Long time series of reliable individual growth estimates are crucial for understanding the status of a fish stock and deciding upon appropriate management. Tagging data provide valuable information about fish growth, and are especially useful when age‐based growth estimates and stock assessments are compromised by age‐determination uncertainties. However, in the literature there is a lack of studies assessing possible changes in growth over time using tagging data. Here, data from tagging experiments performed in the Baltic Sea between 1971 and 2019 were added to those previously analysed for 1955–1970 to build the most extensive tagging dataset available for Eastern Baltic cod (Gadus morhua, Gadidae), a threatened stock with severe age‐determination problems. Two length‐based methods, the GROTAG model (based on the von Bertalanffy growth function) and a Generalized Additive Model, were used to assess for the first time the potential long‐term changes in cod growth using age‐independent data. Both methods showed strong changes in growth with an increase until the end of the 1980s (8.6–10.6 cm/year for a 40 cm cod depending on the model) followed by a sharp decline. This study also revealed that the current growth of cod is the lowest observed in the past 7 decades (4.3–5.1 cm/year for a 40 cm cod depending on the model), indicating very low productivity. This study provides the first example of the use of tagging data to estimate multidecadal changes in growth rates in wild fish. This methodology can also be applied to other species, especially in those cases where severe age‐determination problems exist.

中文翻译：

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根据标签数据估算鱼类生长速度的十年变化：来自东部波罗的海鳕鱼的一个案例研究（Gadus morhua，Gadidae）

长期可靠的个人生长估计值系列对于了解鱼类种群的状况和决定适当的管理至关重要。标记数据可提供有关鱼类生长的有价值的信息，当基于年龄的不确定性而影响基于年龄的生长估计和种群评估时，该数据特别有用。但是，文献中缺乏使用标签数据评估生长随时间变化的可能的研究。在这里，将1971年至2019年在波罗的海进行的标记实验获得的数据添加到了先前对1955年至1970年进行分析的数据中，以建立可用于东波罗的海鳕鱼（Gadus morhua，Gadidae）的最广泛的标记数据集。），具有严重的年龄确定问题的受威胁股票。两种基于长度的方法，即GROTAG模型（基于von Bertalanffy生长函数）和广义加性模型，首次使用了与年龄无关的数据来评估鳕鱼生长的潜在长期变化。两种方法都显示出生长的强烈变化，直到1980年代末（40 cm的鳕鱼视模型而定，每年增长8.6-10.6厘米/年，具体取决于模型），然后急剧下降。这项研究还表明，鳕鱼的当前生长是过去7年中观察到的最低值（40厘米鳕鱼的年增长率为4.3-5.1厘米/年，具体取决于型号），表明生产力非常低。这项研究提供了第一个使用标签数据估算野生鱼类生长速度的十年变化的例子。这种方法也可以应用于其他物种，