GLM methods are applied to compliance data (the “old” database) on confiscations (and abandonments) and on policing effort to estimate recent trends in the amount of rock lobster that is poached. Data for the period in 2016 when Operation Phakisa was launched with associated greatly enhanced levels of marine policing has been omitted from the analyses. The policing effort “sea patrols” has been omitted from the analyses as it has been deemed not to be relevant to rock lobster. The impact of omitting this policing effort type is minimal. The net effect of adding two further years of data suggests that the extent of poaching has increased slightly for Super-area 8+, but dropped more in the Super-areas 3+4+5+6+7.
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    Risk-related aspects of the west coast rock lobster and of the joint sardine and anchovy OMPs to be developed this year
    (2007) Johnston, Susan J; Cunningham, Carryn L; Plagányi, Éva E; Butterworth, Doug S
    In 2006, the west coast rock lobster scientific working group moved from assessing the resource as a single stock, to assessing the stock at a spatially disaggregated “super-area” level, to take better account of different resource monitoring trends in different areas which indicated area-specific dynamics. The resource was divided into five super-areas by combining the existing eights areas (A1 to A8): A1-2, A3-4, A5-6, A7 and A8. Stock assessment updates at the super-area level have now been completed, and work is underway in developing a new OMP for the resource which inputs data on an area-disaggregated basis. This OMP is scheduled for finalisation early during the second half of this year.
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    The size-structured (length-based) stock assessment methodology applied to west coast rock lobster
    (2010) Johnston, Susan J; Butterworth, Doug S
    The model of the west coast rock lobster dynamics is described by a size-structured model which operates at a 1mm interval scale, from l = 1mm to l = lmax, where l refers to the carapace length (which for brevity will also be referred to as “size”) in mm. The largest size class in the model, lmax, is equal to 200mm. Male and female lobsters are modelled separately, with m referring to males and f referring to females. In this report, the superscript s refers to either the male or female sex, where the two sexes are treated separately but similarly. Although the fishing season starts towards the end of year t and runs into year t+1, it is denoted as season t (unless otherwise specified). Where data are collected and represented in 5mm size class intervals, the size class x refers to lobsters of sizes x, x+1, x+2 …x+4 mm.
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    Underlying assumptions for the area-disaggregated stock assessment of west coast rock lobster
    (2007) Johnston, Susan J; Butterworth, Doug S
    The West Coast resource is divided into the following “super” areas: Area 1-2: The most Northern region – only a very small tonnage is currently caught in this area. Area 3-4 (Areas 3 and 4 only) Area 5-6 (Areas 5 and 6 only) Area 7 (Dassen Island), and Area 8+ (areas to the south and east of Dassen Island, which include Area 8 (Cape Point), Area 10 (Hout Bay), Area 11 (False Bay), and Areas 12-14 (East of Hangklip). Figure 1 illustrates the West Coast rock lobster fishing zones and areas. Various methods have been used to collate data from Areas 3, 4, 5 and 6 to produce values for the “super” Area 3-6. Note that the convention used here for referring to split seasons is to quote only the first of the two years for each split season, i.e. the 1992/93 season is referred to here as “1992”. A size-structured modelling approach (as described in RLWS/DEC05/ASS/7/1/2) is used to model the dynamics of each super-areas independently. The area-disaggregated modelling approach assumes that recruitment from each area remains in that area and that there is no immigration or emigration between areas (of larvae or adults)