Title: Applicable statistical model to assess the status of the Namibian orange roughy (Hoplostethus atlanticus)

Author(s): Vasana Tutjavi
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Orange roughy; Namibia; Schaefer surplus production model; biomass; aggregating grounds; overfishing.


A common objective of marine fishery management is to estimate stock sizes and harvesting levels that produce maximum sustainable yields. Relatively little is known about the status of the Namibian orange roughy stock in terms of current biomass levels. This document presents an assessment of the Namibian orange roughy at different aggregating grounds by using the Schaefer surplus production model. Exploration of the Namibian orange roughy began in 1994, but the first Total Allowable Catch was allocated in 1997. Swept-areas and acoustic surveys were conducted from 1997-2007. No fishing or surveys were conducted between 2008 and 2015. However, surveys to assess the possible recovery of orange roughy stocks were resumed in 2016. The annual catches from 1994-2007, survey indices from 1997-2016 and catch-per-unit efforts from 1994-2007 were used as model inputs. The model estimated the biomass to be at very low levels, although there are slight increases at Johnies and Frankies aggregations. Model outputs indicate that the Maximum Sustainable Yield was 661 t at Johnies, 168 t at Frankies and 296 t at Rix in 2016. The replacement yields were 0.366 at Johnies, 0.074 at Frankies and 0.00 at Rix. The stock depletions were 17% at Johnies, 13% at Frankies and 11% at Rix relative to the initial biomass (B0). There are no signs of recoveries at Rix and Hotspot aggregations. Orange roughy species is highly vulnerable to overfishing and can only sustain low rates of fishing. The biomass is still low at all the aggregations, therefore harvesting may not be viable for the time being.

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