High synchrony in size at maturity of Atlantic salmon over a large geographical scale

Size at maturity is an important demographic characteristic due to its strong effect on fecundity. Synchrony in size at maturity across populations suggests similar environmental conditions, partly through shared feeding grounds. We study synchrony in size at maturity over 30 years across 187 populations using data of about 200,000 individual Atlantic salmon belonging to four geographic regions in Norway. Synchrony was very high among the three southern regions, while the northernmost region had more independent fluctuations. Synchrony among closely separated populations was high, declined with distance, but was still significant 1000 km apart. Fulton’s condition factor was consistently larger in the North region, further emphasizing the difference between this region and the three southern regions. The high synchrony reflects that fish within each population have a wide oceanic distribution and therefore, on average, experience a similar environment across populations. Despite that, the northernmost populations forage more north and east of the more southern populations. The high synchrony in size at maturity will generate synchrony in egg deposition, with demographic consequences on a broad geographic scale.成熟体型（Size at maturity）是一项重要的种群统计特征，因其对繁殖力具有显著影响。种群间成熟体型的同步性暗示了环境条件的相似性，这在一定程度上源于种群共享的索饵场。本研究依托挪威境内4个地理区域、共计约20万条大西洋鲑（Atlantic salmon）的个体数据，对187个种群在30年间的成熟体型同步性展开分析。三个南部区域的种群间同步性极高，而最北部区域的种群波动则更为独立。空间距离相近的种群间同步性较高，且同步性随距离增加而减弱，但在相距1000公里的情况下仍具有统计学显著性。北部区域的富尔顿条件系数（Fulton’s condition factor）始终高于南部三个区域，进一步凸显了该区域与南部三个区域的差异。高度的同步性反映出：每个种群的鲑鱼在大洋中具有广泛的分布范围，因此平均而言，不同种群的个体所经历的环境条件相似。尽管如此，最北部种群的索饵区域相较于南部种群更为偏北偏东。成熟体型的高度同步性将引发产卵行为的同步性，进而在大范围地理尺度上产生种群统计层面的影响。