Aquatic Environment and Biodiversity Annual Review 2012

AEBAR 2012: Non-protected bycatch
Figure 6.10: Annual estimates of fish discards in the target jack mackerel trawl fishery for the 2001-02 to
2004–05 fishing years (in black), calculated for jack mackerel (JMA), commercial species (COM), noncommercial
species (OTH), and overall (TOT). Also shown (in grey) are estimates of jack mackerel and
overall discards calculated for 1990–91 to 2000–01 by Anderson et al. (2000) and Anderson (2004a). Error
bars show the 95% confidence intervals.
6.3.5. Southern blue whiting trawl fishery
In the most recent study, covering the period 2002–03 to 2006–07, the ratio estimator used to
calculate bycatch and discard rates in this fishery was based on trawl duration. Linear mixed-effect
models (LMEs) identified fishing depth as the key variable influencing bycatch rates and discard rates
in this fishery, and regression tree methods were used to optimise the number of levels of this variable
in order to stratify the calculation of annual bycatch and discard totals in each catch category.
The key categories of catch/discards examined were; southern blue whiting, other QMS species
combined, commercial species combined (as defined above for hoki/hake/ling), non-commercial
species combined, and three commonly caught individual species, hake, hoki, and ling.
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