David J. Sterling

Energy audit of fishing vessels

Recent dramatic rises in the price of diesel fuel have resulted in the questionable viability of sectors of the Australian commercial fishing industry. Many fishing vessels currently operating in the fleet are over 20 years old and operate in a way that is inefficient in terms of the energy input (combustible fuels) in contrast with the useful energy output (catch). Combined with the global need to reduce greenhouse gas emissions there is a clear need to introduce new efficiencies into fishing vessel operations. This paper reports on the development of an energy audit method for fishing vessels, based on similar systems for land-based industries. It enables the analysis of individual vessels to be made and allows the assessment of their energy usage and current level of efficiency. A sample energy audit has been conducted for an Australian fishing vessel that leads to recommendations for improved efficiencies to combat present and possible future fuel cost increases.

The 'W' prawn-trawl with emphasised drag-force transfer to its centre line to reduce overall system drag

For prawn trawling systems, drag reduction is a high priority as the trawling process is energy intensive. Large benefits have occurred through the use of multiple-net rigs and thin twine in the netting. An additional positive effect of these successful twine-area reduction strategies is the reduced amount of otter board area required to spread the trawl systems, which leads to further drag reduction. The present work investigated the potential of redirecting the drag-strain within a prawn trawl away from the wings and the otter boards to the centre line of the trawl, where top and bottom tongues have been installed, with an aim to minimise the loading/size of the otter boards required to spread the trawl. In the system containing the new ‘W’ trawl, the drag redirected to the centre-line tongues is transferred forward through a connected sled and towing wires to the trawler. To establish the extent of drag redirection to the centre-line tongues and the relative drag benefits of the new trawl system, conventional and ‘W’ trawls of 3.65 m headline length were tested firstly over a range of spread ratios in the flume tank, and subsequently at optimum spread ratio in the field. The developed ‘W’ trawl effectively directed 64% of netting-drag off the wings and onto the centre tongues, which resulted in drag savings in the field of ∼20% for the associated ‘W’ trawl/otter-board/sled system compared to the traditional trawl/otter-board arrangement in a single trawl or twin rig configuration. Furthermore, based on previously published data, the new trawl when used in a twin rig system is expected to provide approximately 12% drag reduction compared to quad rig. The twin ‘W’ trawl system also has benefits over quad rig in that a reduced number of cod-end/By-catch Reduction Device units need to be installed and attended each tow.

Hydrodynamic Evaluation of a Generic Sail Used in an Innovative Prawn-Trawl Otter Board

In prawn-trawling operations, otter boards provide the horizontal force required to maintain net openings, and are typically low aspect ratio (∼0.5) flat plates operating on the seabed at high angles of attack (AOA; 35–40°). Such characteristics cause otter boards to account for up to 30% of the total trawling resistance, including that from the vessel. A recent innovation is the batwing otter board, which is designed to spread trawls with substantially less towing resistance and benthic impacts. A key design feature is the use of a sail, instead of a flat plate, as the hydrodynamic foil. The superior drag and benthic performance of the batwing is achieved by (i) successful operation at an AOA of ∼20° and (ii) having the heavy sea floor contact shoe in line with the direction of tow. This study investigated the hydrodynamic characteristics of a generic sail by varying its twist and camber, to identify optimal settings for maximum spreading efficiency and stability. Loads in six degrees of freedom were measured at AOAs between 0 and 40° in a flume tank at a constant flow velocity, and with five combinations of twist and camber. The results showed that for the studied sail, the design AOA (20°) provides a suitable compromise between greater efficiency (occurring at lower AOAs) and greater effectiveness (occurring at higher AOAs). At optimum settings (20°, medium camber and twist), a lift-to-drag ratio >3 was achieved, which is ∼3 times more than that of contemporary prawn-trawling otter boards. Such a result implies relative drag reductions of 10–20% for trawling systems, depending on the rig configuration.Copyright

Choosing anterior-gear modifications to reduce the global environmental impacts of penaeid trawls

Globally, penaeid-trawl fisheries are faced with three broad sustainability issues: (1) large bycatches; (2) acute benthic-habitat impacts; and (3) high energy consumption. Most resolution efforts have focused on i above, and via bycatch reduction devices (BRDs) installed in the posterior trawl (codend), which typically reduce total bycatches by 30–70%, but are poorly adopted owing to few perceived benefits by fishers. While mandated BRDs will remain a feature of selective penaeid trawling, solutions to habitat impacts and high energy consumption require changes to the anterior trawl, including the spreading mechanisms (e.g. otter boards, beams and sleds), ground gears, and net designs. Further, because such components ultimately determine which organisms enter the codend, it should be feasible to structure anterior-trawl modifications to address all three sustainability issues, including improving selection. We sought to review the feasibility of such an approach here, and located fifty-eight relevant articles: of which 45, 11 and 23 directly or indirectly focused on reducing bycatch, habitat impacts and energy consumption, respectively. Considering these articles, we propose a protocol for holistically improving the environmental efficiency of penaeid trawling involving: (1) selecting the most appropriate multi-net configuration; (2) reducing otter-board angle of attack to ~20°; (3) minimising twine area; and (4) optimising horizontal-trawl opening. Compared to conventional configurations, choosing alternatives within the above protocol could reduce total unwanted bycatches and habitat contact by >70%, while concomitantly lowering drag/fuel costs by >20%. The latter outcome might improve selective penaeid-trawl adoption among global fishing fleets.

