Bell Justin David, Lyle Jeremy Martin
Institute for Marine and Antarctic Studies, University of Tasmania, Hobart, Tasmania, Australia.
PLoS One. 2016 Nov 18;11(11):e0166632. doi: 10.1371/journal.pone.0166632. eCollection 2016.
As fisheries shift towards ecosystem-based management, the need to reduce impacts on by-catch has been increasingly recognised. In this study the catch composition, discard rate, and post-capture survival of species caught by gillnets in Tasmania, Australia, was investigated. Over half the commercial gillnet catch was discarded, with discard rates of ~20% for target and >80% for non-target species. Capture condition, including initial mortality, was assessed using simple criteria for a range of species and related to soak duration. Delayed mortality was also assessed using tank trials and related to capture condition. By combining initial and delayed mortality rates post-capture survival was estimated. Longer soak durations generally resulted in slight, but significant, declines in capture condition and lower initial survival. Nonetheless, when combined with delayed survival, four of the five most commonly caught species (Cheilodactylus spectabilis, Latridopsis forsteri, Aplodactylus arctidens, Cephaloscyllium laticeps) exhibited high post-capture survival (83-100%) for soak durations within the maximum regulated range. Post-capture survival of the one remaining commonly caught species, Notolabrus tetricus, (typically discarded) declined with increased soak duration from 84% to 62%, suggesting that this species would benefit from a further reduction in maximum soak duration. Initial and delayed survival rates for the species retained for tank trials exhibited a significant linear relationship, which was used to estimate delayed survival rates for the rarer species. This method enabled the estimation of potential post-capture survival rates for a diverse range of species and may have application in other data-limited situations where the relationships between fishing practices and by-catch survival are uncertain. Overall, our results suggest that soak duration regulation has been effective in reducing by-catch mortality for many species, noting that some species have low survival rates regardless of soak duration.
随着渔业向基于生态系统的管理方式转变，人们越来越认识到减少对副渔获物影响的必要性。在本研究中，对澳大利亚塔斯马尼亚州刺网捕获的物种的渔获组成、丢弃率和捕获后存活率进行了调查。超过一半的商业刺网渔获物被丢弃，目标物种的丢弃率约为20%，非目标物种的丢弃率超过80%。使用一系列物种的简单标准评估包括初始死亡率在内的捕获状况，并将其与浸泡时间相关联。还通过水槽试验评估延迟死亡率，并将其与捕获状况相关联。通过结合初始死亡率和延迟死亡率来估计捕获后存活率。较长的浸泡时间通常会导致捕获状况略有但显著下降，以及较低的初始存活率。尽管如此，当与延迟存活率相结合时，五种最常捕获的物种中的四种（壮观唇指䲗、福氏裸胸䲗、北极裸胸䲗、宽头睡鲨）在最大规定范围内的浸泡时间内表现出较高的捕获后存活率（83 - 100%）。剩下的一种常捕获物种——四带副唇鱼（通常被丢弃）的捕获后存活率随着浸泡时间的增加从84%下降到62%，这表明该物种将受益于最大浸泡时间的进一步缩短。用于水槽试验的保留物种的初始和延迟存活率呈现出显著的线性关系，该关系用于估计较稀有物种的延迟存活率。这种方法能够估计多种物种潜在的捕获后存活率，并且可能适用于其他数据有限的情况，即捕鱼方式与副渔获物存活率之间的关系不确定的情况。总体而言，我们的结果表明，浸泡时间规定在降低许多物种的副渔获物死亡率方面是有效的，同时要注意到有些物种无论浸泡时间长短，存活率都很低。
