Obtaining a standardised CPUE series for toothfish (Dissostichus eleginoides) in the Prince Edward islands EEZ calibrated to incorporate both longline and trotline data over the period 1997-2013

Brandão, Anabela; Butterworth, Doug S

Obtaining a standardised CPUE series for toothfish (Dissostichus eleginoides) in the Prince Edward islands EEZ calibrated to incorporate both longline and trotline data over the period 1997-2013

Working Paper

2013

Publisher

University of Cape Town

Department

Marine Resource Assessment and Management Group

Faculty

Faculty of Science

Abstract

The previous GLMM standardisation approach for PEI toothfish (Spanish) longline CPUE data is extended to include data for the 2012 and 2013 seasons and the same approach is applied to trotline CPUE data for the 2008–2013 period. CPUE data from a research program carried out in 2012 and 2013 in which longline and trotline sets were paired to within three nautical miles and a period of two weeks is analysed to obtain a calibration factor between longlines and trotlines. A model is then fitted to combine the two individual standardised CPUE series and the calibration factor to obtain a “calibrated” longline CPUE series (incorporating both longline and trotline information) and an estimate of the calibration factor. This indicates an increase of about 18% in standardised CPUE in 2013 compared to the preceding year, but this remains about 20% below the 2011 value. However it should be noted that data for 2013 are available only until July.