Environmental change and fishing activity can produce directional trends in exploited fish populations with consequences for stock productivity. For herring in the Celtic Sea, size at age has been in steady decline since the mid 1980's. In the neighbouring herring stock off the Northwest coast of Ireland, reductions in size at age are noted after 1990. Here, gradient boosting regression trees were used to investigate trends in extended time series (1959–2012) of length-at-age across both populations and to identify important variables associated with the observed declines in size. The predominant signal detected was a non-linear negative relationship between adult size and mean Sea Surface Temperature during the first growing season. Herring length was negatively correlated with the Atlantic Multidecadal Oscillation. Weaker associations with indicators of food availability and population size were also detected. Across both populations a marked decline in length was observed at the upper end of the temperature range (~14^∘C in the Celtic Sea and ~13^∘C in the Northwest). Declines in length and associations with temperature were more pronounced in the Celtic Sea population which may be vulnerable to increasing sea temperatures due to its position at the southern limit of the species distribution.

环境变化和捕捞活动会在被开发的鱼类种群中产生定向趋势，从而影响种群生产力。自1980年代中期以来，在凯尔特海的鲱鱼年龄一直在稳定下降。在爱尔兰西北海岸附近的鲱鱼种群中，1990年后年龄下降了。这里，梯度增强回归树用于研究两个年龄段的年龄增长的延长时间序列（1959-2012年）的趋势。并确定与观察到的大小下降有关的重要变量。在第一个生长季节，检测到的主要信号是成年大小与平均海面温度之间的非线性负相关。鲱鱼长度与大西洋多年代际振荡呈负相关。还发现与粮食供应和人口规模指标之间的联系较弱。在这两个种群中，在温度范围的上限（〜14^∘下在凯尔特海和〜13 ^∘下在西北）。长度的减少以及与温度的联系在凯尔特海种群中更为明显，由于其位于物种分布的最南端，可能容易受到海水温度升高的影响。