Handegard Nils Olav, Tenningen Maria, Howarth Kirsten, Anders Neil, Rieucau Guillaume, Breen Michael
Marine Ecosystem Acoustics, Institute of Marine Research, Bergen, Norway.
Fish Capture Division, Institute of Marine Research, Bergen, Norway.
PLoS One. 2017 Dec 28;12(12):e0190259. doi: 10.1371/journal.pone.0190259. eCollection 2017.
The selectivity of fishing gears with respect to fish species and size is important, both for fisheries management and fishing operations. Purse seining is an efficient, environmentally friendly fish capture methodology generally targeting single species aggregations, but once a fish school has been selected and surrounded by the seine, there is no selections for individual size, species or catch quantity. A common practice for evaluating the catch is to haul the seine to a point where physical samples or inspections of catch composition can be made. The release process is called slipping and may lead to mortality in the released fish. The objective of this study was to simulate a crowding situation and investigate how the behaviour was affected in response to increased fish density, decreased oxygen levels, or a combination of the two, and to see if there is a behavioural measure that can be used to set safe crowding limits. The experiment was conducted on Mackerel (Scomber scombrus) held in net pens. The volume of the net pen was reduced to increase fish density, and a tarpaulin bag was wrapped around the pen to reduce the oxygen levels. Oxygen, fish density and space occupancy was monitored during the experiment, and the behavioural reactions was assessed using an imaging sonar. The main result was that the schooling function, i.e. the response to a predator model, was significantly reduced during crowding but not in response to hypoxia. There were some indications of a slow recovery of the function post-treatment. We conclude that crowding causes behavioural responses that occur before densities that induce fish mortality. Consequently, there is a behavioural response that could be used as a proxy for setting safe crowding limits.
渔具对鱼类种类和大小的选择性对于渔业管理和捕捞作业都很重要。围网捕捞是一种高效、环保的鱼类捕获方法，通常针对单一物种的聚集，但一旦选定鱼群并用围网包围，就无法对个体大小、物种或捕获量进行选择。评估渔获量的一种常见做法是将围网拖到可以进行实物取样或检查渔获物组成的地点。放鱼过程称为“滑放”，可能导致放归的鱼死亡。本研究的目的是模拟拥挤情况，研究鱼类行为如何因鱼密度增加、氧气水平降低或两者结合而受到影响，并查看是否存在可用于设定安全拥挤限度的行为指标。实验在网箱中养殖的鲭鱼（Scomber scombrus）上进行。通过减小网箱体积来增加鱼密度，并用防水油布包裹网箱以降低氧气水平。实验过程中监测氧气、鱼密度和空间占有率，并使用成像声纳评估行为反应。主要结果是，在拥挤期间，鱼群聚集功能（即对捕食者模型的反应）显著降低，但对缺氧情况无反应。有迹象表明处理后该功能恢复缓慢。我们得出结论，拥挤会引发行为反应，且这种反应在导致鱼类死亡的密度之前就会出现。因此，存在一种行为反应可作为设定安全拥挤限度的替代指标。
