Practical and applied knowledge of local fishers can help to improve our understanding of target species ecology and fisheries management decisions. In the Western Baltic Sea (WBS), the spatio-temporal distribution of cod is still largely unknown despite decades of research. We studied changes in cod distribution by obtaining information on temporal depth and habitat use of cod from commercial gillnet fishers using semi-directed interviews supplemented by at-sea observer data. Linear and non-linear regression analyses revealed significant relationships between depth use of cod and sea surface temperature (SST) as well as thermal stratification. Moreover, habitat use was related to SST and residence depth of cod. Areas deeper than 15 m were favoured from late December until March during low SST and a mixed water column (spawning) and also from July until August during high SST and strong thermal stratification (summer aestivation). Shallower areas were favoured during the rest of the year. The depth and habitat use displayed distinct seasonal up- and downslope movements of cod. This study highlights the importance of shallow-water and structured habitats for cod in the WBS and the value of local knowledge held by fishers for a better understanding of the distributional dynamics of important marine resource populations.

中文翻译：

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刺网渔民的知识揭示了西波罗的海鳕鱼（Gadus morhua）的深度和栖息地使用的季节性

当地渔民的实践和应用知识可以帮助增进我们对目标物种生态学和渔业管理决策的了解。在西波罗的海（WBS），尽管进行了数十年的研究，鳕鱼的时空分布仍然未知。我们通过使用半定向访谈和海上观察员数据来获得商业刺网渔民的鳕鱼的时间深度和栖息地利用信息，研究了鳕鱼分布的变化。线性和非线性回归分析揭示了鳕鱼深度使用与海表温度（SST）以及热分层之间的显着关系。此外，栖息地的使用与鳕鱼的海面温度和居住深度有关。从12月下旬至3月，在低SST和混合水柱（产卵）期间，深于15 m的区域受到青睐；在7月到8月，在SST高和强烈的热分层（夏季成年）期间，也偏爱深于15 m的区域。在今年余下的时间里，较浅的地区受到青睐。深度和栖息地利用显示了鳕鱼明显的季节性上，下坡运动。这项研究强调了WBS中鳕鱼的浅水和结构化生境的重要性，以及渔民掌握的当地知识对于更好地了解重要海洋资源种群分布动态的价值。