Browsing by Author "Fairweather, Tracey"

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    The 2018 Operation Management Procedure for the South African Merluccius paradoxus and M. capensis Resources
    (2019) Ross-Gillespie, Andrea; Butterworth, Doug S; Glazer, Jean; Fairweather, Tracey
    Specifications and projection results for the 2018 Operational Management Procedure used for setting South African hake Total Allowable Catches are provided along with various background information, including details of the metarule processes.
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    The 2018 Operational Management Procedure for the South African Merluccius paradoxus and M. capensis resources.
    (2018-10) Ross-Gillespie, Andrea; Butterworth, Doug S; Glazer, Jean; Fairweather, Tracey
    Specifications and projection results for the 2018 OMP used for setting SA hake TACs are provided along with various background information, including details of the metarule process.
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    Establishing a baseline for evaluating changes in fish body condition and population dynamics of Cape hake (Merluccius capensis and M. paradoxus) in South Africa
    (2014) Boyd, Danielle Winona; Moloney, Coleen; Ndjaula, Hilkka O N; Fairweather, Tracey
    Standard weight (Ws) equations were developed and relative weight (Wr) indices calculated for both shallow-water (Merluccius capensis) and deep-water (M . paradoxus) Cape hake. The aim was to provide fixed baselines and Wr indices to aid understanding of temporal and spatial variability in fish condition . Baselines were calculated using the empirical percentiles (EmP) method applied to length (L) – weight (W) data collected by research surveys on the South African west and south coasts, from 1983 to 2013 . Four quadratic Ws equations for each species were generated, based on the following weight statistics for each size class j : first quartile, median, third quartile and mean. Median Ws equations were chosen for the baseline for shallow-water hake (log₁₀ Ws=-2.491 + 3.33 8 *(log₁₀ L)-0.065 *(log₁₀ Lj)²) and deep-water hake (log₁₀ Ws =- 2.161 + 2.930*(log₁₀ L) + 0.0456 *(log 10Lj)²). Shallow-water hake was found to be the heavier of the two species at the same length. Wr indices display good condition values (>100%) for both species throughout all analyses . Fish condition for both species was best between 1988-2009, ranging from 50-1 65% for individual fish and 100 – 109% for annual averages. Monthly mean Wr indices peaked in June and October for shallow-water hake and July and October for deep-water hake. Mean Wr values were different for shallow-water hake on the south (105%) and west (103%) coasts. Deep-water hake showed no spatial variability in mean Wr values. There were no differences between mean Wr values of males and females between, and within, species. Future hake data may be compared to these Ws equation baselines and Wr indices to show changes in body condition for this commercially important stock.
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    Hake Data: problems, solutions and GLM CPUE sensitivity to alternate scenarios
    (2009) Fairweather, Tracey; Glazer, Jean; Leslie, Rob; de Decker, Michelle; Johnston, Susan; Butterworth, Doug S
    The checks carried out on the hake offshore trawl catch and effort data, which provide the basis to split the catches by species and to obtain GLM-standardised CPUE indices of abundance by species, have focused on two separate steps. The first was a re-extract of the data from the original files to check for possible errors in the earlier extracts (this applies to the subset of the data for which size composition information can be unambiguously extracted). The second step was to increase the proportion of the data utilised (and at the same time to check for possible selection biases in the existing sample) by assigning size composition to drags for which this information was not directly available, on the basis of the average for other vessels for which this was available for the area and time at which the fishing concerned took place. The first step revealed a problem with extractions over the last few years which at times for certain vessels had linked the accumulated catch for the day with only the effort for the last trawl of the day, rather than for all trawls that day combined.