Brooks J L, Lédée E J I, Larocque S M, Cooke S J, Brown E, Midwood J D
Department of Biology, Carleton University, 1125 Colonel By Drive, Ottawa, ON, Canada.
Great Lakes Laboratory for Fisheries and Aquatic Science, Fisheries and Oceans Canada, 867 Lakeshore Road, Burlington, ON, Canada.
Mov Ecol. 2025 Jan 7;13(1):1. doi: 10.1186/s40462-024-00505-6.
Globally, temperate lakes are experiencing increases in surface water temperatures, extended periods of summer stratification, and decreases of both surface and deep water dissolved oxygen (DO). The distribution of fish is influenced by a variety of factors, but water temperature and dissolved oxygen are known to be particularly constraining such that with climate change, fish will likely feel the "squeeze" from above and below.
This study used acoustic telemetry to explore the effects of both thermal stratification and the deoxygenation of the hypolimnion on walleye (Sander vitreus) movements in a coastal embayment in Lake Ontario. Using historical water quality monitoring data, we documented seasonal and annual fluctuations in availability of both 'suitable' (all temperatures, DO > 3 mg/L) and 'optimum' (temperatures 18-23 °C, DO > 5mg/L) abiotic habitat for walleye and determined how these changes influenced walleye movements over a three-year period.
Hypoxia (< 3 mg/L DO) was present in Hamilton Harbour every summer that data were available (32 of the 42 years between 1976 and 2018), with a maximum of 68.4% of the harbour volume in 1990. We found that thermal stratification and a hypoxic hypolimnion greatly reduced the volume of suitable habitat during our telemetry study. The reduction of suitable habitat significantly reduced walleye movement distances, however as the summer progressed, this remaining suitable habitat warmed into their thermal optimum range which was found to increase walleye movement distances. Despite the seemingly poor conditions, tagged walleye remained in the harbour for most of the year, and were the fastest growing individuals compared to other sampled coastal subpopulations in Lake Ontario.
Although we documented a reduction in the quantity of non-hypoxic habitat available to walleye, the water temperature of the remaining habitat increased throughout the summer into the physiologically optimum range for walleye and increased in metabolic quality. Many abiotic factors influence how, where, and what habitat fish choose to use, and this study reveals the importance of considering both habitat quality (temperature and dissolved oxygen) and quantity when evaluating fish habitat use and behaviour.
在全球范围内，温带湖泊正经历着地表水温度升高、夏季分层期延长以及表层和深层水溶解氧（DO）含量下降的情况。鱼类的分布受到多种因素的影响，但已知水温与溶解氧对其影响尤为显著，因此随着气候变化，鱼类可能会受到来自上下两方面的“挤压”。
本研究采用声学遥测技术，探究了安大略湖一个沿海港湾内热分层和湖下层脱氧对大眼狮鲈（Sander vitreus）活动的影响。利用历史水质监测数据，我们记录了大眼狮鲈“适宜”（所有温度，溶解氧>3毫克/升）和“最佳”（温度18 - 23°C，溶解氧>5毫克/升）非生物栖息地可用性的季节性和年度波动，并确定了这些变化如何在三年时间里影响大眼狮鲈的活动。
在有数据的每一年夏天（1976年至2018年的42年中有32年），汉密尔顿港都存在低氧情况（溶解氧<3毫克/升），1990年港湾低氧区域占比高达68.4%。我们发现，在遥测研究期间，热分层和低氧的湖下层极大地减少了适宜栖息地的面积。适宜栖息地面积的减少显著缩短了大眼狮鲈的活动距离，然而随着夏季的推进，剩余的适宜栖息地温度升高至其热最佳范围，这使得大眼狮鲈的活动距离增加。尽管条件看似不佳，但被标记的大眼狮鲈一年中的大部分时间都留在港湾内，并且与安大略湖其他采样的沿海亚种群相比，它们是生长速度最快的个体。
尽管我们记录到可供大眼狮鲈使用的非低氧栖息地数量减少，但剩余栖息地的水温在整个夏季升高至大眼狮鲈生理最佳范围，且代谢质量有所提高。许多非生物因素会影响鱼类如何、在哪里以及选择使用何种栖息地，本研究揭示了在评估鱼类栖息地利用和行为时，同时考虑栖息地质量（温度和溶解氧）和数量的重要性。
