Broadhurst Matt K, Sterling David J, Millar Russell B
NSW Department of Primary Industries, Fisheries Conservation Technology Unit, Coffs Harbour, New South Wales, Australia.
Sterling Trawl Gear Services, Manly, Queensland, Australia.
PLoS One. 2014 Jun 9;9(6):e99434. doi: 10.1371/journal.pone.0099434. eCollection 2014.
The effects of reducing mesh size while concomitantly varying the side taper and wing depth of a generic penaeid-trawl body were investigated to improve engineering performance and minimize bycatch. Five trawl bodies (with the same codends) were tested across various environmental (e.g. depth and current) and biological (e.g. species and sizes) conditions. The first trawl body comprised 41-mm mesh and represented conventional designs (termed the '41 long deep-wing'), while the remaining trawl bodies were made from 32-mm mesh and differed only in their side tapers, and therefore length (i.e. 1N3B or 'long' and ∼28o to the tow direction vs 1N5B or 'short' and ∼35o) and wing depths ('deep'-97 T vs 'shallow'-60 T). There were incremental drag reductions (and therefore fuel savings--by up to 18 and 12% per h and ha trawled) associated with reducing twine area via either modification, and subsequently minimizing otter-board area in attempts to standardize spread. Side taper and wing depth had interactive and varied effects on species selectivity, but compared to the conventional 41 long deep-wing trawl, the 32 short shallow-wing trawl (i.e. the least twine area) reduced the total bycatch by 57% (attributed to more fish swimming forward and escaping). In most cases, all small-meshed trawls also caught more smaller school prawns Metapenaeus macleayi but to decrease this effect it should be possible to increase mesh size slightly, while still maintaining the above engineering benefits and species selectivity. The results support precisely optimizing mesh size as a precursor to any other anterior penaeid-trawl modifications designed to improve environmental performance.
研究了在改变一般对虾拖网主体的侧锥度和翼深的同时减小网目尺寸的效果，以提高工程性能并尽量减少兼捕。在各种环境（如深度和水流）和生物（如物种和大小）条件下对五个拖网主体（带有相同的囊网）进行了测试。第一个拖网主体采用41毫米网目，代表传统设计（称为“41长深翼”），而其余拖网主体由32毫米网目制成，仅侧锥度不同，因此长度也不同（即1N3B或“长”，与拖曳方向约成28°， vs 1N5B或“短”，与拖曳方向约成35°）以及翼深不同（“深”-97T vs “浅”-60T）。通过任何一种改进方式减少网线面积，进而尽量减小用于标准化展开的拖板面积，都会带来逐渐的阻力降低（因此节省燃油——每小时和每公顷拖网最多可节省18%和12%）。侧锥度和翼深对物种选择性有交互且不同的影响，但与传统的41长深翼拖网相比，32短浅翼拖网（即网线面积最小）使总兼捕量减少了57%（这归因于更多的鱼向前游动并逃脱）。在大多数情况下，所有小网目拖网也捕获了更多较小的近缘新对虾，但要减少这种影响，应该有可能稍微增大网目尺寸，同时仍保持上述工程效益和物种选择性。这些结果支持精确优化网目尺寸，作为旨在改善环境性能的对虾拖网任何其他前端改进的前提条件。
