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Effect of environmental conditions on the natural activity rhythms and bottom trawl catchability of Atlantic cod (Gadus morhua).

机译：环境条件对大西洋鳕（Gadus morhua）自然活动节律和底拖网可捕性的影响。

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摘要

Environmental conditions such as water temperature and ambient light level are expected to exert a strong influence on the natural behaviour and bottom trawl catchability of marine groundfish species such as Atlantic cod (Gadus morhua). In this thesis, I use acoustic telemetry to investigate this prediction for cod inhabiting coastal inshore waters in the North Atlantic ocean.; Laboratory and field experiments were first conducted to examine two intragastric methods for attaching acoustic transmitters to cod. I found that cod which voluntarily swallowed transmitters wrapped in bait exhibited a delayed onset of initial regurgitation, longer periods of retention, higher food consumption, and lower mortality in comparison to fish tagged using the method of forced insertion into the gut. Under field conditions, cod in shallow coastal waters were successfully tagged by lowering a tagging frame near the seafloor containing baited acoustic transmitters. The technique did not appear to affect natural behaviour and was found to be ideal for short-term telemetry studies.; Temporal patterns in the natural activity level of acoustically tagged cod were investigated using a stationary positioning system. Time-of-day was found to have a significant affect on the activity level of cod inhabiting two study areas, the coastal waters of Norway and Newfoundland. High resolution tracking of juvenile cod revealed significant between-individual variation, suggesting that juvenile cod may make different trade-offs in balancing the demands of foraging and predator avoidance. Adult cod in Smith Sound on the northeast coast of Newfoundland exhibited seasonal variation in diel activity rhythm. During summer, cod were active throughout the diel cycle with a pronounced increase in activity during daylight hours. During winter, cod occupied deeper water and were significantly less active. Water temperature and ambient light intensity are thought to be the key proximate factors responsible for this seasonal difference in behaviour.; Finally, the behaviour of cod was examined in response to an approaching vessel and bottom trawl at different times of year. Using acoustic telemetry, the swimming speed of cod was estimated for the periods before, during, and after passage of a vessel travelling at different speeds as well as in response to this vessel towing a bottom trawl. The likelihood of reaction, reaction distance, and the duration of disturbance produced by the encounter were examined. The results showed that cod are capable of reacting to an approaching vessel from considerable distances and that the disturbance produced by the encounter can persist for periods up to 56 min.; In summary, the findings from this thesis indicate that variation in environmental conditions play an important role in modifying the behaviour of cod. Diel variation in ambient light intensity and seasonal variation in water temperature appear to be important proximate factors. Both are predicted to affect the availability and vulnerability of inshore cod populations to acoustic and bottom trawl sampling tools used in resource assessment surveys.
机译：预计诸如水温和环境光照水平之类的环境条件会对诸如大西洋鳕（Gadus morhua）之类的海底鱼类物种的自然行为和海底拖网捕捞能力产生重大影响。在这篇论文中，我使用声学遥测技术来研究对鳕鱼栖息在北大西洋沿岸近海水域的预测。首先进行了实验室和野外实验，以研究将声发射器与鳕鱼相连的两种胃内方法。我发现，与用强迫插入肠内标记的鱼相比，自愿吞下饵剂的鳕鱼表现出延迟的初始反流，更长的滞留时间，更高的食物消耗量和更低的死亡率。在田间条件下，通过降低包含诱饵声发射器的海底附近的标签框架，可以成功地标记浅海中的鳕鱼。该技术似乎不影响自然行为，被认为是短期遥测研究的理想选择。使用固定定位系统研究了带有声学标签的鳕鱼自然活动水平的时间模式。发现一天中的时间对居住在两个研究区域（挪威和纽芬兰的沿海水域）的鳕鱼的活动水平有重大影响。对幼年鳕鱼的高分辨率跟踪揭示了个体之间的显着差异，这表明幼年鳕鱼在平衡觅食和避免捕食者的需求方面可能会做出不同的取舍。纽芬兰东北海岸史密斯桑德的成年鳕鱼的diel活动节律表现出季节性变化。在夏季，鳕鱼在整个diel周期内都很活跃，白天的活动明显增加。在冬季，鳕鱼占据了更深的水域，活跃度大大降低。水温和环境光强度被认为是造成这种季节性差异的关键因素。最后，对鳕鱼的行为进行了检查，以应对一年中不同时间接近的船只和底部拖网。使用声学遥测技术，在以不同速度行进的船只通过之前，期间和之后，以及响应于该船只拖曳底部拖网，估算了鳕鱼的游泳速度。检查了反应的可能性，反应距离和相遇产生的干扰持续时间。结果表明，鳕鱼能够在相当长的距离内对接近的船只做出反应，相遇产生的干扰可持续长达56分钟。总之，本论文的发现表明环境条件的变化在改变鳕鱼的行为中起着重要的作用。环境光强度的Diel变化和水温的季节性变化似乎是重要的近因。预计两者都会影响近岸鳕种群对资源评估调查中使用的声学和底拖网采样工具的可用性和脆弱性。

著录项

  • 作者

    Winger, Paul D.;

  • 作者单位

    Memorial University of Newfoundland (Canada).;

  • 授予单位 Memorial University of Newfoundland (Canada).;
  • 学科 Biology Zoology.; Agriculture Fisheries and Aquaculture.
  • 学位 Ph.D.
  • 年度 2004
  • 页码 151 p.
  • 总页数 151
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类 动物学;水产、渔业;
  • 关键词

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