Figure 1.
The Pilbara Trawl Fishery off the north-western coast of Australia.
Figure includes: a) the 50 and 100 m depth contours; b) the boundaries of the fishery management areas (Areas 1, 2, 4 and 5; Area 3 in the central southern region of the fishery is closed to trawling); c) the spatial density of fishing effort based on logbook trawls; and d) the location of dolphin bycatch events reported in skippers' logbooks and by independent observers (August 2003 to September 2009).
Table 1.
Total numbers of trawl days, hours and individual trawls in the PTF.
Table 2.
Dolphin bycatch rates reported by skippers and observers.
Figure 2.
Schematic of trawler and trawl net on or near the seabed.
Also illustrated are the typical positions of dolphins in and around the net, as well as following the trawler on the surface. The detailed net diagram represents the typical net specifications used in the Pilbara Trawl Fishery in 2008 and 2009, showing the side and top views, location of the Bycatch Reduction Device and the skirt covering the escape hatch. The lengths of the different panels are given as number of meshes, mesh length (in inches) and diameter of twine (in mm). In the side view, the height of each panel is given as the number of meshes. Diagram not to scale. Modified from Stephenson et al. [29] and Jaiteh et al. [35] following plans by H. McKenna for the ‘Magnet Box Diamond Net’ with short neck.
Table 3.
Presence of dolphin bycatch by individual factors.
Figure 3.
Dolphin bycatch rates by a) vessel and b) time of day.
Mean (±1 SE) dolphin bycatch rates by a) vessel (1–4) and b) time of the day (Morning = 06:00–11:59; Afternoon = 12:00–17:59, Evening = 18:00–23:59; Early Morning = 00:00– 05:59) in the Pilbara Trawl Fishery. For skippers' logbook, n = 27,914; for independent observer, n = 4,178.
Figure 4.
Dolphin bycatch rates by differing net design in the Pilbara Trawl Fishery.
Mean (±1 SE) dolphin bycatch rates by differing net designs. BRD = BRD fitted just forward of the codend and at the aft end of the tubular net extension; BRD forward = BRD moved to the forward end of the extension.
Figure 5.
Dolphin bycatch rates net type x vessel interaction.
Mean (±1 SE) dolphin bycatch rates illustrating the net type (No BRD vs BRD) x vessel (1-4) interaction based on skippers' logbook data.
Table 4.
Summary of full models to predict dolphin bycatch by fitting multiple factors for a) skippers' logbook data and b) independent observer data.
Table 5.
Model comparison with the full model (Table 4) for predicting dolphin bycatch by fitting multiple predictors for a) skippers' logbook data and b) independent observer data.