Saved By The Experimental Design: Testing Bycatch Reduction And Turtle Exclusion Devices In The Png Prawn Trawl Fishery

In trawling for prawns, the prawn catch is often only a small part of the results of any one trawl, with the remainder called “bycatch”. Reducing the bycatch component, while maintaining the prawn catch, is an important industry goal, primarily for environmental accreditation purposes, but also for economic reasons.
We designed an at-sea trial for the Gulf of Papua Prawn Fishery, involving four vessels each towing ‘quad gear’ (that is, 4 separate, but linked trawl nets) in each trawl shot, over 18 days. The experiment was designed to assess the effectiveness of 27 combinations of Turtle Excluder Devices (TEDs) and Bycatch Reduction Devices, (BRDs), with a control net, without any attached device as one of the nets in each quad. At Biometrics 2015 we discussed how we used simulated annealing to generate a highly efficient design, in several stages, to meet the large number of highly specific logistical constraints.
The focus of this talk will be the analysis, which also proved somewhat challenging. We will present the results of our analysis and demonstrate why putting the time into thinking about and generating a non-standard experimental design allowed us to accommodate the various glitches and misfortunes that always seem to happen at sea.