Scale growth data for analysis in Vollset et al. 2021

Scale samples of adult Atlantic salmon were compiled from 180 rivers in Norway, which comprise almost half of all Atlantic salmon rivers in Norway, during 1989-2016. The scales were collected by anglers when sport fishing in the various rivers. The back-calculation of fish length is based on the linear relationship between fish length and the diameter of the fish scale from the centre of the scale to the edge . We have focused on the average growth across four large geographic regions: South-western, south-western, middle-, and north Norway. In total, 52 371 Atlantic salmon were sampled by fishers. For each individual fish, the following data were used: length at capture (cm), back-calculated freshwater growth (cm), back-calculated early marine growth (cm), and smolt year, which is the year they migrated from the rivers as juveniles to the sea. Freshwater growth was defined as the distance from the centre of the scale to the end of the freshwater zone in the scale. Early marine growth, also termed post-smolt growth, was measured as the distance between the end of the freshwater zone and the end of the first winter at sea. Growth estimates from scales may be impacted by the size of the fish when they leave the rivers and enter the sea. To correct for this error, a relative growth estimate can be used where the early marine growth is divided by the freshwater growth of the individual, which we refer to as relative growth. Also, the timing of out-migration will vary by up to two months from north to south in Norway, meaning that the time to grow before winter is shorter for northern populations. Putative monthly growth estimates indicate that growth is limited from November, and we therefore calculate growth from day of out-migration to 31 October. Day of out migration was calculated according to using a model that explains out-migration data based on latitude, longitude, air temperature during winter, and river discharge. The estimated growth is called relative growth per day.本数据集的成年大西洋鲑（Atlantic salmon）鳞片样本采集于1989年至2016年间挪威境内的180条河流，这些河流约占挪威境内已知大西洋鲑河流总数的一半。所有鳞片均由垂钓爱好者在各河流开展休闲垂钓时采集获得。鱼类体长的回溯计算基于体长与鳞片中心至边缘的直径之间的线性关系。本研究聚焦于四个大型地理区域的平均生长情况：西南挪威、西南挪威、中部挪威以及北部挪威。本次研究共采集52371尾大西洋鲑样本。针对每尾样本鱼，采集了如下数据：捕获时体长（单位：厘米）、回溯计算得到的淡水生长量（单位：厘米）、回溯计算得到的早期海洋生长量（单位：厘米），以及降海洄游年（smolt year）——即幼鲑从河流向海洋洄游的年份。淡水生长量定义为鳞片中心至鳞片内淡水生长区末端的距离。早期海洋生长量又称降海后生长（post-smolt growth），其测量值为淡水生长区末端至海洋首个越冬期结束的距离。基于鳞片的生长估算结果可能会受到鱼类离开河流进入海洋时的体型影响。为校正该偏差，可采用相对生长估算方法：将单尾鱼的早期海洋生长量除以其淡水生长量，我们将该比值称为相对生长量（relative growth）。此外，挪威境内的幼鲑洄游时间从北到南可相差长达两个月，这意味着北部种群的越冬前生长时长更短。推及的月度生长估算结果显示，生长活动自11月起受到抑制，因此我们将生长周期定义为从幼鲑洄游当日至10月31日。幼鲑洄游日期通过下述模型计算得出：该模型基于纬度、经度、冬季气温以及河流径流量对洄游数据进行拟合。最终得到的生长估算值即为日均相对生长量。