A ‘Simple Anterior Fish Excluder’ (SAFE) for Mitigating Penaeid-Trawl Bycatch

Various plastic strips and sheets (termed ‘simple anterior fish excluders’−SAFEs) were positioned across the openings of penaeid trawls in attempts at reducing the unwanted bycatches of small teleosts. Initially, three SAFEs (a single wire without, and with small and large plastic panels) were compared against a control (no SAFE) on paired beam trawls. All SAFEs maintained targeted Metapenaeus macleayi catches, while the largest plastic SAFE significantly reduced total bycatch by 51% and the numbers of Pomatomus saltatrix, Mugil cephalus and Herklotsichthys castelnaui by up to 58%. A redesigned SAFE (‘continuous plastic’) was subsequently tested (against a control) on paired otter trawls, significantly reducing total bycatch by 28% and P. saltatrix and H. castelnaui by up to 42%. The continuous-plastic SAFE also significantly reduced M. macleayi catches by ~7%, but this was explained by ~5% less wing-end spread, and could be simply negated through otter-board refinement. Further work is required to refine the tested SAFEs, and to quantify species-specific escape mechanisms. Nevertheless, the SAFE concept might represent an effective approach for improving penaeid-trawl selectivity.

Workload implications for clinic workflow with implementation of three-dimensional printed customized bolus for radiation therapy: A pilot study

Bolus is commonly used in radiation therapy to improve radiation dose distribution to the target volume, but commercially available products do not always conform well to the patient surface. Tumor control may be compromised, particularly for superficial tumors, if bolus does not conform well and air gaps exist between the patient surface and the bolus. Three-dimensional (3D) printing technology allows the creation of highly detailed, variable shaped objects, making it an attractive and affordable option for customized, patient-specific bolus creation. The use of 3D printing in the clinical setting remains limited. Therefore, the objective of this study was to assess the implications on time and clinical fit using a workflow for 3D printing of customized bolus in companion animals with spontaneous tumors treated with radiation therapy. The primary aim of this study was to evaluate the time required to create a clinical 3D printed bolus. The secondary aims were to evaluate the clinical fit of the bolus and to verify the skin surface dose. Time to segmentation and 3D printing were documented, while the clinical fit of the bolus was assessed in comparison to the bolus created in the treatment planner. The mean and median time from segmentation to generation of 3D printed boluses was 6.15 h and 5.25 h, respectively. The 3D printed bolus was significantly less deviated from the planned bolus compared to the conventional bolus (p = 0.0078) with measured dose under the bolus within 5% agreement of expected dose in 88% of the measurements. Clinically acceptable 3D printed customized bolus was successfully created for treatment within one working day. The most significant impact on time is the 3D printing itself, which therefore has minimal implications on personnel and staffing. Quality assurance steps are recommended when implementing a 3D printing workflow to the radiotherapy clinic.

Rising temperatures increased recruitment of brown tiger prawn (Penaeus esculentus) in Moreton Bay (Australia)

Abiotic factors are fundamental drivers of the dynamics of wild marine fish populations. Identifying and quantifying their influence on species targeted by the fishing industry is difficult and very important for managing fisheries in a changing climate. Using multiple regression, we investigated the influence of both temperature and rainfall on the variability of recruitment of a tropical species, the brown tiger prawn (Penaeus esculentus), in Moreton Bay which is located near the southern limit of its distribution on the east coast of Australia. A step-wise selection between 60 environmental variables identified temperature as the most important environmental factor to explain the variations of recruitment between 1990 and 2014. Including temperature into the Beverton and Holt stock–recruitment relationship explained 69% of the recruitment variability compared with 9.5% when omitted. This analysis indicates that increasing temperatures have increased recruitment of brown tiger prawn in Moreton Bay.

High Porosity Net Drag at a Low Angle of Attack in Application to a Representative Prawn Trawl

The presented work investigated the extent by which Reynolds number determines the drag coefficient for high porosity nets at a low angle of attack. A simple prawn trawl model that incorporates the main design features of prawn trawls employed in Australia was developed. Four trawl models of various high porosities were tested in a flume tank with respect to drag and shape over a range of flow velocities. The physical trawl model was analysed as a system of independent plane net sheets, each with an orientation to the flow estimated from analysis of stereo-vision data. The main finding was that the drag coefficient was weakly dependent on the Reynolds number in the range typical for prawn trawl operations, 1000 Re 1700 . These combined findings imply that trawler operators can approximately estimate prawn net drag from a function containing trawl twine area, towing speed and spread ratio.